LMR51420: LMR51420YFDDCR

Adam

Part Number: LMR51420
Other Parts Discussed in Thread: LMZM23600EVM, LMZM23600

I am using LMR51420YFDDCR (1.1MHZ, FPWM) in this configuration:

Vout:3.3V, L=3.3uH, Cout=88uF, Iout=50mA

And I am getting the following output voltage with low frequency ripple of 20mV:

I compared it to the LMZM23600EVM (using default components on the dev board) under same output conditions (50mA load, 3.3Vout, 69uF output capacitance) and I am getting more clear voltage (less low frequency ripple):

As both LMR51420YFDDCR and LMZM23600 has FPWM at around 1MHz, both are peak-current controllers, both have only one LC stage at output - why I don not observe low freq ripple on LMZM23600?

Is there anything I can do with LMR51420YFDDCR design so that output voltage looks like for LMZM23600 (apart adding second LC stage or LDO)?

Adam

over 1 year ago

0 Adam over 1 year ago

Expert 1145 points

To add, I have only MLCCs at output in both LMR51420YFDDCR and LMZM23600

0 Frank De Stasi over 1 year ago in reply to Adam

TI__Guru 64365 points

Hello

Can you show us the schematic you are using and images of your PCB layout.

When you say "low frequency" do you mean the 1MHz switching frequency or something lower ??

Thanks

0 Adam over 1 year ago in reply to Frank De Stasi

Expert 1145 points

Schematic:

PCB can not send.

By low frequency I mean ripple caused by inductor current through output capacitors(not the switching ringing), so this with green marker:

It must have been a way to eliminate it (not using LDO or second LC filter) as similar same controller on LMZM23600EVM dev board is doing it very well

Adam

+1 Frank De Stasi over 1 year ago in reply to Adam

TI__Guru 64365 points

Hello

The inductor value and output capacitors (and ESR) will control the switching frequency ripple.

Also, the PCB layout will have an impact.

Thanks

0 Adam over 1 year ago in reply to Frank De Stasi

Expert 1145 points

Thanks

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LMR51420: LMR51420YFDDCR