JP5477261B2 - MOSFET current determination device - Google Patents

Description

  The present invention relates to a MOSFET current determination apparatus that determines the level of current flowing between the drain and source of a MOSFET.

As a method of detecting the current flowing between the drain / source of the MOSFET, a method is generally used in which the on-resistance of the MOSFET is regarded as a detection resistor and the current is detected by the drain-source voltage.
Although this method can estimate the current value, the on-resistance changes when the temperature of the MOSFET fluctuates, which means that the detection resistance itself changes, so detection is different from the actual current value. Therefore, there is a problem that it is difficult to increase the detection accuracy.

  Therefore, conventionally, as shown in, for example, Patent Document 1, the on-resistance value is predicted by linear approximation from the temperature information of the MOSFET being driven by utilizing the fact that the on-resistance changes almost linearly according to the temperature. It is considered to correct it. As a result, the current detection accuracy can be increased regardless of temperature fluctuations.

JP 2009-111366 A

  However, in the configuration as described above, there is a problem that the detection error becomes large when the temperature characteristic of the on-resistance of the MOSFET does not have linearity in a wide operating temperature range, and as a result, the current of the MOSFET has high accuracy. There is a problem that the level cannot be determined.

  The present invention has been made in consideration of the above-described circumstances, and its object is to determine a current level of a MOSFET that can accurately determine a current level following the temperature characteristics of the on-resistance of the MOSFET. Is to provide.

  The MOSFET current determination device according to claim 1 has a drain / source voltage which is a voltage obtained by multiplying the drain / source current by the on-resistance of the MOSFET as a configuration for determining a current flowing between the drain / source of the MOSFET. Is detected by the voltage detecting means, and the determination voltage is compared with a determination voltage corresponding to the determination current value by the determination means. In consideration, correction is made by the temperature sensing element and the determination voltage setting means.

In this case, the determination voltage setting means divides the temperature characteristics of the MOSFET on-resistance into a plurality of temperature regions, sets approximate on-resistances by applying an approximate line in each temperature region, and sets the temperature detection voltage by the temperature sensing element. A region where the temperature characteristics of the on-resistance of the MOSFET deviate from a single linear approximation by correcting to correspond to the approximate on-resistance value corresponding to the temperature at that time and generating a determination voltage based on the approximate on-resistance value It becomes possible to follow this, and a highly accurate determination can be made.
The determination voltage setting means includes a first correction circuit that corrects a temperature detection voltage by the temperature sensing element to a reference approximate on-resistance value corresponding to a reference approximation line in a predetermined temperature region, and a temperature detection voltage of the temperature sensing element. Corresponds to a temperature range different from the temperature range of the reference approximate line, a second correction circuit that outputs a switching signal for correction, and a reference approximate on-resistance value by the first correction circuit is expressed as a second correction circuit. And a determination voltage generation circuit that generates a determination voltage based on the approximate on-resistance value obtained by correction according to the presence / absence of a correction switching signal. The first correction circuit, the second correction circuit, and the determination voltage generation circuit are all configured by analog circuits.

  According to a second aspect of the present invention, there is provided the MOSFET current determination apparatus according to the first aspect of the invention, wherein the determination voltage setting means is adjacent to an approximate straight line that sets the temperature characteristics of the on-resistance of the MOSFET in a plurality of temperature regions. An approximate straight line having the same inclination between the temperature regions was set as a parallel fit. As a result, when the temperature characteristic of the on-resistance has a curve characteristic that deviates from the linear characteristic, the approximate on-resistance that matches the purpose to the purpose by shifting the approximate straight line with the slope unchanged And generating a determination voltage according to this, it is possible to perform highly accurate determination with reduced determination error.

  According to a third aspect of the present invention, in the MOSFET current determination device, the determination voltage setting means comprises a first correction circuit, a second correction circuit, and a determination voltage generation circuit. The first correction circuit corrects the temperature detection voltage by the temperature sensitive element to a reference approximate on-resistance value corresponding to a reference approximate line in a predetermined temperature region. The second correction circuit outputs a correction switching signal when the temperature detection voltage of the temperature sensing element corresponds to a temperature region different from the temperature region of the reference approximate line. An approximate straight line in which the reference approximate on-resistance value by the first correction circuit is set in the temperature region corresponding to the temperature of the MOSFET according to the presence or absence of the correction switching signal from the second correction circuit by the determination voltage generation circuit. The determination voltage is generated on the basis of the approximate on-resistance value obtained by correction so as to be in line with the level. As a result, when the temperature characteristic of the on-resistance has a curve characteristic that deviates from the linear characteristic, the approximate on-resistance that matches the purpose to the purpose by shifting the approximate straight line with the slope unchanged And generating a determination voltage according to this, it is possible to perform highly accurate determination with reduced determination error.

  According to a fourth aspect of the present invention, there is provided the MOSFET current determination device according to the first aspect of the invention, wherein the determination voltage setting means adjoins the approximate straight line that sets the temperature characteristics of the on-resistance of the MOSFET in a plurality of temperature regions. It was set as the structure which connected between temperature ranges with the broken line. As a result, when the temperature characteristic of the on-resistance has a curve characteristic that deviates from the linear characteristic, an approximate on-resistance is set so as to follow the shape of the curve, and a determination voltage is generated according to this, thereby determining a determination error. A reduced and highly accurate determination can be performed.

