Power p current spike



I have a design that uses the Fastrack Supreme 20 in a battery powered application. On power up the modem draws a narrow but very healthy current spike - 4 to 6 amps.

This is not a problem until the battery discharges some. The battery voltage drops during that turn on current spike, the V regulator on my PCB drops out of regulation, and my processor resets. This effect severely shortens uasable battery life

Has any body seen this problem?
What is the cause? I’m guessing large capacitors in the modem.
Any suggested fix?

Jim Hall


IT is a very well known feature of all GSM devices that they do draw very big “spikes” from their power supplies!

Here’s some measurements I did a while ago on an M1306B (the Supreme’s predecessor): antronics.co.uk/downloads/M1 … Traces.pdf

What voltage is your battery?


My battery is 12 volts.


You should place two low esr 470uF as close as possible to the supply pins of your modem module. This should take good care of those nasty power spikes.


Thank you all for the info and help!


Also make sure that all the power connections are good and solid; low impedance.

Again, note that this is a general requirement for any GSM device - not just Wavecom
(in fact, it’s probably general to any radio transmitter device)

See also: https://forum.sierrawireless.com/t/faq-forum-wiki/3491/13