AMC131M03 datasheet(23/98 Pages) TI

23 / 98 page

The input impedance of the PGA dominates the input impedance characteristics of the AMC131M03-Q1.

The PGA input impedance for gain settings up to 4 behaves according to Equation 4 without accounting for

device tolerance and change over temperature. Minimize the output impedance of the circuit that drives the

AMC131M03-Q1 inputs to obtain the best possible gain error, INL, and distortion performance.

275 kΩ × 4.096 MHz / fMOD

(4)

where:

• fMOD is the ΔΣ modulator frequency, fCLKIN / NDIV

By default, NDIV = 2. NDIV is set by the programmable clock divider, see the Clocking and Power Modes section.

The device uses an input precharge buffer for PGA gain settings of 8 and higher. The input impedance at these

gain settings is very high. Specifying the input bias current for these gain settings is therefore more useful.

8.3.7 Voltage Reference

The AMC131M03-Q1 uses an internally generated, low-drift, band-gap voltage to supply the reference for the

ADC. The reference has a nominal voltage of 1.2 V, allowing the differential input voltage to swing from –1.2 V to

1.2 V. The reference circuitry starts up very quickly to accommodate the fast start-up feature of this device. The

device waits until the reference circuitry is fully settled before generating conversion data.

8.3.8 Internal Test Signals

The AMC131M03-Q1 features an internal analog test signal that is useful for troubleshooting and diagnosis.

A positive or negative DC test signal can be applied to the channel inputs through the input multiplexer. The

multiplexer is controlled through the MUXn[1:0] bits in the CHn_CFG register. The test signals are created by

internally dividing the reference voltage. The same signal is shared by all channels.

The test signal is nominally 2 / 15 × VREF. The test signal automatically adjusts the voltage level with the gain

setting such that the ADC always measures a signal that is 2 / 15 × VDiff Max. For example, at a gain of 1, this

voltage equates to 160 mV. At a gain of 2, this voltage is 80 mV.

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AMC131M03-Q1

SBASAO3A – MAY 2023 – REVISED SEPTEMBER 2023

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AMC131M03 Datasheet(PDF) 23 Page - Texas Instruments