AMC7812B Datasheet, PDF (30/92 Pages) TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS – 12-Bit Analog Monitoring and Control Solution with Multichannel ADC, DACs, and Temperature Sensors

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 V_REF or 0 V 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 device is configured as a differential input, the differential signal is defined as V_DM, 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 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 the V_REF range, or (–2 × V_REF) to (+2 × V_REF) for the (2 × V_REF) range. The results are stored in straight
binary or twos complement format.
V_COMMON
V_DM
2
V_DM
2
V_IN+
V_IN-
(a)
V_IN+
V1
V_IN-
V2
(b)
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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