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Design >> High-Power Design >> > 50 V geneation on-chip from 4 V supplies
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Message started by vivkr on Apr 8^th, 2008, 11:43pm

Title: > 50 V geneation on-chip from 4 V supplies
Post by vivkr on Apr 8^th, 2008, 11:43pm

Hi,

I am looking for literature or ideas on how one could generate 50 V -100 V on-chip from 4 V supplies.
The output needs to switch a large capacitive load.

The basic idea is to use chargepumps. I would welcome any comments regarding feasibility, architecture etc.
So far, my brief experience with chargepumps and a survey of the literature shows me that the best power
efficiency (which is still going to be quite low) may be obtained only by using several Dixon stages where the
drivers are powered off a regulated supply. But this is quite an area-intensive solution as one pushes the voltage
up by 5 V or so each time, leading to large number of stages and the pump caps get larger and larger since they have
to be made with thicker oxide to counter breakdown.

Cascading different kinds of chargepumps seems to put a limit to the efficiency as high voltage transistors
are generally very poor in performance. They seem ideal only in cases where no DC power needs to be delivered,
i.e. charge up output cap once and be done with it.

Regards
Vivek

Title: Re: > 50 V geneation on-chip from 4 V supplies
Post by CMOSSolutions on May 29^th, 2008, 9:51am

Could you use a single external inductor? That would sure make life easier.

Title: Re: > 50 V geneation on-chip from 4 V supplies
Post by loose-electron on Jul 15^th, 2008, 6:14pm

Vivek:

I have used cascaded charge pumps up to about 30V on an older bipolar process. The inductor solution is a good suggestion to consider, and for 50V you need to be fussy about your parasitic diode zener voltages.

Also, take a look at many of the buck/boost voltage regulator structures for some ideas.

my 2 cents,

Jerry

Title: Re: > 50 V geneation on-chip from 4 V supplies
Post by vivkr on Jul 16^th, 2008, 7:30am

Hi Jerry, CMOSSolutions,

Unfortunately, I have no inductors available. In fact, I would be lucky if I can get a small external cap.

Cascaded charge pumps work ok even for higher voltages, but only as long as I am drawing no net current (charging up some small capacitors once), as I already mentioned.As soon as one needs to do some sort of load switching, such as charging up a large capacitive load regularly, then there is trouble with these.

That's why I wanted to know if anyone knows of a good method to build charge pumps to push up the voltage to an arbitrarily high value (breakdown effects permitting) and still provide an average current of a few microamperes. And all this while working off a 4 V supply.

The only "reliable" solution I could think of was to use a string of Dixon stages, all drawing their power from the low-voltage supply which can provide this required current and pushing up voltage step by step, all the way to the top, but the area explodes exponentially with this approach, not least because at the high voltage end, each stage is massive in size.

Regards
Vivek