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LM1117: LM1117MP-3.3

Tushar Sharma
Prodigy 20 points
Part Number: LM1117
Other Parts Discussed in Thread: LM117

Hello,

We are using LM1117MP-3.3 in one of our design.

The input voltage is 5V and on the path we were earlier using LQM21FN4R7M70L (DCR = 455MOHM) in the design at input and now would like to use LQM21FN4R7M80L (DCR = 234MOHM) now.

In the LM117 datasheet there is no specification as such for the allowed input current so would like to understand whether it is possible to use this part or not.

Kindly help.

Thank you,

Tushar

  • +1
    TI__Mastermind 45965 points

    Hi Tushar,

    With the LQM21FN4R7M80L this is fine because the max dropout at full load for this device is 1.3V, leaving 400mV of extra headroom. At full load (800 mA), you have an additional loss of 0.8A * 0.234ohm = 187mV, which is still enough to not be in dropout. 

    I'm not sure what you mean by the allowed input current. The input current to any LDO is the load current plus the biasing current, which is normally dominated by the load current when the device is loaded.

    Regards,

    Nick