AD5764 Analog Devices, AD5764 Datasheet - Page 24

• Manufacturer Part Number: AD5764
• Description: Complete Quad, 16-Bit, High Accuracy, Serial Input, Bipolar Voltage Output DAC
• Manufacturer: Analog Devices

Specifications of AD5764

• Resolution (bits): 16bit
• Dac Update Rate: 1.26MSPS
• Dac Settling Time: 8µs
• Max Pos Supply (v): +16.5V
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5764
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 being shorted to 0 V during this time,
Transmission Gate G1 is also opened (see Figure 35). These condi-
tions are maintained until the power supplies stabilize and a
valid word is written to the data 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 upon 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
DIGITAL OFFSET AND GAIN CONTROL
The AD5764 incorporates a digital offset adjust function with a
±16 LSB adjust range and 0.125 LSB resolution. The coarse gain
register allows the user to adjust the AD5764 full-scale output
range. The full-scale output can be programmed to achieve full-
scale ranges of ±10 V, ±10.2564 V, and ±10.5263 V. A fine gain
trim is also provided.
Figure 35
CONTROL
VOLTAGE
MONITOR
.
AND
Figure 35. Analog Output Control Circuitry
RSTOUT
G1
G2
RSTIN
AGNDA
VOUTA
Rev. F | Page 24 of 28
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:
If the ISCC pin is left unconnected, the short-circuit current
limit defaults to 5 mA. Note 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
programmed short circuit should take into account the size of
the capacitive load being driven.
DIGITAL I/O PORT
The AD5764 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 DV
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 can, for example, be applied to D0
and D1 and can be read back via the digital interface.
LOCAL GROUND OFFSET ADJUST
The AD5764 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, AGNDx, and the REFGND pin, ensuring that the DAC
output voltages are always 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 adjust
feature to adjust VOUTA by +5 mV, eliminating the error.
R
=
I
60
S
C
Data Sheet
CC
and DGND.