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TPS62130: EN Leakage issue

Amita JIndal
Prodigy 80 points
Part Number: TPS62130
Other Parts Discussed in Thread: TPS62135

We are using TPS62130 on one of our designs and seeing high leakage when the regulator is not powered up but EN pin is connected to 3.3V externally. My understanding is that the EN pin has intenal pull down of 400K. Is there any other leakage path for the EN pin within the chip? The functional diagram does not show anything else connected to the EN pin. We are assuming there may be a clamping diode between EN pin and input rail which is causing the leakage. We do not have any pull up resistor between Vin and EN pin. Will any other version of EN62130 (drop in replacement) help? 

  • 0
    TI__Guru**** 151520 points
    Hi Amita,

    Yes, if EN is 3.3V when Vin is not present, this will violate the abs max rating for EN and likely damage the IC. This condition must be prevented.

    A series resistor on EN and schottky diode from EN to Vin can overcome this, if there is not a better way for the system to prevent EN being high without Vin.

    There is no pin to pin device which has a different EN structure, though the TPS62135/6 are newer, smaller devices, though with the same EN pin limitation.
  • 0 in reply to Chris Glaser
    Prodigy 80 points
    Thanks for your prompt response, Chris. Are you suggesting schottky diode directly between EN and VIn and then series resitor between EN and EN pin on IC? Is there anything else we should be concerned about after we implement this solution?
    Can you please confirm if there is an internal clamping diode between EN and Vin?
    Thanks so much!
  • 0 in reply to Amita JIndal
    TI__Guru**** 151520 points
    Yes, the schottky would go from EN to Vin to divert the current outside of the EN pin and IC. Then, a current limiting resistor (10k should be fine) limits the current in this diode. Yes, there is a diode structure from EN to Vin; thus, we have the abs max limit.
  • 0 in reply to Chris Glaser
    Prodigy 80 points
    With this solution input voltage will be at about 3V but our output is set at 4.75V. My understanding is this will turn the regulator ON. But since output>input, what will happen in this case?
  • 0 in reply to Amita JIndal
    TI__Guru**** 151520 points
    If Vin is above UVLO, the IC will turn on and enter 100% mode. If below UVLO, it will stay off.
  • 0 in reply to Chris Glaser
    Prodigy 80 points
    One last question - could you please share how EN pin is connected internally to Vin? I don't see anything in the functional diagram. Why the EN is limited to within 0.3V of Vin? If there is an internal diode between EN and Vin, will schottky now be parallel to that internal diode? Why do we need schottky if there is already an internal diode? Will having just the resistor be sufficient?
  • 0 in reply to Amita JIndal
    TI__Guru**** 151520 points
    Many/most ICs have such limits on their pin's voltages. There are numerous proprietary circuits inside each and every IC.

    Were you able to add the resistor and diode to 1 board and see if it fixed your issue? This is important to do.

    The external schottky should have a lower voltage drop than 0.3V, so it shunts the current out of the internal structure which should not conduct below 0.3V. The internal structure is likely a p-n junction, which creates a silicon diode (with a higher forward voltage).
  • 0 in reply to Chris Glaser
    Prodigy 80 points
    Thanks for all your help, Chris.

    I am working on looking at the schottky and resistor solution. With the amount of re-work and cost involved we wanted to figure out if using just the resistor ( which will limit the current to internal p-n junction to about 1.5mA) will be a robust solution still?
  • 0 in reply to Amita JIndal
    TI__Guru**** 151520 points
    If this makes the EN pin voltage greater than Vin + 0.3V, it is not robust.
  • 0 in reply to Chris Glaser
    TI__Guru**** 151520 points
    Hi Amita,

    Were you able to check if the resistor + schottky diode worked?