• Hi,
    I'd like to use the mosfet of the pico to control power of a GPS (60 mA at 3.3V, 5V tolerant, own ldo regulator integrated).
    So, I got confused somehow from the documentation...
    That is, after bridging the jumper B0/Fet, I should use the example provided here we have

    digitalWrite(B0,1); // Partially turn on the 'Bat' output (this produces 3.3v on the FET, meaning it has just 1.4v between Gate and Drain)
    digitalRead(B0); // turn off the output (also check if USB powered)
    

    a-Does that mean that I will get a 3.3V on VBAT?
    b-What would be the max amperage in this case?
    c-Would the mosfet get hot?
    d-On this Pinout, which pin should I use to connect a load that will be powered through B0 controlled mosfet : VBAT, BAT_IN?

    As a separate problem, I need to connect the GPS on a UART AND an I2C (addtionnal sensor here).
    e-What would the best pins to use: B6 & B7 for UART, which ones for I2C?

    Thank's a lot.

  • Here is the datasheet http://www.onsemi.com/pub/Collateral/FDN­358P-D.PDF , where it says in the Absolute Maximum Ratings that you can draw continuously about ***1.5[A] ***... but this is not the only information to be considered. Since the board (safe) design supports a 500[mA] LDO Voltage Regulator, you are with 500[mA] on the safe - cool(er) - side. You may go higher... but the specs do not say a thing about voltages lower than 4.5[V] 200[mOhm]. With raising on-Resistance more heat has to be dissipated...

    For running a GPS - 60[mA], you are more then fine...

  • I hope so!
    Thanks!
    Still need to,make sure I wont't have random failures: Data sheets don't always give the needed figures or very undirecly:)!

  • Espruino has a lot doc now... the hard part is to find it right away. This may be of interest to you: http://www.espruino.com/Pico+FET+Output

    1.5[A] continuously and 5[A] pulsed is a nice number... you now just need the Battery to support deliver it!

  • Hi,
    Thank's but I am looking for what happens at partially turned on, not fully on... :)
    That said, you are right, almost everything is written but finding it can be more difficult. Gordon is doing a very important job to document and structure this knowledge. However it is a huge task!

  • Hi,

    I'll answer below, but I think the real answer is:

    The FET is connected to the VCC/VBAT voltage rail, and you can't use it like a voltage regulator - so unless the GPS has its own voltage regulator, using the FET won't be a viable option for you. You'd be better off adding your own to the 3.3v rail.

    a-Does that mean that I will get a 3.3V on VBAT?

    No, with nothing connected you'll get VCC/VBAT's voltage on BAT_IN.

    b-What would be the max amperage in this case?

    It totally depends - basically it turns the FET into a resistor. With that little drive voltage the datasheet doesn't specify the resistance, but it should be a few Ohms.

    c-Would the mosfet get hot?

    If you short BAT_IN to GND then yes, it's possible. It's the same as a resistor in this case.

    d-On this Pinout, which pin should I use to connect a load that will be powered through B0 controlled mosfet : VBAT, BAT_IN?

    BAT_IN

    e-What would the best pins to use: B6 & B7 for UART, which ones for I2C?

    I don't think it really matters? It depends if you need any of the other peripherals handy.

  • Hi,
    Thanks again: the gps has its own voltage regulator so I am just using it as is with the mosfet switching it on & off from time to time.
    I expect to use a cheap non protected battery design to recharge a smartphone with a usb connector on its output and a micro usb for recharging it from main. This won't happen while the pico is inserted in the battery.

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Pico's Mosfet maximum Amperage when partial ly turned on?

Posted by Avatar for asez73 @asez73

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