JP2008029137A - Motor drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive circuit which improves control characteristics at constant-current drive. <P>SOLUTION: In the motor drive circuit which performs the constant-current drive to make constant a coil current flowing through a motor coil, the motor drive circuit includes an error amplifier, a threshold voltage generating circuit, and a rise time adjusting circuit. The error amplifier outputs an error voltage between a voltage drop corresponding to the coil current flowing through the motor coil and a reference voltage which is the basis of the coil current, to a control electrode of a drive transistor, and includes power supply for adjusting rise time to shorten the rise time of the error voltage. The threshold voltage generating circuit generates a second threshold voltage, serving as a basis to determine whether adjustment to shorten the rise time is made, wherein the second threshold voltage is lower in level than a first threshold voltage that serves as a basis, to determine whether the drive transistor conducts or not. The rise time adjusting circuit controls to turn on the power supply for adjusting the rise time, from starting of energization of the motor coil, until the error voltage exceeds the second threshold voltage, according to comparison of the error voltage with the second threshold voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a motor drive circuit.

  A constant current drive system is known as one of drive systems for motor drive circuits. The constant current driving method is a method of controlling so that a constant current always flows through the motor coil. As a motor drive circuit that employs this constant current drive system, for example, a motor drive circuit for a shutter mechanism or an aperture mechanism, which is one of actuators of a digital still camera, can be cited. Hereinafter, a motor driving circuit (hereinafter, referred to as “constant current driver”) 300 adopting a constant current driving method will be described with reference to FIG.

  The constant current driver 300 includes a connection point OUTA of the first series connection body formed by the first source-side transistor U1 and the first sink-side transistor D1 disposed between the source-side power supply VCC and the sink-side power supply GND, and the source side A motor coil L is disposed between the second source-side transistor U2 disposed between the power supply VCC and the sink-side power supply GND and the connection point OUTB of the second series connection body formed by the second sink-side transistor D2. It is common to have an H-bridge circuit with an alphabetic H-shaped configuration. In the case of the CMOS process, PMOS transistors may be employed as the first and second source-side transistors U1 and U2, and NMOS transistors may be employed as the first and second sink-side transistors D1 and D2. . In the case of the Bi-CDMOS process, the first and second sink-side transistors D1 and D2 have a high withstand voltage DMOS (Diffuse) having a high current capability as compared with normal NMOS and PMOS and suitable for constant current driving. MOS) transistors may be employed. The DMOS transistor is realized by flattening the gate and double diffusing the channel.

  In the H bridge circuit, when the first source side transistor U1 and the second sink side transistor D2 are turned on, the coil current IL flows through the motor coil L from the connection point OUTA to the connection point OUTB, and the second source side transistor When the transistor U2 and the first sink-side transistor D1 are turned on, a coil current IL is passed through the motor coil L from the connection point OUTB to the connection point OUTA. Since the first and second source side transistors U1 and U2 are in a full-on state, the current capability is adjusted by linearly controlling the gate voltages of the first and second sink side transistors D1 and D2, and the motor. The current flowing through the coil L is controlled. When the constant current driver 300 receives a motor drive command DCTL for starting energization of the motor coil L from a processor (not shown) such as a CPU or a microcomputer, the constant current driver 300 and the first and second sink side transistors D1. , D2 selects one of the first or second sink-side transistors D1 and D2 to be subjected to on / off control.

  The constant current driver 300 is a coil that flows in the motor coil L by a current detection resistor Rd provided between the first and second sink-side transistors D1 and D2 and the sink-side power supply GND in the process of controlling energization of the motor coil L. A voltage drop VD corresponding to the current IL is detected. This voltage drop VD is applied to the inverting input of the error amplifier 310 in which the reference voltage Vr is applied to the non-inverting input. The constant current driver 300 includes first and second sink-side transistors so that an error voltage Vg output from the error amplifier 310 causes an imaginary short between the voltage drop VD and the reference voltage Vr that are two inputs of the error amplifier 310. Control ON / OFF of D1 and D2. As a result, a constant coil current IL corresponding to the reference voltage Vr flows through the motor coil L.

