JP2007306664A - Overvoltage protection circuit, charger using same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably protect a circuit from an overvoltage by making an overvoltage protection circuit built therein. <P>SOLUTION: The overvoltage protection circuit 50 is built in a semiconductor integrated circuit, and clamps power supply voltages Vdd fed to power supply terminals 104a, 104b of the semiconductor integrated circuit to a prescribed clamp voltage or lower. A first clamp circuit 56 and a first switch M1 are arranged in series between the power supply terminal 104b of the semiconductor integrated circuit and a fixed voltage terminal. A reference voltage source 52 generates a prescribed reference voltage Vref. A comparator 54 compares a voltage Vdd" which corresponds to a power supply voltage Vdd' fed to the power supply terminal 104b with the reference voltage Vref. The comparator 54 turns on the first switch M1 so that an expression of Vdd">Vref is satisfied. A current-voltage conversion circuit 60 converts a current Ix flowing to a passage including the first clamp circuit 56 and the first switch M1 into a voltage Vx. When the converted voltage Vx exceeds a prescribed threshold voltage, a part of a function of the semiconductor integrated circuit is stopped. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an overvoltage protection circuit that protects a circuit from an overvoltage.

  Various electronic devices such as mobile phones, PDAs (Personal Digital Assistants), and notebook personal computers in recent years include CPUs (Central Processing Units) that perform digital signal processing, other DSPs (Digital Signal Processors), and liquid crystals. Many electronic circuits such as panels and other analog circuits are installed. These electronic circuits operate with power supplied from a battery or a power supply circuit that stabilizes the battery voltage.

  Circuit elements such as resistors and transistors constituting such an electronic circuit have a withstand voltage. When a voltage exceeding the withstand voltage is applied, a normal function cannot be performed.

Japanese Patent Laid-Open No. 9-219935

  In general, a CPU, a DSP, and the like operate with a voltage stabilized by a power supply circuit built in an electronic device, and thus there are not many situations in which an unexpected overvoltage is applied. On the other hand, a charging circuit or the like that charges a battery receives a power supply voltage from the outside, and performs a circuit operation using the power supply voltage.

  In this case, when the user uses an external power supply circuit that should be used, an unexpected overvoltage is not applied to the charging circuit, but the user uses an external power supply that is not compatible with the electronic device. In such a case, it may be assumed that a very large overvoltage exceeding the breakdown voltage is applied to the charging device.

  The present invention has been made in view of such problems, and an object thereof is to provide an overvoltage protection circuit capable of suitably protecting a circuit from an overvoltage.

  One embodiment of the present invention relates to an overvoltage protection circuit that is built in a semiconductor integrated circuit and clamps a power supply voltage supplied to a power supply terminal of the semiconductor integrated circuit below a predetermined clamp voltage. The overvoltage protection circuit supplies a first clamp circuit and a first switch provided in series between a power supply terminal and a fixed voltage terminal of a semiconductor integrated circuit, a reference voltage source for generating a predetermined reference voltage, and a power supply terminal. A comparator that compares a voltage according to the power supply voltage to a reference voltage. The comparator turns on the first switch when the voltage corresponding to the power supply voltage becomes higher than the reference voltage. “Fixed voltage terminal” refers to a terminal having a fixed potential, such as a ground terminal, a positive / negative power supply terminal, or a reference voltage terminal.

  According to this aspect, when the power supply voltage supplied to the power supply terminal exceeds the threshold voltage, the path including the first switch and the first clamp circuit becomes conductive. As a result, the power supply voltage is clamped to be equal to or lower than the clamp voltage, and overvoltage protection can be realized.

In one aspect, a current-voltage conversion circuit that converts a current flowing through a path including the first clamp circuit and the first switch into a voltage may be further included. When the converted voltage exceeds a predetermined threshold voltage, a part of the function of the semiconductor integrated circuit may be stopped.
In this case, it is possible to prevent a part of the functions of the semiconductor integrated circuit from operating in an overvoltage state and malfunctioning or causing a malfunction.

The overvoltage protection circuit according to an aspect may further include a second clamp circuit and a second switch provided in series in a path parallel to the path from the first switch to the fixed voltage terminal. The reference voltage source is configured to output a low voltage detection signal that is at a predetermined level when a predetermined reference voltage cannot be output due to a low power supply voltage supplied to the semiconductor integrated circuit. The low voltage detection signal may be turned on for a predetermined level.
In this case, even if an overvoltage is applied before the reference voltage source is activated, the path of the second clamp circuit and the second switch is reliably activated, so that the voltage at the power supply terminal can be clamped appropriately.

  The first clamp circuit may include a diode. A plurality of diodes may be connected in series. In this case, the clamp voltage can be adjusted according to the number of diodes.

  In one embodiment, the first switch may be a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The comparator may output a low-level comparison signal to the gate of the P-channel MOSFET that is the first switch when the voltage according to the power supply voltage is higher than the reference voltage. In this case, the P-channel MOSFET can be turned on in the overvoltage state.

  In one embodiment, the first switch is a P-channel MOSFET, and the second clamp circuit and the second switch are connected in series between the gate and the fixed voltage terminal of the P-channel MOSFET and the gate source of the P-channel MOSFET. A pull-up resistor may be provided between them.

  In one embodiment, the current-voltage conversion circuit includes a first transistor provided in series with the first clamp circuit and the first switch, a second transistor connected to the first transistor in a current mirror, and a potential at one end fixed. A current corresponding to the current flowing through the second transistor may be converted into a voltage by flowing through the resistor.

  Another aspect of the present invention is a charging device that charges a battery based on a power supply voltage from an external power supply. This charging device is integrated on a semiconductor substrate with a charging transistor provided on a path from an external power source to the battery, and charging control for adjusting a charging current supplied to the battery by adjusting an ON state of the charging transistor. A circuit and a voltage adjustment circuit that is provided on a power supply path from an external power supply to a power supply terminal of the charge control circuit and generates a necessary voltage drop. The charge control circuit includes the overvoltage protection circuit according to any one of the above aspects that clamps the voltage of the power supply terminal of the charge control circuit below a predetermined clamp voltage, and the battery voltage approaches a predetermined voltage value. And a current adjusting circuit for adjusting an on state of the charging transistor.

  In some embodiments, the voltage regulation circuit may be a resistor.

  In one embodiment, the voltage adjustment circuit includes a protection transistor provided on a power supply path from an external power supply to the power supply terminal of the charge control circuit, a terminal connected to the external power supply of the protection transistor, and a control terminal of the protection transistor. And a provided resistor. The overvoltage protection circuit may clamp the voltage at the power supply terminal of the charge control circuit below the clamp voltage by clamping the voltage at the control terminal of the protection transistor below a predetermined voltage.

  The charging device of a certain aspect may further include a capacitor provided between the control terminal and the fixed voltage terminal of the protection transistor. In this case, since the RC circuit is configured by the resistor and the resistance connected to the control terminal of the protection transistor, reliable circuit protection can be realized even when the voltage supplied from the external power supply suddenly increases.

  In one aspect, the overvoltage protection circuit may stop the charging function of the charging control circuit and cut off the charging current supplied to the battery from the external power supply when the voltage of the power supply terminal of the charging control circuit is clamped. Good.

  Yet another embodiment of the present invention is an electronic device. This electronic device includes a battery and the above-described charging device that charges the battery based on a power supply voltage from an external power supply.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the overvoltage protection circuit of the present invention, the circuit can be suitably protected from overvoltage.

  Hereinafter, a charging circuit and a clamp circuit according to embodiments of the present invention will be described with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. Further, in the following description, reference numerals attached to voltage signals, current signals, resistors, capacitors, and the like are used to represent the respective voltage values, current values, resistance values, and capacitance values as necessary.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of the entire charging circuit 200a and electronic device 1000 according to the first embodiment.
The electronic device 1000 is a battery-driven information terminal device such as a mobile phone terminal, PDA, or notebook PC. The electronic device 1000 includes a charging circuit 200a and a battery 220. In addition, the electronic device 1000 includes a power supply circuit (not shown), a DSP, a liquid crystal panel, and other analog and digital.

  The battery 220 is a secondary battery such as a lithium ion or NiCd (nickel cadmium) battery, and the battery voltage Vbat is supplied to other circuit blocks of the electronic device 1000.

