AMC7812B datasheet(39/92 Pages) TAOS

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)

AMC7812B

www.ti.com

SBAS625A – SEPTEMBER 2013 – REVISED SEPTEMBER 2013

REFERENCE OPERATION

This section describes the operation of the internal and external references.

Internal Reference

The device includes a 2.5-V internal reference. The internal reference is externally available at the REF-OUT pin.

A 100-pF to 10-nF capacitor is recommended between the reference output and GND for noise filtering. The

internal reference is a bipolar transistor-based, precision band-gap voltage reference. The output current is

limited by design to approximately 100 mA.

The internal reference drives all temperature sensors. When connecting the REF-OUT pin to the REF-DAC pin,

the internal reference functions 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 (4.7 µF, 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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