DRV8813_15 Datasheet, PDF (10/27 Pages) Texas Instruments – DRV8813 Dual-Bridge Motor Controller IC

DRV8813
SLVSA72E – APRIL 2010 – REVISED OCTOBER 2015
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Feature Description (continued)
7.3.2 Protection Circuits
The DRV8813 is fully protected against undervoltage, overcurrent and overtemperature events.
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 disables and the nFAULT pin
drives low. The device remains disabled until either nRESET pin is applied, or VM is removed and reapplied.
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. Overcurrent protection does not use the current sense circuitry used
for PWM current control, and is independent of the I_SENSE resistor value or VREF voltage.
7.3.2.2 Thermal Shutdown (TSD)
If the die temperature exceeds safe limits, all FETs in the H-bridge disables and the nFAULT pin drives 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
device is disabled and internal logic resets. Operation resumes when V_M rises above the UVLO threshold.
7.4 Device Functional Modes
7.4.1 Bridge Control
The xPHASE input pins control the direction of current flow through each H-bridge. The xENBL input pins enable
the H-bridge outputs when active high. Table 1 shows the logic.
xENBL
0
1
1
Table 1. H-Bridge Logic
xPHASE
X
1
0
xOUT1
Z
H
L
xOUT2
Z
L
H
The control inputs have internal pulldown resistors of approximately 100 kΩ.
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.
If the current regulation feature is not needed, it can be disabled by connecting the xISENSE pins directly to
ground and connecting the xVREF pins to V3P3.
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.
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