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TPS709 EN pin current

c.amsuess
Prodigy 40 points
Other Parts Discussed in Thread: TPS709

I'm unsure on how to interpret the EN pin behavior of the TPS709: The data sheet gives a typical shutdown current of 150nA both in overview and in 7.4 Device Function Modes as Ishutdown for low EN, but some lines above, it claims that the EN pin is pulled up (ie. into enabled state) by a 300nA current source, which would mean that if EN is externally put to GND (ie. disabled), the current source delivers its full current to the EN pin.

Assuming there is no internal DC-DC converter that boosts the current, how are the 300nA output achieved?

(Background: I'm planning on having a microprocessor switch off its own power supply in deep sleep states, and if startup takes too long, I need the current source to reliably pull up the GPIO pin that has entered high-Z during brownout).

  • 0
    TI__Expert 3540 points

    Hi C.Amsuess,

    The ISHUTDOWN refers to the IGND, when the device is disabled (VEN ≤ 0.4V), in other words ISHUTDOWN = IGND|EN≤0.4V = 150 nA.

    On the other hand, the IEN = 300 nA refers to the typical current going through the EN pin for the case where it is enabled, in the case of the datasheet EN = 1.0 V

    Bet Regards,
    Victor

  • 0 in reply to Victor Salomon
    Prodigy 40 points
    If I_SHUTDOWN is measured at GND and not at IN, that would explain the difference, but would be grossly missleading (because then I_REAL_SHUTDOWN (as measured at IN) would be I_SHUTDOWN + I_EN_PULLUP ~= 150nA + 300nA.

    If the I_EN of 300nA is what pulls up the EN pin, the current must flow out of the pin. If the current source is anything like a real current source (ie. providing outgoing current until its input voltage is exceeded). Note that I was referring to sectio 7.4 where a "300-nA current source" is menmentioned; I only just read the IEN of section 6.5. Nevertheless, unless it's not actually a current source, I don't see how it would send less current in disabled state (when it sends it to an even lower (GND) level) than in enabled state. (It can barely be switched off then, for the whole point of an enable pin pullup is to work when the device is off and should go back to on).

    So, do I need to assume that I_REAL_SHUTDOWN at the IN pin should be estimated to be 450nA?
  • 0 in reply to c.amsuess
    TI__Expert 3540 points

    C.Amsuess,

    You can assume the current being sourced to the Input, IIN(SHUTDOWN) = 450 nA, we are looking into making changes to section 7.4  as well as other sections to make it more clear.

    Thank you very much for your feedback.

    Best Regards,
    Victor