Stepper motor driver and related method

Abstract

Embodiments of the present application relate to average current control in a stepper motor. A stepper motor driver includes an H-bridge including a first output and a second output. The H-bridge includes a low side transistor (LS2) coupled between the first output and ground. A reference current circuit (502) is configured to generate a reference current. The reference current circuit (502) has a reference output. An averager circuit (550) includes an input and an output. The input of the averager circuit (550) is coupled to the first output of the H-bridge. A comparator (555) includes a first comparator input and a second comparator input. The first input of the comparator (555) is coupled to the output of the averager circuit (550) and the second input of the comparator (555) is coupled to the reference output.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 886,983, filed August 15, 2019, entitled “Average Current Control in Stepper Motors,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments of this application generally relate to average current control in stepper motors. Background Technology

[0004] At least one type of stepper motor contains two coils that receive current from a stepper driver. The current to each coil should be sinusoidal, where the current to one coil is 90 degrees out of phase with the current to the other coil. The angular position of the stepper motor is a function of the ratio of the magnitudes of the currents in the coils (e.g., the arctangent of the ratio). Inaccuracy in the magnitude of the coil currents can lead to inaccuracy in the rotational position of the motor. Summary of the Invention

[0005] In at least one instance, the stepper motor driver includes an H-bridge with a first output and a second output. The H-bridge includes a low-side transistor coupled between the first output and ground. A reference current circuit is configured to generate a reference current. The reference current circuit has a reference output. An averager circuit includes an input and an output. The input of the averager circuit is coupled to the first output of the H-bridge. A comparator includes a first comparator input and a second comparator input. The first input of the comparator is coupled to the output of the averager circuit, and the second input of the comparator is coupled to the reference output. Attached Figure Description

[0006] To describe the various examples in detail, reference will now be made to the accompanying drawings, in which:

[0007] Figure 1 A motor control system including an average current controller is shown.

[0008] Figure 2 The current waveform of the motor control system is shown.

[0009] Figure 3 An example of an H-bridge is shown.

[0010] Figure 4 An example waveform of the motor coil current is shown, representing the current flowing through one of the transistors in the H-bridge.

[0011] Figure 5 Demonstrates what can be used Figure 1 An example of a stepper driver in a motor control system.

[0012] Figure 6 An example of an averager circuit used in a stepper driver is shown.

[0013] Figure 7 Another example of an averager circuit used in a stepper driver is shown.

[0014] Figure 8 Demonstrates what can be used Figure 7 An example of a variable resistor in an averaging circuit.

[0015] Figure 9 This demonstrates how to adjust the input offset of the comparator.

[0016] Figure 10 Another technique for determining the average coil current is shown.

[0017] Figure 11 Demonstrates what can be used Figure 1 Another example of a stepper driver in a motor control system.

[0018] Figure 12 The flow of logic implemented by the stepper driver is shown. Detailed Implementation

[0019] Figure 1 An example of a stepper motor system 100 is shown. The example stepper motor system 100 includes a controller 102 coupled to a stepper motor driver 120, which in turn is coupled to a stepper motor M. The stepper motor M includes coil 1 and coil 2, and the stepper driver 120 controls the current flowing through the coils. The current flowing through the coils approximates a sine curve, and the current flowing through coil 2 is 90 degrees out of phase with respect to coil 1.

[0020] In one example, controller 102 includes a processor or other type of digital control circuitry. Controller 102 is coupled to stepper driver 120 via a STEP signal, a direction (DIR) signal, and a programming interface. The programming interface can include any suitable interface, such as Serial Peripheral Interconnect (SPI). Each rising edge of the STEP signal causes stepper driver 120 to advance the motor position by one step, and the DIR signal specifies the direction of the motor change (forward or reverse). Stepper driver 120 includes an average current controller 121 (described below).

