UCC3750: Vcp and REF out works abnormally

Hi Nicky,

From looking at your schematic I can see that the capacitance on the VCP is 44uF of electrolytic and 100nF of ceramic. The datasheet shows 100uF and 2.2uF so maybe you can try increasing the capacitance values on your design to match the schematic.

The capacitors connected between VS1 and VS2 are part of the charge pump circuit used to pump up the voltage from VDD to VCP.

Regards

Peter

Hi Peter,

If lower capacitance Capacitor is used for charge pump circuit, does the voltage from Vdd to VCP become lower?
Please let me know the relation between this capacitor value and charge pumped voltage.

Regards,
Nicky

Hi Nicky,

If lower capacitance values are used in the charge pump circuit then the circuit will not be able to deliver the same amount of energy, the energy stored on the cap is 1/2CV^2. Small values of capacitance means smaller value of energy for the output.

Regards

Peter

Hi Peter,

Some more questions

1. If using Vcp bypass capacitance (44uf) is lower than reference(100uf , 2.2uf ), Need to increase charge pump capacitance? 

2. Can increase charge pump capacitance from 0.22uF to 0.47uF? Is there any side effect?

3. If change  Vcp capacitance to 100uF +  2.2uF, can use the less capacitance than referenced  0.22uF in charge pump circuit?

4. Is 0.22uF capacitance in charge pump circuit the minimum capacitance or Maximum capacitance ?  

Please let me get your answer.

Regards,
Nicky