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TPS3823-30-Q1 Datasheet Question

Anthony F. Seely
Guru 65600 points

I'm trying to understand a spec in the datasheet, and it seems to be contradictory.

Basically, it's how low a voltage will this chip work and keep my MCU's reset pin asserted.


The way this is spec'd it says  down to VDD=0.4V (based on the footnote) but the condition given is VDD > 1.1V.

(contradiction? or misunderstanding on my part?)

  • 0
    TI__Mastermind 20580 points
    Hi Anthony,

    I have assigned this to the appropriate engineer. We will get back to you shortly.

    Scott
  • 0 in reply to Scott Monroe
    TI__Genius 16030 points
    Hi Anthony,

    The TPS382x-Q1 devices only have guaranteed RESET operation above 1.1V. I understand the footnote to say that below 0.4V the RESET output will not be active, and above 0.4V (meaning 0.4V to 1.1V) it could be active. I'm not sure what the VDD >= 1.1V test condition means, but if you need me to I can look in to it. But I can say that below 1.1V, the RESET output is undefined for these devices.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    TI__Guru 65600 points
    Karl,

    Ok but isn't that interpretation a useless one? (meaning not one you could really design with?).

    Most of the other supervisors have a spec like this but they basically say that:
    - even though recommended vdd might be something like 1.8V minimum...
    - this parameter means below that, say down to 0.6 or 0.8V .. the device will start to pull reset

    And then usually there is some (weaker) pull down current for this case where VDD is very low compared to recommended.

    I think for example one of the other supervisors on the product selection page is spec'd to start pulling reset at 0.4V but at that voltage it's only rated to pull 1uA ... so really weak.

    That's what this line item seems like it *should* be but then the 'condition' doesn't make sense.
    The 'weak' IOL=20uA could make sense though at 0.4V...

    -Anthony
  • 0 in reply to Anthony F. Seely
    TI__Genius 16030 points
    Anthony,

    I talked to our test guy. This is actually another type of Vol level at VDD=1.1V. This spec line is saying at VDD=1.1V (power-up threshold), with 20uA of current from the pull-up, then /RESET voltage will be at max 0.4V.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    TI__Guru 65600 points

    Karl,

    But the footnote defines the parameter as 'The lowest supply voltage' ...

  • 0 in reply to Anthony F. Seely
    TI__Genius 16030 points
    Yes, that is a description of the condition for this test. At "The lowest supply voltage where RESET becomes active", which is VDD=1.1V, we test the reset voltage as 0.4V max.

    I agree it's a bit confusing, and I'll take this as feedback for datasheet improvements.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    TI__Guru 65600 points
    Karl,

    Ok so really this VOL, Power-up reset voltage, is one set of the same parameter.

    It would be VOL(POR) or something as an appropriate name, where the footnote would say that this is
    VOL at the minimum power up operating voltage of 1.1V.

    -Anthony