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LP5907UV-3.3EVM: With a almost fully discharged Li-ion

Adam k
Prodigy 40 points

Part Number: LP5907UV-3.3EVM

Hi,

I have an application which draws around 5mA at 3.3V, from a Li-ion battery which is directly regulated with the LP5907 once the battery falls to 3V will the LP5907 turn off? Or continue to operate, as I am unsure if additional low voltage protection would be needed for the battery. 

  • 0
    TI__Mastermind 38115 points

    Hi Adam,

    When the input goes below the target LDO output (or more accurately below the nominal output voltage plus the dropout voltage at the load current), the LDO is in the region of operation called dropout. The LDO does not turn off in dropout, but the output is no longer regulated to the nominal output voltage - the LDO will basically track the input voltage as the supply falls. 

    What is the nominal battery voltage at full charge? If you are using a 3.3V variant of LP5907, it will be in dropout before it gets to 3V. 

    Best regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 40 points

    Hi Nick,

    It is nominally at 3.7V, do you know what the dropout value will be I was unable to find it?

    Regards,

    Adam

  • 0 in reply to Adam k
    TI__Mastermind 38115 points

    Hi Adam,

    Dropout voltage changes with load current; you can find the details in the plots:

    With a small load current such as in your application, dropout voltage is small, in this case on the order of a few mV. So, you can get faithful regulation right up until the battery voltage falls to 3.3V, and as the battery voltage continues to fall the output will track the battery voltage. 

    Are you using this power configuration to power digital devices? Of course if the LDO output starts drooping because the battery voltage falling, this may not be good for the digital components. 

    Best regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 40 points

    Hi Nick,

    I thought so thank you, I am using this for digital devices, but they work well below 3V it was the greater than 3.3 that is the issue.