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TPS40170 EN function

John Rice
Prodigy 430 points
Other Parts Discussed in Thread: TPS40170

My customer is reporting that the EN pin of the TPS40170 does not support pre-bias under certain conditions.  If the enable is toggled on and off as shown below the output is discharages to 4.3V before returning to a programmed output voltage of 23V.   We've  verified the behavior with and with a SCP resistor on the lower gate.  They have a 100nF SS capacitor.  UVLO and Boot Capacitors voltages have been verified to be > 0.9V and 4.4V respectively. 

oltage is 30V.  I confirmed this on the EVM

  • 0
    TI__Genius 17240 points

    Hi John,

    Under high-pre bias voltage condition, there is not enough drive voltage on the bootstrap capacitor, therefore the SCP is triggered. If it is an issue for the customer, they may need some external circuitry to provide the charge to the bootstrap capacitor under the pre-bias condition. One possible solution which has been tried out by our colleague is utilitzing the EN or VDD to provide one-short charge as shown in the following circuit.

    2475.one-shot.tif