Inquiry Regarding CAPGD Signal Behavior on LTC3351

Hi NK304 ,

Could be a layout issue. 

Instead of measuring the SCAP voltage (over supercap terminals?), measure the voltage at R44. Do you see any ripple there?

Could also try adding some positive feedback by placing a high ohmic resistor from CAPFB to CAPGD (not sure if works, may cause instability).

Cheers, heke

Dear heke,

Thank you very much for your advice.
Regarding the waveform at R44, I observed noise of approximately 300–400 mVp-p at 500 kHz. Additionally, the bounce on CAPGD occurred at around 250 kHz. Does this suggest that switching noise is affecting the circuit due to a layout issue, possibly related to the GND plane?

After adding a 470 kΩ resistor between CAPFB and CAPGD, the bounce was suppressed. Could you please explain what effect this resistor has in the circuit? Also, is 470 kΩ an appropriate resistance value for this purpose?

Best regards,