charge pump VS boost converter

[Peng Yao]

recently I am doing some research about DC-DC converters..I found that most of converters which are used are inductor based boost converter while all small applications such as flash memory and LED use charge pump.. is there any limitation behind? besides, is seems that the output current of charge pump is usually a few hundreds of mA, can it be bigger? or it just because charge pump usually applied to low power applications....which is basically the first question...

I hope someone could give me some detailed answer or at least some useful direction so I can dig deeper...thanks!!!

 

[dick_freebird]

Charge pumps are favored for ability to integrate, when the
current is reasonably low and the voltage multiplication is
not huge. I have built 3V:75V charge pumps on chip (some
decoupling external) on specialty technologies but generally
you'd be limited to your available device breakdowns on a
normal junction isolated technology.

A boost converter doesn't limit you if your power switch is
external, but a highly integrated internal boost converter
would want either not-so-common devices (HV LDMOS, HV
Schottky) or some significant design elaborateness and
HV PMOS, or both. And the inductor, fuggedaboudit. That
slug of iron is gonna need its own bedroom.

 

[Peng Yao]

Charge pumps are favored for ability to integrate, when the
current is reasonably low and the voltage multiplication is
not huge. I have built 3V:75V charge pumps on chip (some
decoupling external) on specialty technologies but generally
you'd be limited to your available device breakdowns on a
normal junction isolated technology.

A boost converter doesn't limit you if your power switch is
external, but a highly integrated internal boost converter
would want either not-so-common devices (HV LDMOS, HV
Schottky) or some significant design elaborateness and
HV PMOS, or both. And the inductor, fuggedaboudit. That
slug of iron is gonna need its own bedroom.

thanks!!!

another question...why the charge pump is used when the current is low? could it be used when current is high? is there any fundamental limitation?

 

[dick_freebird]

To get high current out of a capacitor charge pump you
need high C, high fSW or both. High C values are going
to have to be external to the chip, perhaps defeating the
value of integrating. Of course you see piece-parts that
are exactly this (charge pump guts, needing large external
fly and storage caps). But if you have to hang stuff on it,
the choice between topologies becomes more of a BOM
cost and EMI exercise than a simple gut decision.