LMR51420: inductance selection

Gary Zeng

Part Number: LMR51420
Other Parts Discussed in Thread: LMR51430

Tool/software:

Hi TI experts,

My customer used to use LMR51430YDDCR for power supply and input voltage range is from 18V to 30V(TYP 24V). Output is 5V/3A. Inductance is 3.3uF, same as the value in datasheet.

Due to the supply issue of LMR51430, customer wants to use LMR51420 to replace it and don't want to change peripheral circuits.

So their question is that can they still use 3.3uH inductance when they use LMR51420 to replace LMR51430.

I use Webench and the result shows as below:

I need to change peak to peak inductor current ratio from 40% to 60%, which can achieve small inductor from 4.7uH to 3.3uH.

Bad news is that inductor current will increase. Is it ok for IC Over Current protection?

3 months ago

+1 Onkar Bhakare 3 months ago

TI__Genius 14226 points

Hello Gary

Current limit for LMR51420 is 2.7 (min). With 60% ripple current, inductor peak current would be 2.6A which is quite close to min current limit. Also we have to consider inductor tolerance and derating. Thut it won't be advisable to directly replace LMR51430 with LMR51420 without changing the inductor.

Thank you

Regards

Onkar Bhakare

0 Onkar Bhakare 3 months ago in reply to Onkar Bhakare

TI__Genius 14226 points

Hello Garry

Let me know if you need further help

Thank you

Regards

Onkar Bhakare

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LMR51420: inductance selection