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LM5171-Q1: VCC UVLO

Nathanael Teshome
Prodigy 20 points
Part Number: LM5171-Q1
Other Parts Discussed in Thread: LM5171, LM5171EVM-BIDIR

Tool/software:

I am designing a boost circuit using the LM5171 to boost an input voltage (Vin) of 5V to 12V. I am using an external VCC supply (up to 12V) connected to the Vin pin, along with an external MOSFET. My concern is: when Vin drops to 5V, the VCC supply also drops to 5V. Since I read that the internal LDO in the LM5171 requires VCC to be at least 6V to operate properly, will the LDO still be able to drive the external MOSFET effectively to generate the required voltage for VCC? Could you clarify the LDO's operational requirements and suggest any improvements to ensure reliable operation when Vin is 5V?

  • 0
    TI__Mastermind 22365 points

    Hi Nathanael,

    You are right. To ensure proper operation, VCC should be higher than 8.2V (VCCUVLO). LDO is a linear regulator and the output voltage is always less than input voltage. If VCC is powered from Vin by LDO, Vin should also be higher than 8.2V.

    If you want to get 12V VCC at Vin=5V, you need a SEPIC. You may refer to LM5171EVM-BIDIR for the schematic.

    What is the output voltage and current of your application? Maybe you can consider LM5125 which has 5V VCC.

    Best Regards,

    Feng