supply for GPRS module

Yes, the TPS63020 is a great device for such an application.

Golan, did you end up using the TPS603020 for your GPRS application? I am looking to do the same thing but from AA batteries (probably two in series as I think parallel will really be pushing it).

Chris, do you have a recommendation for an appropriate supercap for this application or a reference design for a GPRS application?

Our current design uses a Maxim MAX1708 plus a 0.1F Cellery CLG03P120F28 but we're concerned about cost/availability of these components.

Regards

Yes, I think you should 2 or even 3 AAs in series.  The higher voltage that you get at the input, the easier the boost is to design.

With 3x AA, you could also use the TPS63020.

With either 2x or 3x, the TPS61030 is a boost that fits.

Thanks for the info. I think the form factor will dictate 2 but I'll see if we can squeeze to 3!  

Any thoughts on the need for reservoir caps to tolerate the 2A spikes?  The GPRS module can tolerate a worst case of 3.1V (from a nominal 3.8v) but 3.4 to 4.2V is the normal operating range.  They'll probably be standard AA alkalines.  

Large output caps to supply the power through the transmission pulse are probably required.  I don't think you will be able to draw this power directly from the batteries.

You'll need to size the caps to supply enough current to supplement the output current of the boost while the cap voltage decays from your setpoint (i.e. 3.8V) down to the minimum you can tolerate (3.1V).

Hi,

I did a design for such a converter. I was at a quite high switching frequency, so that I was able to achieve a high loop crossover frequency. I got a company internal schematic, which used a big cap of several hundred µF. With a low bandwidth it worked, but the demo for the GPRS did not have such a big cap... it also sometimes resulted in a short circuit detection... With a good bandwidth of the converter control loop, this capacitor was designed out.

The difference was, that the unit was not powered from a battery. But I would recommend the capacitor at the input of the boost converter. You only mentioned a tolerance from 3,8V to 3,1V. So having a 5% total tolerance may end up in worst case 3,6V. Down to 3,1V, you only use 27% of the energy stored. Perhaps you could setup a boost converter which can operate from ~3V to down to 1V which would end up in 85% energy usage of the cap.

I never created that application for a battery supplied unit, but perhaps the ideas help a bit.

Regards, Torsten

Thanks Torsten.  The current design has the cap at the input.  Not sure why I would prefer input over output (or vice versa?).