Part Number:TPS65131-Q1
Dear team,
My customer use this device, when they tested the radiated EMC, it failed. Vin=5V, Vout1=10V, Vout2=-10V, Ioad current=10mA.
The 1.44M frequency point exceeded the standard in the EMC test radiation emission. Through the testing with near field probe, it is determined to be generated by the 65131 circuit, the waveform of the negative phase power switch has a spike on the oscilloscope. The RC snubber circuit is added, but the result didn't improve. Can you help to provide an operational correction or solution to this frequency?
When testing the EMC, the customer changed 0ohm resistors to magnetic beads;
When using the near field probe to test the waveform, the customer also did some changes as below,
1. Increase the load at the positive and negative output terminals respectively, and the resistor is changed from 1k to three 1k in parallel;
2. Change 2 inductors from 4.7uH to 6.8uH (TDK: SPM5030T-5R6M-HZ);
3. Positive and negative outputs are respectively connected in parallel with 560pF capacitors;
4. Add snubber circuit in parallel with the negative direction diode, is 20R, 680pF;
The switching frequency is 1.38MHz. The EMC test result is as below,
SW waveform(L=4.7uH)
SW waveform(L=6.8uH)
negative phase output noise
near filed probe test
the schematic is as below,
the layout is six-layer, the first top layer is as below,
Thanks & Best Regards,
Sherry