[0021] Figure 2Examples of approximate sinusoidal currents I1 (through coil 1) and I2 (through coil 2) are shown. It can be seen that I1 and I2 are 90 degrees out of phase. Each sinusoidal current is formed as a series of discrete steps generated by a digital-to-analog converter within the stepper driver 120. The stepper driver 120 regulates the current in each coil at each step. The current to the motor coils is controlled by an H-bridge (discussed below). Waveform 210 shows the coil current for a given step. At each step, during the drive mode (DRV), a pair of transistors are turned on, and the current through the coil increases as shown. When the coil current reaches the upper threshold (TH1), the decay mode begins, and another pair of transistors within the H-bridge is turned on. As a result, the coil current decreases. At each step, the H-bridge is controlled between alternating drive and decay modes to maintain the peak coil current at a desired level.

[0022] The average coil current at a given step is lower than the peak coil current. However, the torque in the motor is a function of the average current, not the peak current. By controlling the peak current of each coil, a torque imbalance may occur in the two coils, coil 1 and coil 2. Furthermore, adjusting the coil current based on the peak current of the coil is affected by delays in the control path. The drivers of the transistors used to turn the H-bridge on and off experience delays. The comparator used to compare the peak coil current with a reference value has a delay. Ripple caused by the delay (in...) Figure 2 The difference between the upper and lower coil current values ​​for a given step (shown in the diagram) is a function of the stepper motor system's power supply voltage and the motor's inductance, which can vary with the motor. Ripple is also a function of the driver's off-time during decay mode.

[0023] Figure 3 An example of an H-bridge is shown. This example H-bridge includes high-side (HS) transistors HS1 and HS2 and low-side (LS) transistors LS1 and LS2. The transistors in this example are n-type metal-oxide-semiconductor field-effect transistors (NMOS), but can be implemented as different types of transistors as needed. The drains of HS1 and HS2 are coupled together and coupled to the power supply voltage rail VDD. The sources of LS1 and LS2 are coupled together and grounded. The source of HS1 is coupled to the drain of LS1 and provides the first H-bridge output 310. The source of HS2 is coupled to the drain of LS2 and provides the second H-bridge output 312. The coil of motor M is connected to outputs 310 and 312. Another motor coil is connected to a separate H-bridge.

[0024] Each transistor has a control input (gate) and can be controlled independently. The stepper motor driver 120 can control the transistors of the H-bridge to achieve three operating modes—the aforementioned drive mode and two different decay modes. The two decay modes include fast decay (FD) mode and slow decay (SD) mode. During drive mode, HS1 and LS2 are turned on, while HS2 and LS1 are turned off, resulting in a current I_DRV flowing through HS1, motor M, and LS1. During FD mode, HS2 and LS1 are turned on, while HS1 and LS2 are turned off, resulting in a current I_FD flowing through LS1, motor M, and HS2. During SD mode, LS1 and LS2 are turned on, while HS1 and HS2 are turned off, resulting in a current I_SD flowing through LS1, motor M, and LS2. Therefore, the coil current only flows through LS2 during drive and SD modes. During FD mode, the coil current does not flow through LS2.

[0025] Figure 4 Example waveforms of the coil current I_COIL1 and the drain current through LS2 (labeled I_LS2) are shown. During drive mode, the coil current increases. During FD and SD modes, the coil current decreases as the decay rate during FD mode is greater than that during SD mode. During DRV and SD modes, the I_LS2 current equals the coil current I_COIL1, and is zero during FD mode because LS2 is turned off.

[0026] According to the disclosed example, the stepper driver 120 determines the average coil current and controls the transistors of the H-bridge to adjust the average coil current. The average of I_COIL1 is represented by dashed line 410. The average coil current level 410 is midway between a minimum value 420 and a peak value 425. For the I_LS2 waveform, in each drive mode operation of the H-bridge, the midpoint 412 between the minimum value 430 (the same value as 420) and the peak value 435 (the same value as 425) is represented by dashed line 412, and dashed line 412 also represents the average value of the coil current. Therefore, according to the example, the stepper driver determines the average value of the drain current (I_LS2) through LS2 only during drive mode, and uses said average value in the control of the H-bridge to adjust the coil current to the desired average value.

