JP2021027630A - Current detection circuit and transistor driving circuit - Google Patents

Abstract

To provide a current detection circuit which improve a current detection accuracy by suppressing an influence of a temperature characteristic.SOLUTION: A current detection circuit including a drain to which an application end of a first power supply voltage is connected, and detecting a current flowing through a first driving objective transistor whose gate is driven by a first gate signal, comprises: a first transistor having a drain to which the application end of the first power supply voltage is connected; a constant current source that generates a constant current flowing through the first transistor; a comparator having a first input end to which the voltage generated at a source of the first driving object transistor being on is input as a current detection signal, and a second input end connected to the source of the first transistor; and a second transistor having a drain to which the application end of a second power supply voltage is connected, a source to which the gate of the first transistor is connected, and a gate which is short-circuited with the drain.SELECTED DRAWING: Figure 5

Description

The present invention relates to a current detection circuit.

Conventionally, a current detection circuit that detects a current flowing through a transistor has been used for various purposes. For example, such a current detection circuit is used to detect a current flowing through a high-side transistor of a switching power supply circuit (for example, Patent Document 1).

JP-A-2017-175746

Here, in the current detection circuit, there is a risk that the current detection accuracy may decrease due to the influence of the temperature characteristics of the transistor.

In view of the above situation, it is an object of the present invention to provide a current detection circuit that suppresses the influence of temperature characteristics and improves the current detection accuracy.

The current detection circuit according to one aspect of the present invention in order to achieve the above object
A current detection circuit that has a drain to which the application end of the first power supply voltage is connected and detects a current flowing through a first drive target transistor whose gate is driven by a first gate signal.
A first transistor having a drain to which the application end of the first power supply voltage is connected, and
A constant current source that generates a constant current flowing through the first transistor,
A comparator having a first input terminal in which a voltage generated in the source of the first drive target transistor, which is ON, is input as a current detection signal, and a second input end connected to the source of the first transistor.
A second transistor having a drain to which the application end of the second power supply voltage is connected, a source to which the gate of the first transistor is connected, and a gate shorted to the drain.
(First configuration).

Further, in the first configuration, the first transistor may be a device having the same composition as the first drive target transistor (second configuration).

Further, in the second configuration, the size of the first transistor may be smaller than the size of the first drive target transistor (third configuration).

Further, in any of the first to third configurations, a first current mirror that generates a current flowing from the source of the second transistor may be further provided (fourth configuration).

Further, in the fourth configuration, a third transistor arranged between the first current mirror and the source of the second transistor may be further provided (fifth configuration).

Further, in any of the first to fifth configurations, a first resistor having one end connected to the application end of the first power supply voltage, a drain connected to the other end of the first resistor, and the first resistance. A fourth transistor having a source to which the source of the first drive target transistor is connected and a gate to which the gate of the first drive target transistor is connected is further provided, and the other end of the first resistor and the fourth are provided. The first connection node to which the drain of the transistor is connected may be connected to the first input end (sixth configuration).

Further, the transistor drive circuit according to one aspect of the present invention is
A current detection circuit with any of the above configurations and
A Zener diode having an anode to which the source of the first drive target transistor is connected, and
A fifth transistor having a gate to which the cathode of the Zener diode is connected and a drain to which the application end of the third power supply voltage is connected.
With
The source voltage of the fifth transistor serves as the first gate signal (seventh configuration).

Further, in the seventh configuration, the fifth transistor may be a device having the same composition as the second transistor (eighth configuration).

Further, in the eighth configuration, the size of the first transistor may be smaller than the size of the first drive target transistor, and the size of the second transistor may be smaller than the size of the fifth transistor (the eighth). 9 configuration).

Further, in the ninth configuration, a second current mirror for generating a current flowing from the source of the fifth transistor is further provided, and the current flowing from the source of the second transistor is a current generated by the second current mirror. The amount of current may be smaller than that (10th configuration).