  According to a fifth aspect of the present invention, there is provided the MOSFET current determination device according to the fourth aspect, wherein the determination voltage setting means comprises a first correction circuit, a second correction circuit, and a determination voltage generation circuit. The first correction circuit corrects the temperature detection voltage by the temperature sensitive element to a reference approximate on-resistance value corresponding to a reference approximate line in a predetermined temperature region. The second correction circuit outputs a correction switching signal when the temperature detection voltage of the temperature sensing element corresponds to a temperature region different from the temperature region of the reference approximate line. By the determination voltage generation circuit, the reference approximate on-resistance value obtained by the first correction circuit is approximated in a temperature region corresponding to the temperature of the MOSFET according to the presence / absence of a correction switching signal from the second correction circuit. A determination voltage is generated on the basis of the approximate on-resistance value obtained by correcting along the inclination of the straight line. As a result, when the on-resistance temperature characteristic has a curve characteristic deviating from the linear characteristic, an approximate on-resistance is set so as to follow the shape of the curve, and a determination voltage is generated according to this, thereby determining a determination error. Therefore, it is possible to make a highly accurate determination.

According to a sixth aspect of the present invention, there is provided a MOSFET current determination apparatus comprising the absolute value correction information storage means in the above invention. The absolute value correction information storage means stores absolute value correction information for correcting the approximate line so that the value of the approximate on-resistance at a predetermined temperature matches the actual on-resistance value of the MOSFET at the predetermined temperature. Is done. The determination voltage setting unit corrects the approximate straight line using the absolute value correction information stored in the absolute value correction information storage unit. As a result, the determination voltage is generated using an approximate straight line that matches the temperature characteristics of the on-resistance of the MOSFET that is actually used. Therefore, regardless of individual differences in the characteristics of the MOSFET that is used, the determination error can be reduced. A high determination can be made.

According to a seventh aspect of the present invention, there is provided a MOSFET current determination apparatus comprising the tilt correction information storage means in the above invention. The slope correction information storage means corrects the approximate line so that the slope of the approximate on-resistance approximate line in the predetermined temperature region matches the actual slope of the MOSFET on-resistance in the predetermined temperature region. Tilt correction information is stored. Then, the determination voltage setting unit corrects the approximate straight line using the inclination correction information stored in the inclination correction information storage unit. As a result, the determination voltage is generated using an approximate straight line that matches the temperature characteristics of the on-resistance of the MOSFET that is actually used. Therefore, regardless of individual differences in the characteristics of the MOSFET that is used, the determination error can be reduced. A high determination can be made.

In the MOSFET current determination device according to the eighth aspect of the present invention, the level of the current determined by the determination means is set to a level at which an overcurrent is detected. Thereby, when an overcurrent flows through the load, an overcurrent determination operation can be performed with an appropriate determination voltage in a wide temperature range.

In the MOSFET current determination device according to claim 9 , in the above invention, the temperature sensing element is constituted by a diode disposed in the vicinity of the MOSFET, and the forward voltage of the diode is used as the temperature detection voltage. The fluctuation can be accurately detected using the temperature characteristic of the forward voltage of the pn junction of the diode.

Block configuration diagram in the first embodiment Explanatory drawing of the temperature characteristic and approximate straight line of on-resistance in 1st Embodiment Electrical configuration diagram in the first embodiment Diagram showing approximate straight lines before and after performing absolute value correction and tilt correction Diagram showing approximate straight lines before and after performing absolute value correction Explanatory drawing of the temperature characteristic and approximate straight line of on-resistance in 2nd Embodiment Electrical configuration diagram in the second embodiment Block configuration diagram in the first reference example Functional block diagram of CPU in the first reference example Different functional block configuration diagram of the CPU in the second reference example

(First embodiment)
Hereinafter, a first embodiment when applied to an overcurrent detection device will be described with reference to FIGS.
FIG. 1 is a block diagram showing an N-channel power MOSFET (hereinafter simply referred to as a MOSFET) 1 to be detected. A power supply connected to a drain terminal D when a drive signal is applied from a drive circuit 2 to a gate. Power is supplied from the VDD to the load 3 via the source terminal S, and the load 3 is energized on the high side. The MOSFET 1 is integrally provided with a temperature sensing element 4 for detecting temperature in the package, and outputs a temperature detection voltage Vf corresponding to the temperature of the MOSFET 1.

  The determination circuit unit 5 (corresponding to a current determination device) includes a voltage detection unit 6 (corresponding to voltage detection means) for detecting the drain / source voltage Vds of the MOSFET 1 and a determination voltage setting unit 7 (corresponding to determination voltage setting means). And a comparator 13 and a storage unit 41. The voltage detection unit 6 receives the inter-terminal voltage Vds from the drain and source terminals of the MOSFET 1. This drain / source voltage Vds corresponds to a value obtained by multiplying the current Id flowing between the drain / source of the MOSFET 1 by the on-resistance Ron. Therefore, if the on-resistance Ron is known, the current Id can be detected by reverse calculation.

  In this case, the on-resistance Ron has a characteristic that fluctuates depending on the temperature of the MOSFET 1, and as shown by a broken line in FIG. When the second temperature region is reached, the inclination is deviated from the linearity in the first temperature region, and the curve characteristic is obtained as a whole. The on-resistance Ron having such temperature dependence can be expressed as Ron (T) as a function of the temperature T.

  For example, in-vehicle devices and the like, there are cases where the temperature range of the usage environment is wide and the operation is required to be accurately performed in the range of −40 ° C. to 150 ° C. In such a wide temperature range, the above-described on-resistance Ron (T) does not have a linear change characteristic, but has a characteristic as shown in FIG. If this is the case, the characteristics may deviate depending on the operating temperature conditions, and a highly accurate determination operation cannot be performed.