  When the constant current driver 300 receives a motor drive command DCTL from a processor (not shown) (see FIG. 7A), the first and second sink-side transistors D1 and D2 are not in a full-on state. The gate / source voltage Vgs of the first or second sink-side transistor D1, D2 does not rise rapidly but gradually rises (see FIG. 7B). Accordingly, the first or second sink-side transistor D1, D2 is turned on when the gradually rising gate / source voltage Vgs exceeds the first threshold voltage Vt1, and the coil current IL is applied to the motor coil L. The flow starts (see FIG. 7C). That is, in the constant current driver 300, a delay time Td (see FIG. 7C) can actually occur from when the motor drive command DCTL is received until the coil current IL starts to flow through the motor coil L. Here, in the case of the constant current driver 300 for the shutter, since the shutter speed is an important factor for the shutter performance, the delay time Td needs to be as short as possible. Therefore, the constant current driver 300 requires a rise time adjustment circuit 330 described below (for example, see Non-Patent Document 1 shown below).

  When the rising time adjustment circuit 330 receives a motor drive command DCTL from a processor (not shown) (see FIG. 8A), the gate-source voltage Vgs of the first or second sink-side transistors D1 and D2 is This is a circuit for rapidly rising up to the first threshold voltage Vt1 (see FIG. 8B). Therefore, when the first or second sink-side transistor D1 or D2 receives the motor drive command DCTL, the first or second sink-side transistor D1 or D2 is quickly turned on without causing the delay time Td, and the coil current IL starts to flow through the motor coil L. (See FIG. 8 (c)).

  As shown in FIG. 6, the rise time adjustment circuit 330 functions as a diode by short-circuiting the constant current source 332 that generates the constant current IC and the drain electrode and the gate electrode, so that the constant current IC is in the forward direction. A diode M334 that generates a forward voltage generated by flowing as a second threshold voltage Vt2, and a comparator 336 that generates a rise time adjustment control signal CTL by comparing the second threshold voltage Vt2 and the error voltage Vg. And composed of

  When receiving the motor drive command DCTL, the diode M334 needs to rise rapidly until the gate / source voltage Vgs of the first and second sink-side transistors D1 and D2 becomes the conductive gate / source voltage Vgs. Therefore, the same type of transistors as the first and second sink-side transistors D1 and D2 are employed. For example, as described above, the first and second sink-side transistors D1 and D2 are mainly high-breakdown-voltage N-channel DMOS transistors, so that the diode M334 is similarly employed as a high-breakdown-voltage N-channel DMOS transistor. The Accordingly, in this case, the first threshold voltage Vt1 of the first and second sink-side transistors D1 and D2 and the second threshold voltage Vt2 of the diode M334 are the same.

The comparator 336 generates a rise time adjustment control signal CTL for operating the rise time adjustment power supply 312 to adjust the rise time while the error voltage Vg is lower than the second threshold voltage Vt2. As a result, the error voltage Vg, that is, the gate / source voltage Vgs of the first and second sink-side transistors D1 and D2 rises rapidly until it reaches the first threshold voltage Vt1 (= second threshold voltage Vt2). The rise time will be shortened. The comparator 336 also has a rise time adjustment control signal for stopping the adjustment by the rise time adjustment power supply 312 in order to switch to the normal constant current drive when the error voltage Vg exceeds the second threshold voltage Vt2. Generate CTL.
"Sanyo Semiconductor News, LB8648T-Monolithic Digital Integrated Circuit DSC Driver", [online], Sanyo Electric Semiconductor Company, [Search July 21, 2006], Internet (URL: http: //service.semic. sanyo.co.jp/semi/ds_j/N7892A.pdf)

  By the way, in order to adjust the amount of coil current IL flowing through the motor coil L according to the specification of the constant current driver 300, the reference voltage Vr applied to the error amplifier 310 and to be compared with the coil current IL may be varied. is there. In this case, according to the conventional rise time adjustment circuit 330, when the level of the reference voltage Vr applied to the error amplifier 310 is lowered, the coil detected by the current detection resistor Rd in a form proportional to the reference voltage Vr. The current IL should also decrease.

