AMC7823 datasheet(33/48 Pages) TI

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OUTPUT

SET

REF

0.4

1)GREF

SET

(1)

DIGITAL I/O (See AMC Status/Configuration Register)

GALR Pin

Bit ALR−0

Bit ALR−1

Bit ALR−2

Bit ALR−3

DAV Pin

DAV Pin in Direct Mode

Bit DAVF of AMC

Status / Configuration

DAV Pin in Auto-Mode

[EA3:EA0] is

Converted

µs Pulse

Generator

AMC7823

SLAS453A – APRIL 2005 – REVISED OCTOBER 2005

Table 7. Precision Current Source Configuration

SREF

PTS

PREFB

GREF

Don't care

0.5V/RSET(1)

Don't care

1(2)

Don't care

0(2)

Equation 1

1(2)

Equation 1

(1)

VSET = 0.5 V.

(2)

Make GREF = 1 for 2.5-V external reference; make GREF = 0 for 1.25-V external reference.

When an external reference is used, select a reference value (VREF) close to either 1.25 V or 2.5 V, and write bit

GREF low ('0') for a 1.25-V reference, or write it high ('1') for a 2.5-V reference. These settings make a better

match to the applied external reference value. The output current can be calculated by Equation 1:

The applied external reference voltage may deviate from the recommended values, but it is important to limit the

maximum voltage applied to the set resistor to approximately 0.5 V. Voltages greater than 0.5 V across the set

resistor reduce the specified compliance of the current source to the load.

The AMC7823 has four special function pins: DAV, GALR, ELDAC, and CONVERT, It also has six general I/O

pins (GPIO-n). The GPIO-n pins are used as general digital I/O or analog input out-of-range indicators.

The pin DAV is an output pin that indicates the completion of ADC conversions. Bit DAVF of the AMC

Status/Configuration Register determines the status of the DAV pin. In direct-mode, after the selected group of

input channels has been converted and the ADC has been halted, bit DAVF is set to '1' and pin DAV is driven to

logic low (active). In auto-mode, each time the group of input channels has been sequentially converted, a 2-

µs

pulse (low) appears on the DAV pin after the last channel of the group is converted. This conversion sequence is

repeated and the pulse is repeated.

The GALR pin is an output pin that indicates whether any of the first four analog inputs being converted are

out-of-range. Bits ALR-n of the ALR Register determine the status of GALR pin. GALR is low (or active) if any

one of the bits ALR-n is set to '1'. GALR is high (inactive) if and only if all bits are cleared to '0'. See Figure 50.

Figure 50. DAV Pin and GALR Pin

The CONVERT pin is an input pin for the external ADC trigger signal. When bit ECNVT of the AMC

Status/Configuration Register is set to '1', the AMC7823 works in external trigger mode. The rising edge of

CONVERT starts the ADC conversion.

AMC7823 Datasheet(PDF) 33 Page - Texas Instruments

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