AMC7823IRTAT datasheet(39/55 Pages) TI

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AMC7823

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SLAS453F – APRIL 2005 – REVISED MARCH 2012

When an external reference is used and SREF is set to '1', GREF has no impact on the reference.

However, if SREF is cleared to '0', a 10k

Ω resistor is connected between pin 21, EXT_REF_IN,

and one of the two internal reference values dictated by the value of GREF. In this case, the

external reference must be able to drive the 10k

Ω load. The full-scale range of the ADC input is

equal to 2 x VREF. To avoid ADC input saturation, GREF must be cleared to '0' when AVDD is less

than +5V and the internal reference is used. After power-on or reset, GREF is cleared to '0'.

Table 9 specifies the ADC input range as a function of bits GREF and SREF.

Table 9. Reference and ADC Input Range Configuration

BIT GREF

BIT SREF

REFERENCE

ADC INPUT RANGE

Internal reference, 1.25V

0 to 2.5V

Internal reference, 2.5V, AVDD = 5V only

0 to 5V

Don't care

External reference VREF.

0 to 2 × VREF

2 × VREF must not be greater than AVDD.

Set SREF = '1' when applying external reference.

ECNVT

Enable CONVERT (external conversion trigger). This bit specifies the ADC trigger mode. When

ECNVT = '1', CONVERT is enabled. The ADC is in external trigger mode. The low-to-high

transition of the external trigger signal CONVERT triggers the ADC conversions. A write command

to the ADC Control Register does not initiate conversion, but rather specifies the group of inputs

to convert. After triggered by CONVERT, the AMC7823 sequentially accesses each analog input

one time. The bits [SA3:SA0] of the ADC Control Register comprise the channel address of the

first analog input accessed; [EA3:EA0] is the last analog input accessed. When the conversion

finishes, the ADC is idle and waits for a new CONVERT or a new command. With an external

trigger, the ADC always works in direct-mode (see the ADC Control Register section).

When ECNVT = '0', CONVERT is disabled. The internal ADC trigger is used. A write command to

the ADC Control Register generates the internal trigger and initiates ADC conversion. With an

internal trigger, the ADC can work in either direct-mode or auto-mode (see the ADC Operation

and ADC Control Register sections). Table 10 summarizes the ADC conversion mode

configuration.

After power-on or reset, DAVF, SREF, GREF, and ECNVT are cleared to '0'; RSTC is set to '1'.

Table 10. ADC Conversion Mode Configuration

ECNVT of AMC STATUS/

CMODE of ADC

CONFIGURATION REGISTER

CONTROL REGISTER

ADC CONVERSION MODE

–

External Trigger, Direct-Mode

Internal Trigger, Direct-Mode

Internal Trigger, Auto-Mode

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