AMC7812B_15 Datasheet, PDF (29/92 Pages) Texas Instruments – 12-Bit Analog Monitoring and Control Solution with Multichannel ADC, DACs, and Temperature Sensors

AMC7812B
www.ti.com
SBAS625A – SEPTEMBER 2013 – REVISED SEPTEMBER 2013
THEORY OF OPERATION
ADC OVERVIEW
The AMC7812B 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 500 kSPS and converts
the analog channel inputs, CH0 to CH15. The analog input range for the device can be selected as 0 V to V_REF
or 0 V to (2 × V_REF). The analog input can be configured for either single-ended or differential signals. The device
has an on-chip 2.5-V 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 device 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 device equivalent input circuit. The (peak) input current through the
analog inputs depends on the sample rate, input voltage, and source impedance. The current into the device
charges the internal capacitor array during the sample period. After this capacitance is 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 1 GΩ.
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 © 2013, Texas Instruments Incorporated
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