  The external power source 210 is connected to the electronic device 1000 and is an AC adapter that converts a commercial AC voltage into a DC voltage, a DC / DC converter that steps down the voltage of an in-vehicle battery, and the like, and is connected to the electronic device 1000. The external power supply 210 supplies a DC power supply voltage Vdc to the charging circuit 200a.

  Charging circuit 200a charges battery 220 based on power supply voltage Vdc from external power supply 210. The charging circuit 200a includes a charging transistor Tr1, a charging control circuit 100a, a voltage adjustment circuit 110, and other circuit elements.

  The charging transistor Tr1 is provided on a charging path from the external power source 210 to the battery 220. In the present embodiment, the charging path is a path that reaches the battery 220 via the charging transistor Tr1, the second current control terminal 108 of the charging control circuit 100a, and the battery terminal 102. The charging transistor Tr1 is a PNP-type bipolar transistor, and an emitter is connected to the external power source 210. A second resistor R2 is connected between the emitter and base of the charging transistor Tr1. In addition, a charging control transistor Tr2 is connected between the base of the charging transistor Tr1 and a ground terminal which is a fixed voltage terminal. The charge control transistor Tr2 is an NPN bipolar transistor, and has a collector connected to the base of the charge transistor Tr1 and an emitter connected to the ground terminal.

  The charging control circuit 100a is integrated on the semiconductor substrate, and adjusts the ON state of the charging transistor Tr1 to adjust the charging current Ichg supplied to the battery 220. The charge control circuit 100a includes a battery terminal 102, a power supply terminal 104, a first current control terminal 106, and a second current control terminal 108 as input / output terminals.

  A battery 220 is connected to the battery terminal 102, and a collector of the charging transistor Tr1 is connected to the second current control terminal 108. From the first current control terminal 106, a control voltage Vcnt for controlling the degree of ON of the charging transistor Tr1 is output. This control voltage Vcnt is input to the base of the charge control transistor Tr2. The power supply terminal 104 is a power supply terminal of the charging control circuit 100a itself, and is supplied with the power supply voltage Vdd. Hereinafter, in order to avoid confusion, the power supply voltage from the external power supply 210 is distinguished as the external power supply voltage Vdc, and the power supply voltage supplied to the first current control terminal 106 is distinguished as necessary as the internal power supply voltage Vdd.

  In the present embodiment, voltage adjustment circuit 110 includes voltage control resistor R1 and is provided on a power supply path from external power supply 210 to power supply terminal 104 of charge control circuit 100a. A voltage drop occurs in voltage adjusting circuit 110 according to the operation, and external power supply voltage Vdc is stepped down to internal power supply voltage Vdd. The resistance value of the voltage control resistor R1 is designed to be about 100Ω, for example.

  The charge control circuit 100a includes a clamp circuit 10, a current adjustment circuit 20, and other circuit elements. Circuits inside the charging control circuit 100a including the current adjusting circuit 20 operate using the internal power supply voltage Vdd as a power source.

  For example, the charging control circuit 100a is configured to stably charge the battery 220 in a state where a voltage of about 5 V is supplied from the external power supply 210 as the external power supply voltage Vdc. However, a situation where an unexpected device is connected as the external power supply 210 and an overvoltage of about 30 V, for example, greatly exceeding 5 V as the external power supply voltage Vdc is assumed. The charge control circuit 100a has a built-in overvoltage protection circuit for protecting circuit elements from such overvoltage.

  The clamp circuit 10 functions as an overvoltage protection circuit that clamps the voltage Vdd of the power supply terminal 104 of the charge control circuit 100a to a predetermined clamp voltage Vclmp or less. The clamp voltage Vclmp may be set according to the breakdown voltage determined by the semiconductor manufacturing process of the charge control circuit 100a. In general, a high breakdown voltage process is disadvantageous from the viewpoint of integration. Therefore, it is desirable to select a process with a low breakdown voltage as much as possible after satisfying the reliability. From this point, it is desirable to set a voltage value slightly higher than the external power supply voltage Vdc = 5V assumed during normal operation. For example, the charge control circuit 100a may be designed by a 7V withstand voltage process that is 2V higher than the external power supply voltage Vdc = 5V. The clamp voltage Vclmp of the clamp circuit 10 may be set according to the withstand voltage of the charge control circuit 100a, and is set to about 6.8V, which is lower than 7V, for example.

