DRV8701_15 Datasheet, PDF (21/42 Pages) Texas Instruments – DRV8701 Brushed DC Motor Full-Bridge Gate Driver

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DRV8701
SLVSCX5B – MARCH 2015 – REVISED JULY 2015
7.3.7 Dead Time
Dead time (t_DEAD) is measured as the time when SHx is High-Z between turning off one of the H-bridge FETs
and turning on the other. For example, the output is High-Z between turning off the high-side FET and turning on
the low-side FET.
The DRV8701 inserts a digital dead time of approximately 150 ns. The total dead time also includes the FET
gate turn-on time.
The total dead time is dependent on the IDRIVE resistor setting because a portion of the FET gate ramp (GHx
and GLx pins) includes the observable dead time.
7.3.8 Propagation Delay
The propagation delay time (t_DELAY) is measured as the time between an input edge to an output change. This
time is composed of two parts: an input deglitch time and output slewing delay. The input deglitcher prevents
noise on the input pins from affecting the output state.
The gate drive slew rate also contributes to the delay time. For the output to change state during normal
operation, first, one FET must be turned off. The FET gate is ramped down according to the IDRIVE setting, and
the observed propagation delay ends when the FET gate has fallen below the threshold voltage.
7.3.9 Overcurrent V_DS Monitor
The gate driver circuit monitors the V_DS voltage of each external FET when it is driving current. When the voltage
monitored is greater than the OCP threshold voltage (V_{DS OCP}), after the OCP deglitch time (t_OCP) has expired, an
OCP condition will be detected.
VM
VM
+
Low-side
VDS OCP
Monitor
-
+
Low-side
VDS OCP
Monitor
-
+
High-side
VDS OCP
GH1
Monitor
SH1
-
VM
GL1
+
High-side
VDS OCP
GH2
Monitor
-
SH2
GL2
SP
SN
BDC
RSENSE
Figure 28. Overcurrent VDS Monitors
When IDRIVE is shorted to AVDD, the V_DS OCP monitor on the high-side FETs is disabled. In cases where the
VM supplied to the DRV8701 can be different from the external H-bridge supply, this setting must be used in
order to prevent false overcurrent detection. In this mode, the IDRIVE current is set to 25-mA source and 50-mA
sink.
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