JP7458719B2 - Current detection circuit and transistor drive circuit - Google Patents

Description

The present invention relates to a current detection circuit.

Conventionally, current detection circuits that detect current flowing through transistors have 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 2017-175746 A

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

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

In order to achieve the above object, a current detection circuit according to one aspect of the present invention comprises:
A current detection circuit for detecting a current flowing through a first driven transistor having a drain connected to an application terminal of a first power supply voltage and having a gate driven by a first gate signal,
a first transistor having a drain connected to an application terminal of the first power supply voltage;
a constant current source that generates a constant current through the first transistor;
a comparator having a first input terminal to which a voltage generated at a source of the first driven transistor that is on is input as a current detection signal, and a second input terminal connected to the source of the first transistor;
a second transistor having a drain connected to an application terminal of a second power supply voltage and a source connected to the gate of the first transistor, the second transistor having a gate shorted to the drain;
(first configuration).

Furthermore, in the first configuration, the first transistor may be a device having the same composition as the first transistor to be driven (second configuration).

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

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

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

Further, in any one of the first to fifth configurations, a first resistor having one end connected to an application terminal of the first power supply voltage, a drain connected to the other end of the first resistor, and a drain connected to the other end of the first resistor; a fourth transistor having a source to which the source of the first transistor to be driven is connected, and a gate to which the gate of the first transistor to be driven is connected; The first connection node connected to the drain of the transistor may be connected to the first input terminal (sixth configuration).

Further, a transistor drive circuit according to one embodiment of the present invention includes:
A current detection circuit having one of the above configurations,
a Zener diode having an anode connected to the source of the first driven transistor;
a fifth transistor having a gate connected to the cathode of the Zener diode, and a drain connected to an application end of a third power supply voltage;
Equipped with
The configuration is such that the source voltage of the fifth transistor becomes the first gate signal (seventh configuration).

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

Furthermore, in the eighth configuration, the size of the first transistor may be smaller than the size of the first driven transistor, and the size of the second transistor may be smaller than the size of the fifth transistor. 9 configuration).

The ninth configuration further includes a second current mirror that generates a current flowing from the source of the fifth transistor, 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 (tenth configuration).

Furthermore, in the tenth configuration, a sixth transistor may be further provided between the second current mirror and the source of the fifth transistor (eleventh configuration).

Further, in the tenth or eleventh configuration, a seventh transistor has a gate to which a first gate control signal is applied and switches on/off of the second current mirror;
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 driven transistor, and an input end connected to the second end of the second resistor. and an inverter having
Furthermore,
The output of the inverter may be the first gate signal (twelfth configuration).

Further, a power supply IC according to one aspect of the present invention includes:
A transistor drive circuit having one of the above configurations,
the first driven transistor driven by the transistor drive circuit;
a second driven transistor having a drain connected to the source of the first driven transistor and a source connected to a ground potential application terminal;
(13th configuration).

Further, in the thirteenth configuration, the host voltage is monitored, and when a falling edge of the host voltage is detected, an isolation switch to which the application terminal of the host voltage is connected is turned off, and the first driven target transistor and the second driven transistor are turned off. It is also possible to further include a reduced voltage detection circuit that starts driving the transistor to be driven (fourteenth configuration).

Further, a power supply device according to one embodiment of the present invention includes:
a power supply IC having the fourteenth configuration;
the isolation switch whose on/off is controlled by the voltage reduction detection circuit;
an inductor having a first end connected to a second connection node to which the source of the first transistor to be driven and the drain of the second transistor to be driven are connected;
a capacitor having a first end connected to a second end of the inductor and the isolation switch;
(15th configuration).

Further, an HDD (hard disk drive) according to one aspect of the present invention,
The above power supply device,
At least one of a voice coil motor and a spindle motor that is supplied with power from the power supply device;
The configuration includes the following.

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

1 is a diagram showing the configuration of a power supply device according to an exemplary embodiment of the present invention. 1 is a schematic configuration diagram showing an example of an HDD (hard disk drive) including a power supply device. FIG. 4 is a circuit diagram showing a specific configuration of a high-side drive circuit and a current detection circuit according to a comparative example. 4 is a timing chart showing an example of an operation in the circuit configuration shown in FIG. 3. FIG. FIG. 2 is a circuit diagram showing a specific configuration of a high-side drive circuit and a current detection circuit according to an exemplary embodiment of the present invention.

Exemplary embodiments of the present invention will be described below with reference to the drawings.

<1. Power supply configuration>
FIG. 1 is a diagram showing the 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 assumed to be included in an HDD (hard disk drive), as an example.

