LMR14020: Power supply overshoot

Ryan Goslin

Part Number: LMR14020

I am using the LMR14020 to convert from 24V to 5V. During startup we are noticing an occasional overshoot past 5V along with the soft start not working as intended. We do have a fairly slow ramp on the input side from 0 to 24V (100ms). Does the ramp time influence this?

over 7 years ago

0 Vental Mao over 7 years ago

TI__Expert 5745 points

It's really too slow for the Vin slew rate. You can use the more reliable device LMR14020-Q1.

0 Andy Chen over 7 years ago

TI__Mastermind 33935 points

Hi,

can you upload the Vin and Vout waveforms for checking?

0 Ryan Goslin over 7 years ago in reply to Andy Chen

Prodigy 20 points

CH3/4 is the 24V input to with a current sense across. (red is the current)

5V rail (ch1) doesnt use the soft start and ramps beyond 5V, matching the input voltage.

3V3 rail (ch2) does start up properly with soft start.

0 Andy Chen over 7 years ago in reply to Ryan Goslin

TI__Mastermind 33935 points

Hi,

From the startup waveform, I think you use resistor divider on EN pin to program the system UVLO voltage at about 8V, did you also parallel capacitor on EN pin to GND? what's capacitance? if the cap is used, I suggest you to add a resistor round 75K--100K to EN pin first, then connect resistor another node to original external network. thi shelp to generate a small fast step on EN pin when EN UVLO voltage is tripped.

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LMR14020: Power supply overshoot