  However, when the reference voltage Vr approaches 0 V, the error voltage Vg falls below the second threshold voltage Vt2 in the comparator 336 of the conventional rise time adjustment circuit 330, and an unintended rise time adjustment is performed. It will end up. As a result, when the reference voltage Vr is close to 0V, the rise time is adjusted, so that the error voltage Vg cannot be lowered to 0V, and control for further reducing the coil current IL cannot be performed. In other words, with the configuration of the conventional rise time adjustment circuit 330, the relationship between the reference voltage Vr and the coil current IL becomes nonlinear (see FIG. 9) when the reference voltage Vr is around 0 V, and control during constant current driving is performed. There was a problem that the characteristics deteriorated.

  A main invention for solving the above-described problems is that a coil current that flows through the motor coil when the motor coil is energized by having the four drive transistors connected to the motor coil in an H-bridge connection. In a motor drive circuit that performs constant current driving that keeps constant, a voltage drop corresponding to the coil current flowing in the motor coil and a reference voltage that is a reference for the coil current are applied, respectively. And an error amplifier having a rise time adjusting power source for shortening the rise time of the error voltage and whether the drive transistor is conductive or not. The level is lower than the first threshold voltage that is the standard of the above, and the rise time is shortened. The threshold voltage generation circuit that generates a second threshold voltage serving as a reference for whether or not to perform adjustment, and the error after the energization of the motor coil is started by comparing the error voltage and the second threshold voltage. And a rise time adjustment circuit that performs control to turn on the rise time adjustment power supply until the voltage exceeds the second threshold voltage.

  ADVANTAGE OF THE INVENTION According to this invention, the motor drive circuit which improved the control characteristic in the case of constant current drive can be provided.

<Constant current driver>
FIG. 1 is a diagram showing a configuration of a motor drive circuit (hereinafter referred to as “constant current driver”) 100 employing a constant current drive system according to an embodiment of the present invention. In the present embodiment, it is assumed that the constant current driver 100 is realized as a one-chip integrated circuit by a Bi-CDMOS process. Further, the constant current drive motor that is the subject of the present embodiment is, for example, the case of a voice coil motor or a stepping motor for a shutter mechanism or an aperture mechanism that is one of actuators of a digital still camera. Hereinafter, the constant current driver 100 will be described in detail.

=== Terminal ===
The constant current driver 100 includes an INA terminal 101a and an INB terminal 101b, a reference voltage terminal 102, an OUTA terminal 103a and an OUTB terminal 103b, a VCC terminal 104, and a GND terminal 105.

The INA terminal 101a and the INB terminal 101b are terminals for inputting motor drive commands INA and INB from a processor 200 such as a CPU or a microcomputer that controls the entire motor drive circuit 100.
The reference voltage terminal 102 is a terminal for connecting a voltage source of the reference voltage Vr to be applied to the non-inverting input of the error amplifier 30. That is, the reference voltage Vr is applied from the outside of the constant current driver 100 to the non-inverting input of the error amplifier 40. The reference voltage Vr is determined according to the specifications of the constant current driver 100.
The OUTA terminal 103a and the OUTB terminal 103b are terminals for connecting the motor coil L.
The VCC terminal 104 is a terminal for connecting the source side power supply VCC of the H bridge circuit 10, and the GND terminal 105 is a terminal for connecting the sink side power supply GND of the H bridge circuit 10. A current detection resistor Rd for detecting a coil current IL flowing through the motor coil L is disposed between the GND terminal 105 and the sink-side power supply GND.

