AMC7812SPAPR datasheet(39/92 Pages) TI

39 / 92 page

CH0

CH1

CH14

CH15

ADC

REF-DAC

REF-OUT

DAC-0

DAC0-OUT

Reference

(2.5V)

ADC-REF-IN/CMP

ControlLogic: Bit

ADC-REF-INT= ‘0’

ControlLogic:

BitPREF= ‘0’

Ext.

Ref.

Ext.

Ref.

CH0

CH1

CH14

CH15

ADC

REF-DAC

REF-OUT

DAC-0

DAC0-OUT

Reference

(2.5V)

ADC-REF-IN/CMP

ControlLogic: Bit

ADC-REF-INT= ‘1’

ControlLogic:

BitPREF= ‘1’

C>470nF

(Minimize

Inductance

toPin)

AMC7812

www.ti.com

SBAS513E – JANUARY 2011 – REVISED SEPTEMBER 2013

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

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.

Figure 89. Use of the External Reference

Figure 90. Use of the Internal Reference

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