AD5749

Rev. 0 | Page 16 of 28

THEORY OF OPERATION

The AD5749 is a single-channel, low cost, precision, current

output driver with hardware or software programmable output

ranges. The software ranges are configured via an SPI-/

MICROWIRE-compatible serial interface. The hardware ranges

are programmed using the range pins (R0 to R3). The analog

input to the AD5749 is provided from a low voltage, single-supply

DAC (0 V to 4.096 V), which is internally conditioned to provide

the desired output current range.

The output current range is programmable across two ranges:

0 mA to 24 mA, or 4 mA to 20 mA. An overrange of 2% is

available on the 0 mA to 24 mA and 4 mA to 20 mA current

ranges. The output range is selected by programming the R3

to R0 bits in the control register (see Table 7 and Table 8).

Figure 31 and Figure 32 show a typical configuration of AD5749 in

software mode and in hardware mode, respectively, in an output

module system. The HW SELECT pin chooses whether the part

is configured in software or hardware mode. The analog input to

the AD5749 is provided from a low voltage, single-supply DAC

such as the AD506x or AD566x, which can provide an output

range of 0 V to 4.096 V. The supply and reference for the DAC,

as well as the reference for the AD5749, can be supplied from a

reference such as the ADR392. The AD5749 can operate with a

single supply up to 55 V.

SOFTWARE MODE

The software-selectable output ranges are 0 mA to 24 mA, or

4 mA to 20 mA.

VIN

SCLK

VDD

REFIN

SDI/DIN

SDO

SYNC1

SYNC

SDO

SDIN

SCLK

MCU

STATUS REGISTER

VREF

HW SELECT

FAULT

ADP1720

ADR392

AVDD

AGND

AVDD

GND

AD5749

AD506x

AD566x

SERIAL

INTERFACE

IOUT OPEN FAULT

OVERTEMP FAULT

IOUT

RANGE

SCALE

IOUT

0mA TO 20mA,

0mA TO 24mA,

4mA TO 20mA

Figure 31. Typical System Configuration in Software Mode (Pull-Up Resistors Not Shown for Open-Drain Outputs)