[0027] Figure 5 This demonstrates how to determine the average value of I_LS2 and use it to control the coil current. Figure 5 It demonstrates what can be used to achieve Figure 1This is an example of stepper driver 500, specifically stepper driver 120. Stepper driver 500 includes an H-bridge comprising transistors HS1, HS2, LS1, and LS2. A coil 1 is shown in this schematic, but the coil itself is not typically a component of a semiconductor die containing the other components shown for stepper driver 500. In addition to the H-bridge, stepper driver 500 includes a reference current circuit 502, a comparator 520, digital logic and a driver 511, and an average current controller 121.

[0028] The reference current circuit 502 includes a voltage-to-current (VtoI) converter 214, a sinusoidal digital-to-analog converter (DAC) 506, and a sensing transistor (SNS FET), which in this example is an NMOS transistor. Figure 5 The examples shown (and the above regarding) Figure 3 As explained, the drains of HS1 and HS2 are coupled together at the power supply voltage rail (VDD), while the sources of LS1 and LS2 are coupled together at the ground node. The source of HS1 is connected to the drain of LS1 at node A. Similarly, the source of HS2 is connected to the drain of LS2 at node B. The motor's coil 1 can be coupled between nodes A and B. A separate H-bridge and sensing FET are provided for the other coil (coil 2).

[0029] Digital logic and driver 511 includes logic 512 coupled to gate driver 413. Gate driver 413 provides gate assertion gate signals Hson1, Hson2, Lson1, and Lson2 for transistors HS1, HS2, LS1, and LS2, respectively. Comparator 520 includes a positive (+) input, a negative (-) input, and an output. The output of comparator 520 is coupled to digital logic and driver 511. The positive input of the comparator is coupled to node B, which also represents the drain-to-source voltage of transistor LS2. The gate of transistor LS2 is connected to the gate of an SNS FET, and the drain of the SNS FET is coupled to the negative input of comparator 520. The source of the SNS FET is connected to ground.

[0030] The sinusoidal DAC 506 includes one input for receiving a microstepping indexer bit (s[n:0]) and another input for receiving a reference voltage VREF. The microstepping indexer bit represents the control signal for the switches internal to the sinusoidal DAC 506. The microstepping indexer bit is generated based on the DAC code, and the sinusoidal DAC converts each DAC code into an analog output voltage (Vsine), which is then converted into an analog reference current Iref via VtoI 504. The transfer function of the sinusoidal DAC is a sine curve, meaning that the Vsine curve changes as the DAC code increases or decreases linearly. For example, Figure 2This demonstrates the progression of the analog current from the VtoI 504 as the DAC code increases linearly and then decreases linearly.

[0031] The output of VtoI converter 504 is coupled to the drain of the SNS FET and the negative input of comparator 520. The reference current Iref output by VtoI 504 flows through the SNS FET, generating a voltage at the drain of the SNS FET, and thus also a voltage at the negative input of the comparator. This voltage is a function of the magnitude of Iref. A voltage is created across LS2 (node ​​B), which is a function of I_LS2 (the drain current through the low-side transistor LS2). Comparator 520 generates an output comparator signal indicating whether the drain-to-source voltage of LS2 (a function of I_LS2) is less than or greater than the drain-to-source voltage of the SNS FET (a function of Iref). In other words, comparator 520 determines whether I_LS2 is greater than or less than Iref. Logic 512 receives and responds to the comparator's output signal to control the timing of the transistors within the H-bridge and enters a decay mode within a fixed time period.

[0032] The average current controller 121 includes an averager circuit 550 and an offset compensation amplifier 555. The input of the averager circuit 550 is coupled to the drain of LS2 (node ​​B), and the output of the averager circuit 550 is coupled to the negative input of the offset compensation amplifier 555. The positive input of the offset compensation amplifier 555 is coupled to the drain of the SNS FET. The averager circuit 550 determines the average drain-to-source voltage of LS2 in DRV mode. The averager circuit 550 generates an average control signal 551, which indicates the average drain-to-source voltage of LS2 in DRV mode (a function of I_LS2). The offset compensation amplifier 555 compares the average control signal 551 with the drain-to-source voltage of the SNS FET (Iref) and generates an error control signal 557, which indicates whether the average value of the I_LS2 current (i.e., the drain current through LS2) is less than or greater than Iref.

