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How to verify the ADC value is currect or not?(ADPD105/108)

as title ,
Just like g-sensor will define a tolerance to verify the chip.
if I set LED1 current is 30 mA,
How to verify the ADC value I get is correct ?(in darkroom or other situation)

  • Hello,

    The resolution of the ADC, in nA/LSB, is specified in the spec table. If you can drive a known current source into the input of the device then you can verify that the ADC has the correct output. If you are unsure of what your input current is then you wouldn't be able to verify this. There is no reason to believe that the output of the ADC would be incorrect. Each of the devices is fully tested at ADI. 



  • Hi 

    Following is my config for ADPD105 

    according to datasheet ,
    I should get a ADC output like this

    14.9 (mA)* 10^6(Convert to nA) * 3.27(ADC Resolution) / 1 (number of pulses) = ideally ADC output value

    is that currect?

  • Hello,

    At 25k TIA gain the ADC resolution is 3.27nA/LSB. THis is based on how much current is being seen at the input to the device. You wouldn't use the LED current in that calculation except in the context of what the CTR (Current Transfer Ratio) of your system is. THe CTR is the amount of PD current generated in nA for every mA of LED current supplied. So you need to know what your CTR is so that you know how much input current the device will see when you drive 14.9mA of LED current. The correct equation then would be:

    ADC_OUT = ((14.9mA) * CTR (nA/mA))/3.27nA/LSB on a per pulse basis.

    Also, your confiuration shows 50k gain in timeslot B, so the conversion factor for that timeslot would be 1.64nA/LSB

    Also, you need to take into account that the ADC output is at ~8192 codes per pulse unless you null that out using the ADC offset registers (0x18/19/1A/1B/1E/1F/20/21). The equation above would be the number of codes added to whatever is present at the output of the ADC when there is no input current.