  The determination voltage setting unit 7 generates a determination voltage Vdsref (T) based on the temperature detection voltage Vf (T) from the temperature sensing element 4, and includes a first correction circuit 8, a second correction circuit 9, and a current. It comprises a reference value generator 10 and a determination voltage generator 11. In addition, a determination voltage generation circuit 12 is configured by the current reference value generation unit 10 and the determination voltage generation unit 11.

  The first correction circuit 8 performs a correction process for generating a current reference value Isref (T) that is a determination current value based on the temperature detection voltage Vf (T) from the temperature sensing element 4. Here, in order to conform to the temperature characteristic of Ron (T) of MOSFET 1 shown in FIG. 2, the temperature detection voltage Vf (T) is a first approximation having a close slope in the first temperature region where the temperature is equal to or higher than Tx. Data corresponding to the approximate on-resistance Ron (Vf) corrected by being converted along a straight line (corresponding to a reference approximate straight line) is generated. Note that the data corresponding to the approximate on-resistance Ron (Vf) (corresponding to the reference approximate on-resistance value) is generated as the current reference value Isref (T) in the current reference value generation unit 10.

  In the second correction circuit 9, the value of the temperature detection voltage Vf (T) from the temperature sensing element 4 indicates whether the temperature T of the MOSFET 1 corresponds to the temperature in the first temperature region or the second temperature region. The switching signal Sc is output. Specifically, from the value of the temperature detection voltage Vf (T), whether the temperature T of the MOSFET 1 is equal to or higher than the temperature Tx (inflection point) at which the region is switched. And a switching signal Sc corresponding to the temperature region is output to the current reference value generation unit 10.

The current reference value generation unit 10 is a circuit that generates and sets a current reference value Idref (T) corresponding to a determination current for overcurrent detection. Since the value of the current reference value Idref itself for determining the overcurrent is not related to the temperature, it should be set as a constant, but the determination obtained by multiplying this by the on-resistance Ron (T) The voltage Vdsref (T) is a value including the temperature characteristic of the on-resistance Ron. Here, the above-described on-resistance Ron (T) is
Ron (T) = K (T) × Ron (1)
Ron: On-resistance value at a predetermined temperature K (T): Judged as a temperature coefficient of Ron, and an element of Ron's temperature coefficient K (T) included in the current reference value Idref is considered as Idref (T) From the relationship of the voltage Vdsref (T), the following equation is established.

Vdsref (T) = Idref × Ron (T)
= Idref × K (T) × Ron
= Idref (T) x Ron (2)
Idref (T); Determination current value considering temperature characteristics Idref (T) = Idref × K (T) (3)
Also, the temperature coefficient K (T) of Ron can be expressed as a function of Vf (T) in the first correction circuit 8 and the second correction circuit 9 described above from the relationship with the temperature detection voltage Vf (T). Therefore, the determination voltage value Vdsref (T) can be set by this. The determination voltage generation unit 11 generates the determination voltage value Vdsref (T) using this relationship.

  Further, the current reference value generation unit 10 performs a process of correcting the slope of the on-resistance Ron (T) in accordance with the switching signal Sc from the second correction circuit 9, and the temperature coefficient K (T) of the on-resistance Ron. Is calculated and reflected in the calculation of the determination voltage value Vdsref (T). Specifically, when the switching signal Sc corresponding to the first temperature region is given, the current reference value generation unit 10 has a temperature at which the gradient of the determination voltage value Vdsref (T) becomes a gradient along the first approximate line. The coefficient K (T) is obtained by calculation. In addition, when the switching signal Sc corresponding to the second temperature region is given, the current reference value generation unit 10 has a temperature coefficient K (() such that the gradient of the determination voltage value Vdsref (T) becomes a gradient along the second approximate line. T) is obtained by calculation.

  The comparator 13 as a determination unit receives the signal of the drain / source voltage Vds of the MOSFET 1 from the voltage detection unit 6 and the signal of the determination voltage value Vdsref (T) from the determination voltage generation unit 11. Then, the comparator 13 uses the overcurrent detection signal Sp as a determination output for determining whether or not an overcurrent flows in the MOSFET 1 depending on whether or not the drain / source voltage Vds exceeds the determination voltage value Vdsref (T). Output.

  The storage unit 41 (corresponding to an absolute value correction information storage unit and an inclination correction information storage unit) is configured by a nonvolatile semiconductor memory such as an EEPROM or a flash memory, for example. The storage unit 41 stores data representing a first approximate line and a second approximate line preset based on average characteristics (such as temperature characteristics of on-resistance) of the MOSFET 1 to be used. The determination voltage setting unit 7 generates a determination voltage value Vdsref (T) based on the data stored in the storage unit 41. However, the actually used MOSFET 1 usually has slightly different characteristics for each individual. Since such individual differences exist, if the data of the average first approximate line and the second approximate line stored in the storage unit 41 are used as they are, the temperature characteristics of the on-resistance of the MOSFET 1 that is actually used are determined. The matched determination voltage value Vdsref (T) is not always generated.

  For this reason, the storage unit 41 corrects the first approximate line and the second approximate line set in advance based on the average characteristics to those that match the characteristics of the MOSFET 1 that is actually used. Absolute value correction information and tilt correction information are stored. The correction information is set as follows in consideration of the characteristics of the MOSFET 1 and the characteristics of other components in the manufacturing process. In the present embodiment, each correction information for correcting the first approximate line is stored, and the second approximate line is corrected in accordance with the corrected first approximate line. In addition, you may make it memorize | store the correction information with respect to each of a 1st approximate line and a 2nd approximate line as each said correction information.

