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syncing 2 ADS1234's

DanR
Prodigy 240 points
Other Parts Discussed in Thread: ADS1234

We are using 2 ADS1234 ADCs in our circuit.  If we use an external clock source to drive both ADCs, will they convert at the same time and remain in sync?  If they would remain in sync, we could watch for completion of one conversion (DRDY low) and then clock both conversions out at the same time from both ADCs.  Is there any way to get two ADCs in sync?  Can I power up an external oscillator first then power up both ADCs later?

Can I power them up (using an external oscillator) and then force them into conversion by clocking out 25 bits?  Or can I put both ADCs in STANDBY mode and wake them up together with the SCLK?  Would this synchronize them and would they stay in sync?

  • 0
    Prodigy 240 points

    Hi, my customer has adjusted his question below...

    Actually a better question with the use of our 2 ADCs is this:

    Using the internal clock, if we place the ADC in standby or power down mode, will the 2 ADCs be in sync at least for the first few conversions?  Also how much time can elapse between the 2 converters for a conversion?  In other words, if I watch DT1 for a low signifying data ready, how much time before the other converter completes its cycle?   This assumes that DT1 completes first.  However, if I interrupt on DT1 going low then check the status of DT2 (if low yet), it might be faster or slower than DT1 to complete its conversion and give valid data.  What is that time variance? 

  • 0 in reply to DanR
    TI__Guru** 113765 points

    Hi Dan,

    There was not a specific method for SYNCing this part family.  There are no registers and no commands.  Everything is controlled by hardware.  The best way to keep the devices in SYNC would be to use the same clock and toggle the POWERDOWN pins of both devices at the same time.

    Using the internal clock, the internal oscillator will vary so that the data rate can vary by the numbers shown in the Electrical Characteristics table.  Oscillator startup will vary as well, so again it would be best to use the POWERDOWN pin after startup.  There is no way to completely be sure of one finishing before the other, but at 10sps, there is 100ms to retrieve the data, so it should be doable to some degree.

    Best regards,

    Bob B