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

In FIG. 1, the isolation switch 15 is configured by an n-channel MOSFET as an example. The drain of the isolation switch 15 is connected to the application terminal of the host voltage Vhost. The host voltage Vhost is, for example, 5 V. The source of the isolation switch 15 is connected to one end of the capacitor C1. The isolation switch 15 is a switch that switches the conduction/cutoff of the path between the application terminal of the host voltage Vhost and one end of the capacitor C1.

The power supply IC 1 includes a reduced voltage detection circuit 2, a logic section 3, a high side drive circuit 4, a low side drive circuit 5, a current detection circuit 6, a high side transistor (first driven transistor) QH, and a low side transistor. (second driven transistor) QL are integrated. Further, the power supply IC1 has terminals T1 to T4 as external terminals for establishing 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. Thereby, the reduced voltage detection circuit 2 controls the on/off state of the isolation switch 15 by driving the gate of the isolation switch 15 via the terminal T1. Further, the voltage reduction 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, which will be described later.

High-side transistor QH is formed by an n-channel MOSFET. The drain of the high-side transistor QH is connected to the application terminal 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 a connection node N1. The source of the low-side transistor QL is connected to a ground potential application terminal.

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 this connection relationship, the high-side transistor QH, the low-side transistor QL, the inductor L1, and the capacitor C1 form a step-down DC/DC converter 10.

The logic section 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.

The logic unit 3 also outputs a low-side gate control signal LGCTR to the low-side drive circuit 5 to control the gate of the low-side transistor QL. 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 controls the on/off 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, 5 V for an input voltage Vin of 12 V. At this time, a switching voltage Vsw is generated at 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 when the current flowing through the high-side transistor QH reaches a predetermined limit value, and outputs a limit current detection signal ILIMIT_det to the logic unit 3.

Note that 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 explained. Here, the description will be made assuming 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. Thereby, the host voltage Vhost is supplied to the voice coil motor 30, spindle motor 31, etc., which are examples of loads, via the isolation switch 15.

When a power outage occurs and the host voltage Vhost falls below 5V, the reduced voltage detection circuit 2 detects this and turns off the isolation switch 15. This prevents the capacitor C1 from discharging and reducing the voltage supplied to the load. At this time, the voltage reduction detection circuit 2 instructs the logic section 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 outputting the high-side gate control signal HGCTR and the low-side gate control signal LGCTR, and the step-down DC/DC converter 10 receives the input voltage Vin of 12V. Based on this, generation of the output voltage Vout of 5V is started. Therefore, even in a power outage state, the power supply voltage of 5V can be continuously supplied to the load.

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

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

The magnetic disk 32 is a hard disk with a magnetic material on its surface. There may be multiple magnetic disks 32 or only one. The spindle motor 31 rotates the magnetic disk 32 at high speed. The magnetic head 34 generates a magnetic field to read and write data from and to the magnetic disk 32. The magnetic head 34 is attached to the tip of the swing arm 33.

The swing arm 33 swings around an axis relative 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 a magnetic field between a current-carrying coil and a magnet.

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

<3. High-side drive circuit and current detection circuit>
Next, details of the high side drive circuit 4 and the current detection circuit 6 included in the power supply IC 1 will be explained. First, before describing the embodiments of the present invention, a comparative example and its problems will be described.

FIG. 3 is a circuit diagram showing specific configurations of the high-side drive circuit 4 and the current detection circuit 6 according to a 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. Furthermore, the high-side drive circuit 4 and the current detection circuit 6 constitute a transistor drive circuit that drives the high-side transistor QH.

The high-side drive circuit 4 includes a resistor R4, a Zener diode Z4, a transistor M4, and an inverter IV4, as well as a level shift circuit 41.

One end of the resistor R4 is connected to the application end of the high side voltage VHSD. The other end of resistor R4 is connected to the cathode of Zener diode Z4 at connection node N41. The anode of Zener diode Z4 is connected to 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.

Connection node N41 is connected to the gate of transistor M4 constituted by an n-channel MOSFET. The drain of the transistor M4 is connected to the application terminal of the high side voltage (third power supply voltage) VHSD. Due to this connection relationship, the source voltage Vsm4 generated at the source of the transistor M4 becomes Vsm4=Vsw+Vz-Vgs4. However, Vgs4 is the drain-source voltage of the transistor M4.

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

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

The gate of transistor M43 is connected to the gate of transistor M44, which is an n-channel MOSFET. The source of transistor M44 is connected to the application terminal of the ground potential. The drain of transistor M44 is connected to the source of transistor M45, which is an n-channel MOSFET. The gate of transistor M45 is connected to the application terminal of the high-side gate control signal HGCTR. Transistors M43 and M44 form a current mirror CM4.

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 at a connection node N42. The transistor M45 is a high voltage transistor and has a function of protecting the source side element of the transistor M45.

With this configuration of level shift circuit 41, high side gate control signal HGCTR is level shifted to level shift voltage Vsht generated at connection node N42.