[0033] An error control signal 557 is provided to the control input of comparator 520, causing comparator 520 to adjust its input offset. The input offset of comparator 520 is the minimum voltage value at which the positive input must be greater than the negative input. For example, if the offset is 1 mV, the positive input must be at least 1 mV greater than the negative input to keep the output voltage from comparator 520 at a high logic level. The input offset of comparator 520 is adjustable and can be adjusted based on the error control signal 557 from the offset compensation amplifier 555. By adjusting the input offset of comparator 520, the control loop formed by comparing I_LS2 with Iref and used to control the peak coil current is adjusted so that the coil current reaches an average value equal to Iref. If the average value of I_LS2 is less than Iref (i.e., the average coil current is too low), the error control signal 557 causes comparator 520 to decrease its input offset, which causes the output of comparator 520 to become logic high for the peak value of the I_LS2 current. Conversely, if the average value of I_LS2 is greater than Iref, the error control signal 557 causes comparator 520 to increase its input offset, which will require the peak current of I_LS2 to be smaller before the output of comparator 520 goes logic high.

[0034] Figure 5 The example illustrates that the logic 512 of the digital logic and driver 511 outputs two control signals – DRV 515 and SD 517. In some instances, logic 512 outputs DRV 515 but not SD 517. DRV 515 is a control signal indicating (e.g., high) when the H-bridge operates in drive mode. SD 517 is a control signal indicating (e.g., high) when the H-bridge operates in SD mode. The control signals DRV 515 and SD 517 are provided to the control inputs of the averager circuit 550.

[0035] Figure 6 and 7 This shows what can be used to implement Figure 5 An example implementation of the 550 averaging circuit. Figure 6 The example averager circuit 600 uses the DRV 515 control signal, while Figure 7 The averaging circuit 700 uses DRV 515 control signals and SD 517 control signals. First, refer to... Figure 6The averager circuit 600 includes a switch SW1, a resistor R1, and a capacitor C1. SW1 is connected between the drain of LS2 and one terminal of resistor R1. The other terminal of resistor R1 is coupled to C1 and provides the averaging control signal 551. R1 and C1 form a low-pass filter. The DRV signal 515 controls the on / off state of SW1. When the H-bridge operates in drive mode, the DRV signal 515 closes SW1, causing the low-pass filter, including R1 and C1, to average the drain-to-source voltage of LS2 to the averaging control signal 551.

[0036] The RC time constant of the low-pass filter can be long enough that the averager circuit 600 requires multiple cycles (i.e., multiple drive mode instantiations in a step) to generate the final value of the average control signal 551. Figure 7 The example averager circuit 700 implements a mode to accelerate the averaging of the control signal 551 to stabilize its final value. The averager circuit 700 includes two low-pass filters, each including a resistor coupled to a capacitor, and averages the drain-to-source voltage of LS2. The averager circuit 700 also includes a comparator 710. One low-pass filter includes SW1 and C1, and a resistor R11. Figure 6 R1 in the equation has a fixed resistance value, but Figure 7 R11 in the circuit has an adjustable resistance value based on the output signal from comparator 710. Another low-pass filter includes switch SW2, resistor R2, and capacitor C2. R2 is coupled between SW2 and C2. The connection between R11 and C1 is coupled to the negative input of comparator 710, while the connection between R2 and C2 is coupled to the positive input of comparator 710. When the H-bridge is in drive mode, switch SW1 is closed; when the H-bridge is in SD mode, switch SW2 is closed. Comparator 710 compares the average drain-to-source voltage of LS2 generated iteratively during drive mode with the average drain-to-source voltage of LS2 generated iteratively during SD mode. The time constants of R2 and C2 are less than ( Figure 6 The time constants of R1 and C1 mean that the average drain-to-source voltage of LS2 generated during SD mode stabilizes faster than the average drain-to-source voltage of LS2 generated iteratively during drive mode. (Brief reference) Figure 4During SD mode, the average drain-to-source voltage of LS2 is shown as dashed line 450. Dashed lines 412 and 450 indicate the average drain-to-source voltage of LS2, but the drain-to-source voltage of LS2 requires a finite amount of time to stabilize at values ​​of 412 and 450. Dashed line 470 shows an example level of the average control signal 551 when the low-pass filter begins to stabilize to its final value 412. Comparator 710 determines that level 470 is less than 450 (the low-pass filter of R2 and C2 stabilizes very quickly). In response, the output signal from comparator 710 causes R11 to change (e.g., decrease) its resistance, thereby reducing the RC time constant of the filter applying the drain-to-source voltage of LS2 during drive mode, and thus causing the low-pass filter of R11 and C1 to begin stabilizing much faster than in other cases. Once the average control signal 551 exceeds the level of 450 (the drain-to-source voltage of LS2 during SD mode), comparator 710 causes R11 to increase its resistance, thereby increasing the RC time constant as the average control signal 551 begins to approach its final value 412. A higher RC time constant (> current ripple frequency) in the average control circuit helps reduce or avoid ripple and provides an average current for offset compensation.

