EVAL-AD5765EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD5765EBZ' PDF : 28 Pages View PDF
Data Sheet
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 output pins are clamped to 0 V via a low impedance path.
To prevent the output amp being shorted to 0 V during this
time, transmission gate G1 is also opened (see Figure 28). These
conditions are maintained until the power supplies stabilize and
a valid word is written to the DAC register. At this time, G2
opens and G1 closes.
Both transmission gates are also externally controllable via the
reset logic (RSTIN) control input. For instance, if RSTIN is
driven from a battery supervisor chip, the RSTIN input is
driven low to open G1 and close G2 on power-down 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 28.
RSTOUT
RSTIN
VOLTAGE
MONITOR
AND
CONTROL
G1
G2
VOUTA
AGNDA
Figure 28. Analog Output Control Circuitry
DIGITAL OFFSET AND GAIN CONTROL
The AD5765 incorporates a digital offset adjustment function
with a ±16 LSB adjustment range and 0.125 LSB resolution. The
gain register allows the user to adjust the AD5765 full-scale
output range. The full-scale output can be programmed to
achieve full-scale ranges of ±4.096 V, ±4.201 V, and ±4.311 V. A
fine gain trim is also provided.
PROGRAMMABLE SHORT-CIRCUIT PROTECTION
The short-circuit current of the output amplifiers can be pro-
grammed by inserting an external resistor between the ISCC
pin and PGND. 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 ≈ 60
I SC
AD5765
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 programmed should take into
account the size of the capacitive load being driven.
DIGITAL I/O PORT
The AD5765 contains a 2-bit digital I/O port (D1 and D0).
These bits can be configured as inputs or outputs independently
and can be driven or have their values read back via the serial
interface. The I/O port signals are referenced to DVCC 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 via the digital interface.
DIE TEMPERATURE SENSOR
The on-chip die temperature sensor provides a voltage output
that is linearly proportional to the centigrade temperature scale.
Its nominal output voltage is 1.44 V at +25°C die temperature,
varying at 3 mV/°C and resulting in 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 ADCs. The temperature sensor is provided
as more of a convenience than a precise feature; it is intended to
indicate a die temperature change for recalibration purposes.
LOCAL-GROUND-OFFSET ADJUSTMENT
The AD5765 incorporates a local-ground-offset adjustment
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 with respect to the local
DAC ground pin. For instance, if Pin AGNDA 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 adjustment feature to adjust VOUTA by +5 mV,
thereby eliminating the error.
Rev. C | Page 23 of 28
Share Link: 