Further, in the tenth configuration, a sixth transistor arranged between the second current mirror and the source of the fifth transistor may be further provided (11th configuration).

Further, in the tenth or eleventh configuration, the seventh transistor having a gate to which the first gate control signal is applied and switching the on / off of the second current mirror, and the seventh transistor.
A second resistor having a first end connected to the source of the fifth transistor and a second end connected to the second current mirror.
A high potential end connected to the first end of the second resistor, a low potential end connected to the source of the first drive target transistor, and an input end connected to the second end of the second resistor. And with an inverter,
With more
The output of the inverter may be the first gate signal (12th configuration).

Further, the power supply IC according to one aspect of the present invention is
A transistor drive circuit with any of the above configurations and
The first drive target transistor driven by the transistor drive circuit and
A second drive target transistor having a drain connected to the source of the first drive target transistor and a source connected to the application end of the ground potential.
(13th configuration).

Further, in the thirteenth configuration, when the host voltage is monitored and the falling edge of the host voltage is detected, the isolation switch to which the application end of the host voltage is connected is turned off, and the first drive target transistor and the second drive target transistor are turned off. A voltage reduction detection circuit for starting the driving of the transistor to be driven may be further provided (14th configuration).

Further, the power supply device according to one aspect of the present invention is
The power supply IC having the above 14th configuration and
The isolation switch whose on / off is controlled by the reduced voltage detection circuit and
An inductor having a first end connected to a second connection node to which the source of the first drive target transistor and the drain of the second drive target transistor are connected.
A capacitor having a second end of the inductor and a first end connected to the isolation switch,
(15th configuration).

Further, the HDD (hard disk drive) according to one aspect of the present invention is
With the above power supply
At least one of a voice coil motor and a spindle motor supplied with power from the power supply device,
It is configured to be equipped with.

According to the current detection circuit of the present invention, it is possible to suppress the influence of temperature characteristics and improve the current detection accuracy.

It is a figure which shows the structure of the power-source device which concerns on an exemplary embodiment of this invention. It is a schematic block diagram which shows an example of HDD (hard disk drive) provided with a power-source device. It is a circuit diagram which shows the specific structure of the high-side drive circuit and the current detection circuit which concerns on a comparative example. It is a timing chart which shows an example of the operation in the circuit configuration shown in FIG. It is a circuit diagram which shows the specific structure of the high-side drive circuit and the current detection circuit which concerns on an exemplary embodiment of this invention.

An exemplary embodiment of the present invention will be described below with reference to the drawings.

<1. Power supply configuration>
FIG. 1 is a diagram showing a configuration of a power supply device 20 according to an exemplary embodiment of the present invention. The power supply device 20 shown in FIG. 1 is provided in an HDD (hard disk drive) as an example.

As shown in FIG. 1, the power supply device 20 includes a power supply IC 1 configured as a semiconductor integrated circuit, an isolation switch 15, an inductor L1, and a capacitor C1. The isolation switch 15, the inductor L1, and the capacitor C1 are external elements for the power supply IC1.

The isolation switch 15 is configured by an n-channel MOSFET as an example in FIG. The drain of the isolation switch 15 is connected to the application end of the host voltage Vhost. The host voltage Vhost is, for example, 5V. The source of the isolation switch 15 is connected to one end of the capacitor C1. The isolation switch 15 is a switch for switching the continuity / interruption of the path between the application end of the host voltage Vhost and one end of the capacitor C1.

The power supply IC 1 includes a voltage reduction detection circuit 2, a logic unit 3, a high-side drive circuit 4, a low-side drive circuit 5, a current detection circuit 6, a high-side transistor (first drive target transistor) QH, and a low-side transistor. (Second drive target transistor) QL and QL are integrated and possessed. Further, the power supply IC1 has terminals T1 to T4 as external terminals for establishing an electrical connection with the outside.