[0037] Figure 8 An example implementation of R11 is shown. As illustrated, R11 includes fixed resistors R81 and R82 and transistor M11 (e.g., an NMOS device). One terminal of R81 is connected to the drain of M1. The other terminal of R81 is connected to SW1. The source of M1 is connected to C1. R82 is connected across M11 (between the drain and source). The gate of M1 is coupled to the output of comparator 710. Therefore, comparator 710 controls the gate voltage of M1. By controlling the gate-to-source voltage of M1 and operating M1 in the linear region, the drain-to-source resistance of M1 is adjustable. Therefore, the effective resistance across R11 is adjustable based on the output signal from comparator 710. If M1 is off, the effective resistance is the sum of the resistances of R81 and R82. If M1 is on, the effective resistance is the sum of the resistance of R81 and the on-resistance of M1.

[0038] Figure 9 An example of a comparator 520 with input offset control is shown. Figure 9 The comparator 520 in this example includes offset compensation circuitry 920 coupled to the Itrip comparator stage 940. The Itrip stage includes a current source device M6 and a differential transistor pair 912 (including transistors M4 and M5). Reference current (Iref) Figure 5This generates a voltage that is supplied to the gate of M4 within the differential transistor pair 912, and the gate of M5 of the differential transistor pair is coupled to node B of the H-bridge. The bias current from M6 is distributed between M4 and M5 based on the relative magnitudes of the gate-to-source voltages of M4 and M5.

[0039] The offset compensation circuit 920 includes a current source device M3 and transistor pairs M1 and M2. The gate of M2 is also coupled to the gate of M4 to an SNS FET. The gate of M1 is coupled to the output of the offset compensation amplifier 555, as shown in the figure. The gates of M3 (and M6) are biased at PBIAS, generating a current shunt between M1 and M2 and flowing into the Itrip comparator 910. The current from M3 is distributed between M1 and M2 based on the relative magnitudes of their gate-to-source voltages. The current through M1 plus the current through M4 equals the current I4. Similarly, the current through M2 plus the current through M5 equals the current I5. Therefore, by changing the gate voltage of M1 via the offset compensation amplifier, the input offset of comparator 520 is adjustable.

[0040] Figure 10 An example is shown in which the coil current across all three modes (DRV, SD, and FD) is detected and used to reconstruct the complete coil current waveform 930. This current waveform is then averaged (940). The direction of current flow through LS1 during FD mode (source to drain) is opposite to the direction of current flow through LS2 during DRV and SD modes (drain to source). Therefore, the current LS2 during DRV and SD modes is added together, while the current LS1 during FD mode is subtracted by subtractor 1020. A sensing FET can be connected to LS1 (gate connected together, source connected together) to generate a scaled copy of the current through LS1.

