AD5744R
DESIGN FEATURES
If the ISCC pin is left unconnected, the short-circuit current
limit defaults to 5 mAꢀ It should be noted that limiting the short-
circuit current to a small value can affect the slew rate of the
output when driving into a capacitive loadꢀ Therefore, the value
of the short-circuit current that is programmed should take into
account the size of the capacitive load being drivenꢀ
ANAꢁOG OUTPUT CONTROꢁ
In many industrial process control applications, it is vital that
the output voltage be controlled during power-up and during
brownout conditionsꢀ When the supply voltages are changing,
the VOUTx pins are clamped to 0 V via a low impedance pathꢀ
To prevent the output amp from being shorted to 0 V during this
time, Transmission Gate G1 is also opened (see Figure 42)ꢀ
DIGITAꢁ I/O PORT
The AD5744R contains a 2-bit digital I/O port (D1 and D0)ꢀ
These bits can be configured independently as inputs or outputs
and can be driven or have their values read back via the serial
interfaceꢀ The I/O port signals are referenced to DVCC and DGNDꢀ
When configured as outputs, they can be used as control signals
to multiplexers or can be used to control calibration circuitry
elsewhere in the systemꢀ When configured as inputs, the logic
signals from limit switches, for example, can be applied to D0
and D1 and can be read back using the digital interfaceꢀ
RSTOUT
RSTIN
VOLTAGE
MONITOR
AND
CONTROL
G1
VOUTA
AGNDA
G2
DIE TEMPERATURE SENSOR
Figure 42. Analog Output Control Circuitry
The on-chip die temperature sensor provides a voltage output that
is linearly proportional to the Celsius temperature scaleꢀ Its nom-
inal output voltage is 1ꢀ47 V at 25°C die temperature, varying at
5 mV/°C, giving a typical output range of 1ꢀ175 V to 1ꢀ9 V over the
full temperature rangeꢀ Its low output impedance and linear output
simplify interfacing to temperature control circuitry and analog-to-
digital converters (ADCs)ꢀ The temperature sensor is provided
as more of a convenience than as a precise feature; it is intended
for indicating a die temperature change for recalibration purposesꢀ
These conditions are maintained until the power supplies stabilize
and a valid word is written to the DAC registerꢀ G2 then opens, and
G1 closesꢀ Both transmission gates are also externally controllable
RSTIN
RSTIN
via the reset in ( ) control inputꢀ For example, if
is
RSTIN
driven from a battery supervisor chip, the
input is driven
low to open G1 and close G2 on power-off or during a brownoutꢀ
RSTOUT
Conversely, the on-chip voltage detector output (
) is
also available to the user to control other parts of the systemꢀ
The basic transmission gate functionality is shown in Figure 42ꢀ
ꢁOCAꢁ GROUND OFFSET ADJUST
PROGRAMMABꢁE SHORT-CIRCUIT PROTECTION
The AD5744R incorporates a local ground offset adjust feature
that, when enabled in the function register, adjusts the DAC
outputs for voltage differences between the individual DAC ground
pins and the REFGND pin, ensuring that the DAC output voltages
are always referenced to the local DAC ground pinꢀ For example, if
the AGNDA pin is at +5 mV with respect to the REFGND pin, and
VOUTA is measured with respect to AGNDA, a −5 mV error
results, enabling the local ground offset adjust feature to adjust
VOUTA by +5 mV, thereby eliminating the errorꢀ
The short-circuit current (ISC) of the output amplifiers can be
programmed by inserting an external resistor between the ISCC
pin and the PGND pinꢀ The programmable range for the current is
500 μA to 10 mA, corresponding to a resistor range of 120 kΩ to
ꢁ kΩ ꢀ The resistor value is calculated as follows:
ꢁ0
R ≈
ISC
Rev. A | Page 26 of 32
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