DRV8701_15 Datasheet, PDF (16/42 Pages) Texas Instruments – DRV8701 Brushed DC Motor Full-Bridge Gate Driver

DRV8701
SLVSCX5B – MARCH 2015 – REVISED JULY 2015
www.ti.com
7.3.3 Current Regulation
The maximum current through the motor winding is regulated by a fixed off-time PWM current regulation, or
current chopping. When an H-bridge is enabled in forward or reverse drive, current rises through the winding at a
rate dependent on the DC voltage and inductance of the winding. After the current hits the current chopping
threshold, the bridge enters a brake (low-side slow decay) mode until t_OFF has expired.
Note that immediately after the current is enabled, the voltage on the SP pin is ignored for a period of time
(t_BLANK) before enabling the current sense circuitry.
The PWM chopping current is set by a comparator which compares the voltage across a current sense resistor
connected to the SP pin, multiplied by a factor of A_V, with a reference voltage from the VREF pin. The factor A_V
is the shunt amplifier gain, which is 20 V/V in the DRV8701.
The chopping current is calculated as follows:
I_CHOP

9_REF ± 9_OFF
A_V K R_SENSE
(1)
Example: If a 50 mΩ sense resistor is used and VREF = 3.3 V, the full-scale chopping current will be 3.25 A. A_V
is 20 V/V and V_OFF is assumed to be 50 mV in this example.
For DC motors, current regulation is generally 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 tying VREF directly to AVDD and tying SP and SN
to GND.
I_CHOP
Drive
9_9BLANK
VREF
Brake / Slow Decay
tOFF
Drive
9_9BLANK
Brake / Slow Decay
tOFF
Figure 21. Sense Amplifier and Current Chopping Operation
During brake mode (slow decay), current is recirculated through the low-side FETs. Because current is not
flowing through the sense resistor, SO does not represent the motor current.
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