The reduced voltage detection circuit 2 is connected to the application end of the host voltage Vhost via the terminal T2, and is also connected to the gate of the isolation switch 15 via the terminal T1. As a result, the voltage reduction detection circuit 2 controls the on / off of the isolation switch 15 by driving the gate of the isolation switch 15 via the terminal T1. Further, the reduced voltage detection circuit 2 can monitor the state of the host voltage Vhost via the terminal T2.

The logic unit 3 is a control unit that controls the power supply IC 1, and particularly controls the step-down DC / DC converter 10 described later.

The high-side transistor QH is composed of an n-channel MOSFET. The drain of the high-side transistor QH is connected to the application end of the input voltage (first power supply voltage) Vin via the terminal T3. The input voltage Vin is, for example, 12V. The source of the high-side transistor QH is connected to the drain of the low-side transistor QL at the connection node N1. The source of the low-side transistor QL is connected to the application end of the ground potential.

The connection node N1 is connected to one end of the inductor L1 via the terminal T4. The other end of the inductor L1 is connected to one end of the capacitor C1.

With such a connection relationship, the step-down DC / DC converter 10 is configured by the high-side transistor QH, the low-side transistor QL, the inductor L1, and the capacitor C1.

The logic unit 3 outputs a high-side gate control signal HGCTR for controlling the gate of the high-side transistor QH to the high-side drive circuit 4. The high-side drive circuit 4 generates a high-side gate signal HG based on the high-side gate control signal HGCTR and applies it to the gate of the high-side transistor QH.

Further, the logic unit 3 outputs a low-side gate control signal LGCTR for controlling the gate of the low-side transistor QL to the low-side drive circuit 5. The low-side drive circuit 5 generates a low-side gate signal LG based on the low-side gate control signal LGCTR and applies it to the gate of the low-side transistor QL.

As a result, the logic unit 3 performs on / off control of each of the high-side transistor QH and the low-side transistor QL, and an output voltage Vout is generated at the other end of the inductor L1 based on the input voltage Vin. The output voltage Vout is a voltage obtained by stepping down the input voltage Vin, and is, for example, 5V with respect to an input voltage Vin of 12V. At this time, a switching voltage Vsw is generated in the connection node N1 by switching the high-side transistor QH and the low-side transistor QL.

The current detection circuit 6 is a circuit for detecting the current flowing through the high-side transistor QH. More specifically, the current detection circuit 6 detects that the current flowing through the high-side transistor QH has reached a predetermined limit value, and outputs the limit current detection signal ILIMIT_det to the logic unit 3.

The details of the configurations of the high-side drive circuit 4 and the current detection circuit 6 will be described later.

Here, the operation of the power supply device 20 will be described. Here, it is assumed that the host voltage Vhost is 5V and the input voltage Vin is 12V. While the host voltage Vhost is 5V, the voltage reduction detection circuit 2 turns on the isolation switch 15 and keeps the step-down DC / DC converter 10 in a stopped state. As a result, the host voltage Vhost is supplied to the voice coil motor 30, the spindle motor 31, and the like as an example of the load via the isolation switch 15.

When the host voltage Vhost drops below 5V in a power failure state, the voltage reduction detection circuit 2 detects this and turns off the isolation switch 15. This prevents the capacitor C1 from being discharged and the voltage supplied to the load from dropping. At this time, the voltage reduction detection circuit 2 instructs the logic unit 3 to start the step-down DC / DC converter 10.

As a result, the logic unit 3 starts switching control of the high-side transistor QH and the low-side transistor QL by the output of the high-side gate control signal HGCTR and the low-side gate control signal LGCTR, and the step-down DC / DC converter 10 has an input voltage Vin of 12 V. The generation of the output voltage Vout of 5V is started based on the above. Therefore, even if a power failure occurs, a power supply voltage of 5 V can be continuously supplied to the load.

<2. HDD configuration>
Here, the configuration of the HDD including the power supply device 20 according to the exemplary embodiment of the present invention will be described. FIG. 2 is a schematic configuration diagram showing an example of an HDD including the power supply device 20.

