DRV8701_15 Datasheet, PDF (17/42 Pages) Texas Instruments – DRV8701 Brushed DC Motor Full-Bridge Gate Driver

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DRV8701
SLVSCX5B – MARCH 2015 – REVISED JULY 2015
7.3.4 Amplifier Output SO
The SO pin on the DRV8701 outputs an analog voltage equal to the voltage seen across the SP and SN pins
multiplied by A_V. The factor A_V is the shunt amplifier gain, which is 20 V/V in the DRV8701. SO is only valid
during forward or reverse drive. The H-bridge current is approximately equal to:
I  ^{62 ± 9OFF}
A_V K R_SENSE
(2)
When SP and SN are 0 V, SO outputs the amplifier offset voltage V_OFF. No capacitor is required on the SO pin.
VCC
SNSOUT
Logic
+
-
R
SP
+
-
SN
AV/(AV-1) x R
AV x R
I
R_SENSE
SO
VREF
Figure 22. Sense Amplifier Diagram
If the voltage across SP and SN exceeds 1 V, then the DRV8701 flags an overcurrent condition.
The SO pin can source up to 5 mA of current. If the pin is shorted to GND, or if a higher-current load is driven by
this pin, the output acts as a constant-current source. The output voltage is not representative of the H-bridge
current in this state.
This shunt amplifier feature can be disabled by tying the SP and SN pins to GND. When the amplifier is disabled,
current regulation is also disabled.
AVDD
Slope = A_v
V_OFF
SP - SN (V)
Figure 23. Sense Amplifier Output
7.3.4.1 SNSOUT
The SNSOUT pin of the DRV8701 indicates when the device is in current chopping mode. When the driver is in
a slow decay mode caused by internal PWM current chopping (I_CHOP threshold hit), the open-drain SNSOUT
output is pulled low. If the current regulation is disabled, then the SNSOUT pin will be high-Z.
Note that if the H-bridge is put into a slow decay mode using the inputs (PH/EN or IN1/IN2), then SNSOUT is not
pulled low.
During forward or reverse drive mode, SNSOUT is high until the DRV8701 is internally forced into current
chopping. If the drive current rises above I_CHOP, the driver enters a brake mode (low-side slow decay). The
SNSOUT pin will be pulled low during this current chopping brake mode. After the driver is re-enabled, the
SNSOUT pin is released high-Z and the drive mode is restarted.
Copyright © 2015, Texas Instruments Incorporated
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