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ez430-rf2500 (MSP430x2xx)

CF
Intellectual 300 points


Hi,

I have an ez430-rf2500 board and I'm trying to use the ADC10 to read an analog voltage of 5V. I tried connecting 5V to to the VREF+ pin unfortunately if I do that it starts drawing current excessively. 

Could you please confirm this or would you be able to suggest how I may read 5V using the ADC on board?

Thanks,

Cris

  • 0
    Expert 2855 points

    Hi,

    The positive external reference voltage shouldn’t be bigger than VCC. You can confirm this information in device’s datasheet.  
    A possible solution will be to use a voltage divider to properly step down the analogue signal, followed by a voltage follower in order to reduce the impedance seen by the ADC sampling circuit.

    Best Regards,
    AES  


  • 0 in reply to Antonio Espirito-Santo
    Genius 4925 points

    A voltage follower will not only reduce the impedance seen by the ADC but also reduce the load on the divider circuit - which in some cases can be crucial (especially on high resistance divider networks).

    Just to explain why you see a rise in current consumption: the port pins of the MSP are equipped with ESD protection circuitry and contain clamping diodes (rated Vf=0.3V @2mA iirc)  to the supply rails, so any voltage higher than the supply rails (or lower than GND) will switch on the clamping diode and give rise to additional currents - this also happens if you have an unpowered MSP in your system and apply a voltage to a pin of it.

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