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

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

As a result, inverter IV4 outputs source voltage Vsm4 at 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 mentioned 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, transistors M42 and M45 are turned off. Then, since no current flows through the resistor R42, the level shift voltage Vsht matches the source voltage Vsm4. As a result, inverter IV4 outputs 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 depending on the high or 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 explained. 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 the input voltage Vin is applied to it. The other end of resistor R6 is connected to the drain of transistor M61 constituted by an n-channel MOSFET. The source of transistor M61 is connected to connection node N1. A 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 terminal (-) of the comparator CP6. The gate of transistor M61 is connected to the output terminal of 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 constituted by an n-channel MOSFET is connected to the terminal T3, and the input voltage Vin is applied thereto. The gate of the transistor M62 is connected to the application terminal of the high side voltage VHSD. The source of the transistor M62 is connected to the constant current source CI6 and also to the non-inverting input terminal (+) of the comparator CP6.

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

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

First, immediately before 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 and the low-side transistor QL is on, the switching voltage Vsw is 0 V, and the inductor current IL flowing from ground to the low-side transistor QL and through the inductor L1 via the terminal T4 decreases.

At this time, since the transistor M61 is off, the current detection signal Videt matches the input voltage Vin. Here, the reference voltage Vref is expressed as Vref=Vin−(Rdson2×Ic). However, Rdson2 is the on-resistance of the transistor M62, and Ic is the constant current generated by the constant current source CI6. Therefore, the current detection signal Videt becomes higher than the reference voltage Vref, and the limited current detection signal ILIMIT_det becomes low level.

Then, at timing t1, when the inductor current IL reaches 0A and the high-side gate control signal HGCTR is switched to high level and the low-side gate control signal LGCTR is switched to 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 from the terminal T3 to the high-side transistor QH and the inductor L1 via the terminal T4 starts increasing from 0A.

Here, since the switching voltage Vsw = Vin - (Rdson1 x IL) (where Rdson1 is the on-resistance of the high-side transistor QH), as the inductor current IL increases, the switching voltage Vsw drops from the input voltage Vin. At this time, the transistor M61 is on, and the resistance value of the resistor R6 is sufficiently high compared to the on-resistance of the transistor M61, so the current detection signal Videt is almost equal to the switching voltage Vsw. Therefore, as shown in Figure 4, the current detection signal Videt also drops from the input voltage Vin, just like the switching voltage Vsw.

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

In response to the limit current detection signal ILIMIT_det becoming high level, the logic unit 3 switches the high side gate control signal HGCTR to low level and the low side gate control signal LGCTR to high level. Then, the high side transistor QH turns off, the low side transistor QL turns on, and the switching voltage Vsw falls to 0V. At this time, the transistor M61 turns off, so the current detection signal Videt rises to the input voltage Vin. This causes the limit current detection signal ILIMIT_det to become low level. The inductor current IL decreases from the limit current value Ilimit.

Here, as mentioned above, since the threshold voltage Vth=Vin-(Rdson1×Ilimit) and the reference voltage Vref=Vin-(Rdson2×Ic), in order to match the temperature characteristics of the on-resistances Rdson1 and Rdson2, 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. Thereby, the influence of the temperature characteristics of the on-resistance can be canceled by the high-side transistor QH and the transistor M62, and the detection accuracy of the limited current can be improved.

However, in the configuration of FIG. 3, the high side gate signal HG applied to the gate of high side transistor QH when high side transistor QH is on is HG = Vsm4 = Vsw + Vz - Vgs4, but the voltage applied to the gate of transistor M62 is high side voltage VHSD. The voltage applied to the gate of a transistor affects the on-resistance of the transistor, but the voltage applied to the gate of transistor M62 lacks the Vgs element like the high side gate signal HG. Because Vgs has temperature characteristics, it cannot be said that the effects of the temperature characteristics of the on-resistance are sufficiently canceled out between high side transistor QH and transistor M62.

In order to solve the problems uniquely discovered by the inventor of the present application, embodiments of the present invention as described below have been devised.

<4. Embodiments 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 comparative example described above. . The difference between the circuit configuration according to the present embodiment shown in FIG. 5 and that shown in FIG. 3 is the configuration of the current detection circuit 60.

Compared to the current detection circuit 6 shown in FIG. 3, the current detection circuit 60 includes transistors M63 to M66 and a resistor R61.

The drain of the transistor M63 constituted by an n-channel MOSFET is connected to the application terminal of the high side voltage (second power supply voltage) VHSD, and shorted to 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 transistor M63 is applied to the gate of transistor M62. The source voltage Vsm63 is Vsm63=VHSD-Vgs63, where Vgs63 is the gate-source voltage of transistor M63.

