Hi,
I'm using a TC7660H charge pump to provide the negative voltage for a OP2134 op amp.

When not connected to the op amp the charge pump output registers as the full -5V on my meter as expected. However once it's connected to the opamp the negative voltage drops to -4.4V and hence the opamp doesn't work properly.

I am using 1uF tantalum caps with the charge pump.

The opamp is a dual op amp. The first one is an active LPF, the second one adjusts the gain and DC bias of the input.

The effect of the opamp not working is that the output of the opamp can't output the full range of voltage on the output (i.e. if I put a sinewave in, I see a sinewave out, but with a bit of the top clipped off).

Any ideas why the charge pump isn't working? Should I be using tantalum caps?

Paul

 

Tantalum is good. The 7660 chip has an internal impedance of about 55 ohms. Trying to get 10ma to 11ma out of it would explain that voltage loss.