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Original question:

TPS7A25: Starting even softer, what level of series resistance would be possible?

TPS7A25: How to interpret max V_UVLO falling = 2.25V considering min Vin = 2.4V?

Southern Engineering
Intellectual 715 points
Part Number: TPS7A25
Other Parts Discussed in Thread: TPS7A26,

Hi,

The TPS7A25 (and TPS7A26) datasheet states a Vmin of 2.4V. How should this be interpreted with regards to the stated V_UVLO numbers?

It is very beneficial for our design if the LDO can be said to stay on until Vin falls to 2.25V (max V_UVLO falling), but we cannot rely on that it "might" stay on (if 2.4V is the only limit to trust).

The load is very small, a couple of mA at most after initial start-up / inrush.

  • 0
    TI__Genius 12511 points

    Hi,

    With a tested UVLO max falling of 2.25V, the device UVLO circuitry will not kick on until VIN drops below that voltage. The VIN min spec is allowing safe headroom so that small perturbations on unstable or noisy inputs do not inadvertently push VIN below the UVLO threshold. The device will not initiate UVLO until that threshold is crossed

    Regards,

    John

  • 0 in reply to John Schneider
    Intellectual 715 points

    Thank you John.

    Does that mean that we can count on the LDO to work in the 2.25V to 2.4V range when the voltage is falling, and in the 2.35V to 2.4V range when the voltage is rising (only I would risk triggering UVLO being close to it in those ranges)?

    Edit: We found "Understanding Undervoltage Lockout in Power Devices" (https://www.ti.com/lit/an/slva769a/slva769a.pdf?ts=1691456583041) and note that the region we are asking about is the one referred to as Functional. Could anything be stated about what would be the risk area(s) for TPS7A25 when operating in the Functional area under constant (no transients) single milliamp load, within all other recommended operating conditions?

  • +1 in reply to Southern Engineering
    TI__Genius 12511 points

    Hi,

    Yes, The device will operate functionally under these conditions. Really what this means is that we do not test the device under these input voltage conditions so the EC table conditions may be marginally inaccurate and we cannot say the min/max values are true as we did not test. However with very light load and little/no transient the device should perform well within specifications and I do not forsee any real concern. The only concern would be increased Dropout at high current conditions, possible VIN sag at high current conditions, and marginally higher noise to signal ratio, but all three of these are minimized if not outright removed by utilizing a low load, single mA, condition.

    Regards,

    John