AMC7836_15 Datasheet, PDF (30/87 Pages) Texas Instruments – AMC7836 High-Density, 12-Bit Analog Monitor and Control Solution With Multichannel ADC, Bipolar DACs, Temperature Sensor, and GPIO Ports

AMC7836
SLAS986B – NOVEMBER 2014 – REVISED FEBRUARY 2015
www.ti.com
7.3.2.1.1 Bipolar Analog Inputs
The AMC7836 can support up to 16 bipolar analog inputs. The analog input range for these channels is –12.5 to
12.5 V. The bipolar signal is scaled internally through a resistor divider so that it maps to the native input range
of the ADC (0 V to 2 × V_ref). The input resistance of the scaling network is 175 kΩ.
The bipolar analog input conversion values are stored in straight binary format in the ADC data registers
(address 0x20 through 0x49). The LSB (least-significant bit) size for these channels is 25 × V_ref / 4096. With the
internal reference equal to 2.5 V, the input voltage is calculated by Equation 1.
Voltage
5
§
¨©
CODE u
4096
5

2.5
·
¸¹
(1)
A typical application for the bipolar channels is monitoring of the 16 DAC outputs in the device. In this application
the bipolar inputs can be driven directly. However, in applications where the signal source has high impedance,
buffering the analog input is recommended. When driven from a low impedance source such as the AMC7836
DAC outputs, the network is designed to settle before the start of conversion. Additional impedance can affect
the settling and divider accuracy of this network.
7.3.2.1.2 Unipolar Analog Inputs
In addition to the bipolar input channels, the AMC7836 device includes five unipolar analog inputs. The analog
input range for these channels is 0 V to 2 × V_ref and the LSB size for these channels is 2 × V_ref / 4096.
The unipolar analog input conversion values are stored in straight binary format in the ADC-Data registers
(address 0x40 through 0x49). With the internal reference equal to 2.5 V, the input voltage is calculated by
Equation 2.
Voltage  ^{CODE K 5}
4096
(2)
In applications where the signal source has high impedance, externally buffering the unipolar analog input is
recommended.
7.3.2.2 ADC Sequencing
The AMC7836 ADC conversion sequence is shown in Figure 52. The ADC supports direct mode and auto mode
conversion. The conversion method is selected in the ADC configuration register (address 0x10). The default
conversion method is direct mode.
In both methods, the single channel or sequence of channels to be converted by the ADC must be first
configured in the ADC MUX configuration registers (address 0x13 through 0x15). The input channels to the ADC
include 16 external bipolar inputs, five external unipolar inputs, and the internal temperature sensor.
In direct-mode conversion, the selected ADC input channels are converted on demand by issuing an ADC trigger
signal. After the last enabled channel is converted, the ADC enters IDLE state and waits for a new trigger.
In auto-mode conversion, the selected ADC input channels are converted continuously. The conversion cycle is
initiated by issuing an ADC trigger. Upon completion of the first conversion sequence another sequence is
automatically started. Conversion of the selected channels occurs repeatedly until the auto-mode conversion is
stopped by issuing a second trigger signal.
30
Submit Documentation Feedback
Product Folder Links: AMC7836
Copyright © 2014–2015, Texas Instruments Incorporated