How to test the charge pump's output current?

[dsj_guilin]

Hi,

When the charge pump only has a load capacitor, I can only see the output voltage and the current at the output looks like noise. When I have a resistor in parallel with the load capacitor, the output is oscillating. How can I test the output current of the charge pump?

Many thanks.

 

[dick_freebird]

If your charge pump oscillator is unbuffered, a big load
capacitance could conceivably kill it (by stealing all of the
signal, leaving nothing to wrap back and oscillate).

Extreme ground / supply spiking can also kill oscillation
if it is of the right (wrong) phase.

You may have to put constraints on the application load range
to make the design work, or vice versa.

 

[dsj_guilin]

Thank you for your reply. Can I prevent the oscillation by set the output's frequency (1/RC) less than the clock frequency?

 

[cdh7]

What kind of regulation is the charge pump using? Some types have an LDO regulator at the output, and you have to select an output filter capacitor within a particular range of ESR values to avoid oscillation.

As for the maximum current, can you use a potentiometer rated for a few watts to check how much of a load causes the output voltage to droop?

Regards,
Chris