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TPS7B7702-Q1: Reverse current protection fault

Sam Kim
Prodigy 510 points
Part Number: TPS7B7702-Q1

Hello 

Customer is seeing frequent shutdown issue with TPS7B7702-Q1 due to short to battery protection in cold cranking test. Output voltage setting is 10.5V for AM/FM antenna. From the scope shot, it looks input voltage drops more quickly than output voltage and it leads latched shutdown due to short to battery protection. Customer may reduce output capacitor(2x 10uF) to discharge output voltage faster but it may affect RF sensitivity, so customer doesn't want to change output capacitance.

Customer changed the schematic to check nERR pin to toggling EN pin during this event, but they want to check if there is any other solutions to avoid this kind of shutdown.

Regards,

Sam

  • 0
    TI__Guru 55940 points
    Hi Sam,

    Another potential solution is to increase the input capacitance. More capacitance on the input will hold the LDO input higher longer. This is similar with your idea of decreasing the output capacitance.

    Could you give me more information on how you intend to use the /ERR pin to re-enable the LDO?

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Prodigy 510 points
    Hi Ryan,
    The MCU reads /ERR pin and toggles the EN pin when /ERR pin goes to low.

    Regards,
    Sam
  • 0 in reply to Sam Kim
    TI__Guru 55940 points

    Hi Sam,

    Thank you for the quick reply.  This method should work; however, keep in mind that if any other fault occurs that causes /ERR to transition to logic low, the MCU will toggle enable.  If this is okay in your customer's application, then this looks to be a valid solution for their application.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    TI__Prodigy 510 points

    Hi Ryan,

    What do you think about adding a blocking diode so that input capacitor is not discharged by battery voltage drop.

    Regards,

    Sam

  • 0 in reply to Sam Kim
    TI__Guru 55940 points
    Hi Sam,

    The diode may help; however, the effectiveness will somewhat depend on the load current during the transients as well. Additional capacitance between the diode and the LDO will again help supply the load if it pulls enough to discharge the input capacitor.

    Keep in mind that you now need to consider the voltage drop of the diode now. The LDO is input voltage is now Vbatt minus the forward voltage of the diode.

    Very Respectfully,
    Ryan