As mentioned earlier, 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 HG applied to the gate of the high-side transistor QH and Vsm63 applied to the gate of the transistor M63 can include an element of Vgs. Thereby, 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. Furthermore, corresponding to the fact that the size of the transistor M62 is made smaller than the size of the high-side transistor QH, the size of the transistor M63 is made smaller than the size of the transistor M4. This leads to space savings.

Furthermore, in this 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 a transistor M64 formed by an n-channel MOSFET. The drain and gate of transistor M64 are short-circuited. The source of the transistor M64 is connected to a ground potential application terminal.

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

As a result, the current flowing through the transistor M64 caused by the low side voltage VLSD and the resistor R61 becomes the current I65 flowing through the transistor M65 by the current mirror CM60. Current I65 flows from connection node N62 through transistor M66. Corresponding to the fact that the size of the transistor M63 is smaller than the size of the transistor M4, the amount of the current I65 is made smaller than the current I44 flowing through the current mirror CM4. Thereby, Vgs63 of the transistor M63 is adjusted with respect to Vgs4 of the transistor M4.

In this way, according to the present embodiment, the influence of temperature characteristics can be further suppressed, and the detection accuracy of the limited current 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 spirit of the present invention.

INDUSTRIAL APPLICATION This invention can be utilized for the current detection in a switching power supply circuit, for example.

1 Power IC
2 Reduced voltage detection circuit 3 Logic section 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 30 Voice coil motor 31 Spindle motor 32 Magnetic disk 33 Swing arm 34 Magnetic head 35 Housing 40 HDD (hard disk drive)

Claims (15)

A current detection circuit having a drain connected to an application terminal of a first power supply voltage and detecting a current flowing through a first driven transistor whose gate is driven by a first gate signal,
a first transistor having a drain connected to an application end of the first power supply voltage;
a constant current source that generates a constant current flowing through the first transistor;
a comparator having a first input terminal into which a voltage generated at the source of the first driven transistor that is on is input as a current detection signal; and a second input terminal connected to the source of the first transistor;
a second transistor having a drain to which a second power supply voltage application terminal is connected, a source to which the gate of the first transistor is connected, and a gate short-circuited to the drain;
a current detection circuit comprising;
a Zener diode having an anode connected to the source of the first driven transistor;
a fifth transistor having a gate connected to the cathode of the Zener diode, and a drain connected to the application end of the second power supply voltage;
Equipped with
A transistor drive circuit in which a case where the source voltage of the fifth transistor becomes the first gate signal and a case where the source voltage of the first driven transistor becomes the first gate signal are switched by a first gate control signal. The transistor drive circuit according to claim 1, wherein the first transistor is a device having the same composition as the first transistor to be driven. The transistor drive circuit according to claim 2 , wherein a size of the first transistor is smaller than a size of the first driven transistor. The transistor drive circuit according to claim 1 , further comprising a first current mirror that generates a current flowing from the source of the second transistor. 5. The transistor drive circuit according to claim 4, further comprising a third transistor disposed between the first current mirror and the source of the second transistor. a first resistor having one end 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 connected to the source of the first driven transistor, and a gate connected to the gate of the first driven transistor; ,
Furthermore,
6. 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 terminal. Transistor drive circuit. 7. The transistor drive circuit according to claim 1, 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 driven transistor,
The size of the second transistor is smaller than the size of the fifth transistor.
7. The transistor drive circuit according to 7 . further comprising a second current mirror that generates a current flowing from the source of the fifth transistor,
9. The transistor drive circuit according to claim 8 , wherein the amount of 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 9 , further comprising a sixth transistor disposed between the second current mirror and the source of the fifth transistor. a seventh transistor having a gate to which the first gate control signal is applied, and switching the second current mirror on and off;
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 driven transistor, and an input end connected to the second end of the second resistor. and an inverter having
Furthermore,
The transistor drive circuit according to claim 9 , wherein the output of the inverter is the first gate signal. The transistor drive circuit according to any one of claims 1 to 11 ,
the first driven transistor driven by the transistor drive circuit;
a second driven transistor having a drain connected to the source of the first driven transistor and a source connected to a ground potential application terminal;
A power supply IC. A switch that monitors a host voltage and, when detecting a falling edge of the host voltage, turns off an isolation switch to which an application terminal of the host voltage is connected and starts driving the first transistor to be driven and the second transistor to be driven. The power supply IC according to claim 12 , further comprising a voltage detection circuit. A power supply IC according to claim 13 ;
the isolation switch whose on/off is controlled by the voltage reduction detection circuit;
an inductor having a first end connected to a second connection node to which the source of the first transistor to be driven and the drain of the second transistor to be driven are connected;
a capacitor having a first end connected to a second end of the inductor and the isolation switch;
A power supply device comprising: A power supply device according to claim 14 ;
At least one of a voice coil motor and a spindle motor to which power is supplied from the power supply device;
A hard disk drive (HDD).

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