Hi,
During full compliance testing we encountered too high emissions which seem to be related to the TPS55340 boost converter.
The boost converters steps up a 2S LiPo battery voltage (6 V - 8.4 V) to 20 V with 800 mA max output current. When there's no load on the output we pass the tests but with a load of already 400 mA we fail:
The emission from the boost seem to be from 125 to 250 MHz. The frequency of the boost is set to 779 kHz, which can also be seen as harmonics when you zoom in:
- 162.000 MHz
- 162.743 MHz (Δ743 kHz)
- 163.485 MHz (Δ742 kHz)
- 164.255 MHz (Δ770 kHz)
- 164.970 MHz (Δ715 kHz)
With a field probe I was able to see the same spikes and by increasing the frequency to 1 MHz the spikes were separated by 1 MHz.
When measuring the output and switching node of the boost with an oscilloscope I notice quite some peaks on the output as the switch turns on and off:
It's probably caused by ringing but my scope is not fast enough to see this I think:
This is how the switching node behaves:
Can you maybe help me with ideas on how to possibly fix this issue?
Kind regards,
Martin
