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ADS1282 doesn't deliver data samples

Fedesor
Prodigy 80 points
Other Parts Discussed in Thread: MSP430F5438, ADS1282

We are developing a data logger board with an ADS1282 converter being controlled by a MSP430F5438 uC.

The analog circuitry is the exactly the same as the one shown on the ADS1282 datasheet for a geophone interface.

The converter seems to be working fine but we cant retrieve any data

Please give us a hint on what to try!

 

The voltage measured on the converter are:

V bypass =  1.8V

V Dvdd   =  3.3V

V Avdd   =  2.5V

V Avss   = -2.5V

Vrefp   =  2.5V

Vrefn   = -2.5V

The clock input is at a 4.096MHz

There is No power supply sequencing, as this should not be a problem according to the datasheet.

After Power on, the converter start in the Read Data Continuos mode and asserts the DRDY pin periodically indicating the presence of new data.

The MSP set the M0, M1 and MCLK pins to gnd, and the SYNC, PWDN and RESET to vdd on start. Then issues a reset pulse (with correct duration) and waits for 100ms.

After this we have tried all sort of things to get the conversion data out of the converter, including sync pulses, RESET commands, SPI reset, different Mux connections, but the data present at DOUT 

after DRDY is asserted is always 0x7FFFFFFF (with Sync and Fir filter on).

By the way the mux is ok, connecting the 2 channels together allow an input voltage on one channel to ouptut trough the other channel.

We have no idea of what is going on, the converter chip is mounted in several boards with the same problem. It has been changed several times.

The spi communications works fine, as the internal registers can be written and read without problems.

 

  • 0
    TI__Guru* 97775 points


    If you're able to communicate with the part by reading and writing to the registers, you're probably pretty close to getting it together.

    First, make sure that you are able to read back the registers correctly. Once the part is powered up, make sure all the register values match the default (reset) values. You can find that on page 36 of the datasheet (the third column of table 21).

    Then I would put the ADS1282 into the most basic configuration. Set the gain to 1. Set the inputs to the full scale and perform a gain calibration. Short the inputs together and perform a offset calibration. You can find the method of calibration in the ADS1282 datasheet on pages 31 and 32.

    Then read back the offset calibration register, and the full scale calibration registers to see that the values make sense. OCR typ = 000000h and FSC typ = 400000h (approx.)

    Then I would make sure the input pin voltages are where you expect them by measuring the input pins directly on the part. I would also do the same for the reference voltage. Make sure that the reference input pins aren't connected backward. 

    It almost sound like the inputs are floating off or you are overranged in a high gain. Regardless, post again if you continue to have problems.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 80 points

    Following your suggestion we start measuring the input  pin voltages directly and we found that the capp pin was shorted to the +2.5V supply. Bad choice not to paid for electrical verification of the PCB. Turns out that all the PCB manufactured had the same error, so hands to rework!.

    On the good nows, we were greatly surprised by the fact that the PGA survived this sort of mistreatment, so there were no need of replacement.

     

    Thanks for your support!