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ADS1278 Input Driver Bandwidth

Other Parts Discussed in Thread: ADS1278, THS4531A, THS4521

Hello,

   I'm using the ADS1278, and I'm wondering if I can get away with using the THS4531A instead of the THS4521 because of it's lower bias current.  I intend on using a 40kHz data rate in low power mode for the ADC, the THS4531A has a lower bandwidth (36MHz vs 145 MHz); I wonder if it's good enough?

  • Michael -

    You are probably safe using the 4531A, however the ultimate validation of "good enough" lie with your design/system specs.

    The goal of the higher bandwidth is to make sure the sample and hold capacitor of the data converted is charged and settled within the acquisition time of the device.  For Delta Sigma ADC, tsample= 1/2 * fMOD. At the settings you indicated above, fMOD should be 2.56MHz, which should be adequate margin with a 36MHz op-amp.  Make sure to include the parallel capacitor mentioned in the datasheet pg 37 or Figure 88.  You may also need to consider adding resistors in series with the op-amp outputs for stability purposes.  (Similar to EVM schematic shown in user guide).