=== Internal structure ===
The H bridge circuit 10 is configured by H-bridge connection of the four first and second source side transistors U1 and U2 and the first and second sink side transistors D1 and D2 as follows. That is, the H-bridge circuit 10 includes a connection point OUTA of the first series connection body formed by the first source-side transistor U1 and the first sink-side transistor D1 disposed between the source-side power supply VCC and the sink-side power supply GND. A motor coil L is arranged between a second source side transistor U2 disposed between the source side power supply VCC and the sink side power supply GND and a connection point OUTB of the second series connection body by the second sink side transistor D2. This is a circuit having an alphabetic H-shaped configuration. In the present embodiment, PMOS transistors are employed as the first and second source-side transistors U1 and U2, and the first and second sink-side transistors D1 and D2 are compared with normal NMOS and PMOS. Assume that a high-breakdown-voltage N-channel DMOS (Diffuse DMOS) transistor having a high current capability is employed. Hereinafter, the first threshold voltage of the N-channel DMOS transistor is “Vt1”.

  When the first source-side transistor U1 and the second sink-side transistor D2 are conductive (turned on), the H-bridge circuit 10 causes the coil current IL to flow through the motor coil L from the connection point OUTA to the connection point OUTB. When the second source-side transistor U2 and the first sink-side transistor D1 are turned on, a coil current IL is supplied to the motor coil L from the connection point OUTB to the connection point OUTA. Thus, the first source side transistor U1 and the second sink side transistor D2, and the second source side transistor U2 and the first sink side transistor D1 are turned on and off in a complementary manner. In the present embodiment, the first and second source-side transistors U1 and U2 are in a full-on state, and the motor coil L is energized by on / off control of only the first and second sink-side transistors D1 and D2. Suppose. On the other hand, the first and second sink-side transistors D1 and D2 are in a fully-on state, and the motor coil L is energized only by the conduction control of the first and second source-side transistors U1 and U2. It is also possible to make it.

  Regenerative diodes 5a and 5d are provided between the drain and source of the first source-side transistor U1 and the second sink-side transistor D2, respectively. The regenerative diodes 5a and 5d compensate for the regenerative operation when the direction of the coil current IL flowing through the motor coil L is switched from the direction from the connection point OUTA to the connection point OUTB and from the connection point OUTB to the connection point OUTA. . Similarly, regenerative diodes 5b and 5c are also provided between the drain and source of the second source side transistor U2 and the first sink side transistor D1, respectively.

  The resistance elements RA and RB and the hysteresis amplifiers 20a and 20b are provided until the motor drive commands INA and INB are supplied to the drive control circuit 30 from the INA terminal 101a and INB terminal 101b. The resistance elements RA and RB are provided to stabilize the operation of the constant current driver 100 when the INA terminal 101a and the INB terminal 101b are in the zero input state. In other words, when the INA terminal 101a and the INB terminal 101b are in the zero input state, the drive control circuit 30 becomes a GND input through the resistance elements RA and RB, so that the operation is stabilized. The hysteresis amplifiers 20a and 20b are stable in operation because they remove noise mixed in the motor drive commands INA and INB inputted to the INA terminal 101a and INB terminal 101b.

  The drive control circuit 30 receives the motor drive commands INA and INB from the processor 200, and turns on and off the first source-side transistor U1 to perform bipolar drive of the H-bridge circuit 10 according to a predetermined energization timing. The motor drive signal C1 to be turned on, the motor drive signal C2 to turn on / off the second source side transistor U2, and the motor drive signal C3 to turn on or off one of the first or second sink side transistors D1 and D2 are generated. Further, the drive control circuit 30 generates an enable signal EN serving as a trigger for operating the rise time adjustment circuit 50 in response to the start of driving of the motor.

  The error amplifier 40 detects the error voltage Vg between the reference voltage Vr applied to the reference voltage terminal 102 and the voltage drop VD corresponding to the coil current IL detected by the current detection resistor Rd, and the first or Output as the gate voltage of the second sink side transistors D1 and D2. In this embodiment, the reference voltage Vr is applied to the non-inverting input of the error amplifier 40, and the voltage drop VD is applied to the inverting input of the error amplifier 40.

  The switch 60 applies the error voltage Vg output from the error amplifier 40 to one of the gate electrodes of the sink-side transistors D1 and D2 based on the motor drive signal C3 supplied from the drive control circuit 30.

