LM5122-Q1: FET in feedback path, low iq

Jared Becker

Part Number: LM5122-Q1
Other Parts Discussed in Thread: LM5122

Hi Team,

If I was to place a FET in series with the feedback resistors for the LM5122-Q1 to have 0A of Iq during low power state, would this be acceptable? If it is acceptable, are there any risks to consider? Also, where in the feedback path should the FET be placed?

Thank you in advance for your support!

Jared

over 5 years ago

0 Youhao Xi over 5 years ago

TI__Guru 68675 points

Hi Jared,

I am kind of understanding what you want to do. If you disable/enable the LM5122 at the same time as you turn-off/turn-on the FET, there should be no issue. If you enabled the IC but turn-off the FET, the IC would become open loop and forces max duty cycle.

Thanks,
Youhao

0 Jared Becker over 5 years ago in reply to Youhao Xi

TI__Genius 11515 points

Hi Youhao,

You are exactly correct, the FET would only be turned off when the LM5122 is disabled. If the FET is included in the feedback path, should it go between the bottom resistor and ground?

Thank you!

Jared

0 Youhao Xi over 5 years ago in reply to Jared Becker

TI__Guru 68675 points

Hi Gared,

The location that you marked with a green circle looks good, but leaves FB floating and it may violate FB max rating because of the VOUT pull-up. I would recommend to place the FET between the FB and the high side resistor.

Thanks,

Youhao

0 Jared Becker over 5 years ago in reply to Youhao Xi

TI__Genius 11515 points

Thank you Youhao!

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LM5122-Q1: FET in feedback path, low iq