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Minimum Vin

Brian Winkler
Prodigy 10 points
Part Number: LM5171-Q1
Other Parts Discussed in Thread: LM5125-Q1, LM5171EVM-BIDIR, LM5171

Tool/software:

We are working on an automotive design and are considering using the LM5171-Q1 but have a question regarding the minimum input voltage.

Our design is a 2-channel 12V DC-DC voltage stabilizer where we will boost two inputs to guarantee a stable12V on both outputs which have independent loads. In terms of utilization, we would only be using the boost function of the switching regulator. But the dual outputs of the LM5171-Q1 allow us to achieve our design with a single IC which is appealing. And since our input voltages will sometimes be below 9V, we would apply the external LDO MOSFET to generate a bias supply for VCC. 

What is the minimum input voltage that can be maintained while in Power Delivery mode without transitioning to Shutdown? And what is the minimum input voltage while in Standby mode without transitioning to Shutdown?

In WEBENCH, the minimum input voltage it will allow as a parameter for this IC is 6V, but I'm having difficulty determining the corresponding information in the datasheet. We noticed for another IC (the LM5125-Q1), if the output voltage can be maintained at or above 6V then the input voltage can go as low as 2.5V. Does the LM5171-Q1 operate similarly?

Please let me know if I missed any information needed to answer this and I'll be glad to provide it.

Thank you in advance for your time!

  • 0
    TI__Mastermind 22610 points

    Hi Brain,

    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.

    LM5171 is different from LM5125. You need to make sure VCC is always higher than 8.2V.

    Best Regards,

    Feng