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ADS7924: Problem with only 1 channel working

Mitchell
Expert 4915 points
Part Number: ADS7924

Hi Team,

My customer is having an issue with the ADS7924 in that only CH0 reading is matching the real measurement.

The following were the I2C communications between the host PC to the ADS7924, used Manual-single mode.

Host PC reads:

vN13v0_code = 0x555

vN13v0 = 1.67 V.

iN13v0_code = 0x34A

iN13v0 = 1.03 V.

vP6v0_code = 0x505

vP6v0 = 1.57 V.

iP6v0_code = 0x23C

iP6v0 = 0.70 V.

However, the real measurement to the pins:

Pin 12 = CH0: 1.67V

Pin 11 = CH1: 1.61V

Pin10 = CH2: 3.0V

Pin 9 = CH3: 0.223V

Schematic:

Thanks,
Mitchell

  • 0
    TI__Mastermind 22950 points

    Hi Mitchell,

    Taking a quick look at the I2C transactions... they look good to me and I don't see anything immediately wrong with them. The schematic looks good as well but it would be nice to see exactly what is connected to the inputs. Are you able to specify? I wonder if there might be a settling issue caused by the RC pair at between the MUX output and ADC input. Can the customer try replacing R248 with a 0ohm resistor and removing C670?

    Besides this, I would also like to see if manual scan mode works. Based on the I2C transactions, manual single mode is selected. Manual scan will convert all the inputs at once where manual single mode only converts the selected channel. 

    Regards,
    Aaron Estrada