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DRV8844: Unknown behaviors for FMECA

Giovanni Mezzina
Prodigy 20 points
Part Number: DRV8844

Tool/software:

Dear all,

I am doing FMECA (Failure mode, effects, and criticality analysis) on an electronic board that includes the DRV8844.

I am having difficulty deriving possible behaviors of the component in 4 specific cases. Could you help me?

The cases are:
- the capacitor between VCP and VM is open (interrupted)
- the capacitor between VCP and VM is short-circuited
- the capacitor between CP1 and CP2 is open (interrupted)
- the capacitor between CP1 and CP2 is short-circuited

What should I expect on the OUTs? What should I expect, in general, from the device? The datasheet does not report indicative data to deduce its operation, without the need to perform a targeted failure test.

  • +1
    TI__Expert 4530 points

    Hi Giovanni, 

    Thank you for your question. 

    Following are the assumptions of use and the device configuration assumed for the pins

    Giovanni Mezzina said:
    the capacitor between VCP and VM is open (interrupted)

    The charge pump is used provide a gate drive voltage higher than the VM power supply  to fully enhance the high-side FETs. If VCP is open, the VCP stays at 0V or undefined and the High side MOSFET can not go high. 

    Giovanni Mezzina said:
    the capacitor between VCP and VM is short-circuited

    In this case since the gate drive voltage is not higher than VM power supply, the High side MOSFET cannot go high. 

    Giovanni Mezzina said:
    the capacitor between CP1 and CP2 is open (interrupted)

    Giovanni Mezzina said:
    the capacitor between CP1 and CP2 is short-circuite

    The capacitor between CPH and CPL is essential for generating a boosted voltage on VCP. Shorting / opening these pins is like removing the energy storage element of the pump.
     Without proper switching across a capacitor, the charge pump cannot step up the voltage. VCP will remain low and insufficient to turn on high-side MOSFETs and The outputs (OUTx) cannot drive high.

    Please let me know if you have any more questions. 

    Best regards, 

    Mojtaba,

  • 0 in reply to Mojtaba Afshar
    Prodigy 20 points

    Hi Mojtaba,

    Thanks for the point-by-point reply. Everything reported seems reasonable to me.

    Sincerely,
    Giovanni

  • 0 in reply to Giovanni Mezzina
    TI__Expert 4530 points

    Hi Giovanni, 

    Thank you! Please close this thread if this issue is resolved. 

    Best regards

    Mojtaba.