AMC7812B datasheet(30/92 Pages) TAOS

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COMMON

V -

V +

(a)

V -

V +

(b)

AMC7812B

SBAS625A – SEPTEMBER 2013 – REVISED SEPTEMBER 2013

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Single-Ended Analog Input

In applications where the signal source has high impedance, TI recommends buffering the analog input before

applying it to the ADC. The analog input range can be programmed to be either 0 V to VREF or 0 V to (2 × VREF).

In 2 × VREF mode, the input is effectively divided by two before the conversion takes place. Note that the voltage

with respect to GND on the ADC analog input pins cannot exceed AVDD.

Fully-Differential Input

When the device is configured as a differential input, the differential signal is defined as VDM, as shown in

Figure 81(a). The differential signal is the equivalent of the difference between the V1 and V2 signals, as shown

in Figure 81(b). The common-mode input VCOMMON is equal to (V1 + V2) / 2.

When the conversion occurs, only the differential mode voltage (VDM) is converted; the common-mode voltage

(VCOMMON) is rejected. This process results in a virtually noise-free signal with a maximum amplitude of –VREF to

+VREF for the VREF range, or (–2 × VREF) to (+2 × VREF) for the (2 × VREF) range. The results are stored in straight

binary or twos complement format.

Figure 81. Fully-Differential Analog Input

PRIMARY ADC OPERATION

This section describes the operation of the primary ADC.

ADC Trigger Signals (see AMC configuration register 0)

The ADC can be triggered externally by the falling edge of the external trigger CNVT, or internally by writing to

the ICONV bit in AMC Configuration Register 0. The ADC channel registers specify which external analog

channel is converted.

When a new trigger activates, the ADC stops any existing conversion immediately and starts a new cycle. For

example, the ADC is programmed to sample channel 0 to channel 3 repeatedly (auto-mode). During the

conversion of channel 1, an external trigger is activated. The ADC stops converting channel 1 immediately and

starts converting channel 0 again, instead of proceeding to convert channel 2.

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