  The current adjusting circuit 20 controls the charging current Ichg by adjusting the on state of the charging transistor Tr1 so that the voltage Vbat of the battery 220 approaches a predetermined voltage value. The current adjustment circuit 20 includes an error amplifier 22, a third resistor R3, and a fourth resistor R4. The third resistor R3 and the fourth resistor R4 divide the battery voltage Vbat appearing at the battery terminal 102, and output the feedback voltage Vfb given by Vbat × R4 / (R3 + R4) to the inverting input terminal of the error amplifier 22. A predetermined reference voltage Vref is applied to the non-inverting input terminal of the error amplifier 22. The output terminal of the error amplifier 22 is connected to the base of the charge control transistor Tr2 via the first current control terminal 106, and outputs the charge control voltage Vcnt. When the turn-on degree of the charge control transistor Tr2 is controlled by the charge control voltage Vcnt, the collector current of the charge control transistor Tr2 changes and the voltage drop in the second resistor R2 changes. As a result, the base-emitter voltage of the charging transistor Tr1 changes, and the degree of ON of the charging transistor Tr1 is adjusted.

  A charge stop switch M3 and a fifth resistor R5 are provided in series between the second current control terminal 108 and the battery terminal 102 of the charge control circuit 100a. The charging current Ichg flowing through the charging transistor Tr1 is supplied to the battery 220 via the charging stop switch M3 and the fifth resistor R5.

  In the present embodiment, the clamp circuit 10 clamps the internal power supply voltage Vdd of the power supply terminal 104 of the charge control circuit 100a, that is, in a state where the external power supply voltage Vdc supplied from the external power supply 210 has increased. The charging current Ichg supplied from the external power source 210 to the battery 220 is cut off. Specifically, the charging current Ichg is cut off by turning off a charging stop switch M3 provided on the path of the charging current Ichg from the external power supply 210 to the battery 220.

  The operation of the charging circuit 200 configured as described above will be described. When a normal external power supply voltage Vdc of about 5 V is supplied from the external power supply 210, the clamp function of the clamp circuit 10 does not work, and the charge control circuit 100a executes a normal charge function. The error amplifier 22 adjusts the base voltage of the charging transistor Tr1, that is, the on-state so that the voltages of the inverting input terminal and the non-inverting input terminal are equal, that is, Vfb = Vref, and is appropriate for the battery 220. A charging current Ichg is supplied.

  Now, it is assumed that an overvoltage of about 30 V is applied from the external power supply 210 as the external power supply voltage Vdc. At this time, the internal power supply voltage Vdd of the power supply terminal 104 tends to increase as the external power supply voltage Vdc increases, but the clamp circuit 10 clamps the internal power supply voltage Vdd so that it does not rise above the clamp voltage Vclmp. Function. A voltage drop corresponding to the difference between the external power supply voltage Vdc = 30V and the internal power supply voltage Vdd = Vclmp occurs in the voltage control resistor R1 that is the voltage adjustment circuit 110.

  According to the charging circuit 200a according to the present embodiment, the clamp voltage Vclmp is set according to the withstand voltage of the charging control circuit 100a, and the clamping circuit 10 is built in the charging control circuit 100a, whereby the overvoltage is set as the power supply voltage Vdc. Even if is applied, a voltage drop is generated by the voltage adjustment circuit 110, so that a voltage exceeding the clamp voltage Vdc can be prevented from being applied to the power supply terminal 104.

  In addition, the clamp circuit 10 turns off the charging stop switch M3 and cuts off the charging current Ichg in a state where the internal power supply voltage Vdd is clamped. By stopping the charging function in the overvoltage state, safer circuit protection can be realized.

  Further, since the circuit configuration can be realized simply by incorporating the clamp circuit 10 in the charge control circuit 100a and adding the voltage control resistor R1, it is possible to suitably realize overvoltage protection without increasing the number of circuit components. Can do.

(Second Embodiment)
FIG. 2 is a circuit diagram showing a configuration of a charging circuit 200b according to the second embodiment. Hereinafter, the difference from the first embodiment will be mainly described.

