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LTM4662 Power Good

Category: Hardware

Hello, I am using the LTM4662 to generate 0.85V. I have configured the device for parallel 30A output using Vout1+Vout2. The problem I am having is the Power Good pin will go high for about 1.7msec and then go low. The output does reach 0.85V and stays at that level. 

PDF

What could be causing this problem?

Thank you very much,

Joe

  • Joe,

    The schematic looks ok. There are a few things that you can look into:

    1. From the waveform, it looks like the output voltage ripple is pretty large, PGOOD will be pulled low if Vout is out of +/-7.5% window of reference voltage. One issue is that the Cth (C539)=100pF is too small. There could possibly be some oscillation on the output voltage. A zoomed in Vout waveform is needed to make sure. I would recommend increase Cth to around 1000pF and see if that helps.

    2. If 1 doesn't help, please check the layout file and make sure the SEQ1_PL_0v85_PG trace is not very close to noisy traces or TP.

    Thanks!

    Yan