NDP 6020P P-Channel Mosfet Oddness

[TomWS]

Another idea.

Power directly from a pin?  With battery backup the acquisition phase should be a few seconds at most @28mA and then drop to 20mA tracking.

I plan to add an active antenna.

I didn't check what the low power options were on this device, so I couldn't comment if you were using conventional batteries, but, if I recall correctly, you have marine SLA batteries being recharged by solar power, so, in this case, leaving the GPS on would be a nit...

Tom

[gregcope]

Correct on the battery.  Solar pannels have died and need replacing, so low consumption is still key.  The battery is left unattended for long periods.

[gregcope]

Antenna looks like it will consume 8ma;

http://php2.twinner.com.tw/files/onshine/ANT555-2006-NEW.pdf

I looked at the enable pin for the module, but this seems to only cut consumption to 400uA due to a 10k pull resistor on the board;

https://forums.adafruit.com/viewtopic.php?f=22&t=41452

[gregcope]

TomS looking at your idea, soldering the Mosfet Drain to the 3.3V line should be easy.

I see two places to do this; See picture with Red arrows.

Would appreciate a hint/nudge as this is me guessing on Eagle.

[TomWS]

TomS looking at your idea, soldering the Mosfet Drain to the 3.3V line should be easy.

I see two places to do this; See picture with Red arrows.

Would appreciate a hint/nudge as this is me guessing on Eagle.

LOL!  Just tie it to the 3.3V pin on the header...

[gregcope]

Yes LOL I worked that out too ...

Oddness mind.

From the mosfet Drain to GRD I get 3.29v

Mosfet drain to the 3.3V pin I get only get 1.1V again.

Measuring the GPS draw is 28mA when searching for a fix.

[gregcope]

Going a bit potty.

Made a breadboard version to rule out the Mosfet...

And it works (red LED).... GRH.

But only if I Mosfet Drain connected to 3.3V header as you suggest Tom.  Which does have the advantage of not using another regulator!

Conclusion - the mosfet on my veraboard, or the veraboard circuit is duff.

[gregcope]

And this version had the battery backup powered and works like a champ - 3 secs for a warm fix.

[perky]

Although a pin may be specified to drive 20mA,  this is to logic levels - you shouldn't generally use a pin to power anything that takes more than a few mA and also requires voltage close to Vcc, the MCU won't be able to supply it.
Mark.

[gregcope]

Thanks Perky.   Good to know.