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LM76005-Q1: EN pin high before Vin

Nathan V
Prodigy 25 points
Part Number: LM76005-Q1
Other Parts Discussed in Thread: TL7700, TPS37

Dear TI Team,

I have a question regarding the enable input of the LM76005-Q1 DC-DC converter.

  • Is there any risk in damaging the IC when increasing the EN voltage before Vin is high?
  • In this design, the EN pin would be able to go up to 17V while Vin is still low (at this point Vin is being pulled low through high value resistors: total of around 300k).
  • In this design there is a 100k resistor in front of the EN pin.
  • I checked on the Evaluation kit and when applying a voltage to the EN pin (while leaving Vin open), there seems to be no increase in voltage on Vin. This leads me to believe that there is no ESD diode from EN to Vin protecting against EN going higher than Vin.

The main concern is if I should place an external diode between EN and Vin to comply to the datasheet requirement where EN<Vin+0.3V or if there is no real danger to having a high EN voltage before Vin goes high.

Thank you in advance,

Nathan

  • 0
    TI__Guru 50120 points

    Hi Nathan,

    The datasheet specification of EN < VIN + 0.3V implies that there would be an issue if VEN is present before VIN. 

    As such it is suggested to have EN pin tied directly to VIN or through UVLO resistive divider network to have EN come after VIN.

    Also the EN pin voltage of 17V would be over the absolute maximum pin voltage rating as previously mentioned.

    Anything outside of this has not been tested or verified and is up to the customer to evaluate.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Mastermind 22301 points

    Hi Nathan,

    In addition to what Jimmy said, you can use a power sequencer IC like TPS37 or TL7700 to sequence the LM76005-Q1 after the 17V comes up.

    Hope this helps,

    -Orlando