[0041] Figure 11 An example of a stepper driver 1100 is shown, which in many ways is similar to... Figure 5 The stepper driver 500 is identical. However, one difference is that the error control signal 557 is coupled to the digital logic and the logic 1112 of the driver 1111. In this implementation, the logic 1112 responds to the error control signal 557 by adjusting the timing of the transistors in the H-bridge, thereby adjusting the coil current based on the determination of its average value. For example, if the average coil current is too low (below IRef), the logic 1112 can increase the duration of the drive mode relative to the duration of the FD and / or SD modes by increasing the duration of the drive mode or decreasing the duration of the FD and / or SD modes. Alternatively, if the average coil current is too high, the logic 1112 can increase the duration of the SD mode.

[0042] Figure 12An example method illustrating the operation of stepper driver 120 is shown. At 1201, the method includes averaging the drain-to-source voltages of the transistors (e.g., the low-side transistor of LS2) within the H-bridge. At 1202, the method includes comparing the average value with a reference signal. If the average value is greater than the reference signal, the method includes modifying the stepper driver control at 1203 to cause a decrease in the coil current. If the average value is less than the reference signal, the method includes modifying the stepper driver control at 1204 to cause an increase in the coil current. Various techniques for modifying a stepper driver to cause changes in the coil current have been described above.

[0043] The term "coupled" is used throughout this specification. This term may cover a connection, communication, or signaling path that achieves a functional relationship consistent with the description of this disclosure. For example, if device A generates a signal to control device B to perform an action, in a first instance, device A is coupled to device B; or in a second instance, if intermediate component C substantially does not alter the functional relationship between device A and device B, device A is coupled to device B via intermediate component C, such that device A controls device B via a control signal generated by device A.

[0044] Within the scope of the appended claims, modifications to the described embodiments are possible, and other embodiments are also possible.

Claims

1. A stepper motor driver, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager circuit comprising an input and an output, wherein the input of the averager circuit is coupled to the first output of the H-bridge; as well as A comparator comprising a first comparator input and a second comparator input, the first input of the comparator being coupled to the output of the averager circuit, and the second input of the comparator being coupled to the reference output; The comparator is a first comparator, and the stepper motor driver further includes a second comparator having a first input and a second input, the first input of the second comparator being coupled to the first output of the H-bridge, and the second input of the second comparator being coupled to the reference output; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

2. The stepper motor driver according to claim 1, wherein: The first comparator has an output; The second comparator has an offset adjustment input; and The output of the first comparator is coupled to the offset adjustment input of the second comparator.

3. The stepper motor driver of claim 1, wherein the first comparator has an output, the second comparator has an output, and the stepper motor driver further includes a digital logic circuit having a first input and a second input, the first input of the digital logic circuit being coupled to the output of the second comparator, and the second input of the digital logic circuit being coupled to the output of the first comparator.

4. A stepper motor driver, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager circuit comprising an input and an output, wherein the input of the averager circuit is coupled to the first output of the H-bridge; as well as A comparator comprising a first comparator input and a second comparator input, the first input of the comparator being coupled to the output of the averager circuit, and the second input of the comparator being coupled to the reference output; The comparator is a first comparator, and the stepper motor driver further includes a second comparator having a first input and a second input, the first input of the second comparator being coupled to the first output of the H-bridge, and the second input of the second comparator being coupled to the reference output; The averager circuit includes a switch and a low-pass filter coupled to the switch; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

5. A stepper motor driver, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager circuit comprising an input and an output, wherein the input of the averager circuit is coupled to the first output of the H-bridge; as well as A comparator comprising a first comparator input and a second comparator input, the first input of the comparator being coupled to the output of the averager circuit, and the second input of the comparator being coupled to the reference output; The comparator is a first comparator, and the averager circuit includes: First switch; A first low-pass filter, which is coupled to the first switch; Second switch; A second low-pass filter is coupled to the second switch; as well as A second comparator includes a first input and a second input, wherein the first input of the second comparator is coupled to the first low-pass filter, and the second input of the second comparator is coupled to the second low-pass filter; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

6. The stepper motor driver of claim 5, wherein the first low-pass filter has an adjustable angular frequency.

7. The stepper motor driver of claim 6, wherein the first low-pass filter has a control input, the second comparator has an output, and the output of the second comparator is coupled to the control input of the first low-pass filter.