  When the rise time adjustment circuit 50 receives the motor drive commands INA and INB from the processor 200 and receives the enable signal EN from the drive control circuit 30, the rise time adjustment circuit 50 gates / sources of the first or second sink-side transistors D 1 and D 2 This is a circuit for performing adjustment to shorten the rise time by rapidly rising until the inter-voltage Vgs becomes the first threshold voltage Vt1. The adjustment for shortening the rise time means that a rise time adjustment control signal CTL for operating the rise time adjustment power supply 46 in the error amplifier 40 is generated, and the first or second sink side transistor D1 from the error amplifier 40 is generated. , The error voltage Vg applied to the gate electrode of D2 is boosted. Accordingly, when the first or second sink-side transistor D1 or D2 receives the motor drive command INA or INB from the processor 200, the first or second sink-side transistor D1 or D2 is quickly turned on without a delay time, and the coil current IL flows through the motor coil L. start.

<Error amplifier>
FIG. 2 is a diagram showing a configuration of the error amplifier 40 according to the embodiment of the present invention. The error amplifier 40 includes a differential amplifier circuit 42, a current mirror circuit 44, and a rise time adjusting power supply 46.

  The differential amplifier circuit 42 includes a constant current source 41 that supplies a constant current IA, and a differential transistor pair (B1, B2) through which currents IA1 and IA2 obtained by dividing the constant current IA flow. The reference voltage Vr is applied to the base electrode of one PNP transistor B1 of the differential transistor pair (B1, B2), and the voltage drop VD is applied to the base electrode of the other PNP transistor B2. That is, when the voltage drop VD is higher than the reference voltage Vr, the PNP transistor B1 is more capable of sinking the constant current IA than the PNP transistor B2, and therefore the current IA1 flowing through the PNP transistor B1. The amount of current is larger than the amount of current IA2 flowing through the PNP transistor B2. On the other hand, when the voltage drop VD is at a low level compared to the reference voltage Vr, this is the reverse of the above example, and the current IA2 flowing through the PNP transistor B2 has a current amount larger than the current IA1 flowing through the PNP transistor B1. Become more.

  The current mirror circuit 44 is arranged on the collector side of the PNP transistors B1 and B2, and has the gate electrodes of the NMOS transistors M1 and M2 short-circuited between the drain electrode and the gate electrode, and the gate electrodes of the NMOS transistors M5 and M6. Connected and configured. That is, the current IA1 flowing through the PNP transistor B1 is replicated as a current flowing through the NMOS transistor M6, and the current IA2 flowing through the PNP transistor B2 is replicated as a current flowing through the NMOS transistor M5. Note that the PMOS transistor M3 and the PMOS transistor M4 in which the drain electrode and the gate electrode are short-circuited, and the current mirror circuit configured by commonly connecting the gate electrodes of the PMOS transistor M3 and the NMOS transistor M5 and M6 are constant current loads.

  Accordingly, the error amplifier 40 determines the current flowing from the PMOS transistor M4 to the NMOS transistor M6 according to the error voltage between the reference voltage Vr and the voltage drop VD, and the PMOS transistor M4 and the NMOS transistor M6 according to the amount of the current. The voltage at the connection point is applied as an error voltage Vg to the gate electrodes of the first or second sink-side transistors D1 and D2 via the switch 60.

  The rise time adjustment power supply 46 turns on and off the constant current source IC by a constant current source IC and a rise time adjustment control signal CTL (normal time: L level, rise time adjustment: H level) from the rise time adjustment circuit 50. An NMOS transistor M7, PMOS transistors M8 and M9, and a current mirror circuit including PMOS transistors M10 and M11 are included. For example, when the rise time adjustment control signal CTL is at an H level that instructs to shorten the rise time, the NMOS transistor M7 is switched from off to on. Then, the current mirror circuit composed of the PMOS transistors M10 and M11 is operated, and the constant current IB that duplicates the constant current source IC is generated in the current mirror circuit composed of the PMOS transistors M8 and M9. As a result, since the constant current IB is superimposed on the output of the error amplifier 40, the potential of the error voltage Vg increases and the rise time of the error voltage Vg is shortened.