The HDD 40 shown in FIG. 2 has a voice coil motor 30, a spindle motor 31, a magnetic disk 32, a swing arm 33, and a magnetic head 34 as a configuration housed inside the housing 35.

The magnetic disk 32 is a hard disk having a magnetic material on its surface. The number of magnetic disks 32 may be a plurality or a single number. The spindle motor 31 rotates the magnetic disk 32 at high speed. The magnetic head 34 reads and writes data to and from the magnetic disk 32 by generating a magnetic field. The magnetic head 34 is attached to the tip of the swing arm 33.

The swing arm 33 swings about an axis with respect to the rotating magnetic disk 32. The voice coil motor 30 is an actuator that drives the swing arm 33. The boil coil motor 30 is driven by the action of a magnetic field between a coil through which an electric current is passed and a magnet.

The configuration of the power supply IC 1 and the power supply device 20 (not shown in FIG. 2) is housed inside the housing 35.

<3. High-side drive circuit and current detection circuit>
Next, the details of the high-side drive circuit 4 and the current detection circuit 6 included in the power supply IC 1 will be described. Here, first, before explaining the embodiment of the present invention, a comparative example and its subject will be described.

FIG. 3 is a circuit diagram showing a specific configuration of the high-side drive circuit 4 and the current detection circuit 6 according to the comparative example. Note that FIG. 3 also shows the configurations of the step-down DC / DC converter 10 and the low-side drive circuit 5. Further, a transistor drive circuit for driving the high-side transistor QH is configured from the high-side drive circuit 4 and the current detection circuit 6.

The high-side drive circuit 4 has a level shift circuit 41 in addition to the resistor R4, the Zener diode Z4, the transistor M4, and the inverter IV4.

One end of the resistor R4 is connected to the application end of the high side voltage VHSD. The other end of the resistor R4 is connected to the cathode of the Zener diode Z4 by a connection node N41. The anode of the Zener diode Z4 is connected to the connection node N1. The high-side voltage VHSD is a voltage obtained by adding the Zener voltage Vz of the Zener diode Z4 to the input voltage Vin. For example, when the input voltage Vin is 12V and the Zener voltage Vz is 5V, the high side voltage VHSD = 12V + 5V = 17V.

The connection node N41 is connected to the gate of the transistor M4 composed of the n-channel MOSFET. The drain of the transistor M4 is connected to the application end of the high side voltage (third power supply voltage) VHSD. Due to such a connection relationship, the source voltage Vsm4 generated at the source of the transistor M4 is Vsm4 = Vsw + Vz-Vgs4. However, Vgs4 is the drain-source voltage of the transistor M4.

The level shift circuit 41 has resistors R41 and R42, and transistors M42 to M45. An application end of the low side voltage VLSD is connected to one end of the resistor R41. As shown in FIG. 3, the low-side voltage VLSD is the power supply voltage of the low-side drive circuit 5, for example, 5V.

The other end of the resistor R41 is connected to the drain of the transistor M42 composed of the n-channel MOSFET. The gate of the transistor M42 is connected to the application end of the high side gate control signal HGCTR. The other end of the transistor M42 is connected to the drain of the transistor M43 composed of an n-channel MOSFET. The drain gate of the transistor M43 is short-circuited. The source of the transistor M43 is connected to the application end of the ground potential.

The gate of the transistor M43 is connected to the gate of the transistor M44 composed of an n-channel MOSFET. The source of the transistor M44 is connected to the application end of the ground potential. The drain of the transistor M44 is connected to the source of the transistor M45 composed of an n-channel MOSFET. The gate of the transistor M45 is connected to the application end of the high side gate control signal HGCTR. The current mirror CM4 is configured by the transistors M43 and M44.

One end of the resistor R42 is connected to the source of the transistor M4. The other end of the resistor R42 is connected to the drain of the transistor M45 by the connection node N42. The transistor M45 is a high withstand voltage transistor and has a function of protecting an element on the source side of the transistor M45.

