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LMP91000EVM Standalone Sinking Current off Arduino Uno

Bradley Feest
Prodigy 40 points
Other Parts Discussed in Thread: LMP91000EVM, LMP91000

Hello all, this is my first time posting here, so I'm sorry if it's in the wrong location.

I"m setting up a LMP91000EVM to be controlled by an Arduino Uno (power, setup as well as providing VRef).  I've gotten everything to be setup correctly, but when I connect the output from my Arduino to the VRef pin, it drops by 2 volts.  I.e. If I measure the output from the Arduino without the VRef pin connected, I see 4 volts.  When I connect the VRef pin and measure again, I see around 2 volts.  I'm really unsure where this issue could be stemming from.  Looking at the current going into the VRef pin, it's only a few mA which, according to Arduino, should be able to be sourced/sunk by the Arduino pin without any problems.

I'm fairly certain the LMP91000 is functioning correctly because if I setup a 3v power supply and connect it, I get the correct outputs.  I've taken off both R6 and R7 in order to enable standalone operation, but otherwise the board is normal.

Let me know if there's any information I've left out!

Thanks for any help,

Bradley

  • 0
    TI__Genius 9655 points

    Hi Bradley,

    can you provide me with more details on the voltage supplies applied to the EVM ?

    Are you going to use the ADC present on the EVM or the ADC of the microcontroller ?

    regards,

    Domenico

  • 0 in reply to domenyko
    Prodigy 40 points

    Domenico,

    The Arduino outputs a PWM signal that I'm putting through a RC low pass filter to get the steady value.  Eventually it will put out a range of voltages, but until I get the EVM working correctly I'm just having it output 3V.  I've tried changing the capacitor/resistor values to see if my LPF was causing the issue but nothing changed.

    As of now I'm using the ADC on the microcontroller, not sure if I'll need to use the one on the EVM at any point.

    Let me know if you need any other information! Any suggestions are appreciated!

  • 0 in reply to Bradley Feest
    TI__Genius 9655 points

    Hi Bradley,

    I've done some test in the lab and the only way to sink a lot of currents from VREF  (>5mA) is forcing a voltage at VREF connector > VDD voltage. This condition goes again the Datasheet of the LMP91000.

    So make sure that the VREF voltage is always <=VDD voltage.

    regards,

    Domenico