  That is, in the manufacturing process, the temperature Ta of the MOSFET 1 actually used and the on-resistance values a1 and b1 at the temperature Tb higher than the temperature Ta are measured (see FIG. 4). As shown in FIG. 4, the temperatures Ta and Tb may be higher than the inflection point of the temperature characteristic Ron (T) of the on-resistance of the MOSFET. Here, the relationship of temperature Tb> temperature Ta is established, but the relationship of temperature Tb <temperature Ta may be employed. Subsequently, the slope of the temperature characteristic Ron (T) of the actual on-resistance is obtained from the on-resistance values a1 and b1 at the measured temperatures Ta and Tb. Then, inclination correction information for making the inclination of the average first approximate straight line (indicated by a two-dot chain line in FIG. 4) coincide with the obtained actual inclination is stored in the storage unit 41.

  In addition, the value b2 at the temperature Tb of the data (indicated by a one-dot chain line in FIG. 4) representing the approximate line after correcting the average slope of the first approximate line to match the actual slope, and the measured temperature Tb The difference from the on-resistance value b1 at is obtained. Then, the obtained difference is stored in the storage unit 41 as absolute value correction information. The data representing the average first approximate line is corrected for the inclination based on the inclination correction information, and shifted by this difference, so that the first approximate line that more closely matches the characteristics of the MOSFET 1 actually used (FIG. 4). (Indicated by a solid line).

  In addition, when it is considered that there is not much difference in inclination between the temperature characteristics of the MOSFET 1 actually used and the average approximate straight lines set in advance, correction for inclination can be omitted. It is. In such a case, the procedure is as follows (see FIG. 5). That is, in the manufacturing process, the on-resistance value a1 at the temperature Ta of the MOSFET 1 actually used is measured. Subsequently, a difference between the measured on-resistance value a1 at the temperature Ta and the value a2 at the temperature Ta of data representing an average first approximate straight line (indicated by a one-dot chain line in FIG. 5) is obtained. Then, the obtained difference is stored in the storage unit 41 as absolute value correction information. By shifting the data representing the average first approximate straight line by this difference, a first approximate straight line (shown by a solid line in FIG. 5) that matches the characteristics of the MOSFET 1 actually used is obtained.

  With the configuration as described above, the current flowing through the load 3 is detected as the voltage Vds while the current Id flowing between the drain and source of the MOSFET 1, while the on-resistance Ron of the MOSFET 1 is used as a current reference value for determining overcurrent. In consideration of the above, the determination voltage setting unit 7 compares the temperature detection voltage Vf of the temperature sensing element 4 that detects the temperature of the MOSFET 1 with a determination voltage Vdsref (T) that is obtained by calculation. Thereby, even when the on-resistance Ron varies depending on the temperature in the wide temperature range of the MOSFET 1, it is possible to accurately determine the overcurrent.

Next, the specific circuit configuration of FIG. 1 will be described with reference to FIG.
In the N-channel MOSFET 1, a temperature-sensitive diode group 4 a (corresponding to a diode) as a temperature-sensitive element 4 is provided in the package so that the forward voltage Vf varies depending on the temperature of the MOSFET 1. Here, for example, a temperature sensing diode group 4a in which four temperature sensing diodes are connected in series is configured in consideration of sensitivity due to temperature. However, the number of temperature sensing diodes may be three or less. The number may be greater than or equal to the number required.

  The power supply circuit 14 provided in the integrated circuit is supplied with power from the power supply terminal VDD via the power supply terminal + B, generates a DC voltage of, for example, a voltage VREG of 5 V as a predetermined voltage, and supplies the power to the inside. Further, the reference voltage generation unit 15 steps down the voltage VREG from the power supply circuit 14 to generate a reference voltage VREF of, for example, 0.5V. The constant current circuit 16 is a constant current source for supplying a constant current to the anode terminal side of the temperature-sensitive diode group 4a via the terminal VA.

In the voltage detector 6, the operational amplifier 17 has a drain and a source of the MOSFET 1 connected between two input terminals via terminals VD and VS.
In the first correction circuit 8, the anode terminal and the cathode terminal of the temperature sensing diode group 4a are connected via the input terminals VA and VK, and the forward voltage of the temperature sensing diode group 4a is input as the temperature detection voltage Vf. The The operational amplifier 18 has a non-inverting input terminal connected to a terminal VA via a resistor R1a and grounded via a resistor R2a. Further, the operational amplifier 18 is supplied with the reference voltage VREF of the reference voltage generation unit 15 via the resistor R1b at the inverting input terminal, and is connected to the emitter of the pnp transistor 19 via the resistor R2b. The operational amplifier 18 has an output terminal connected to the base of the pnp transistor 19. The resistors R1a and R1b described above have the same resistance value R1, and the resistors R2a and R2b are set to the same resistance value R2. These resistance values R1 and R2 are variable, and are set in consideration of the characteristics of MOSFET 1 and other characteristics in the manufacturing process, as will be described later.

  In the second correction circuit 9, the operational amplifier 20 has a terminal VA connected to the inverting input terminal, and receives the temperature detection voltage Vf of the temperature-sensitive diode group 4a. The switching voltage Vx is set to be generated at the voltage dividing point S of the voltage dividing circuit of the resistors R5 and R6 connected between the output terminal of the reference voltage generating unit 15 and the ground. The operational amplifier 20 has a voltage dividing point S connected to a non-inverting input terminal and receives a switching voltage Vx.

  The current reference value generation unit 10 is connected to the emitter of the pnp transistor 19 by connecting a resistor R3a and a resistor R3b in series from the output terminal of the power supply circuit 14. The source / drain of the p-channel type MOSFET 21 is connected between both terminals of the resistor R3b. The output terminal of the operational amplifier 20 is connected to the gate of the MOSFET 21. When the operational amplifier 20 outputs a low level signal, the MOSFET 21 is turned on and the resistor R3b is short-circuited. The current reference value generation unit 10 generates a current reference value by the combined resistor R3 of the resistors R3a and R3b when the MOSFET 21 is off and by the resistor R3a when the MOSFET 21 is on.

