UCC28704: PMP11612 Voltage Spikes at Output Capacitor

Hi Lu,

Thanks for reaching out. This waveform looks like switching noise might be coupling into the measurement. Could you tell me where in the layout you have your probe points connected?

Best Regards,
Ben Lough

Hello,

i measure directly at output capacitor. i have to mention our board is really small 25x30mm due to size limitations.

used Mosfet has really fast switching times and low RDS(on) around 500mOhm

Turn-on Delay Time td(on)8 nS
Turn-on Rise Time tr 6 nS
Turn-Off Delay Time td(off) 75 nS
Turn-Off Fall Time tf 15 nS

i also played around with no effects:

- series drv resistor on gate (0ohm - 130ohm)
- RLc Series Current Sensor Resistor (200hm - 1.8kohm)
- adding some ceramic capacitors on output


Why on all reference designs two low-side VS sense resistors are used?


thanks for help :-)

winding ration is 60 -> 4

Hi Lu,

Would it be possible for you to send me images of your layout? The noise might be coupling from somewhere else in the layout. The two low side VS resistors are designer preference. The UCC28704 EVM does not have two low side resistors for example.

Best Regards,
Ben Lough

Hi Lu,

How is your testing going? Is this issue still open?

Best Regards,
Ben Lough