With such a configuration of the level shift circuit 41, the high side gate control signal HGCTR is level-shifted to the level shift voltage Vsht generated in the connection node N42.

Further, the high potential end of the inverter IV4 is connected to the connection node N43 to which one end of the resistor R42 and the source of the transistor M4 are connected. The low potential end of the inverter IV4 is connected to the connection node N44 to which the anode of the Zener diode Z4 and the connection node N1 are connected. The input end of the inverter IV4 is connected to the connection node N42, and the level shift voltage Vsht is input. The output end of the inverter IV4 is connected to the gate of the high-side transistor QH.

The high side gate control signal HGCTR is, for example, 1.5 V as the high level and 0 V as the low level. When the high side gate control signal HGCTR reaches a high level, the transistors M42 and M45 are turned on. As a result, the current flowing through the transistor M43 generated by the low-side voltage VLSD and the resistor R41 becomes the current I44 flowing through the transistor M44 by the current mirror CM4. Since the current I44 also flows through the resistor R42, a level shift voltage Vsht, which is a voltage reduced by the voltage drop in the resistor R42 from the source voltage Vsm4, which is the voltage of the connection node N43, is generated in the connection node N42.

As a result, the inverter IV4 outputs the source voltage Vsm4 as a high level. Since the output of the inverter IV4 is the high-side gate signal HG applied to the gate of the high-side transistor QH, HG = Vsm4. As described above, since Vsm4 = Vsw + Vz-Vgs4, the high-side transistor QH is turned on.

On the other hand, when the high side gate control signal HGCTR is at a low level, the transistors M42 and M45 are turned off. Then, since no current flows through the resistor R42, the level shift voltage Vsht coincides with the source voltage Vsm4. As a result, the inverter IV4 outputs the switching voltage Vsw as a low level. Therefore, since the high-side gate signal HG = Vsw, the high-side transistor QH is turned off.

In this way, the high-side transistor QH can be turned on and off according to the high-level and low-level of the high-side gate control signal HGCTR.

Next, the configuration of the current detection circuit 6 shown in FIG. 3 will be described. The current detection circuit 6 includes a resistor R6, transistors M61 and M62, a constant current source CI6, and a comparator CP6.

One end of the resistor R6 is connected to the terminal T3, and an input voltage Vin is applied. The other end of the resistor R6 is connected to the drain of the transistor M61 composed of the n-channel MOSFET. The source of the transistor M61 is connected to the connection node N1. The connection node N61 to which the other end of the resistor R6 and the drain of the transistor M61 are connected is connected to the inverting input end (−) of the comparator CP6. The gate of the transistor M61 is connected to the output end of the inverter IV4. That is, the transistor M61 is turned on and off in synchronization with the high-side transistor QH by the high-side gate signal HG.

Further, the drain of the transistor M62 composed of the n-channel MOSFET is connected to the terminal T3, and the input voltage Vin is applied. The gate of the transistor M62 is connected to the application end of the high side voltage VHSD. The source of the transistor M62 is connected to the constant current source CI6 and is connected to the non-inverting input end (+) of the comparator CP6.

The transistor M62 and the constant current source CI6 are provided to generate a reference voltage Vref to be applied to the non-inverting input end of the comparator CP6. The comparator CP6 compares the current detection signal Video generated at the connection node N61 to which the resistor R6 and the transistor M61 are connected with the reference voltage Vref, and outputs the current limit detection signal ILIMIT_det as the comparison result.

Next, the operation in the circuit configuration shown in FIG. 3 will be described with reference to the timing chart shown in FIG. FIG. 4 shows the switching voltage Vsw, the current detection signal Video, the inductor current IL flowing through the inductor L1, the limit current detection signal ILIMIT_det, the high side gate control signal HGCTR, and the low side gate control signal LGCTR in this order from the top.

