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Low Power Mode leakage current ?

Fredoo.net
Intellectual 730 points

Hello,

In my project I want to go Low-Power therefore I am using a P-MOS to switch off the VCC of my GPS.

This is the datasheet of my P-MOS : http://www.mouser.com/ds/2/115/ds31447-44532.pdf

So everything goes well and works fine but I noticed that when turn my Output (GPS_STBY) High to turn the device off the VCC Pin of the GPS is still at somewhere like 2.6V

Therefore an unnecessary 5mA are hanging out there ... :@

I thought of having a pull-down resistor on VCC but I did not find anything suggesting it and my trials did not show any improvement with it...

I need to be in High-Side switch mode due to the GPS Module so I cannot switch the GND... 

According to the PMOS datasheet the current would be less than 1uA .. so thats good enough if I get the output to 0

Another question, is it more efficient to use an internal pull-up resistor than to set the output of my MCU ?

  • 0
    Guru 25210 points

    You have the drain and source pins of your PMOS wired backwards. The leakage is through the intrinsic body diode of the FET.

    Connect the source to 3.3V, the drain to Vcc, and then the gate should be high for "off", low for "on".

    Question 2.... The FET gate current is extremely low. It probably doesn't matter either way that much.

  • 0 in reply to Brian Boorman
    Intellectual 730 points

    Brian Boorman said:
    You have the drain and source pins of your PMOS wired backwards

    Oh my gosh ... Such a stupid mistake... 

    Thanks so much for taking a fresh look at my design ... I never even thought the mistake would lie there .... 

  • 0 in reply to Fredoo.net
    Intellectual 730 points

    Now I have another question.. 

    After much testing I ended up prototyping with a through hole component :

    ZVP4424A which is a p-channel Mosfet as well and works fine for the job.

    But when I try to replace it with a SMD component then...well it doesn't work anymore.

    I compared both datasheets but I cannot find much difference.

    What should I be looking for in a PMOS to be sure it would work ?

    Should I be using a driver or something ?

  • 0 in reply to Fredoo.net
    Guru 46710 points

    Maybe you just messed-up with smd part pinout?

    To be honest - your choice of mosfet is wrong. High voltage (240 volts!) mosfets have high on-resistance value (yours have 8.8 ohms!!!) which can be source of your problems too. Pick 12V part having low GS treshold voltage.

  • 0 in reply to Ilmars
    Intellectual 730 points

    Ilmars said:
    To be honest - your choice of mosfet is wrong.

    Yes I know the component was not adapted.. I just picked one I had lying arround...

    Ilmars said:
    Maybe you just messed-up with smd part pinout?

    As for the SMD part pinout I double checked and it is not the source of the problem.

    I picked another SMD part as you recommend with low Vgs Threshold and low DS ON resistance.

    DMP2100U

    http://www.diodes.com/products/catalog/detail.php?item-id=9209

    Thanks for your help 

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