AMC7823IRTAT datasheet(32/55 Pages) TI

32 / 55 page

10kW

Bufferand

Controller

Bandgap

Reference

ToPrecision

CurrentSource

ToADC

1.25V

2.5V

Bit

GREF=0

Bit

SREF=1

(Refertodiagram

ofCurrentSource,

Figure49)

CFilter

ToDACs

AMC7823

SLAS453F – APRIL 2005 – REVISED MARCH 2012

www.ti.com

REFERENCE

The AMC7823 requires a reference voltage to drive the ADC, the DACs, and the precision current source. It can

accommodate the application of an external reference voltage, or it can supply reference from an internal

bandgap voltage circuit as shown in Figure 48. Pin 21, EXT_REF_IN, is common to either source. An internal

10k

Ω resistor connects the internal reference source to pin 21. This pin provides a point for noise filtering by

placing a capacitor, if desired, from the pin to analog ground. The time constant of this filter is [ (10k

Ω) ×

(CFILTER) ]. The resistor also allows an external reference applied to pin 21 to override the internal reference,

provided it can drive the 10k

Ω load. The filter capacitor can be 10μF when the internal reference is selected.

When using an external reference, it is recommended to use a buffered reference (such as the REF5025).

Figure 48. Reference

Logic bits SREF and GREF of the AMC Status/Configuration Register specify operation of the internal reference

and also should be considered when applying an external reference, as explained below. These bits also provide

information to the precision current source and are used in configuring that source (refer to the Precision Current

Source section for details).

When SREF is cleared to '0' (the default or power-on reset condition), the internal reference is selected and

connected to pin 21 by the 10k

Ω resistor. When SREF is set to '1', the internal reference is de-selected and

disconnected from pin 21. Pin 21 then floats unless an external reference is applied.

The bit GREF selects one of two pre-set values for the internal reference voltage. When GREF is cleared to '0',

the internal reference voltage is +1.25V. When GREF is set to '1', the internal reference voltage is +2.5V.

It is recommended to always set SREF to '1' when using an external source; otherwise, the external reference

must sink or source a current of value equal to the difference in the reference voltages divided by 10k

Ω. For

example, if SREF and GREF are both cleared to '0' and a 2.5V external reference is applied, the AMC7823 must

unnecessarily sink 125

μA.

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AMC7823IRTAT Datasheet(PDF) 32 Page - Texas Instruments

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