AMC7812 Datasheet, PDF (29/92 Pages) Texas Instruments – 12-Bit ANALOG MONITORING AND CONTROL SOLUTION with Multichannel ADC, DACs, and Temperature Sensors

AMC7812
www.ti.com
SBAS513D – JANUARY 2011 – REVISED OCTOBER 2012
THEORY OF OPERATION
ADC OVERVIEW
The AMC7812 has two analog-to-digital converters (ADCs): a primary ADC and a secondary ADC. The primary
ADC features a 16-channel multiplexer, an on-chip track-and-hold, and a successive approximation register
(SAR) ADC based on a capacitive digital-to-analog converter (DAC). This ADC runs at 500kSPS and converts
the analog channel inputs, CH0 to CH15. The analog input range for the device can be selected as 0V to V_REF or
0V to (2 · V_REF). The analog input can be configured for either single-ended or differential signals. The AMC7812
has an on-chip 2.5V reference that can be disabled when an external reference is preferred. If the internal ADC
reference is to be used elsewhere in the system, the output must first be buffered. The various monitored and
uncommitted input signals are multiplexed into the ADC. The secondary ADC is a part of the temperature
sensing function that converts the analog temperature signals.
ANALOG INPUTS
The AMC7812 has 16 uncommitted analog inputs; 12 of these inputs (CH4 to CH15) are single-ended. The
inputs for CH0 to CH3 can be configured as four single-ended inputs or two fully-differential channels, depending
on the setup of the ADC Channel Registers, ADC Channel Register 0 and ADC Channel Register 1. See the
Registers section for details. Figure 80 shows the equivalent input circuit of the AMC7812. The (peak) input
current through the analog inputs depends on the sample rate, input voltage, and source impedance. The current
into the AMC7812 charges the internal capacitor array during the sample period. After this capacitance has been
fully charged, there is no further input current. The source of the analog input voltage must be able to charge the
input capacitance to a 12-bit settling level within the acquisition time. When the converter goes into hold mode,
the input impedance is greater than 1GΩ.
AV_DD
CH0
AV_DD
50W
40W
40pF
CH3
AV_DD
50W
CH4
50W
AV_DD
Device in Hold Mode
50W
CH15
ADC-GND
50W
40W
40pF
Figure 80. Equivalent Input Circuit
Copyright © 2011–2012, Texas Instruments Incorporated
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