LMR14020-Q1: LMR14020 output response

ZYT

Part Number: LMR14020-Q1
Other Parts Discussed in Thread: LMR14020

Hi Sir,

i used LMR14020-Q1 to design a power suplier, Input:12v; output:3.3v/1.2A, but when power on and power off , the output voltage will have a 1.3v voltage spike as the attachment;

i want to konw the reasons and how to solve this issue, the voltage will restar our MCU.

over 6 years ago

0 ZYT over 6 years ago

Intellectual 350 points

LMR14020 issue.xlsx

0 Jason Wang (BSR-MV) over 6 years ago in reply to ZYT

TI__Genius 9550 points

hi ZYT,
The issue is odd! We will give you more comments tomorrow. Before that, for "issue 1", please upload more waveforms which plot VIN together with OUTPUT, SW.

0 Andy Chen over 6 years ago

TI__Mastermind 34875 points

Hi ZYT,

On your circuit, what's ESR of output capacitor C13?

Pls make below change on your circuit:

1. remove C16 390pF

2. Increase C17 to 10nF

Re-test circuit to see if problem solved.

0 ZYT over 6 years ago in reply to Andy Chen

Intellectual 350 points

Hi Andy,

thanks for your suggestions.

the issue wasn't solved, the attachment is the waveform, the green channel is input voltage, the yellow is output ,and blue is SW pin.

0 Jason Wang (BSR-MV) over 6 years ago in reply to ZYT

TI__Genius 9550 points

hi ZYT,
Vout has a voltage spike, and SW has a voltage spike in your waveform. I suspect Vout spike first. Please check your system if there is another path to feed Vout? Try to remove R2 and plot C14/C15 voltage. Check if the voltage spike on Vout can disappear.

0 ZYT over 6 years ago in reply to Jason Wang (BSR-MV)

Intellectual 350 points

Hi Jason,

thanks a lot, i will try the methed what you said.

wether you have a EVM test waveform about the output ,input and SW pin ?

0 Andy Chen over 6 years ago in reply to ZYT

TI__Mastermind 34875 points

Hi ZYT,

There is Output startup waveforms on LMR14020 data sheet.

On the waveform you provided, the output jump at input just ramp up from zero, but LMR14020 will be enabled at about 6V, so the output spike should not be caused by LMR14020. as Jason suggested, you may remove R2 and check if spike still there.

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LMR14020-Q1: LMR14020 output response