<Rise time adjustment circuit>
=== Function of Diode M20 ===
FIG. 3 is a diagram showing a configuration of the rise time adjustment circuit 50 according to the embodiment of the present invention.

  The rise time adjustment circuit 50 includes a constant current source 52 that generates a constant current IC, a diode M20, and a comparator 55. The circuit constituted by the constant current source 52 and the diode M20 is an embodiment of the “threshold voltage generation circuit” according to the present invention, and is constituted by the comparator 55 and the NMOS transistor M7 of the rise time adjusting power supply 46. This circuit is an embodiment of the “rise time adjustment circuit” according to the present invention.

The diode M20 functions as a diode by short-circuiting the drain electrode and the gate electrode, and generates a second threshold voltage Vt2 ′ (forward voltage) when the constant current IC flows in the forward direction. As the diode M20 of the present embodiment, a MOS transistor having a second threshold voltage Vt2 ′ lower than the first threshold voltage Vt1 of the first and second sink-side transistors D1 and D2 is employed. That is, the following formula (1) is established.
2nd threshold voltage Vt2 '<1st threshold voltage Vt1 ... Formula (1)
For example, when DMOS transistors are used as the first and second sink-side transistors D1 and D2, the threshold voltage becomes higher as the higher withstand voltage MOS transistor is used. Therefore, a low withstand voltage NMOS transistor is used as the diode M20. By doing so, the condition of Formula (1) can be easily satisfied.

  The comparator 55 compares the second threshold voltage Vt <b> 2 ′ with the error voltage Vg, and generates a rise time adjustment control signal CTL for operating or stopping the rise time adjustment power supply 46 included in the error amplifier 40. The comparator 55 adjusts the rise time while the error voltage Vg is lower than the second threshold voltage Vt2 ′, so that the rise time adjustment control signal CTL at H level for adjustment by the rise time adjustment power supply 46 is performed. Is generated. As a result, the error voltage Vg, that is, the gate / source voltage Vgs of the first and second sink-side transistors D1 and D2 rapidly rises to the second threshold voltage Vt2 '. Further, the comparator 55 has an L level for stopping the rise time adjustment by the rise time adjustment power supply 46 in order to switch to the normal constant current drive when the error voltage Vg exceeds the second threshold voltage Vt2 ′. The rise time adjustment control signal CTL is generated.

  With the above configuration, when the rise time adjustment circuit 50 receives the motor drive commands INA and INB from the processor 200 (see FIG. 4A), the gate / source of the first or second sink-side transistors D1 and D2 The voltage Vgs does not rise rapidly until it reaches the first threshold voltage Vt1 of the first and second sink-side transistors D1 and D2 (see the broken line in FIG. 4B), but from the first threshold voltage Vt1 Until the second threshold voltage Vt2 ′ becomes lower (see the solid line in FIG. 4B). When the gate / source voltage Vgs of the first or second sink-side transistor D1, D2 exceeds the second threshold voltage Vt2 ′, the rise time adjustment by the rise time adjustment circuit 50 is stopped, and the first The gate / source voltage Vgs of the first or second sink-side transistors D1 and D2 gradually rises due to the error voltage Vg during normal operation that is not affected by the rise time adjusting power supply 46. When the gate / source voltage Vgs of the first or second sink-side transistor D1 or D2 exceeds the first threshold voltage Vt1, conduction is established, and the coil current IL starts to flow through the motor coil L (FIG. 4). (See (c)).

  As a result, when the reference voltage Vr applied to the error amplifier 40 is reduced to near 0 V in accordance with the specifications of the constant current driver 100, the error voltage Vg also decreases in a manner following the reference voltage Vr. Since the reference voltage for adjusting the rise time in the device 55 is lowered in advance from the conventional first threshold voltage Vt1 to the second threshold voltage Vt2 ′, the current detection resistor Rd is proportional to the reference voltage Vr. The coil current IL detected by the above is further reduced.

