Charge pump function and the effect of light for scope

[sean202]

I design a charge pump circuit similar to Dickson charge pump for my embedded flash IP.
There is one thing I can not understand so far when I test charge pump at a probe station with several continuous write commands.

If the light for scope on probe station is turn-off, there is only one and the 1st high-voltage pulse appears at the charge pump output.

While the light for scope on probe station is turn-on, all what we needed high-voltage pulses appear at the charge pump output.

I probe all related internal logic signals and find nothing wrong.

May I have your advice on what the effect of light is on charge pump circuit/layout?

 

[sean202]

Re: charge pump function

I guess the problem comes from latchup issue.

 

[tsanlee]

charge pump function

The leakage current is raised by light .
The charge of output charge is losed by leakage path to substrate.

logic circuit is ok, but the switch mos Rdson is not the same in this two condition .