Datasheet

Data Sheet AD5764R
Rev. D | Page 27 of 32
DESIGN FEATURES
ANALOG OUTPUT CONTROL
In many industrial process control applications, it is vital that
the output voltage be controlled during power-up and during
brownout conditions. When the supply voltages are changing,
the VOUTx pins are clamped to 0 V via a low impedance path.
To prevent the output amp from being shorted to 0 V during
this time, Transmission Gate G1 is also opened (see Figure 42).
G1
G2
RSTOUT
RSTIN
VOUTA
AGNDA
VOLTAGE
MONITOR
AND
CONTROL
06064-063
Figure 42. Analog Output Control Circuitry
These conditions are maintained until the power supplies stabilize
and a valid word is written to the data register. G2 then opens, and
G1 closes. Both transmission gates are also externally controllable
by using the reset in (
RSTIN
) control input. For example, if
RSTIN
is driven from a battery supervisor chip, the
RSTIN
input is driven
low to open G1 and close G2 on power-off or during a brownout.
Conversely, the on-chip voltage detector output (
RSTOUT
) is
also available to the user to control other parts of the system.
The basic transmission gate functionality is shown in
Figure 42.
DIGITAL OFFSET AND GAIN CONTROL
The AD5764R incorporates a digital offset adjust function with
a ±16 LSB adjust range and 0.125 LSB resolution. The gain register
allows the user to adjust the AD5764R full-scale output range.
The full-scale output can be programmed to achieve full-scale
ranges of ±10 V, ±10.25 V, and ±10.5 V. A fine gain trim is also
available.
PROGRAMMABLE SHORT-CIRCUIT PROTECTION
The short-circuit current (I
SC
) of the output amplifiers can be pro-
grammed by inserting an external resistor between the ISCC
pin and the PGND pin. The programmable range for the current
is 500 µA to 10 mA, corresponding to a resistor range of 120 kΩ
to 6 kΩ. The resistor value is calculated as follows:
R ≈
SC
I
60
If the ISCC pin is left unconnected, the short circuit current
limit defaults to 5 mA. 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 load. Therefore, the
value of the short-circuit current that is programmed should
take into account the size of the capacitive load being driven.
DIGITAL I/O PORT
The AD5764R 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 interface.
The I/O port signals are referenced to DV
CC
and DGND. When
configured as outputs, they can be used as control signals to
multiplexers or can be used to control calibration circuitry
elsewhere in the system. 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 interface.
DIE TEMPERATURE SENSOR
The on-chip die temperature sensor provides a voltage output
that is linearly proportional to the Celsius temperature scale.
Its nominal output voltage is 1.47 V at +25°C die temperature,
varying at 5 mV/°C, giving a typical output range of 1.175 V to
1.9 V over the full temperature range. Its low output impedance,
and linear output simplify interfacing to temperature control
circuitry and analog-to-digital converters (ADCs). The temper-
ature sensor is provided as more of a convenience than as a precise
feature; it is intended for indicating a die temperature change for
recalibration purposes.
LOCAL GROUND OFFSET ADJUST
The AD5764R 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 pin. 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
VO U TA b y + 5 m V, thereby eliminating the error.