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DRV8353R: DRV8353 Turns on PBLS Immediately after EN is High Without Input Signals

Part Number: DRV8353R
Other Parts Discussed in Thread: DRV8353

Tool/software:

We are using the DRV8353 in 6xPWM mode. Upon asserting EN = HIGH, the PBLS (Phase B Low-Side Gate) output turns on immediately, even though no input signals (INHx/INLx) are applied — all 6 PWM inputs are confirmed LOW and are disabled.

This issue:

  • Happens consistently on multiple boards.

  • Persists even after replacing the IC three times.

  • Occurs before any switching signal is given.

  • Triggers a gate drive fault due to LS FET turning on unintentionally.

Additional observation:

  • With no VREF connected, we observe ~2.8 V between gate and source of PBLS the moment EN is high.

  • When 5 V VREF is supplied, the PBLS gate voltage jumps to ~7.8 V, again with no PWM input.

  • This behavior is specific to Phase B low-side — PHASE A and C behave normally and no fault is shown for other MOSFETs.

  • The other phase mosfets can be operated once the fault is disabled, but the voltage of 2.8/7.8 V across gate (GLB) and source (SPB) is still persistant and this is driving the PBLS FET.

We have verified:

  • 6xPWM.

  • INL_B has a pulldown and no signal is applied.

  • Bootstrap caps and decoupling are in place.

  • No SPI writes are done before the fault occurs.

  • VM, VCP, and VGLS voltages are within expected range.

  • Hello,

    Sorry for the delay. 

    Would you be able to provide schematic and layout of the affected area (PBLS)?

    Would you be able to provide waveforms of the affected phase B low side, as well as one of the normal phase behavior for comparison?

    I will work to continue debugging with this information.

    Thank you,

    Joseph