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REF3212: How to generate a non-standard high accuarncy refence voltage

Part Number: REF3212
Other Parts Discussed in Thread: LMT70, REF3430, CC2640, OPA376, REF3318, OPA192

Hi Guys,

 I'm now working on a   project measuring skin temperature .The sensor is LMT70 from TI.  Base on human-body temperature(35℃~40℃) , the output voltage of LMT70 is about 0.8V-0.9V.

Through lots of experiment data, we found the ADC in controller  has a small but fixed deviation,  this deviation cause about 1℃ gap( unbearable :( ) between a actual temperature measured by

a much more precise thermometer .   

So I need 2  reference voltage points   to calibrate my controller's ADC.  According to the application, I hope the voltage calibtared point is as close to 0.9V as possible. Hope helps from you.

Thanks .

B.R

Seafesse

  • Hi Seafesse,

    To get a non-standard voltage it will be necessary to use either one of two options:
    1. adjustable shunt voltage reference. Very common but also not as precise as a series voltage reference. Adjustable voltage options are 1.24v and above.
    2. Shunt/Series voltage reference -> voltage divider -> buffer. The voltage divider needs to be very accurate. The buffer needs to have a very small input current and small offset. This option allows for any voltage to be created because of the divider. This is the only way to go below 1V. This is very common in level shifting applications.
     
    I would choose a voltage reference with the low temp co like the REF3430 family and divide that down. It is also important to know your ADC error. Which ADC are you using?

    -Marcoo

  • Marcoo Z said:
    It is also important to know your ADC error. Which ADC are you using?

    Hi Marcoo,

    The ADC is ADC12 embedded in CC2640.

  • Hi SeaFesse,

    If you need exactly 0.9V then I would use a REF3318 (1.8V VREF) and voltage divide by 1/2 and then use a buffer to ensure that there is minimal IR loss. the same technique can be used for a 0.8V device. The buffer requirements are very low. I usually use OPA376 or OPA192.

    -Marcoo