MAX11410 Datasheet, PDF (22/95 Pages) Maxim Integrated Products – 24-Bit Multi-Channel Low-Power

MAX11410
24-Bit Multi-Channel Low-Power
1.9ksps Delta-Sigma ADC with PGA
Input current in PGA mode is much lower than in the
Buffered or Direct modes, so the PGA mode is a good
choice for maintaining precision when source resistances
are high. Note that the input current in PGA mode is
dominated by multiplexer leakage current, and is highest
when the input voltage, including that of unused inputs,
is nearest AVDD or GND. For applications that are most
sensitive to the effects of input current, connect any
unused inputs to a voltage near AV_DD/2.
Note that the maximum usable gain will be limited by
the reference voltage and input voltage. Ensure that the
differential input voltage multiplied by the PGA gain is less
than or equal to the reference voltage:
V_IN x GAIN ≤ V_REF
Where
V_IN = differential input voltage
GAIN = PGA gain
V_REF = reference voltage
Also ensure that the input common-mode voltage (V_CM)
falls within the acceptable common-mode voltage range
of the PGA:
200mV + (V_IN x GAIN)/2 ≤ V_CM ≤ A_VDD – 200mV -
(V_IN x GAIN)/2 for gains of 32 to 128 or
100mV + (V_IN x GAIN)/2 ≤ V_CM ≤ A_VDD - 100mV -
(V_IN x GAIN)/2 for gains of 1 to 16
Where
V_CM = (AIN_P- AIN_N)/2
Digital Gain
Programmable digital gain settings of 2 and 4 are available
in the Direct and Buffered modes. Select the desired
gain using the Gain bits of the PGA register. Digital gain
selections greater than or equal to 4 will result in digital
gain equal to 4. The input range is 0V to V_REF/GAIN for
unipolar conversions or ±V_REF/GAIN for bipolar conversions.
The modulator produces 32 bits of data, and for unity
gain, the 8 LSBs are truncated before the data is stored
in the 24-bit conversion data registers. Selecting a digital
gain of 2 causes the MSB and the 7 LSBs to be discarded,
thus producing 24 bits of data with an effective “gain” of 2.
Note that, for any data rate, the noise floor remains
constant, independent of the digital gain setting. Digital
gain is useful for systems whose input noise is dominated
by the source, or systems that can take advantage of
averaging multiple readings to improve effective
resolution. For cases when the output noise is below an
LSB, using digital gain can decrease the input-referred
noise at the expense of reduced dynamic range.
Figure 1. Digital Programmable Gain Example.
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