AMC7891_14 Datasheet, PDF (29/42 Pages) Texas Instruments – Analog Monitor and Control Circuit with 10-Bit, Multi-Channel ADC and Four DACs, Temperature Sensor, and 12 GPIOs

AMC7891
www.ti.com
SBAS518A – AUGUST 2011 – REVISED DECEMBER 2011
REFERENCE OPERATION
The AMC7891 includes a buffered internal reference for the ADC, DACs and temperature sensor. The internal
reference is a 2.5 V, bipolar transistor-based, precision bandgap reference.
The internal reference always drives the DACs and the internal temperature sensor directly (unbuffered);
however the ADC can be driven either by the internal reference (buffered) or by an external one as determined
by the ref_on bit (AMC_power register, bit 13). If used, the external reference is applied to the dual purpose REF
pin. A decoupling capacitor is recommended between the external reference output an AGND for noise filtering.
In internal ADC reference mode, the buffered internal reference is available at the REF pin. A compensating
4.7µF capacitor is recommended between the internal buffered reference output and AGND.
On power-up, the AMC7891 is configured for ADC external reference (ref_on bit cleared to ‘0’). In this case it is
important that the external reference source is not input into the REF pin until AV_DD is stable. If using the internal
reference to drive the ADC, the ref_on must be set to ‘1’ to enable the internal reference buffer.
ref_on = 0
External
Reference
ADC Reference
AIN0
AIN1
AIN2
AIN3
ADC
AIN4
10-b
AIN5
AIN6
AIN7
Internal Reference
(2.5 V)
DAC and Temp Sensor
Reference
DAC0
10-b
DACOUT0
DAC1
10-b
DACOUT1
DAC2
10-b
DACOUT2
DAC3
10-b
DACOUT3
Temperature
Sensor
Figure 31. External ADC Reference
C>4.7 mF
(Minimize
inductance to pin)
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
ref_on = 1
ADC Reference
Internal Reference
(2.5 V)
DAC and Temp Sensor
Reference
DAC0
10-b
DACOUT0
DAC1
10-b
DACOUT1
ADC
10-b
DAC2
10-b
DACOUT2
DAC3
10-b
DACOUT3
Temperature
Sensor
Figure 32. Internal ADC Reference
Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): AMC7891
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