  That is, according to the rise time adjustment circuit 50 according to the present invention, as compared with the conventional rise time adjustment circuit 330, there is a slight delay until the coil current IL starts to flow after receiving the motor drive commands INA and INB from the processor 200. Although time (see time t0 to time t1 in FIG. 4C) is involved, the relationship between the reference voltage Vr and the coil current IL is not nonlinear when the reference voltage Vr is around 0V, and the reference voltage Vr is increased from 0V. As a result, the linearity of the coil current IL can be ensured. In other words, a reduction in the delay time from when the motor drive commands INA and INB are received until the coil current IL starts to flow and the linearity between the reference voltage Vr and the coil current IL can be realized in a balanced manner. Therefore, the malfunction of the rise time adjustment circuit 50 can be prevented when the reference voltage Vr is around 0 V, and the control characteristics during constant current driving in the constant current driver 100 can be improved.

=== Function of the threshold voltage adjusting resistor ===
By the way, when the first and second sink-side transistors D1 and D2 are DMOS transistors and the diode M20 is an NMOS transistor, the levels of the first threshold voltage Vt1 and the second threshold voltage Vt2 ′ are too far apart. There is a possibility that the delay time until the coil current IL starts to flow after receiving the motor drive commands INA and INB, which is the original purpose of the rise time adjustment circuit 50, may be increased. Therefore, the rise time adjustment circuit 50 adjusts the second threshold voltage Vt2 ′ to be close to the first threshold voltage Vt1, and therefore, between the source electrode of the diode M20 and the sink-side power supply GND as shown in FIG. Further, it is preferable to provide a threshold voltage adjusting resistor R20. In this case, the second threshold voltage Vt2 applied to the non-inverting input of the comparator 55 is generated when the constant current IC generated in the constant current source 52 flows to the threshold voltage adjusting resistor R20 via the diode M20. A voltage obtained by adding the voltage drop (= R20 × IC) of the threshold voltage adjusting resistor R20 and the second threshold voltage Vt2 ′ is established, and the relationship of the following equation (2) is established.
Vt2 = Vt2 ′ + R20 × IC <Vt1 Formula (2)

  With the configuration in which the threshold voltage adjusting resistor R20 is added, the rise time adjusting circuit 50 receives the motor drive commands INA and INB from the processor 200 (see FIG. 5A), and the first or second sink. Until the gate / source voltage Vgs of the side transistors D1 and D2 exceeds the second threshold voltage Vt2 ′ and reaches the second threshold voltage Vt2 (= Vt2 ′ + R20 × IC) (see the solid line in FIG. 5B). Get up quickly. Then, when the gate / source voltage Vgs of the first or second sink-side transistor D1, D2 exceeds the second threshold voltage Vt2, the adjustment by the rise time adjustment circuit 50 stops, and the first or second The gate-source voltage Vgs of the sink-side transistors D1 and D2 gradually rises due to the error voltage Vg that is not affected by the rise time adjusting power supply 46. Then, when the gate / source voltage Vgs of the first or second sink side transistor D1, D2 exceeds the first threshold voltage Vt1, it is turned on, and the coil current IL starts to flow through the motor coil L (FIG. 5). (See (c)).

  As a result, even when the levels of the first threshold voltage Vt1 and the second threshold voltage Vt2 ′ are too far apart, the delay time from when the motor drive commands INA and INB are received until the coil current IL starts to flow is reduced. Shortening and linearity between the reference voltage Vr and the coil current IL can be realized with a better balance. Therefore, the malfunction of the rise time adjustment circuit 50 can be prevented when the reference voltage Vr is around 0 V, and the control characteristics at the time of constant current driving in the constant current driver 100 can be further improved.

<Other embodiments>
DMOS transistors may be employed as the first and second sink-side transistors D1 and D2, and the same DMOS transistor as the first and second sink-side transistors D1 and D2 may be employed as the diode M20. In this case, the diode M20 needs to be a diode having a second threshold voltage Vt2 ′ lower than the first threshold voltage Vt1 of the first and second sink-side transistors D1 and D2. For example, two types of DMOS transistors having different threshold voltages can be adopted by performing threshold adjustment by an ion implantation step in a Bi-CDMOS process.

