AFE4490: Negative values being read from ADC register

bijoyp17

Part Number: AFE4490

I'm using AFE4490 in a custom board to generate a PPG signal as in the pulse ox application. I'm reading negative values from the ADC register (see snippet below). We have a photodiode connected to the RXP & RXN pins. Plotting the values does show a PPG signal. So there's a valid signal but not clear why there would be negative values.

e1607b

e15ff5

e15dc4

e15e02

e15bc8

e15c20

e159c3

e153db

e15388

e15359

e1535b

e1521c

e13a6b

e13b03

e13851

e1378d

e134a4

e133dc

over 7 years ago

0 Prabin Yadav over 7 years ago

TI__Genius 12575 points

Hi Bijoy,

Can you please share the connection of PD to AFE4490?
Also which PD are you using?

Regards,
Prabin

0 bijoyp17 over 7 years ago in reply to Prabin Yadav

Prodigy 50 points

Hi Prabin,

I'm using MTPD1346D-100, a PD in the the 800nm to 1700nm range. The wavelength I'm using is 940nm in this case.

The Anode (pin 3) is connected to RXP and Cathode (pin 2) is connected to RXN.

Please let me know if you need more information.

Thanks,

Bijoy

0 bijoyp17 over 7 years ago in reply to bijoyp17

Prodigy 50 points

Correction. In the previous message, please read RXP and RXN as INP & INP on the AFE device. See the section of schematic for the connectivity.

0 bijoyp17 over 7 years ago in reply to bijoyp17

Prodigy 50 points

Turns out to be a pilot error. PD was reverse connected. Realized that while responding here and once fixed, it works fine now. Sorry for the trouble.

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AFE4490: Negative values being read from ADC register