Part Number: LM5145
Using LM5145 EVM, when controller enters standby mode, there is a approximately 1.2V Vout in over 40s. And I am also wandering why there is a standby mode in almost every buck controllers which are with UVLO. The corresponding pic is shown as below: in which
Red line indicates UVLO;
Blue line indicates VIN;
Sky-blue line indicates Vout.
My questions are:
1. Why controller must feature Standby Mode? Is it because VCC needs time to rise?
2. Why there is a 1.2V output with rise time RC similar to Cout*(Rfb1+Rfb2)?
Thank you very much for your help!
In reply to Wenhao Wu:
Please also share a picture of the back of the board.
I'll be receiving EVMs shortly. Once I do I'll recreate your tests with your setup.
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In reply to Samuel Jaffe:
I tried to reproduce this in the lab and got similar results until I realized I incorrectly assumed which pin is pin 1. I thought it was the first on the long side but it's actually the one on the edge closest to the dot. I was tying RT to GND instead of EN. Once I tied EN to GND I found regular operation - very low input current and no output.
Please check that you're pulling the correct pin to GND.
I understand now. I've been able to reproduce this in the lab. I will investigate and get back to you.
Thank you that you have recreated the issues. Looking forward to your reply.
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