AMC7836IPAPRG4 datasheet(31/91 Pages) TI2

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CODE

Voltage

4096

CODE

Voltage

2.5

4096

AMC7836

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SLAS986D – NOVEMBER 2014 – REVISED FEBRUARY 2018

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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 × Vref). 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 × Vref / 4096. With the

internal reference equal to 2.5 V, the input voltage is calculated by Equation 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 × Vref and the LSB size for these channels is 2 × Vref / 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.

(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.

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