DRV8828

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SLVSA11G – OCTOBER 2009 – REVISED NOVEMBER 2015

7.3 Feature Description

7.3.1 PWM Motor Drivers

The DRV8828 contains one H-bridge motor driver with current-control PWM circuitry. A block diagram of the

motor control circuitry is shown in Figure 5. A bipolar stepper motor is shown, but the driver can also drive a DC

motor.

Figure 5. Motor Control Circuitry

Note that there are multiple VM, ISEN, OUT, and VREF pins. All like-named pins must be connected together on

the PCB.

7.3.2 Bridge Control

The PHASE input pin controls the direction of current flow through the H-bridge. The ENBL input pin enables the

H-bridge outputs when active high. The logic inputs ENBL and PHASE have internal pulldown resistors of 100

k

Ω. Table 1 shows the logic.

Table 1. H-Bridge Logic

ENBL

PHASE

OUT1

OUT2

0

X

Z

Z

1

1

H

L

1

0

L

H

7.3.3 Current Regulation

The current through the motor winding is regulated by a fixed-frequency PWM current regulation, or current

chopping. When the H-bridge is enabled, current rises through the winding at a rate dependent on the DC

voltage and inductance of the winding. Once the current hits the current chopping threshold, the bridge disables

the current until the beginning of the next PWM cycle.

For stepping motors, current regulation is normally used at all times, and changing the current can be used to

microstep the motor. For DC motors, current regulation is used to limit the start-up and stall current of the motor.

The PWM chopping current in the bridge is set by a comparator which compares the voltage across a current

sense resistor connected to the ISEN pin, multiplied by a factor of 5, with a reference voltage. The reference

voltage is input from the xVREF pins, and is scaled by a 5-bit DAC that allows current settings of zero to 100% in

an approximately sinusoidal sequence.

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