8. The stepper motor driver of claim 7, further comprising digital logic and driver circuitry coupled to the H-bridge, wherein: The first switch has a control input coupled to the digital logic circuit and the driver circuit; The second switch has a control input coupled to the digital logic circuit and the driver circuit.

9. The stepper motor driver of claim 8, wherein the digital logic circuit and the driver circuit are configured to: During the drive mode of the H-bridge, an assertion control signal is sent to the control input of the first switch to close the first switch; and During the slow decay mode of the H-bridge, the control input assertion control signal is sent to the second switch to close the first switch.

10. A stepper motor driver, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager circuit comprising an input and an output, wherein the input of the averager circuit is coupled to the first output of the H-bridge; as well as A comparator comprising a first comparator input and a second comparator input, the first input of the comparator being coupled to the output of the averager circuit, and the second input of the comparator being coupled to the reference output; The averager circuit is configured to: In response to a signal at the output of the averager circuit exceeding a first threshold, the signal at the first output of the H-bridge is averaged at a first angular frequency; and In response to the signal at the output of the averager circuit being lower than the first threshold, the signal at the first output of the H-bridge is averaged at a second angular frequency; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

11. A stepper motor driver for an electric motor, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager current controller, coupled to the low-side transistor, is configured to generate an average signal in response to the average current level through the low-side transistor. The H-bridge is configured to control the current through the motor coils in response to the average signal; The averager current controller includes: An averager circuit having an input and an output, wherein the input of the averager circuit is coupled to the low-side transistor; as well as A comparator having a first input and a second input, the first input of the comparator being coupled to the output of the averager circuit, and the second input of the comparator being coupled to the reference current circuit; The comparator is a first comparator, and the stepper motor driver further includes a second comparator having a first input and a second input, the first input of the second comparator being coupled to the first output of the H-bridge, and the second input of the second comparator being coupled to the reference output; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

12. A stepper motor driver for an electric motor, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager current controller, coupled to the low-side transistor, is configured to generate an average signal in response to the average current level through the low-side transistor. The H-bridge is configured to control the current through the motor coils in response to the average signal; It further includes a comparator having a control input configured to adjust the offset of the comparator, and the averager current controller is configured to provide its average signal to the control input of the comparator; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

13. A stepper motor driver for an electric motor, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager current controller, coupled to the low-side transistor, is configured to generate an average signal in response to the average current level through the low-side transistor. The H-bridge is configured to control the current through the motor coils in response to the average signal; It further includes: A comparator comprising a first input and a second input, the first input being coupled to the reference current circuit and the second input being coupled to the low-side transistor; and A digital logic circuit having a first input and a second input, the first input of the digital logic circuit being coupled to the output of the comparator, and the second input of the digital logic circuit being coupled to the averager current controller; The comparator is a second comparator, and the averager current controller includes a first comparator having a first input and a second input, the first input of the first comparator being coupled to the reference output; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

14. A stepper motor driver for an electric motor, comprising: An H-bridge includes a first output and a second output, the H-bridge including a low-side transistor coupled between the first output and ground; A reference current circuit configured to generate a reference current, the reference current circuit having a reference output; An averager current controller, coupled to the low-side transistor, is configured to generate an average signal in response to the average current level through the low-side transistor. The H-bridge is configured to control the current through the motor coils in response to the average signal; The averager current controller includes a low-pass filter with an adjustable angular frequency. The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

15. A method for a motor driver, the method comprising: The current flowing through the low-side transistors in the H-bridge is averaged to generate an average control signal. The average control signal is compared with the reference signal; as well as The current through the motor coil is controlled based on the comparison between the average control signal and the reference signal; The average current through the low-side transistor includes adjusting the corner frequency of the low-pass filter; The average coil current value is determined by adding; The average coil current value is used to control the H-bridge; and The control of the H-bridge causes the coil current to be adjusted to an average value.

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