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Tips and questions relating to the GPS modules from SFE
By BigRedBee
#39557
I'm currently running a Lassen IQ at 3.3V regulated down from a single LiPoly cell (4.2V max). I'm looking into using EM406 -- it's almost the same size, but spec says it requires 4.5 - 6.5 volts DC input.

Any idea if I can run it lower? I would assume that this module has an on-board power regulator that's creating 3.3V onboard -- does anyone know if 3.5 volts or so will work? I'd hate to have to bump up my Voltage just to have it regulated back down.


Thanks, Greg
By winston1
#40861
I'm running it off 3.3v derived by 2 AA NiMH batteries running through a Max756 booster and don't seem to be having any issue from it. I'm still debugging my target usage for the module so I think its only run 30 or so hours at this voltage, but I would figure that any problems would have shown up by now if they existed.
By seulater
#40926
i too have ran mine at 3.3v with no noticable problems.
but now i am using a TPS63002 to kick the voltage from 1 cell up to the 5v
User avatar
By ohararp
#40972
Both the EM406 and EB-85A run just fine off 3.3V. If you are using li-ion you will get a much longer runtime out of the device if you run at 3.3V since the regulator will not have to work as hard and is probably more efficient at 3.3V.
By BigRedBee
#41203
OK -- thanks for all the responses -- I've got mine up and running with a 3.3V input.

Now I have another question -- How are the transmit paramters stored on the chip? Ie, if I reconfigure which NMEA sentences are sent, is the config stored in non-volatile memory? Or in some battery backed ram? If it's ram, I assume that there is a "supercap" of sorts that's keeping he memory alive -- how long will that charge last before the configuration is lost?

-- Greg
By busonerd
#41209
Just as a note - not all EM406A modules work down to 3.3V - I would suggest boosting to 5V.

Cheers,

--David Carne
User avatar
By ohararp
#41273
David, I have shipped about 150 units using them at 3.3V. No problems so far with power. I am curious as to some of the problems you experienced running at 3.3V. Do you mind expanding on this?
By saipan59
#41620
David, I have shipped about 150 units using them at 3.3V. No problems so far with power. I am curious as to some of the problems you experienced running at 3.3V. Do you mind expanding on this?
The datasheet clearly says it's a 5V device. Running it on 3.3V will almost certainly affect something. The maker would certainly tell us in the datasheet if they believed it worked just as well on 3.3. So, even if it "works" in your product with 3.3V, I would expect some parameters to be degraded. Given that the 'logic' obviously works in your product, one guess is that the RF performance is reduced (sensitivity, etc.).

Pete
User avatar
By ohararp
#41630
Saipan...I am willing to bet they are using a LDO regulator for the RF power side of things. The sirf runs off 1.8V and is most certainly regulated down. Using the LDO and supplying 3.3V - worst case say .3V drop that leaves 3.0V to work with and is within normal tolerances of 3.3V parts in most cases.

I am usually reporting reception of 8-11 satellites and have some really good accuracy with a load of data to back it up. In this case, I feel pretty good about the design scheme I am implementing.

Running at 5.0V just killed the efficiency on the buck-boost regulator I was using.
By saipan59
#41631
Still, there has to be a reason for the spec being what it is... Nobody de-rates their parts "just for fun".
Another idea: maybe it's temperature. At 3.3V, it may only work in a narrower temperature range.

Pete
By busonerd
#41650
Just as a note, when I was at SparkFun, we found some modules would not behave properly when run @ 3.3V external instead 5V external, for example, not coming out of reset, not achieving lock, etc. Most modules would work fine, but some just wouldn't.

Cheers,

--David Carne
By BigRedBee
#44587
BUMP: Anyone care to comment on the memory backup?
BigRedBee wrote: Now I have another question -- How are the transmit paramters stored on the chip? Ie, if I reconfigure which NMEA sentences are sent, is the config stored in non-volatile memory? Or in some battery backed ram? If it's ram, I assume that there is a "supercap" of sorts that's keeping he memory alive -- how long will that charge last before the configuration is lost?
-- Greg
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