Why Vboost doesn't increase when VCC increases?

[tok47]

Dear All,

Recently, I am studying a voltage booster circuit.

Some info regarding my circuit. There were a 3 stage boosting for 1.8v application. The desired output is around 5v. In each of the stage, I parrallel 3 capacitors with different values. And there some logic to let the voltage pass from 1 stage to another.

The theory behind this is Vboost = [1+Cboost/(Cboost+Cload)]*VCC.

From the equation, can know that the Vboost will increase when VCC increase. But in the simulation, it not work like that. Vboost will go up and down. The Vboost vs VCC curve looks like a saw wave.

Why will this happen?


Rdgs
tok

 

[sunking]

Voltage Booster

the result of simulation is right.
Vboost = [1+Cboost/(Cboost+Cload)]*VCC shows the peak voltage.

 

[tok47]

Re: Voltage Booster

Dear ALL,

I have some concern after I run a simulation on my voltage booster circuit.

I attach my reult and my circuit here.

Can any1 tell me why the VBOOST will vary with the VCC like that?


Rdgs
yylau

Added after 20 minutes:

Attach again.

 

[munfook]

Re: Voltage Booster

The array of booster cap is disabled one by one as VCC increases. The sudden drop in the boosted voltage is the point when one of the array cap is disabled.
The array of comparator will decide how many booster cap is used based on the VCC level. This is to maintain the boosted voltage as flat as possible accross VCC.

 

[tok47]

Re: Voltage Booster

Thanks. I already figure it out.

Now, is trying to flatten the variation.

rdgs
tok