First, immediately before the timing t1, the high-side gate control signal HGCTR is at a low level and the low-side gate control signal LGCTR is at a high level, so the high-side transistor QH is off, the low-side transistor QL is on, and the switching voltage Vsw is 0V. Then, the inductor current IL flowing from the ground through the low-side transistor QL and the terminal T4 to the inductor L1 decreases.

At this time, since the transistor M61 is off, the current detection signal Video matches the input voltage Vin. Here, the reference voltage Vref is represented by Vref = Vin− (Rdson2 × Ic). However, Rdson2: the on-resistance of the transistor M62, Ic: the constant current due to the constant current source CI6. Therefore, the current detection signal Video becomes higher than the reference voltage Vref, and the current limit detection signal ILIMIT_det becomes a low level.

Then, at timing t1, when the inductor current IL reaches 0A and the high-side gate control signal HGCTR is switched to the high level and the low-side gate control signal LGCTR is switched to the low level, the high-side transistor QH is turned on and the low-side transistor QL is turned off. Become. As a result, the switching voltage Vsw rises to the input voltage Vin, and the inductor current IL flowing through the inductor L1 from the terminal T3 via the high-side transistor QH and the terminal T4 starts to increase from 0A.

Here, since the switching voltage Vsw = Vin− (Rdson1 × IL) (where Rdson1: the on-resistance of the high-side transistor QH), the switching voltage Vsw decreases from the input voltage Vin as the inductor current IL increases. At this time, since the transistor M61 is on and the resistance R6 has a sufficiently high resistance value as compared with the on resistance of the transistor M61, the current detection signal Video substantially matches the switching voltage Vsw. Therefore, as shown in FIG. 4, the current detection signal Video also drops from the input voltage Vin as well as the switching voltage Vsw.

Then, when the inductor current IL reaches a predetermined limit current value Illimit at the timing t2, the switching voltage Vsw reaches the threshold voltage Vth = Vin− (Rdson1 × Illimit). Here, if the reference voltage Vref is set to match the threshold voltage Vth, the current detection signal Vidot reaches the reference voltage Vref at the timing t2, so that the current limit detection signal ILIMIT_det becomes a high level.

The logic unit 3 switches the high-side gate control signal HGCTR to a low level and the low-side gate control signal LGCTR to a high level in response to the current limit detection signal ILIMIT_det becoming high level. Then, the high-side transistor QH is turned off, the low-side transistor QL is turned on, and the switching voltage Vsw drops to 0V. At this time, since the transistor M61 is turned off, the current detection signal Video rises to the input voltage Vin. As a result, the current limit detection signal ILIMIT_det becomes low level. The inductor current IL decreases from the limit current value Illimit.

Here, as described above, since the threshold voltage Vth = Vin− (Rdson1 × Illimit) and the reference voltage Vref = Vin− (Rdson2 × Ic), the temperature characteristics of the on-resistors Rdson1 and Rdson2 are high. The side transistor QH and the transistor M62 are paired as devices having the same composition. However, the size of the transistor M62 is made smaller than the size of the high-side transistor QH to save space. This makes it possible to cancel the influence of the temperature characteristic of the on-resistance in the high-side transistor QH and the transistor M62 and improve the detection accuracy of the limiting current.

However, in the configuration of FIG. 3, the high-side gate signal HG applied to the gate of the high-side transistor QH when the high-side transistor QH is on is HG = Vsm4 = Vsw + Vz-Vgs4, but the gate of the transistor M62 The applied voltage is the high side voltage VHSD. The voltage applied to the gate of the transistor affects the on-resistance of the transistor, but the voltage applied to the gate of the transistor M62 lacks a Vgs element such as the high side gate signal HG. Since Vgs has a temperature characteristic, it cannot be said that the influence of the temperature characteristic of the on-resistance can be sufficiently canceled by the high-side transistor QH and the transistor M62.

In order to solve the problems uniquely found by the inventor of the present application, an embodiment of the present invention as described below has been devised.

