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ADS1234 issue for DRDY pin : Getting two pulses just before data convertions

Harsh Goel
Prodigy 10 points
Other Parts Discussed in Thread: ADS1234

Helllo Sir/Madam,

We are using below ADC interfaces:

ADC = ADS1234         Channel 1 for loadcell [bipolar]     Channel 2 for pressure senosr[unipolar]

Gain : Both channels has same gain 128

Problem Statement : When we read Loadcell at channel 1 we get proper sequnce of DRDY ,SCLK, and Data then DRDY high at 25th  clock  and data read is proper. as per datasheet.But after switching the channel [2] for pressure sensor below sequence has been observerd:

Switch channel [1 to 2nd] -> add 50 microsecond delay  -> DRDY High for 50 msecond -> DRDY Low -> DRDY High for 20 msecond -> Data [with 24 clocks] + 25th clock + DRDY high.

So queries are

1. Is that whether above sequence is OK  ?If not then why DRDY pin is high for second time[20ms]

2. Can we use combination of bipolar and unipolar inputs on same ADC.

Harsh Goel

Bosch India

+91-9886001802

 

  • 0
    TI__Guru** 112895 points

    Hi Harsh,

    Welcome to the forum!  I'm a little confused by the timing values you have given.  Are you using an external clock or the internal clock?  If using an external clock, what is the clock frequency?  What SPEED pin setting are you using (high or low)?  Do you have any scope/logic analyzer shots of SCLK and DOUT/DRDY that you can send to me that shows this sequence?

    You can use combinations of both differential and unipolar inputs on the same device.  However there is a restriction when using unipolar inputs that are referred to AGND using gains of 64 or 128.  Page 3 of the datasheet indicates the common mode input range of the ADS1234.  You can measure all the way to the rails at a gain of 1 or 2, but the input must be greater than 1.5V above GND and less than 1.5V below AVDD for both the AINP and AINN inputs.

    Best regards,

    Bob B