JAJSRL2A October 2023 – December 2023 RES11A-Q1
ADVMIX
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The RES11A-Q1 can be used to implement a common-mode attenuator at the high-impedance inputs of an instrumentation amplifier (INA). This configuration extends the usable signal range, so long as the maximum differential voltage limitation of each resistor divider is respected.
Figure 8-6 shows an example of a high-side current-sense circuit where a differential voltage, VSHUNT, develops across a sense resistor with an undesirably high common-mode voltage VCM. VREF is used to shift input common-mode voltages VMID1 and VMID2 to levels within the specified input common-mode range of the INA. The amplifier output, VOUT, is a scaled function of VSHUNT, such that nominally:
VOUT can be gained up further by the INA stage, to make maximal use of the effective resolution of a downstream ADC. In practice REQUIV is optional; however, if REQUIV = RSHUNT, this resistance equalizes the nominal impedance between VCM and each of the INA high-impedance inputs, thus improving CMRR performance. Select an INA with input bias currents IB1 and IB2 << ISTATIC1 and ISTATIC2, such as the INA333 or INA823. Select a RES11A-Q1 device with a sufficiently high divider series resistance so that ISTATIC1 and ISTATIC2 << ILOAD.
To achieve a desired nominal input common-mode voltage, VMID1TARGET, set VREF as follows: