AMC7812 Datasheet, PDF (30/92 Pages) Texas Instruments – 12-Bit ANALOG MONITORING AND CONTROL SOLUTION with Multichannel ADC, DACs, and Temperature Sensors

AMC7812
SBAS513D – JANUARY 2011 – REVISED OCTOBER 2012
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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 V_REF or 0V to (2 · V_REF). In
2 · V_REF 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 AV_DD.
Fully-Differential Input
When the AMC7812 is configured as a differential input, the differential signal is defined as V_DM, 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 V_COMMON is equal to (V1 + V2)/2.
When the conversion occurs, only the differential mode voltage (V_DM) is converted; the common mode voltage
(V_COMMON) is rejected. This process results in a virtually noise-free signal with a maximum amplitude of –V_REF to
+V_REF for V_REF range, or (–2 · V_REF) to (+2 · V_REF) for (2 · V_REF) range. The results are stored in straight binary or
twos complement format.
V_COMMON
V_DM
2
V_IN+
AMC7812
V_DM
2
V_IN-
(a)
V_IN+
V1
AMC7812
V_IN-
V2
(b)
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.
Conversion Mode
Two types of ADC conversions are available: direct mode and auto mode. The CMODE (conversion mode) bit of
the AMC Configuration 0 Register specifies the conversion mode.
In direct mode, each analog channel within the specified group is converted a single time. After the last channel
is converted, the ADC goes into an idle state and waits for a new trigger.
Auto mode is a continuous operation. In auto mode, each analog channel within the specified group is converted
sequentially and repeatedly.
The flow chart of the ADC conversion sequence in Figure 82 shows the conversion process.
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