LM5117: low frequency oscillation on Vout ripple by webench simulation

Hi 

do you used orignal TINA file?

I modified the TINA files, only change the feedback resistor, below is the result:

Hello Daniel,

Yes, I follow you way to change feedback divider only as 6.04k on the top and 1.15k on the bottom, Vin to 57V, loading to 8A.

I still could see the oscillation. Please see the ripple simulation waveform below as well as TINA model I used.

LM5117 (57Vin, 5Vout, 8A).TSC

<Run simulation in time period from 1.8ms to 2ms>

<Run simulation in time period from 9.5ms to 10ms >

I use original TINA model download from ti.com without any chnage and run the simulation. I could see the same issue.

LM5117 TINA-TI Transient Reference Design (Rev. A)

<Run simulation in time period from 9.5ms to 10ms with original TINA model>

If you still couldn't see the same issue in your side, please provide the TINA model you used. I could double verify in my side.

or

Please guide me how to fix the low frequency oscillation issue. Customer has concern the audio noise if they use LM5117 in thier system.

Sincerely,

Jason

Hi

I modified the 5V 8A example, there is still some low freqency noise, but it less than 2mV, I don't think it will cause audio noise based on 2mV 

1. change 470uF capacitor ESR to 50mohm which is more close to electrical cap 

2. reduce snubber to 100pF

3 change inductor to 22uH

the output shows as below, and I think simulation normally used for verify the circuit, but some detailed like ripple or low frequency jitter will be much different from practical circuit , so I recomend customer use our EVM to evaluted the solution with their system .

Thanks

LM5117 (57Vin, 5Vout, 8A) update.TSC

Daniel,

Good to hear that you could duplicate and see the same issue in your side.

I already applied EVM board to double check.

Meanwhile, in the simulation, what is the possible reason to cause the oscillation?

Based on your expert experience, how much amplitude at low frequency could cause heard-able audio noise?

The possible application to use LM5117 is IP CAM with micro-phone.

Any audio-able noise will be amplified by micro-phone. They suffered to use power IC with ship mode to generate audio noise amplified through micro phone.

That's why customer is pretty concern this low frequency issue.

Please share your expert idea on two questions above.

Sincerely,

Jason