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TPS61291 EN/BYP pin floating

Jonas Meyer
Prodigy 80 points
Other Parts Discussed in Thread: TPS61291, MSP430F2618

In my application an MSP MCU controls the EN/BYP pin of the TPS61291 (like in circuits in the datasheet).

My question is: what happens during start up of TPS61291 if the EN/BYP pin is floating?

This condition is met as long as the MCU’s flash is not yet programmed or during programming. In both cases the MCU pins are switched to input mode and it is not able to actively drive the EN/BYP pin.

Best regards,

Jonas

  • 0
    TI__Mastermind 46905 points
    depend on the voltage at EN/BYP, it could be logic high or logic low. but it should be low voltage if there is no leakage current path into the pin. and i think logic high or low at this pin does not impact the normal operation of the whole system, right?
  • 0 in reply to Jasper Li
    Prodigy 80 points

    The MSP430f2618 states a leakage current of ±50 nA for high impedance pins (leakage current is measured with VSS or VCC applied to the corresponding pins). To me it is not clear to which potential the EN/BYP pin will be floating if MSP430 pins are switched to inputs. It could happen that the voltage at EN/BYP pin floats to a potential between VIL and VIH.


    However, from the TPS61291 block diagram it becomes clear that there is a current path through the P channel bypass switch's body diode. So there will always be a voltage of at least VIN-VF (body diode forward voltage) at the output of TPS61291. This should be true for independently of EN/BYP pin's voltage.

  • 0 in reply to Jonas Meyer
    TI__Mastermind 46905 points
    EN/BYP=L, the device operates at bypass mode, VOUT follows VIN
    EN/BYP=H, the device operates at boost mode, the VOUT reach the setting value.
    so the VOUT should be equal or higher than VIN.