The determination voltage generation unit 11 includes a resistor R4 connected between the collector of the pnp transistor 19 and the ground. The determination voltage generator 11 generates a determination voltage Vdsref (T) from the collector current of the pnp transistor 19 flowing through the resistor R4.
The resistance values R3a, R3b, and R4 described above are also variable, and are set in consideration of the characteristics of the MOSFET 1 and other characteristics in the manufacturing process, as will be described later.
The comparator 13 receives the drain / source voltage Vds of the MOSFET 1 from the output terminal of the operational amplifier 17 and the determination voltage Vdsref (T) generated by the determination voltage generation unit 11, and outputs the determination output as an overcurrent. The detection signal Sp is output.

Next, the operation of the above configuration will be described.
Prior to the operation of the above-described configuration, appropriate resistance values R1, R2, R3a, R3b for the resistors R1a, R1b, R2a, R2b, R3a, R3b, R4 for setting the determination voltage value in the above-described configuration R4 is set. The on-resistance Ron (T) of the MOSFET 1 and the temperature characteristics of the temperature-sensitive diode group 4a may vary depending on manufacturing variations, individual element variations, package variations, and the like, and the temperature detection voltage Vf ( It is necessary to set the determination voltage value Vdsref (T) with high accuracy from T). That is, the setting of the resistance values R1 to R4 corresponds to the correction of the first approximate line and the second approximate line described above.

  The resistors R1a to R4 are all configured as follows. That is, although illustration is omitted, MOSFETs that can partially short-circuit each resistor are provided for each of the resistors R1a to R4. Each resistance value can be set (adjusted) to a desired value according to the on / off state of the MOSFET. The on / off state of the MOSFET is determined based on absolute value correction information and inclination correction information stored in the storage unit 41. In this case, it is not necessary to adjust all the above-described resistors, and it can be set by adjusting the resistance value of the resistor necessary for setting the determination voltage value Vdsref (T) determined by the equation (4) described later.

  The on / off of the MOSFET may be determined based on the setting of an external terminal derived outside the chip (fixing the H / L level of the voltage applied to the terminal). In that case, the voltage applied to the external terminal may be set according to the absolute value correction information and the inclination correction information obtained in the manufacturing process as described above. In such a configuration, the setting of the external terminal corresponds to the absolute value correction information storage unit and the inclination correction information storage unit.

  Further, the setting of the resistance values R1 to R4 is not limited to the above-described electrical trimming. That is, the resistors R1a to R4 are not limited to those having a MOSFET for adjusting the resistance value, and may be configured to be trimmed. In that case, an appropriate resistance value R1 to R4 may be set by performing a trimming process such as laser trimming in the manufacturing process. In such a configuration, the trimming process for the resistors R1a to R4 corresponds to an absolute value correction information storage unit and an inclination correction information storage unit.

  First, the current flowing between the drain and source of the MOSFET 1, that is, the current Id flowing through the load 3 is input to the operational amplifier 17 of the voltage detection unit 6 as the drain / source voltage Vds multiplied by the on-resistance Ron of the MOSFET 1. At this time, the on-resistance Ron of the MOSFET 1 changes as shown in FIG. 2 according to the temperature T of the MOSFET 1, and therefore can be expressed as a function Ron (T) of the temperature T.

  A current Id flowing between the drain / source of the MOSFET 1 is detected as a drain / source voltage Vds, and this voltage Vds is compared with a determination voltage Vdsref (T) for determining an overcurrent in the comparator 13. At this time, the setting of the determination voltage value Vdsref (T) is generated by the temperature detection voltage Vf (T) of the temperature-sensitive diode group 4a. As described above, the value of the on-resistance Ron (T) of the MOSFET 1 is approximated by the first approximate line and the second approximate line to convert the temperature detection voltage Vf (T) to obtain a determination voltage approximated to Vdsref (T). Vdsref (Vf (T)) is obtained. With the circuit configuration of the first correction circuit 8, the second correction circuit 9, the current reference value generation unit 10, and the determination voltage generation unit 11 described above, the determination voltage value Vdsref (T) is expressed by the following equation (4). Can be obtained.

Vdsref (T) ≈Vdsref (Vf (T))
= R4 / R3 {VREG-R2 / R1 (Vf (T) -VREF)} (4)
In this case, the value of the temperature detection voltage Vf (T) is adjusted by taking a difference from the reference power supply voltage VREG that the inclination tendency is opposite to the characteristic of the on-resistance Ron (T) of the MOSFET 1, and the inclination The absolute value shift amount is adjusted by the resistance values R1 to R4.

In the equation (4), the value of the resistor R3 is switched under the condition of the following equation by switching according to the switching signal Sc output from the second correction circuit 9.
When Vf (T) ≧ Vf (Tx) (T ≦ Tx),
R3 = R3a + R3b (5a)
When Vf (T) <Vf (Tx) (T> Tx),
R3 = R3a (5b)
In this case, when the temperature T of the MOSFET 1 is equal to or higher than Tx, the temperature detection voltage Vf (T) of the temperature sensing diode group 4a decreases from the value of the switching voltage Vx as the temperature rises. A high level switching signal Sc is output. In this state, the MOSFET 21 is in the off state, and the resistance value R3 of the current reference value generation unit 10 is a combined resistance value of the resistors R3a and R3b in series as shown in the equation (5a).