The charging circuit 200a of FIG. 1 uses a resistance element as the voltage adjustment circuit 110. As a result, the power consumption in the voltage control resistor R1 may increase when an overvoltage is applied. For example, when the external power supply voltage Vdc = 30V and the clamp voltage Vclmp = 7, a voltage drop of 23V occurs. Therefore, when the resistance value is 100Ω, power consumption of about 23 ² / 100≈5W is generated. Therefore, it is necessary to select an element having a rated power of 5 W or more as the voltage control resistor R1. In some cases, it is desirable to avoid using a resistive element having a large rated power from the viewpoint of the size and cost of the component. The charging circuit 200b according to the second embodiment described below is effective when it is not desired to use a resistance element having a large rated power.

  In the present embodiment, the voltage adjustment circuit 110 includes a protection transistor Tr3 and a sixth resistor R6. The protection transistor Tr3 is provided on a power supply path from the external power supply 210 to the power supply terminal 104a of the charge control circuit 100b. The protection transistor Tr3 is an NPN bipolar transistor, and has an emitter connected to the power supply terminal 104a side of the charge control circuit 100b and a collector connected to the external power supply 210 side. The sixth resistor R6 is provided between a base that is a control terminal of the protection transistor Tr3 and a collector that is a terminal connected to the external power supply 210 of the protection transistor Tr3.

  The base of the protection transistor Tr3 is connected to the power supply terminal 104b of the charge control circuit 100b. In the present embodiment, the clamp circuit 10 clamps the base voltage of the protection transistor Tr3 to a predetermined threshold voltage Vth or less, thereby setting the voltage Vdd of the power supply terminal 104a of the charge control circuit 100b to the clamp voltage Vclmp or less. Clamp to In the present embodiment, Vclmp = Vth−Vf is established between the threshold voltage Vth and the clamp voltage Vclmp. Here, Vf is a forward voltage of the base-emitter diode of the protection transistor Tr3.

  A capacitor C1 is provided between the base of the protection transistor Tr3 and the ground terminal.

  The operation of the charging circuit 200b configured as described above will be described. When an overvoltage is applied as the external power supply voltage Vdc by the external power supply 210, the collector voltage of the voltage adjustment circuit 110 increases, and accordingly, the base voltage, that is, the voltage of the power supply terminal 104b also increases. Since the clamp circuit 10 clamps the power supply terminal 104b so that the voltage does not exceed the threshold voltage Vth, the internal power supply voltage Vdd is clamped to Vclmp (= Vth−Vf) or less.

  At this time, the current flowing through the sixth resistor R6 is 1 / hfe of the collector current of the protection transistor Tr3. Here, hfe is a current amplification factor of the protection transistor Tr3. That is, in the second embodiment, the current flowing through the sixth resistor R6 is very small compared to the current flowing through the voltage control resistor R1 of the first embodiment. As a result, the sixth resistor R6 can have a resistance value of several tens to 100 times the resistance value of the voltage control resistor R1. At this time, the power consumed by the sixth resistor R6 in the overvoltage state is reduced to about 1 to 1/100 that is several tenths of the power consumed by the voltage control resistor R1 of the first embodiment.

  As a result, the rated power of the sixth resistor R6 can be lowered, and the degree of freedom in circuit design can be increased.

  In the charging circuit 200b according to the present embodiment, the sixth resistor R6 and the capacitor C1 form a CR time constant circuit. Therefore, even when the external power supply voltage Vdc suddenly rises, the rise of the voltage at the power supply terminals 104a and 104b is delayed with respect to the rise, so that even if the operation speed of the clamp circuit 10 is slow, it is ensured. It is possible to prevent the internal power supply voltage Vdd supplied to the charge control circuit 100b from exceeding the clamp voltage.

  Next, a configuration of overvoltage protection used as a clamp circuit in the charging circuits 200a and 200b according to the first and second embodiments will be described.

  FIG. 3 is a circuit diagram showing a configuration of an overvoltage protection circuit 50 used as the clamp circuit 10 in the first and second embodiments. The overvoltage protection circuit 50 is a clamp circuit that is built in the semiconductor integrated circuit and clamps the power supply voltage Vdd supplied to the power supply terminal 104a of the semiconductor integrated circuit below a predetermined clamp voltage.

