AD5732 Analog Devices, AD5732 Datasheet - Page 18

• Manufacturer Part Number: AD5732
• Description: Complete, Dual, 14-Bit, Serial Input, Unipolar/Bipolar, Voltage Output DAC
• Manufacturer: Analog Devices

Specifications of AD5732

• Resolution (bits): 14bit
• Dac Update Rate: 1MSPS
• Dac Settling Time: 10µs
• Max Pos Supply (v): +16.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5722/AD5732/AD5752
THEORY OF OPERATION
The AD5722/AD5732/AD5752 are dual, 12-/14-/16-bit, serial
input, unipolar/bipolar, voltage output DACs. They operate
from unipolar supply voltages of +4.5 V to +16.5 V or bipolar
supply voltages of ±4.5 V to ±16.5 V. In addition, the parts have
software-selectable output ranges of +5 V, +10 V, +10.8 V, ±5 V,
±10 V, and ±10.8 V. Data is written to the AD5722/AD5732/
AD5752 in a 24-bit word format via a 3-wire serial interface.
The devices also offer an SDO pin to facilitate daisy-chaining
or readback.
The AD5722/AD5732/AD5752 incorporate a power-on reset
circuit to ensure that the DAC registers power up loaded with
0x0000. When powered on, the outputs are clamped to 0 V via
a low impedance path.
ARCHITECTURE
The DAC architecture consists of a string DAC followed by an
output amplifier. Figure 38 shows a block diagram of the DAC
architecture. The reference input is buffered before being
applied to the DAC.
The resistor string structure is shown in Figure 39. It is a string
of resistors, each of value R. The code loaded to the DAC register
determines the node on the string where the voltage is to be
tapped off and fed into the output amplifier. The voltage is
tapped off by closing one of the switches connecting the string
to the amplifier. Because it is a string of resistors, it is guaranteed
monotonic.
DAC REGISTER
Figure 38. DAC Architecture Block Diagram
RANGE CONTROL
RESISTOR
REF (–)
REF (+)
STRING
REFIN
GND
OUTPUT
CONFIGURABLE
OUTPUT
AMPLIFIER
V
OUT
X
Rev. D | Page 18 of 32
Output Amplifiers
The output amplifiers are capable of generating both unipolar
and bipolar output voltages. They are capable of driving a load
of 2 kΩ in parallel with 4000 pF to GND. The source and sink
capabilities of the output amplifiers can be seen in Figure 26.
The slew rate is 3.5 V/μs with a full-scale settling time of 10 μs.
Reference Buffers
The AD5722/AD5732/AD5752 require an external reference
source. The reference input has an input range of 2 V to 3 V,
with 2.5 V for specified performance. This input voltage is then
buffered before it is applied to the DAC cores.
SERIAL INTERFACE
The AD5722/AD5732/AD5752 are controlled over a versatile
3-wire serial interface that operates at clock rates up to 30 MHz.
It is compatible with SPI, QSPI™, MICROWIRE™, and DSP
standards.
Input Shift Register
The input shift register is 24 bits wide. Data is loaded into the
device MSB first as a 24-bit word under the control of a serial
clock input, SCLK. The input register consists of a read/write
bit, three register select bits, three DAC address bits, and 16 data
bits. The timing diagram for this operation is shown in Figure 2.
R
R
R
R
R
REFIN
Figure 39. Resistor String Structure
TO OUTPUT
AMPLIFIER