<4. Embodiment of the present invention>
FIG. 5 is a circuit diagram showing a specific configuration of the high-side drive circuit 4 and the current detection circuit 60 according to the exemplary embodiment of the present invention, and is a diagram corresponding to FIG. 3 according to the above-mentioned comparative example. .. The difference from FIG. 3 in the circuit configuration according to the present embodiment shown in FIG. 5 is the configuration of the current detection circuit 60.

The current detection circuit 60 adds transistors M63 to M66 and resistors R61 as compared with the current detection circuit 6 shown in FIG.

The drain of the transistor M63 composed of the n-channel MOSFET is connected to the application end of the high side voltage (second power supply voltage) VHSD and short-circuited with the gate of the transistor M63. The source of transistor M63 is connected to the gate of transistor M62.

As a result, the source voltage Vsm63 of the transistor M63 is applied to the gate of the transistor M62. The source voltage Vsm63 is Vsm63 = VHSD-Vgs63. However, Vgs63: the gate-source voltage of the transistor M63.

As described above, the high-side gate signal HG applied to the gate of the high-side transistor QH when the high-side transistor QH is on is HG = Vsm4 = Vsw + Vz-Vgs4, and Vsm63 is as described above. Both the HG applied to the gate of the high-side transistor QH and the Vsm63 applied to the gate of the transistor M63 can include a Vgs element. As a result, the influence of the temperature characteristics of the on-resistance Rdson1 of the high-side transistor QH and the on-resistance Rdson2 of the transistor M62 can be further canceled.

Further, the transistor M4 and the transistor M63 are paired as devices having the same composition in order to match the temperature characteristics of Vgs. Further, the size of the transistor M63 is smaller than the size of the transistor M4 in response to the size of the transistor M62 being smaller than the size of the high-side transistor QH. This leads to space saving.

Further, in the present embodiment, one end of the resistor R61 is connected to the application end of the low side voltage VLSD. The other end of the resistor R61 is connected to the drain of the transistor M64 composed of the n-channel MOSFET. The drain gate of the transistor M64 is short-circuited. The source of the transistor M64 is connected to the application end of the ground potential.

The gate of the transistor M64 is connected to the gate of the transistor M65 composed of an n-channel MOSFET. The source of the transistor M65 is connected to the application end of the ground potential. The drain of the transistor M65 is connected to the source of the transistor M66 composed of an n-channel MOSFET. The gate of the transistor M66 is connected to the application end of the high side voltage VHSD. The drain of the transistor M66 is connected to the connection node N62 to which the source of the transistor M63 and the gate of the transistor M62 are connected. The current mirror CM60 is configured by the transistors M64 and M65. The transistor M66 is a high withstand voltage transistor and has a function of protecting an element on the source side of the transistor M66.

As a result, the current flowing through the transistor M64 generated by the low-side voltage VLSD and the resistor R61 becomes the current I65 flowing through the transistor M65 by the current mirror CM60. The current I65 flows from the connection node N62 via the transistor M66. The current I65 has a smaller current amount than the current I44 flowing through the current mirror CM4, corresponding to the size of the transistor M63 being smaller than the size of the transistor M4. As a result, Vgs63 of the transistor M63 is adjusted with respect to Vgs4 of the transistor M4.

As described above, in the present embodiment, the influence of the temperature characteristic can be further suppressed, and the detection accuracy of the current limit by the comparator CP6 can be further improved.

<5. Others>
Although the embodiments of the present invention have been described above, the embodiments can be modified in various ways within the scope of the gist of the present invention.

The present invention can be used, for example, for current detection in a switching power supply circuit.