  On the other hand, when the temperature T of the MOSFET 1 falls below Tx, the temperature detection voltage Vf (T) of the temperature sensing diode group 4a becomes lower than the switching voltage Vx, so that the operational amplifier 20 outputs a low level switching signal Sc. In this state, the MOSFET 21 is turned on and the resistor R3b is short-circuited. Therefore, the resistance value R3 of the current reference value generation unit 10 has a resistance value lower than that in the above case as shown in the equation (5b). Switch to resistor R3a.

As a result, in accordance with the value of the temperature detection voltage Vf, switching is performed along the inclinations θ1 and θ2 of the first approximate line and the second approximate line with the switching voltage Vx as a boundary, as shown in FIG. The determination voltage value Vdsref (Vf (T)) can be set following the change in the on-resistance Ron (T).
Therefore, the comparator 13 can determine the overcurrent with high accuracy by the drain / source voltage Vds corresponding to the current Id flowing through the MOSFET 1 even in the use environment where the temperature fluctuation occurs in a wide range. Become.

  According to the above-described embodiment, the temperature-sensitive diode group 4a is used as a temperature-sensitive element, and this terminal voltage is set as the temperature detection voltage Vf, which is used as the first correction circuit 8, the second correction circuit 9, and the current reference value. By setting the determination voltage value Vdsref (Vf (T)) by the generation unit 10 and the determination voltage generation unit 11, the on-resistance Ron (T ), And overcurrent can be determined with high accuracy.

  Moreover, since the structure which provides the diode group 4a for temperature sensing as a temperature sensing element is employ | adopted, since it can implement by the existing process which employ | adopts the process which builds a diode in MOSFET1, it manufactures without a new process design. be able to.

(Second Embodiment)
FIGS. 6 and 7 show a second embodiment of the present invention. Hereinafter, parts different from the first embodiment will be described. In the second embodiment, the switching method by the second correction circuit 9 is changed. That is, in this embodiment, as shown in FIG. 6, the first approximate line is applied to the temperature characteristic of the on-resistance Ron (T) of the MOSFET 1 in the first temperature region as in the first embodiment. In the second temperature region below the temperature Tx, the second approximate line is set in which the absolute value is greatly shifted with the slope of the first approximate line as it is.

  In this case, the size (shift amount) of the intercept of the second approximate line is set so that the second approximate line intersects at a lower temperature in the second temperature region. This is due to the following reason. That is, when the on-resistance Ron (T) is adjusted with a single approximate line, if the slope and intercept are matched on the first temperature region side that is the high temperature side that is frequently used, the second temperature that is on the low temperature side. Since the determination voltage value is set low on the region side, there is a case where it is determined that the current is actually overcurrent even though the drain-source current Id is small. Therefore, in this embodiment, instead of keeping the slope of the approximate straight line the same, by setting the intercept on the second temperature region side, the overcurrent is determined with a small current Id on the low temperature side. Is to prevent. As a result, a highly accurate determination operation can be secured on the first temperature region side where the usage frequency is high, and the occurrence of erroneous determination can be suppressed even on the second temperature region side where the usage frequency is low. is there.

Next, with reference to FIG. 7, a description will be given of a specific circuit configuration that is different from the first embodiment.
Instead of the current reference value generation unit 10 in the first embodiment, a current reference value generation unit 10a having a configuration excluding the resistor R3b is provided. Further, in place of the P-channel type MOSFET 21 for short-circuiting the resistor R3b, a P-channel type MOSFET 22 and a constant current circuit 23 are provided. The MOSFET 22 has a source terminal connected to the constant current circuit 23, a drain terminal connected to the collector of the pnp transistor 19, and a gate terminal connected to the output terminal of the operational amplifier 20. In this embodiment, the resistance value R3 of the resistor R3 is set to correspond to the resistance value R3 obtained by combining the resistance values of the resistors R3a and R3b in the first embodiment.

  Next, the operation of the above configuration will be described. In the state where the temperature T of the MOSFET 1 is in the first temperature region equal to or higher than Tx, the temperature detection voltage Vf () along the first approximate line is satisfied in the same manner as in the first embodiment under the condition according to the equation (4). T) is converted into a determination voltage value Vdsref (Vf (T)).

  When the temperature of the MOSFET 1 enters the second temperature range below Tx, the level of the temperature detection voltage Vf (T), which is the forward voltage of the temperature sensing diode group 4a, increases, and the switching voltage Vx, which is the comparison voltage, is set. It will exceed. Then, the output of the operational amplifier 20 of the second correction circuit 9 is inverted to a low level, so that the MOSFET 22 is turned on and flows with a predetermined current added from the constant current circuit 23 to the resistor R4. As a result, the determination voltage value Vdsref (Vf (T)), which is the comparison input of the comparator 13, is added by the amount corresponding to the voltage component generated when the current from the constant current circuit 23 flows through the resistor R4. The determination voltage value Vdsref (Vf (T)) is set along the second approximate line as shown in FIG.

  Therefore, the comparator 13 can determine an overcurrent with high accuracy from the drain / source voltage Vds corresponding to the current Id flowing through the MOSFET 1 even in a usage environment where the temperature fluctuation occurs in a wide range. In the second temperature region where the frequency is low, erroneous determination can be reduced.

( First reference example )
8 and 9 show a first reference example of the present invention. The difference from the first embodiment is that the signal processing is configured to be digital processing. That is, as shown in FIG. 8, a determination circuit unit 5a as a current determination device is connected to two analog-to-digital converters (ADCs) 24 and 25 (A) for a MOSFET 1 having a temperature sensitive element 4 (4a). / Corresponding to a D conversion unit) and a CPU 26.
The drain / source voltage Vds of the MOSFET 1 is input to the ADC 24 as Vds information that is input to the ADC 24 and converted into a digital signal. The temperature detection voltage Vf of the temperature sensing element 4 is input to the ADC 26 as temperature information input to the ADC 25 and converted into a digital signal.

