AD74115H datasheet(49/113 Pages) AD

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Data Sheet

AD74115H

THEORY OF OPERATION

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Rev. 0 | 49 of 113

Interpreting ADC Data

The ADC is not required for digital input operation. However, the

ADC is available for voltage and current measurements when the

digital input, loop powered mode is enabled. In digital input, loop

powered mode, the ADC, by default, measures the voltage across

the I/OP to I/ON screw terminals in a 0 V to 12 V range. Use

the ADC measurement result to calculate this voltage by using the

following equation:

VADC = (ADC_CODE/65,536) × Voltage Range

where:

VADC is the measured voltage in volts.

ADC_CODE is the value of the ADC_RESULT1 register.

Voltage Range is 12 V, the measurement range of the ADC.

Digital Output

The AD74115H supports sourcing and sinking digital outputs. An

internal digital output function is available for sourcing or sinking up

to 100 mA continuous current. For currents higher than 100 mA,

use the external digital output function. A push-pull feature is also

available that combines both the source and sink capabilities to

provide high speed, high voltage switching.

When the digital output functionality is enabled, the recommended

configuration of the CH_FUNC_SETUP register is to set it to high

impedance.

Sourcing and Sinking Currents Greater Than

100 mA

The external sourcing digital output operates with an external,

P-channel field effect transistor (PFET), and the sinking digital

output operates with external N-channel FET (NFET). Push-pull

mode uses both PFET and NFET. Choose the FET types to suit the

application requirements. Determine the absolute current value by

the RSET and short-circuit voltage values. Short-circuit voltages are

indicated in the Table 11.

Configure the digital output using the DO_EXT_CONFIG register:

►

Select source, sink, or push-pull capability by using the

DO_EXT_MODE bits.

►

Select the source of the data for the digital output circuit using

the DO_EXT_SRC_SEL bit. The digital output data can be pro-

vided by the SPI (via the DO_DATA_EXT bit) or by the GPIO_B

pin for direct hardware control of the circuits.

►

Configure the short-circuit timers using the DO_EXT_T1 and

DO_EXT_T2 bits. See the Short-Circuit Protection section for

more information on short-circuit functionality. Note that T1 short-

circuit limits are not available in push-pull mode

Once the configuration settings are applied, provide stimulus to

turn on the selected external FET. For SPI control, a new write is re-

quired to the DO_EXT_CONFIG register, to set the DO_DATA_EXT

bit. Setting the DO_DATA_EXT to 1 turns on the selected external

FET. In push-pull mode, set the bit to 0 to drive a low on the output

and to 1 to drive a high on the output.

For GPIO control, configure the GPIO_x pin to control the digital

output circuit by writing 0x0004 to the GPIO_CONFIGx register.

Drive the GPIO_x pin high to turn on the FET. In push-pull mode,

set the GPIO_x pin low for a low on the output and high for a high

on the output.

If changing from one digital output function to another, first disable

the digital output function before changing to the new mode (set

DO_EXT_MODE to digital output external disable).

Figure 46 shows the current and voltage paths of the sourcing

digital output mode with the external FET. Figure 47 shows the

current and voltage paths of the sinking digital output mode with the

external FETs.

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