GH1

GL1

SH1

GH2

GL2

SH2

VM

BDC

High-side

VDS OCP

Monitor

High-side

VDS OCP

Monitor

Low-side

VDS OCP

Monitor

+

-

+

-

+

-

Low-side

VDS OCP

Monitor

+

-

VM

VM

SP

RSENSE

SN

DRV8701

www.ti.com

SLVSCX5B – MARCH 2015 – REVISED JULY 2015

7.3.7 Dead Time

Dead time (tDEAD) 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 (tDELAY) 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 VDS Monitor

The gate driver circuit monitors the VDS voltage of each external FET when it is driving current. When the voltage

monitored is greater than the OCP threshold voltage (VDS OCP), after the OCP deglitch time (tOCP) has expired, an

OCP condition will be detected.

Figure 28. Overcurrent VDS Monitors

When IDRIVE is shorted to AVDD, the VDS 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.

Copyright © 2015, Texas Instruments Incorporated

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