FIG. 9 shows a process in the CPU 26 as a block configuration. In FIG. 9, the temperature information is input to the calculation unit 27, and an adder 28 and a multiplier 29 perform calculation processing corresponding to Expression (4) in the first embodiment.
Here, an electrical trimming process is performed. Instead of setting the resistance values corresponding to the resistors R1a, R1b, R2a, R2b, R3a, R3b, and R4, the value of each resistance value of the equation (4), which is an arithmetic expression, is stored in the memory correction unit 30 as data. I remember it. The resistance value data can be read out during the arithmetic processing, and the approximation of the on-resistance Ron (T) corresponding to each MOSFET 1 can be approximated by the first and second approximate lines. That is, in the present embodiment, the memory correction unit 30 corresponds to an absolute value correction information storage unit and an inclination correction information storage unit.

In this way, the calculation unit 27 calculates the determination voltage value Vdsref (Vf (T)), and the comparator 31 (corresponding to the determination unit) compares the data with the drain / source voltage Vds data of the MOSFET 1 as Vds information. The determination output can be obtained by determining whether or not an overcurrent flows through the MOSFET 1.
As described above, since the processing configuration corresponding to the first embodiment is implemented by digital signal processing, the same effects as those of the first embodiment can be obtained.

( Second reference example )
FIG. 10 shows a second reference example of the present invention. The difference from the first reference example is that a block unit in the CPU 26 is provided with a table unit 32 instead of the calculation unit 27. This is because, when temperature information, which is a digital signal of the temperature detection voltage Vf (T), is input, the calculation result data corresponding to the corresponding determination voltage value Vdsref (Vf (T)) is stored in the memory as a table. It is what I did. Even in this case, the basic calculation portion is stored as a corresponding table, and data for correcting this is stored in the memory correction unit 30 in the electric trimming process.

Even with such a configuration, the same effects as those of the first reference example can be obtained. In the second reference example , since the table for converting data is stored and held by the table unit 32, the conversion accuracy is determined by the storage capacity of the data. For this reason, in the case of a configuration in which the data storage capacity of the memory can be increased, it is possible to perform a quick determination process with less arithmetic processing.

(Other embodiments)
The present invention is not limited to the embodiments described above or shown in the drawings, and the following modifications or expansions are possible.
In each of the above embodiments, the determination voltage value Vdsref (Vf (T)) is set by approximating the temperature characteristic of the on-resistance Ron (T) of the MOSFET 1 with two approximate lines. For the purpose of increasing, three or more approximate straight lines may be set.
In this case, in the first embodiment, the switching voltage Vx by the second correction circuit 9 is set as switching voltages Vx1, Vx2,... Corresponding to the number of switching stages, and the respective switching voltages are obtained. It is configured to output switching signals Sc1, Sc2,. Further, the current reference value generation unit 10 is provided with MOSFETs that are turned on / off corresponding to each of the plurality of switching signals Sc1, Sc2,..., And provided with resistors R3b, R3c,. The determination voltage value Vdsref (Vf (T)) converted along each approximate line can be set by sequentially setting the resistors R3b, R3c,...

  Further, in the second embodiment, the configuration of the second correction circuit 9 is configured in the same manner as described above as a configuration in which three or more approximate lines are set, and is set as switching voltages Vx1, Vx2,. The switching signals Sc1, Sc2,... Corresponding to the respective switching voltages are output. Further, in the current reference value generation unit 10, MOSFETs that are turned on / off corresponding to each of the plurality of switching signals Sc1, Sc2,... Are provided in parallel to the collector of the transistor 19, and each time the MOSFETs are turned on, the constant current source is used. The determination voltage value Vdsref (Vf (T)) converted so as to follow each approximate line can be set by increasing the current that is sequentially added every time the temperature is shifted to the low temperature region.

By setting the resistance values R1 to R4, the slope of the approximate line and the intercept are set to be larger or smaller than the on-resistance Ron (T) so as to meet the overcurrent determination conditions. It is possible to selectively set whether to match.
Although the temperature-sensitive diode group 4a in which four temperature-sensitive diodes are connected in series is used as the temperature-sensitive element 4, the number can be set as appropriate. Further, instead of using the forward voltage of the diode, for example, the temperature detection voltage may be obtained by using the temperature dependence characteristic of the Zener voltage of the Zener diode. Further, instead of the temperature sensing diode, for example, a structure in which a MOSFET 1 and another temperature sensing MOSFET are integrally provided is provided, and the variation of the on resistance Ronref (T) similar to the temperature characteristic of the on resistance Ron (T) of the MOSFET 1 Can be determined to set the determination voltage value Vdsref (T).

Although the present invention is configured to determine the detection voltage Vds (T) by correcting the determination voltage, the detection voltage Vds (T) is converted to the temperature of the on-resistance Ron (T) of the MOSFET 1 using the same concept. A configuration may be employed in which the current value Id is calculated by performing correction in consideration of the characteristics. In this case, it can be set as the structure which detects an electric current directly. Further, the determination voltage or determination current value to be compared can be set to a predetermined level.

In the first embodiment and the second embodiment, as a specific circuit configuration, the first correction circuit 8, the second correction circuit 9, the current reference value generation unit 10, and the determination voltage generation unit 11 are replaced with an operational amplifier or the like. However, the circuit configuration is not limited to this, and other circuit elements and circuit configurations can be used as long as the configuration is an analog signal processing circuit .

