New GPS Module
wass
Posts: 151
I see that Parallax finally has the new PAM-7Q GPS module available:
http://www.parallax.com/product/28509
Kudos for being the first place anywhere I've seen that has that available for purchase!
The specs on this GPS look fantastic in terms of accuracy, power consumption and features. I especially like the settable GPS-locked time pulse output.
Looking at the schematic for the module, I have a question about whether it's possible to power the PAM-7Q at 3 volts without hacking up the PCB. The GPS chip itself can run at 2.7 volts to 3.6 volts, Parallax has chosen to run it at 3.3 volts, but could I run this module at 3 volts VDD (or 2.7 volts) and have it work?
Thanks,
Katie
http://www.parallax.com/product/28509
Kudos for being the first place anywhere I've seen that has that available for purchase!
The specs on this GPS look fantastic in terms of accuracy, power consumption and features. I especially like the settable GPS-locked time pulse output.
Looking at the schematic for the module, I have a question about whether it's possible to power the PAM-7Q at 3 volts without hacking up the PCB. The GPS chip itself can run at 2.7 volts to 3.6 volts, Parallax has chosen to run it at 3.3 volts, but could I run this module at 3 volts VDD (or 2.7 volts) and have it work?
Thanks,
Katie
Comments
http://www.ti.com/lit/ds/symlink/lp2992.pdf
Parallax is cheating a little bit with their names on the schematic: if the input voltage is 3.3v, then the bus labeled 3.3v will be about 3.2v, assuming 50mA operating current. That 100mV drop is taken from the regulator datasheet page 8.
The 100mV dropout is roughly constant for 50mA at temperatures below 50C. Assuming that the dropout holds when the input is below the regulation target (3.3v), you should be fine down to your target of 3v. You might be able to go as low as 2.8v, but that's getting close to the limit.
The other chips should be fine as well: the two M74VHC1GT50DFT2G go down to 1.65v.
And yep: I like the u-blox modules. They seem to have the best combination of features among the big 3 (Mediatek, SiRF, and u-blox).
Katie, yes, you should be fine running the module at 3 volts, but I wouldn't go much lower due to the drop-out of the regulator. SRLM described the reason more concisely than I could have (thank you!). Also keep in mind that the TXD and T_P signals are going to have a high voltage of whatever voltage you supply the module. If you do supply 3.0 volts, then a logic "high" on these pins will be about 3.0 volts. Logic "low" will be pulled to the module's GND reference. Just make sure that your receiving device (probably a microcontroller) can correctly interpret the 3.0 volt high as a logic high.