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Ultimate GPS - MOSFET & Pro Trinket 3V
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Ultimate GPS - MOSFET & Pro Trinket 3V

by adam_g on Sat May 12, 2018 4:23 pm

Hi guys,

I have a quick question about controlling power to the the Ultimate GPS Breakout using an N-channel MOSFET.

In the past, I've used the FQP30N06L N-channel logic-level MOSFET to turn power to the GPS on and off when I have the MOSFET's drain pin connected directly to my 4.2-5V battery. However, as I'm now looking to power my circuit from a 7.4-11.1V battery, I'm wondering if it would be possible to power the GPS from the 3V pin of my Pro Trinket 3V. The Ultimate GPS notes that it has a minimum operating voltage of 3.0 V and a current draw of ~25 mA and the Pro Trinket's regulator can output a maximum of 150 mA. I am able to connect the GPS directly to the Trinket's 3V/GND pins and have the GPS work without any issues. However, when I add the MOSFET and connect the circuit as shown below, I end up with my Pro Trinket stuck in a reboot loop as soon as I turn the MOSFET on. I have on hand two different N-channel MOSFETS: the FQP30N06L and the TN0702 and the issue occurs with both components.

I have a feeling this problem is likely due to my lack of knowledge of MOSFETs, and that I'm probably missing something rather obvious that would prevent the circuit from working as such. I'd appreciate if you have any suggestions on what I might be doing wrong!

Cheers,
Adam
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adam_g
 
Posts: 19
Joined: Sat Feb 18, 2017 11:41 pm

Re: Ultimate GPS - MOSFET & Pro Trinket 3V

by adam_g on Tue May 15, 2018 1:15 pm

Hi there,

Just a quick update. From researching this issue further, it appears that the reset loop problem may be due to the voltage drop experienced by the Pro Trinket when the MOSFET is enabled and power is supplied to the Ultimate GPS. It sounds like the voltage drop may be triggering the ATmega328's brown-out detection and reseting the microcontroller.

The strange thing is, when I replace the Pro Trinket 3V with SparkFun's Pro Mini 3.3V, the circuit operates normally and power is supplied to the GPS as expected. Could this perhaps be explained by the differences between the Pro Trinket's MIC5225 and the Pro Mini's MIC5205 regulator? It looks like the Trinket's 5225 has on average about twice the dropout voltage than that of the Pro Mini's 5205, though I'm unsure if this would be the cause of the problem.

Given that I'd like to continue using the Pro Trinket, I'm wondering how to best tackle this issue. Possible solutions I've seen involve slowing the power on/off cycles of the GPS, adding a capacitor to buffer the spike and/or using a high-side P-MOSFET.

Cheers,
Adam

adam_g
 
Posts: 19
Joined: Sat Feb 18, 2017 11:41 pm

Please be positive and constructive with your questions and comments.