AMC7812SPAPR datasheet(29/92 Pages) TI

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COMMON

V -

V +

(a)

V -

V +

(b)

AMC7812

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SBAS513E – JANUARY 2011 – REVISED SEPTEMBER 2013

Single-Ended Analog Input

In applications where the signal source has high impedance, it is recommended to buffer the analog input before

applying it to the ADC. The analog input range can be programmed to be either 0V to VREF or 0V 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 AMC7812 is configured as a differential input, the differential signal is defined as VDM, as shown in

Figure 81(a). It is the equivalent of the difference between the signals of V1 and V2, 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 VREF range, or (–2 · VREF) to (+2 · VREF) for (2 · VREF) range. The results are stored in straight binary or

twos complement format.

Figure 81. Fully-Differential Analog Input

PRIMARY ADC OPERATION

The following sections describe 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 the conversion of channel 1 immediately

and starts the conversion of channel 0 again, instead of proceeding to convert channel 2.

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