Internal Reference

(2.5 V)

Temperature

Sensor

AIN0

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

DACOUT0

DACOUT1

DACOUT2

DACOUT3

External

Reference

ADC Reference

DAC and Temp Sensor

Reference

DAC3

10-b

DAC0

10-b

DAC1

10-b

DAC2

10-b

ADC

10-b

ref_on = 0

Internal Reference

Temperature

Sensor

AIN0

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

DACOUT0

DACOUT1

DACOUT2

DACOUT3

DAC and Temp Sensor

Reference

ADC Reference

(2.5 V)

DAC3

10-b

DAC0

10-b

DAC1

10-b

DAC2

10-b

ADC

10-b

ref_on = 1

C>4.7 F

(Minimize

inductance to pin)

m

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

4.7

µF 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 AVDD 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.

Figure 31. External ADC Reference

Figure 32. Internal ADC Reference

Copyright

© 2011, Texas Instruments Incorporated

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