1 Power supply IC
2 Low voltage detection circuit 3 Logic part 4 High side drive circuit 5 Low side drive circuit 6, 60 Current detection circuit 10 Step-down DC / DC converter 15 Isolation switch 20 Power supply device 30 Voice coil motor 31 Spindle motor 32 Magnetic disk 33 Swing arm 34 Magnetic head 35 housing 40 HDD (hard disk drive)

Claims (16)

A current detection circuit that has a drain to which the application end of the first power supply voltage is connected and detects a current flowing through a first drive target transistor whose gate is driven by a first gate signal.
A first transistor having a drain to which the application end of the first power supply voltage is connected, and
A constant current source that generates a constant current flowing through the first transistor,
A comparator having a first input terminal in which a voltage generated in the source of the first drive target transistor, which is ON, is input as a current detection signal, and a second input end connected to the source of the first transistor.
A second transistor having a drain to which the application end of the second power supply voltage is connected, a source to which the gate of the first transistor is connected, and a gate shorted to the drain.
A current detection circuit. The current detection circuit according to claim 1, wherein the first transistor is a device having the same composition as the first drive target transistor. The current detection circuit according to claim 2, wherein the size of the first transistor is smaller than the size of the first drive target transistor. The current detection circuit according to any one of claims 1 to 3, further comprising a first current mirror that generates a current flowing from the source of the second transistor. The current detection circuit according to claim 4, further comprising a third transistor arranged between the first current mirror and the source of the second transistor. A first resistor whose one end is connected to the application end of the first power supply voltage,
A fourth transistor having a drain connected to the other end of the first resistor, a source to which the source of the first drive target transistor is connected, and a gate to which the gate of the first drive target transistor is connected. ,
With more
The first connection node to which the other end of the first resistor and the drain of the fourth transistor are connected is connected to the first input end, according to any one of claims 1 to 5. Current detection circuit. The current detection circuit according to any one of claims 1 to 6.
A Zener diode having an anode to which the source of the first drive target transistor is connected, and
A fifth transistor having a gate to which the cathode of the Zener diode is connected and a drain to which the application end of the third power supply voltage is connected.
With
A transistor drive circuit in which the source voltage of the fifth transistor becomes the first gate signal. The transistor drive circuit according to claim 7, wherein the fifth transistor is a device having the same composition as the second transistor. The size of the first transistor is smaller than the size of the first drive target transistor.
The transistor drive circuit according to claim 8, wherein the size of the second transistor is smaller than the size of the fifth transistor. A second current mirror that generates a current flowing from the source of the fifth transistor is further provided.
The transistor drive circuit according to claim 9, wherein the current flowing from the source of the second transistor is smaller than the current generated by the second current mirror. The transistor drive circuit according to claim 10, further comprising a sixth transistor arranged between the second current mirror and the source of the fifth transistor. A seventh transistor having a gate to which a first gate control signal is applied and switching on / off of the second current mirror, and a seventh transistor.
A second resistor having a first end connected to the source of the fifth transistor and a second end connected to the second current mirror.
A high potential end connected to the first end of the second resistor, a low potential end connected to the source of the first drive target transistor, and an input end connected to the second end of the second resistor. And with an inverter,
With more
The transistor drive circuit according to claim 10 or 11, wherein the output of the inverter is the first gate signal. The transistor drive circuit according to any one of claims 7 to 12.
The first drive target transistor driven by the transistor drive circuit and
A second drive target transistor having a drain connected to the source of the first drive target transistor and a source connected to the application end of the ground potential.
A power supply IC. When the host voltage is monitored and the falling edge of the host voltage is detected, the isolation switch to which the application end of the host voltage is connected is turned off to start driving the first drive target transistor and the second drive target transistor. The power supply IC according to claim 13, further comprising a voltage detection circuit. The power supply IC according to claim 14,
The isolation switch whose on / off is controlled by the reduced voltage detection circuit and
An inductor having a first end connected to a second connection node to which the source of the first drive target transistor and the drain of the second drive target transistor are connected.
A capacitor having a second end of the inductor and a first end connected to the isolation switch,
A power supply device. The power supply device according to claim 15,
At least one of a voice coil motor and a spindle motor supplied with power from the power supply device,
HDD (hard disk drive).

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