REFX

CHOP

ISENSE

V

I

5

R

u

DRV8802

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SLVSAM9D – APRIL 2011 – REVISED DECEMBER 2015

Feature Description (continued)

7.3.2.1 Overcurrent Protection (OCP)

An analog current limit circuit on each FET limits the current through the FET by removing the gate drive. If this

analog current limit persists for longer than the OCP time, all FETs in the H-bridge are disabled and the nFAULT

pin are driven low. The device remains disabled until either nRESET pin is applied, or VM is removed and re-

applied.

Overcurrent conditions on both high and low side devices; that is, a short-to-ground, supply, or across the motor

winding results in an overcurrent shutdown. Note that overcurrent protection does not use the current sense

7.3.2.2 Thermal Shutdown (TSD)

If the die temperature exceeds safe limits, all FETs in the H-bridge are disabled and the nFAULT pin are driven

low. Once the die temperature has fallen to a safe level operation automatically resumes.

7.3.2.3 Undervoltage Lockout (UVLO)

If at any time the voltage on the VM pins falls below the undervoltage lockout threshold voltage, all circuitry in the

7.4 Device Functional Modes

7.4.1 Bridge Control

The xPHASE input pins control the direction of current flow through each H-bridge, and hence the direction of

rotation of a DC motor. The xENBL input pins enable the H-bridge outputs when active high, and can also be

used for PWM speed control of the motor. Table 1 shows the logic.

Table 1. H-Bridge Logic

xENBL

xPHASE

xOUT1

xOUT2

0

X

1

1

H

L

1

0

L

H

(1)

Depends on state of the DECAY pin. See Decay Mode and Braking.

7.4.2 Current Regulation

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

chopping. When an 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 can 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 is set by a comparator which compares the voltage across a current sense resistor

connected to the xISEN pins, multiplied by a factor of 5, with a reference voltage. The reference voltage is input

from the xVREF pins, and is scaled by a 2-bit DAC that allows current settings of 100%, 71%, 38% of full-scale,

plus zero.

The full-scale (100%) chopping current is calculated in Equation 1.

(1)

Example:

If a 0.5-

Ω sense resistor is used and the VREFx pin is 3.3 V, the full-scale (100%) chopping current is 3.3 V /

(5 × 0.5

Ω) = 1.32 A.

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