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ADS1298: Input Differential Dynamic Range

Colleen Leung
Prodigy 40 points
Part Number: ADS1298

I am uncertain as to how the 300mV value was achieved in the following equation

If VREF is 2.4V and 2*Vref / Gain = Full-Scale Range = 2*2.4V/6 = 4.8/6 = .800V. 

  • 0
    TI__Guru 59136 points
    Hello Colleen,

    Thank you for your post and welcome to our forum!

    The power consumption of the PGA stage scales with differential input voltage. The larger the differential voltage, the more current that is forced through the resistor string at the PGA output (see Figure 29). I would assume that statement implies that the quiescent current of the amplifiers in the PGA dominates the overall power consumption of the gain stage if the PGA output is kept to less than 1.8 V on a 3-V supply.

    What you are calculating instead is the maximum differential input voltage that is acceptable for a given reference voltage. When making that calculation, you do not need to multiply VREF by a factor of 2. The span of acceptable input voltages is from -VREF to +VREF (i.e. "2xVREF"), but the absolute differential voltage can never exceed VREF in magnitude. So for a 2.4-V reference and Gain = 6 V/V, the differential input voltage can range from -400 mV to +400 mV. +800 mV would exceed full-scale and result in a clipped output with a code of 7FFFFFh.

    Best regards,