  In the present embodiment, the laser trimming method and the electric trimming method are shown as the trimming process, but a Zener zap method can be used in addition. In this case, when the MOSFET 1 and the determination circuit unit 5 are configured on the same chip, laser trimming and zener zap trimming can be performed. In addition, in the configuration in which the MOSFET 1 and the determination circuit unit 5 are provided separately, the above method is difficult, and thus an electric trimming method can be employed.

  In the above embodiment, since the present invention is applied to an overcurrent detection device that detects that an overcurrent has flowed between the drain / source of the MOSFET 1, the level of the current determined by the determination unit is set to a level at which the overcurrent is detected. However, the present invention is not limited to this. That is, the current level determined by the determination means can be set to an arbitrary value.

  In the drawing, 1 is a MOSFET (FET), 3 is a load, 4 is a temperature sensing element, 4a is a temperature sensing diode group (diode), 5 and 5a are judgment circuit parts (current judgment devices), and 6 is a voltage detection part ( (Voltage detection means), 7 is a determination voltage setting unit (determination voltage setting means), 8 is a first correction circuit, 9 is a second correction circuit, 10 is a current reference value generation unit, 11 is a determination voltage generation unit, 12 Is a determination voltage generation circuit, 13 and 31 are comparators (determination means), 24 and 25 are ADCs (A / D conversion units), 30 is a memory correction unit (absolute value correction information storage unit and inclination correction information storage unit), Reference numeral 41 denotes a storage unit (absolute value correction information storage means and tilt correction information storage means).

Claims (9)

Voltage detection means for detecting the drain-source voltage of the MOSFET provided in the power supply path to the load;
A temperature-sensitive element provided to measure the temperature of the MOSFET and outputting a temperature detection voltage that linearly changes with respect to a temperature change;
Determination means for comparing the drain-source voltage detected by the voltage detection means and a determination voltage obtained by multiplying the determination current value by the on-resistance value of the MOSFET to determine the current level of the MOSFET;
The temperature characteristics of the on-resistance of the MOSFET is divided into a plurality of temperature regions, and approximate on-resistances are set by applying approximate lines in each temperature region, and the temperature detection voltage by the thermosensitive element corresponds to the temperature at that time Correction voltage corresponding to the approximate on-resistance value, and determination voltage setting means for generating the determination voltage based on the approximate on-resistance value ;
With
The determination voltage setting means includes
A first correction circuit for correcting a temperature detection voltage by the temperature sensing element to a reference approximate on-resistance value corresponding to a reference approximate line in a predetermined temperature region;
A second correction circuit for outputting a switching signal for correction when the temperature detection voltage of the temperature sensing element corresponds to a temperature range different from the temperature range of the reference approximate line;
The determination voltage based on the approximate on-resistance value obtained by correcting the reference approximate on-resistance value by the first correction circuit according to the presence or absence of the correction switching signal from the second correction circuit. A determination voltage generation circuit for generating
With
The MOSFET current determination device, wherein each of the first correction circuit, the second correction circuit, and the determination voltage generation circuit is configured by an analog circuit . In the MOSFET current determination device according to claim 1,
The determination voltage setting means is obtained by fitting an approximate straight line in which the temperature characteristics of the on-resistance of the MOSFET are divided and set into a plurality of temperature regions by translating an approximate straight line having the same inclination between adjacent temperature regions. A MOSFET current determination device, characterized in that: In the MOSFET current determination device according to claim 2,
The determination voltage generation circuit includes:
The approximate straight line in which the reference approximate on-resistance value by the first correction circuit is set in a temperature region corresponding to the temperature of the MOSFET according to the presence or absence of the switching signal for correction from the second correction circuit. MOSFET current determination device comprising a benzalkonium generates the determination voltage, based on the approximation on-resistance obtained by correcting along the level. In the MOSFET current determination device according to claim 1,
The determination voltage setting unit sets an approximate straight line that sets the temperature characteristics of the on-resistance of the MOSFET by dividing it into a plurality of temperature regions as a result of connecting adjacent temperature regions with a broken line. MOSFET current determination device. In the MOSFET current determination device according to claim 4,
The determination voltage generation circuit includes:
The approximate straight line in which the reference approximate on-resistance value by the first correction circuit is set in a temperature region corresponding to the temperature of the MOSFET according to the presence or absence of the switching signal for correction from the second correction circuit. MOSFET current determination device comprising a benzalkonium generates the determination voltage, based on the approximation on-resistance obtained by correcting along the slope of the. In the MOSFET current determination device according to any one of claims 1 to 5,
An absolute value correction information storage means for storing absolute value correction information for correcting the approximate straight line so that the value of the approximate on-resistance at a predetermined temperature matches the actual on-resistance value of the MOSFET at the temperature; Prepared,
The MOSFET current determination device, wherein the determination voltage setting means corrects the approximate straight line using the absolute value correction information stored in the absolute value correction information storage means. In the MOSFET current determination device according to any one of claims 1 to 6,
Slope correction information for correcting the approximate line so that the slope of the approximate straight line of the approximate on-resistance in a predetermined temperature region matches the slope of the actual on-resistance value of the MOSFET in the temperature region is stored. Inclination correction information storage means,
The determination voltage setting means corrects the approximate straight line using the inclination correction information stored in the inclination correction information storage means. In the MOSFET current determination device according to any one of claims 1 to 7,
A current determination device for a MOSFET, wherein the current level determined by the determination means is set to a level for detecting an overcurrent. In the MOSFET current determination device according to any one of claims 1 to 8,
2. The MOSFET current determination device according to claim 1, wherein the temperature sensing element is constituted by a diode disposed in the vicinity of the MOSFET, and a forward voltage of the diode is used as the temperature detection voltage.

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