ADC161S626: ADC161S626: adc output calculation with the negative input connected to GND

Jenny Cao

Part Number: ADC161S626

Hi,

I have a circuit like below:

The input range is 1 to 3V, I intended to use single-ended. Since I have only a positive signal, I connected the -IN pin to GND.

But when I tested I found that I have to do "4 * " to get the reading to match the input:

For example: if I have 1V at input:

I got adcRawValue = 0x0a5f, voltage = adcRawValue * 3V / 2^15 = 0.243079931

But if I do voltage = 4 * adcRawValue * 3V / 2^15 = 4* 0.243079931 =0.972319722

Could you please let me know if I have anything wrong with the circuit? Must the IC have a common-mode voltage at the input?

Thanks and regards,

Jenny

over 3 years ago

0 Keith Nicholas over 3 years ago

TI__Mastermind 39450 points

Hello Jenny,

Your circuit looks correct, with proper supply voltages. You can connect -IN to ground, and then you will get positive only readings from 0x0000 to 0x7FFF, or 2^15 total codes.

Please keep in mind that to read all 16b, you will need 18 SCLK's. After /CS is taken low, the first falling edge of SCLK will keep DOUT in HI-Z state, the second SCLK falling edge will force DOUT to 0, and the next 16 SCLK falling edges will clock the 16b result.

If you are just sending 16 SCLK's, then the first 2 bits are probably reading 0, which the result would appear as divide by 4. Please check your communications and verify that you are sending 18 SCLK's to retrieve the data.

Regards,
Keith Nicholas
Precision ADC Applications

0 Jenny Cao1 over 3 years ago in reply to Keith Nicholas

Prodigy 110 points

Thank you Keith.

Works now.

Jenny

0 Keith Nicholas over 3 years ago in reply to Jenny Cao1

TI__Mastermind 39450 points

Happy to hear it is now working.

Regards,
Keith

0 Jenny Cao1 over 3 years ago in reply to Keith Nicholas

Prodigy 110 points

Hi Keith,

Somehow, when I click on “This resolved my issue”

I got “You do not have permissions to perform the requested action.”

Regards,

Jenny Cao

0 Keith Nicholas over 3 years ago in reply to Jenny Cao1

TI__Mastermind 39450 points

Hi Jenny,

The TI E2E has been going through some recent upgrades. This appears to be a bug.

Thanks for letting me know.

Regards,

Keith

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ADC161S626: ADC161S626: adc output calculation with the negative input connected to GND