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LM22676: Output Power Applied, Input Unpowered

Larry Stanton1
Prodigy 20 points
Part Number: LM22676

What, if any, are the consequences of applying an output voltage sourced from another power supply with the input unpowered but connected to various components. This is an adjustable version set to 5.25V.

In the unusual condition:

The Vo = 5.218V. We lifted pin 8 and measured 14.0 mA into pin 8.

We measured Vfb (pin pin 4) to be 0.0V. The current into pin 4 was 1.69mA.

We lifted pin 7 (Vin) and measured the current out of pin 7 to be 11.22 mA and the Vin = 4.66V

After the unusual condition, there appears to be no damage and the supply still functions normally when powered properly from Vin.

Regards,

Larry

  • 0
    TI__Expert 4555 points

    Hi Larry,

    Applying voltage on output from different power-supply with input unpowered is actually a 'Prebias-Startup' scenario. Start-up includes the short delay (approximately 10 ms) prior to the output voltage rising, followed by the rise of the output voltage under the part’s internal soft-start control. Start-up is complete when the output voltage has risen to either the set-point voltage or the voltage equaivalent to softstart pin, whichever is lowest.I don't expect any damage in this scenario.

    Best Regards,

    Ankit Gupta

    Application Engineer