AMC7812 Datasheet, PDF (39/92 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
REFERENCE OPERATION
The following sections describe the operation of the internal and external references.
Internal Reference
The AMC7812 includes a 2.5V internal reference. The internal reference is externally available at the REF-OUT
pin. A 100pF to 10nF capacitor is recommended between the reference output and GND for noise filtering. The
internal reference is a bipolar transistor-based, precision bandgap voltage reference. The output current is limited
by design to approximately 100mA.
The internal reference drives all temperature sensors. When connecting the REF-OUT pin to the REF-DAC pin,
the internal reference works as the DAC reference.
The ADC-REF-IN/CMP pin has a dual function. When an external reference is connected to this pin, the external
reference is used as the ADC reference. When a compensation capacitor ( 4.7µF, typical) is connected between
this pin and AGND, the internal reference is used as the ADC reference. When using an external reference to
drive the ADC, the ADC-REF-INT bit in AMC Configuration Register 0 must be cleared ('0') to turn off the ADC
reference buffer. When using the internal reference to drive the ADC, the ADC-REF-INT bit in AMC Configuration
Register 0 must be set to '1' to turn on the ADC reference buffer.
External Reference
Figure 89 shows how the external reference is used as the DAC reference when applied on the DAC-REF pin,
and as the ADC reference when applied on the ADC-REF pin. Figure 90 shows the use of the internal reference.
CH0
CH1
CH14
CH15
ADC
Ext.
ADC-REF-IN/CMP
Ref.
Control Logic: Bit
ADC-REF-INT = ‘0’
Reference
(2.5V)
Control Logic:
Bit PREF = ‘0’
REF-OUT
REF-DAC
Ext.
Ref.
CH0
CH1
CH14
CH15
ADC
C > 470nF
(Minimize
Inductance
to Pin)
ADC-REF-IN/CMP
Reference
(2.5V)
Control Logic:
Bit PREF = ‘1’
Control Logic: Bit
ADC-REF-INT = ‘1’
REF-OUT
REF-DAC
DAC-0
DAC0-OUT
DAC-0
DAC0-OUT
Figure 89. Use of the External Reference
Figure 90. Use of the Internal Reference
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: AMC7812
Submit Documentation Feedback
39