Choose Switching Regulator for Telit GM862-GPS module...

[pucca]

Hi I want to use a step down regulator from 9 Volt battery to 3.8 Volts of GM862-GPS module of Telit. I have looked at maxim's regulators but I can't figure out which one is more suitable for the GSM. I want a regulator as simple as possible (with one DC output).....
Thanks in avanced

 

[MacGyverS2000]

What's the problem in your selection? Pick one that meets your size and power requirements using their interactive parameter table...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[treez]

In order to best answer your question, it would be good to know....

Required output power.
Max input line change.
do you need isolation.


are you over 50watts in output power because if so then you need some PFC too.

but to me (if its low power) it sounds like a really easy job for an 8-pin voltage mode controller with perhaps some way for over current limit too.

or if you wanted better efficiency you could go for a synchronous buck controller IC.

its nice to have soft start
also UVLO.

If you want really really cheap and low component count then go for the TL497. This is also really easy to use...though the on-chip transistor is not fit for mega high frequency and only does i think 500mA.....but you can use it with external circuitry for higher powers as on the datasheet

I'm not sure whether or not it uses voltage mode or current mode control....but actually i think (suspect) its a hysteretic controller because it works in burst mode.

 

[pucca]

Thanks treez!It should be an easy job if you knew what all these parameters of the regulators really mean. I know the basic specs that the regiulator should meet , Vin(3-9Volts)
Vout(3.4-4.2Volts), Iout max = 2A, and switching frequency at least 500kHz, but those I find have so many other characteristics that I get confused! I am new with all this

 

[Comcokid]

Having designed a buck regulator for product incorporating a Wavecom GSM module to use with a 12V battery 2 years ago, I know the issues you may be facing: a) certain switching frequencies can be forbidden as they might 'modulate' the RF output violating the PTCRB pre-approvals of the module, b) digital GSM RF transmissions is done as short pulses ever few milliseconds, so the buck regulator needs to react very quickly without overshooting and creating issues with the module, c) the large difference between the RX current and TX maximum current means you need a buck regulator that's efficient at both low and high currents, and, if operating off a battery only once or twice a day, you need one that has very low shutdown current.

What I used successfully was a Linear Tech LT3481, and programmed it for about 1.1 MHz. Had to be careful selecting the inductor as many high-current SMT inductors are not designed for the frequency (mainly a skin-effect and wire-size issue).

Between National, Maxim, TI, Linear Tech, Micrel, and others, there are lots of choices in switching regulators which can get you confused as to which one is the "BEST" choice. What I used may not be the best for your application, but may provide another one for you to look at.

 

[pucca]

I am very happy because LT3481 was the one in the top of my list(as well as LT3681). I have found some inductors by TOKO:

http://www.tokoam.com/passives/indu...df/TOKO_SMD_Fixed_Inductor_Ferrite_Series.pdf

However in the datasheet only the inductance and the Rated DC current are specified. The SRF (self resonance freq)is not mentioned. Should I suppose that it is ok for the 800Khz I'll use?

 

[Comcokid]

The TOKO sheet of you link is really a selector guide - not a data sheet. The GSM device I designed was for a previous employer, so I don't recall the inductor I used and no longer have the design information. In fact, I had to search Linear Tech website to rediscover which chip I used.

Power inductors generally don't list a SRF. This is usually done only for inductors used at RF. I quickly searched for an example, and came up with this:

http://specfinder.delevan.com/pdf/sds130.pdf

The part is only an example. Note that the test frequencies for the data are in the range you will be switching at. I don't know if the value or current capability are suitable for the LT part - I took a guess to get a part in the ballpark.

 

[pucca]

Thanks comco!