  The overvoltage protection circuit 50 includes a reference voltage source 52, a comparator 54, a first clamp circuit 56, a second clamp circuit 58, a first switch M1, a second switch M2, and a current-voltage conversion circuit 60.

  The first clamp circuit 56 and the first switch M1 are provided in series between the power supply terminal 104b and the ground terminal of the charge control circuit 100b. The first clamp circuit 56 includes a plurality of diodes having an anode connected to the power supply terminal 104b side and a cathode connected to the ground terminal side. The first switch M <b> 1 is a P-channel MOSFET whose source is connected to the first clamp circuit 56.

  The reference voltage source 52 is a band gap regulator or the like, and generates a predetermined reference voltage Vref and applies it to the non-inverting input terminal of the comparator 54. The seventh resistor R7 and the eighth resistor R8 divide the voltage Vdd 'of the power supply terminal 104b and apply it to the inverting input terminal of the comparator 54.

  The comparator 54 compares the voltage Vdd ″ corresponding to the power supply voltage Vdd ′ of the power supply terminal 104b applied to the inverting input terminal with the reference voltage Vref, and controls on / off of the first switch M1 according to the comparison result. . In the present embodiment, the comparator 54 outputs a comparison signal Vcmp that is at a low level when Vdd ″> Vref. The first switch M1 is turned on when the comparison signal Vcmp is at a low level and turned off when the comparison signal Vcmp is at a high level.

  The current-voltage conversion circuit 60 converts a current Ix flowing through a path including the first clamp circuit 56 and the first switch M1 into a voltage Vx. The current-voltage conversion circuit 60 stops part of the functions of the semiconductor integrated circuit when the voltage Vx obtained by the conversion exceeds a predetermined threshold voltage. In the first and second embodiments, the case where the charging function is stopped has been described.

  The current-voltage conversion circuit 60 includes a first transistor Q1 to a fourth transistor Q4 and a ninth resistor R9. The first transistor Q1 is provided on the same current path in series with the first clamp circuit 56 and the first switch M1. The second to fourth transistors Q2 to Q4 are current mirror connected to the first transistor Q1. The current Ix ′ replicated by the second to fourth transistors Q2 to Q4 is passed through a ninth resistor R9 having a fixed potential at one end, and a voltage of Vx = R9 × Ix ′ is generated.

  The voltage Vx is input to the base of the fifth transistor Q5 whose emitter is grounded. The tenth resistor R10 is provided between the collector of the fifth transistor Q5 and the power supply terminal 104b. When the voltage Vx exceeds the threshold voltage and the fifth transistor Q5 is turned on, the output of the inverter 62 becomes high level. The output signal of the inverter 62 is used to stop a part of the function of the semiconductor integrated circuit. In the first and second embodiments, the output signal of the inverter 62 is used as a signal supplied to the gate of the charge stop switch M3.

  The second clamp circuit 58 and the second switch M2 are connected in series, and are arranged in a path parallel to the path from the first switch M1 to the ground terminal. More specifically, the second clamp circuit 58 and the second switch M2 are connected in series between the gate of the first switch M1 and the ground terminal. A pull-up resistor R11 is provided between the gate and source of the first switch M1. The second switch M <b> 2 is an N-channel MOSFET, the source is grounded, and the drain is connected to the second clamp circuit 58.

  Here, since the reference voltage source 52 operates by the power supply voltage Vdd supplied to the power supply terminal 104a, when the power supply voltage Vdd is low, the predetermined reference voltage Vref may not be output. In such a case, the reference voltage source 52 is configured to output a low voltage detection signal VLOW that becomes a high level. The low voltage detection signal VLOW is applied to the gate of the second switch M2. As a result, the second switch M2 is turned on while the low voltage detection signal VLOW is at a high level, that is, during a period when the predetermined reference voltage Vref is not generated.

The operation of the overvoltage protection circuit 50 configured as described above will be described.
When the power supply voltage Vdd applied to the power supply terminal 104a and the power supply voltage Vdd ′ applied to the power supply terminal 104b are normal operating voltages, Vdd ″ <Vref is established, so that the first switch M1 is turned off, and the first switch M1 is turned off. No current flows through the path including the clamp circuit 56 and the first switch M1, and the clamp function does not work.

