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LM3478: unstable PWM

Expert 3255 points

Replies: 2

Views: 50

Part Number: LM3478

Team,

we'd like to use LM3478 for first boost stage in our design (around 12W). Vin=5.8-8.2V, Vout=12V, Iout=1A, f=170kHz.

While testing it, we found that the PWM is very unstable. The output voltage is stable (despite the 0.5V dip happening on full load). 

We tried different compensation methods, without effect. On the CS pin there's max 25mV now. 

Attaching block diagram and scopeshot below.

Looking forward for your help.

Thanks and regards

lm3478.zip

  • Hi Bart,

    Thank you for reaching out.  It seems a noise issue.  Can you increase C366 from 10pF to 1000pF and see if there is any improvement?  Also, can you cross check you layout against the EVM layout, and make modifications in accordance?

    Thanks,

    Youhao Xi, Applications Engineering

  • In reply to Youhao Xi:

    Can I assume that the issue is resolved?  Let me close it here but you can re-open it by add a new post.


    Thanks,

    Youhao