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ADS1278: Application problem

zhang ping
Genius 3865 points

Part Number: ADS1278
Other Parts Discussed in Thread: OPA2350, , THS4521

why do VCOM pins need to go through opa2350 when connecting ADS1278 and ths4521? If not, how should two VCOM pins be handled?

  • 0
    TI__Mastermind 49820 points

    Hello Zhang,

    The common mode output pin on ADS1278 (Vcom) is a resistor divider, and cannot drive a low impedance load (<1megOhm).  If the input amplifier operates from a different supply voltage than the ADS1278 AVDD supply, you will need the buffer to drive the amplifier's Vcom input.

    However, in the case of THS4521 operating from the same AVDD supply as the ADS1278, you do not need to connect Vcom from ADS1278 to Vocm input on THS4521.  You can simply connect a 0.1uF cap from Vocm to ground on the THS4521 and it will default to AVDD/2 common mode, which meets the input common mode requirements of the ADS1278.

    In the case of THS4521 operating from the same AVDD supply as ADS1278, you do NOT need an amplifier.

    Regards,
    Keith Nicholas
    Precision ADC Applications