  In an overvoltage state, when the power supply voltage Vdd applied to the power supply terminal 104a and the power supply voltage Vdd ′ applied to the power supply terminal 104b rise, the comparison signal Vcmp output from the comparator 54 becomes low level, and the first switch M1 is turned on. It becomes a state. At this time, a current Ix flows through a path including the first switch M1 and the first clamp circuit 56, and the voltage Vdd 'of the power supply terminal 104b is clamped to a predetermined threshold voltage Vth or less by the first clamp circuit 56. The threshold voltage Vth at this time is given by Vth≈Vf × 2 + VdsM1 + VceQ1. Here, Vf is the forward voltage of the diode of the first clamp circuit 56, VdsM1 is the drain-source voltage of the first switch M1, and VceQ1 is the collector-emitter voltage of the first transistor Q1.

  When the voltage Vdd ′ at the power supply terminal 104b is clamped, the voltage Vdd at the power supply terminal 104a is clamped to a clamp voltage Vclmp = Vth−Vf or less. Here, Vf is a base-emitter voltage of the protection transistor Tr3. As a result, the power supply voltage Vdd applied to the comparator 54 and the reference voltage source 52 is suppressed to a clamp voltage or less, so that circuit protection is realized.

  At this time, when the current Ix is converted into the voltage Vx by the current-voltage conversion circuit 60 and Vx> Vf, the fifth transistor Q5 is turned on, and the overvoltage protection circuit 50 is built in by the output signal of the inverter 62. A part of the function of the semiconductor integrated circuit is stopped.

  Furthermore, according to the present embodiment, circuit protection can be suitably realized even when the external power supply voltage Vdc from the external power supply 210 suddenly rises from around 0V. When the external power supply voltage Vdc is near 0 V, the reference voltage source 52 cannot generate the reference voltage Vref, and the comparator 54 itself cannot perform voltage comparison.

  In this state, the reference voltage source 52 outputs the high level low voltage detection signal VLOW, so that the second switch M2 is turned on. As a result, a path including the first clamp circuit 56, the pull-up resistor R11, the second clamp circuit 58, and the second switch M2 becomes active and functions as a clamp circuit. Therefore, even when the external power supply voltage Vdc suddenly increases, the power supply voltage Vdd 'of the power supply terminal 104b and the power supply voltage Vdd of the power supply terminal 104a can be reliably clamped.

  When the external power supply voltage Vdc rises to some extent and the reference voltage source 52 generates a predetermined reference voltage Vref, the second switch M2 is turned off and includes the first clamp circuit 56 and the first switch M1. Transition to clamping operation in the path.

  Although the present invention has been described above based on the embodiments, it should be understood that the embodiments merely illustrate the principles and applications of the present invention, and the embodiments are within the scope of the claims. Needless to say, many modifications and arrangements can be made without departing from the concept of the present invention.

  In the embodiment, the MOSFET and the bipolar transistor can be appropriately replaced as necessary. Further, the N channel and P channel of the MOSFET or the NPN type and PNP type of the bipolar transistor may be appropriately replaced.

  Further, although the case where the charging transistor Tr1 and the charging control transistor Tr2 are provided outside the charging control circuit 100 has been described in the embodiment, they may be provided inside the charging control circuit 100. Therefore, which circuit element is formed in the semiconductor integrated circuit can be changed as appropriate according to the semiconductor process to be used, the specifications required for the circuit, and the like.

  Further, in the present embodiment, the setting of high level and low level logical values is merely an example, and can be freely changed by appropriately inverting it with an inverter or the like.

It is a circuit diagram which shows the structure of the charging circuit which concerns on 1st Embodiment, and the whole electronic device. It is a circuit diagram which shows the structure of the charging circuit which concerns on 2nd Embodiment. It is a circuit diagram which shows the structure of the overvoltage protection circuit used as a clamp circuit in 1st, 2nd embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Clamp circuit, 20 Current adjustment circuit, 50 Overvoltage protection circuit, 52 Reference voltage source, 54 Comparator, 56 1st clamp circuit, 58 2nd clamp circuit, 60 Current voltage conversion circuit, 100 Charge control circuit, 104 Power supply terminal, 210 External power supply, 220 battery, 1000 electronic device, Tr1 charge transistor, Tr2 charge control transistor, Tr3 protection transistor, M1 first switch, M2 second switch, R11 pull-up resistor.