  Further, the H bridge circuit 10 may be configured using NPN type or PNP type bipolar transistors as the first and second source side transistors U1, U2 and the first and second sink side transistors D1, D2. . In this case, the rise time adjustment circuit 50 adjusts the rise time of the base current supplied to the base electrodes of the first and second sink-side transistors D1 and D2. In this case, the diode M20 has the same NPN as the first and second sink-side transistors D1 and D2 for the same reason as the case where the first and second sink-side transistors D1 and D2 are DMOS transistors. A PNP type bipolar transistor may be adopted.

  As mentioned above, although embodiment of this invention was described concretely based on the embodiment, it is not limited to this and can be variously changed in the range which does not deviate from the summary.

It is a figure which shows the structure of the constant current driver which concerns on one Embodiment of this invention. It is a figure which shows the structure of the error amplifier which concerns on one Embodiment of this invention. It is a figure which shows the structure of the rise time adjustment circuit which concerns on one Embodiment of this invention. It is a figure for demonstrating operation | movement of the rise time adjustment circuit which concerns on one Embodiment of this invention. It is a figure for demonstrating operation | movement of the rise time adjustment circuit which concerns on one Embodiment of this invention. It is a figure which shows the structure of the conventional constant current driver. It is a figure for demonstrating operation | movement of the conventional rise time adjustment circuit. It is a figure for demonstrating operation | movement of the conventional rise time adjustment circuit. It is a figure for demonstrating operation | movement of the conventional rise time adjustment circuit.

Explanation of symbols

5a to 5d Regenerative diode 10 H bridge circuit 20a, 20b Hysteresis amplifier 30 Drive control circuit 40, 310 Error amplifier 42 Differential amplifier circuit 44 Current mirror circuit 46 Rise time adjustment power supply 50, 330 Rise time adjustment circuit 52, 332 Constant current Source 55 Comparator 60, 320 Switch 100, 300 Constant current drivers 101a, 101b INA terminal, INB terminal 102 Reference voltage terminals 103a, 103b OUTA terminal, OUTB terminal 104 VCC terminal 105 GND terminal 200 Processor

Claims (4)

A motor drive that has four drive transistors connected to a motor coil in an H-bridge connection, and performs constant current drive that keeps the coil current flowing through the motor coil constant when the drive transistor is turned on to energize the motor coil. In the circuit
A voltage drop corresponding to the coil current flowing through the motor coil and a reference voltage used as a reference for the coil current are applied, and an error voltage between the voltage drop and the reference voltage is directed toward the control electrode of the drive transistor. An error amplifier having a power supply for rise time adjustment for reducing the rise time of the error voltage,
Threshold value for generating a second threshold voltage that is lower than a first threshold voltage that is a criterion for determining whether or not the drive transistor is conductive and that is a criterion for determining whether or not to perform the adjustment for shortening the rise time A voltage generation circuit;
Rise that performs control to turn on the rise time adjustment power source from the start of energization of the motor coil by comparing the error voltage and the second threshold voltage until the error voltage exceeds the second threshold voltage A time adjustment circuit;
A motor drive circuit comprising: The motor drive circuit according to claim 1,
The threshold voltage generation circuit includes:
A constant current source and a diode connected in series between the source side power source and the sink side power source,
A forward voltage of the diode generated by a current generated in the constant current source flowing in the forward direction to the diode is set as the second threshold voltage;
A motor drive circuit characterized by the above. In the motor drive circuit according to claim 2,
The drive transistor is a DMOS transistor,
The diode is an NMOS transistor in which a drain electrode and a gate electrode are short-circuited,
A motor drive circuit characterized by the above. In the motor drive circuit according to claim 2 or 3,
A threshold voltage adjusting resistor disposed between the diode and the sink-side power supply;
A voltage obtained by adding a voltage drop of the threshold voltage adjusting resistor generated by the current generated in the constant current source flowing through the diode to the threshold voltage adjusting resistor and the forward voltage of the diode. The second threshold voltage;
A motor drive circuit characterized by the above.

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