IOUT

Drive

Decay

Drive

Decay

VIPROPI

Control

Input

Drive

nFAULT

Chop

ITRIP

VOUT

15

DRV8874

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SLVSF66A – AUGUST 2019 – REVISED DECEMBER 2019

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Figure 14. Cycle-By-Cycle Current Regulation Where nFAULT Acts as Current Chopping Indicator

No device functionality is affected when the nFAULT pin is pulled low for the current chopping indicator. The

nFAULT pin is only used as an indicator and the device will continue normal operation. To distinguish a device

fault (outlined in the Protection Circuits section) from the current chopping indicator, the nFAULT pin can be

compared with the control inputs. The current chopping indicator can only assert when the control inputs are

commanding a forward or reverse drive state (Figure 10). If the nFAULT pin behavior deviates from the operation

shown in Figure 14 then one of the following situations has occurred:

•

If a device fault has occurred, then the nFAULT pin pulls low to indicate a fault condition rather than current

chopping. Depending on the device fault, nFAULT may remain low even when the control inputs are

commanding the high-Z or slow-decay states.

•

When the control inputs transition from drive to slow decay, the nFAULT pin will go high for tBLK then be

pulled low again if IOUT > ITRIP. This may be caused by a PWM frequency or duty cycle on the control inputs

with a off-time that is too short for the IOUT current to decay below the ITRIP threshold. Figure 15 shows an

example of this condition. The condition IOUT > ITRIP can be viewed on an oscilloscope as VIPROPI > VREF.