Claims (14)

An overvoltage protection circuit that is embedded in a semiconductor integrated circuit and clamps a power supply voltage supplied to a power supply terminal of the semiconductor integrated circuit below a predetermined clamp voltage,
A first clamp circuit and a first switch provided in series between a power supply terminal and a fixed voltage terminal of the semiconductor integrated circuit;
A reference voltage source for generating a predetermined reference voltage;
A comparator that compares a voltage according to a power supply voltage supplied to the power supply terminal with the reference voltage;
With
The overvoltage protection circuit, wherein the comparator turns on the first switch when a voltage corresponding to the power supply voltage becomes higher than the reference voltage. A current-voltage conversion circuit that converts a current flowing through a path including the first clamp circuit and the first switch into a voltage;
2. The overvoltage protection circuit according to claim 1, wherein when the converted voltage exceeds a predetermined threshold voltage, a part of the function of the semiconductor integrated circuit is stopped. A second clamp circuit and a second switch provided in series in a path parallel to the path from the first switch to the fixed voltage terminal;
The reference voltage source is configured to output a low voltage detection signal that is at a predetermined level when the power supply voltage supplied to the semiconductor integrated circuit is low and the predetermined reference voltage cannot be output.
3. The overvoltage protection circuit according to claim 1, wherein the second switch is turned on while the low voltage detection signal is at the predetermined level. 4.   The overvoltage protection circuit according to claim 1, wherein the first clamp circuit includes a diode.   The overvoltage protection circuit according to claim 1, wherein the first switch is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor).   6. The comparator outputs a low level comparison signal to a gate of the P-channel MOSFET as the first switch when a voltage corresponding to the power supply voltage is higher than the reference voltage. The overvoltage protection circuit described in 1. The first switch is a P-channel MOSFET;
The second clamp circuit and the second switch are connected in series between the gate and the ground terminal of the P-channel MOSFET,
4. The overvoltage protection circuit according to claim 3, wherein a pull-up resistor is provided between the gate and source of the P-channel MOSFET. The current-voltage conversion circuit is
A first transistor provided in series with the first clamp circuit and the first switch;
A second transistor in current mirror connection with the first transistor;
A resistor with a fixed potential at one end;
The overvoltage protection circuit according to claim 2, wherein a current corresponding to a current flowing through the second transistor is converted into a voltage by flowing through the resistor. A charging device for charging a battery based on a power supply voltage from an external power source,
A charging transistor provided on a path from the external power source to the battery;
A charge control circuit that is integrated on a semiconductor substrate and adjusts an on-state of the charging transistor to adjust a charging current supplied to the battery;
A voltage adjustment circuit that is provided on a power supply path from the external power supply to the power supply terminal of the charge control circuit and generates a necessary voltage drop;
With
The overvoltage protection circuit according to any one of claims 1 to 8, wherein the charge control circuit clamps a voltage at a power supply terminal of the charge control circuit below a predetermined clamp voltage;
A current adjusting circuit that adjusts the on state of the charging transistor so that the voltage of the battery approaches a predetermined voltage value;
A charging device comprising:   The charging device according to claim 9, wherein the voltage adjustment circuit is a resistor. The voltage adjustment circuit includes:
A protection transistor provided on a power supply path from the external power supply to the power supply terminal of the charge control circuit;
A resistor provided between a terminal connected to the external power source of the protection transistor and a control terminal of the protection transistor;
Including
The overvoltage protection circuit clamps the voltage at the power supply terminal of the charge control circuit below the clamp voltage by clamping the voltage at the control terminal of the protection transistor below a predetermined voltage. Item 10. The charging device according to Item 9.   The charging device according to claim 11, further comprising a capacitor provided between a control terminal and a fixed voltage terminal of the protection transistor.   The overvoltage protection circuit stops a charging function of the charging control circuit and cuts off a charging current supplied to the battery from the external power supply in a state where the voltage of the power supply terminal of the charging control circuit is clamped. The charging device according to claim 11. Battery,
The charging device according to claim 9, wherein the battery is charged based on a power supply voltage from an external power supply;
An electronic device comprising:

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