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LMR50410-Q1: How does this regulator behave when Vout > Vin?

Ben Adamson
Prodigy 90 points
Part Number: LMR50410-Q1
Other Parts Discussed in Thread: LMR50410

We have an 18-25V battery input to the LMR50410 which is set for 19V output.

I've seen from other topics on this forum that the LMR50410 goes into a low-dropout mode when Vin < Vout + 0.7V

In our application, it's fine for the 19V output to decrease to approx. 17.3V when the battery is at 18V.

When trying to simulate this in WEBENCH, the calculation refused to proceed as "Calculated duty cycle exceeds limit". 

Can we safely ignore this if we can accept the output voltage reducing when our input voltage is low?

  • +1
    TI__Expert 5250 points

    Hi,

    What is the lowest Vo you can accept for the system? When Vin< Vo set, the device operates with maximum duty cycle to make Vo follow Vin with a voltage drop. And the voltage difference will increase with larger load. If we consider HS and LS switch Rdson and inductor DCR, the actual duty cycle required can be written as below. So if with no load, 18Vin should be able to support 17.3V output; if with 1A load, it will be around 17V. If you have stringent requirement for the Vo, it's better to test on EVM and see the result. 

    Regards,

    Hongjia