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TPS65217: channel(DCDC,LDO) behavior when Vbat is low voltage

Part Number: TPS65217

I saw this thread from several months ago and have a similar question, though I don't see a definitive answer in the original thread.

I will try to state my question in a more restricted fashion.  In our configuration of TPS65217(D), LDO2 and LDO4 are configured for 3.3V output.  According to the datasheet, the drop-out voltage specification for these LDO's is 200mV (max).  My question is do these LDO's have defined behavior below this 3.5V input level?  I.e. will they transition to an "Unregulated Pass-Through" mode?  Is there a chance they may become unstable or have anomalous behavior?  

Regards

  • I measured this on a TPS65217CEVM:

    When VBAT = 3.400V, VLDO2 = 3.299, and it can supply up to the full load of 100mA (soft current limiting observed beyond 100mA, where the output voltage drooped slightly). The LDO shuts off when the voltage drops below 3.15V
    When VBAT = 3.302V, VLDO2 = 3.299V, but it can only supply a load of up to about 42mA before the LDO drops out and shuts off. The LDO2 voltage was 3.222 before shutting off.

    LDO4 exhibits similar behavior but the current limiting kicks in at 400mA load when VBAT=3.4V
    At VBAT= 3.302V, the behavior is identical because the LDO shuts off before current limiting is needed.

    Neither LDO exhibited any unstable behavior in my testing.