# Charge pump high output resistance

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#### Avala Lokesh

##### Newbie level 5
Hi all,
I designed a charge pump(dickson) with input 750mV and output 2V. It has a very high output impedance. Whenevr I connect any other circuit like a VCO the charge pump voltage doesnt even reach 500mV . Any solutions on how chargepump is used in systems?

Lokesh

#### erikl

##### Super Moderator
Staff member
You need to adapt clock, charge pump current capability and capacitances to the output load.

#### Avala Lokesh

##### Newbie level 5
You need to adapt clock, charge pump current capability and capacitances to the output load.

And could you explain a bit more how I can do that.....I tried diffenrent chargepumps but same results....is there any additional componenets to be added after chargepump?

Lokesh

##### Super Moderator
Staff member
Suppose you want 10 mA output at 2V.
Then your charge pump must draw average 27 mA at 750mV input. (Add some more to make up for losses.)

The internal waveforms might peak at 50 or 100 mA. Therefore your circuitry must have a low enough internal resistance to admit that much current. This includes your 750mV power supply.

You must turn on all transistors/mosfets, enough so they admit sufficient current.

In addition, select capacitor values which are large enough, so they do not lose much voltage during the discharge part of the cycle. It also may help if you try a faster operating frequency. The two behaviors are inter-related.

#### kartheekRP

##### Junior Member level 1
When you draw current from Cout of chargepump : Vout=kvin-Rout*Iout
& Rout of charge pump is inversely related to f,Cpump,Cout.
So try to increase these parameters to get your required Vout.

#### dick_freebird

All you have for current is input CVf. C is series reduced.
V, you've already picked. More C or more f or less load.

#### yangyukuo

##### Newbie level 3
In your case, you need to put more CP stages in parallel.
Could you past your circuit? it might help to see what causes this issue.

#### kartheekRP

##### Junior Member level 1
hello all,
Have doubt in calculation of converter power efficiency in 4 phase charge pump, do we have to consider current from clocks also as input current (As clocks charges Pump-capacitor)?

#### kartheekRP

##### Junior Member level 1
CMOS Four phase chargepump Design

Hi,
Am designing a four phase chargepump, but efficiency of whole system is degraded because of drivers, as drivers which drive capacitance of 20pF of each stage (Total stages N=4) they consume more than 80% of power consumption, Is there any way to decrease this driver consumption?

#### anhnha

##### Full Member level 6
I am also facing the same problem with my basic Dickson charge pump. The output resistance is equal to N/C*f. To reduce output resistance I tried to increase or f by a large factor but there is not any noticeable improvement. Any suggestions will be much appreciated.

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