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TPS737: Avoiding damage to TPS737

Franklin Cooper
Intellectual 2060 points
Part Number: TPS737


Hi,

I am interested if the above use case is safe for the TPS73733DCQR or if it can cause damage to it.

Device setup is as follows:

  • Vin = 5V 
  • EN = Vin (5V)
  • Vout (3.3V) may also be powered externally by a 3.3V.

Use Case:

  • Power to Vin may abruptly be removed
  • Vout still powered externally 

My observation during this use case is that the Vout voltage is seen on Vin. 

There is no way for me to disable EN before Vin is disconnected. So my observation seems to match the following from the datasheet "If the EN pin is not driven low, the pass element may be left on because of stored charge on the gate."

My question is if the above use case can cause damage to the TPS737.

  • 0
    TI__Mastermind 23361 points

    Hi Franklin, 

    Can you clarify what do you mean by "Vout is also powered externally"? What's the input capacitor? Do you have any load before Vin being abruptly removed?

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    TI__Intellectual 2060 points

    Hi Jason,

    Vout is connected to a 3.3V rail on the MSP432P04 launchpad. The MSP432P04 when powered by the PC via USB will output 3.3V on this 3.3V rail. Therefore, it’s possible that the TPS737 and the MSP432 on board 3.3V regulator will be outputting a voltage at the same time on the same rail. The TPS737 is needed to power the launchpad when it isn't connected to the PC.

     

    .1 uF and 1uF capacitor in parallel connected to Vin. Yes there can be a load before Vin is abruptly removed.

  • 0 in reply to Franklin Cooper
    TI__Mastermind 23361 points

    Hi Franklin,

    Ideally, as datasheet suggested, pulling down the EN before removing the Vin can fully discharge the voltage on the gate of the FET which is the recommended way. Based on the information you provided, even abruptly removing Vin and EN, it's not likely to cause the device to be damged. After removing the Vin and EN, the two pin can be discharged by leakage current and to accelarate this discharge, you could add a high-resistance pull down resistor at the input side.

    When using TPS737's output together with the 3.3V output rail from the microcontroller, please note that if the 3.3V output from the launchpad is lower than the nominal voltage of the LDO, it will have current sinking from the LDO into the 3.3V pin of the launchpad. Even a few milli-volts difference could create tens of mili-amps of reverse current sourcing into the launchpad. If the 3.3V from the launchpad is slightly higher than the nominal output of the LDO, it will create a small (in hundreds of micro-amps range) reverse current to the LDO which is not a concern to damage the LDO as long as the voltage is not violating the absolute maximum voltage on the output pin of the LDO.

    Regards,
    Jason Song