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TPS7A7100: About startup problem

Tsukui Yusuke
Guru 21930 points
Part Number: TPS7A7100
Other Parts Discussed in Thread: TPS7A91, TPS7A83A, TPS74701, LP5907, TLV717P

Hi,

When the output voltage is activated under the negative voltage condition, the output does not rise.
Does this device support negative voltage bias?
Could you give me advice on this issue?

TPS7A7100.pdf

Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Guru 55940 points

    Hi Yusuke-san,

    This is a common phenomenon with devices with a foldback current limit. Since the current limit is reduced at lower voltages, when a negative voltage is present on the output, the current limit is too low to allow the output to rise. TPS7A7100 was not designed to be able to start with a negative bias on OUT.

    Please consider TPS7A91 or TPS7A83A which have a foldback current limit circuit specifically designed so that they can start from a negative bias voltage on OUT.

    Very Respectfully,
    Ryan

  • 0 in reply to Ryan Eslinger
    Guru 21930 points

    Ryan-san,

    Thank you for your response.
    Let me ask you one more thing.

    ・Is ” TPS7A7100 was not designed to be able to start with a negative bias on OUT.” listed in the data sheet?
    ・Does TPS74701 and LP5907 support negative voltage start up?

    Could you give me your advice?

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru 55940 points
    Hi Yusuke-san,

    TPS7A7100 as with most early LDOs with a foldback current limit does not directly discuss that it was not designed to start with a negative bias on OUT. As a positive LDO this was considered implied at the time of release. If you are interested in continuing to use an LDO with a foldback current limit, TPS7A91 and TPS7A83A have foldback current limits that were redesigned in order to allow startup from a negative bias.

    Both TPS74701 and LP5907 have "brick-wall" current limits and are therefore not susceptible to the foldback current limit issue with a negative bias startup.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Guru 55940 points

    Hi Yusuke-san,

    I should add, the following blog goes into the differences between the two kinds of current limit used in LDOs.

    LDO basics: Current limit
    Other Parts Discussed in Post: TLV717P The key goal of DC power management is to provide a regulated, steady voltage for the slew of electronic content present in any system. This is particularly true…
    By in Technical articles > Power management

    Very Respectfully,

    Ryan