Tool/software:
Hi,
I am working on a CC/CV charger for 36v battery using the TPS923654HMDMTR in boost (step up) mode operation. I post the full schematic:
During testing I notice a weird behavior that can be summarized as:
1. There is huge ringing on the SW node.
2. Output voltage goes far above the 42V of the design.
3. The switching frequency is not the one set by FSET resistors.
In order to better understand the behavior I described I attach oscilloscope captures so it is more clear. The two figures represent the operation at 300mA load and 1A load.
Note that yellow is the SW node, red is OVP node, blue the inductor current and green the output voltage.
- 300mA load
- 1A load
From those figures it can be noted that the inductor frequency is just tens of kHz while the FSET configures it to be around 200kHz, neither the output voltage is keept at 42V, instead it goes 47V and beyond.
Moreover, there is 5MHz switching at the SW node during the FET off time. Does it look like the IC is not capable of driving the FET properly?
I would appreciate if someone can suggest anything to solve this.
Regards,
Denys
