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ADS1220: START/SYNC to many ads1220

user4261913
Prodigy 180 points
Part Number: ADS1220
Other Parts Discussed in Thread: ADS1246, , ADS124S06, SN74LVC1G02, SN74LVC1G125

I have build a test board with two ADS1246 to sample two bridge sensors (in a ratiometric way) simoultaneously at a sampling rate of about 1kHz. The start of conversion is controlled using the START pin which are both connected to a PWM with 1kHZ frequency.
I would use the ADS1220 but it has no START pin. Can I send the START/SYNC (0000 100x) command helding both CS pin low at the same time?

  • 0
    TI__Guru** 113765 points
    Hi user4261913,

    The ADS1246 is now well suited for ratiometric bridge measurements as the AVDD supply voltage cannot be used as a reference voltage. The maximum reference voltage that can be used with the ADS1246 is (AVDD-AVSS) - 1V. The ADS1220 and the ADS124S06 do not have this restriction.

    You are correct in that the ADS1220 does not have a START pin to be used to start conversions. Instead the START/SYNC command is used. If you want to communicate to 2 separate ADS1220 devices at the same time to start them together should not be an issue. I would suggest that you use an external clock source to drive both devices so that they will have the same clocking characteristics. The internal oscillator can vary from part to part.

    You will also need to prevent contention from the device output (DOUT/DRDY). When CS goes low on each device, the DOUT/DRDY will be driven and will most likely be at different logic levels. There are a variety of ways to do this. One method would be to use a gated buffer (SN74LVC1G125). The buffer would be gated by the output of a NOR gate (SN74LVC1G02) where the input is connected to each of the device's CS. When both CS goes low, the output of the NOR gate would go high disabling both DOUT/DRDY connections. Individual CS would work as normal.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 180 points
    Thanks, if I understand correct I have to use two gated buffer, one for the DOUT pin of each ADS1220?
  • 0 in reply to user4261913
    TI__Guru** 113765 points
    Hi user4261913,

    Yes, that is correct. When you attempt to send the START/SYNC command to both ADS1220 devices at the same time you must make sure the DOUT are not actively driving at the same time. One way to accomplish this is by using two gated buffers.

    Best regards,
    Bob B