AD5744R Analog Devices, AD5744R Datasheet - Page 21

• Manufacturer Part Number: AD5744R
• Description: Complete Quad, 14-Bit, High Accuracy, Serial Input, Bipolar Voltage Output D/A Converter
• Manufacturer: Analog Devices

Specifications of AD5744R

• Resolution (bits): 14bit
• Dac Update Rate: 1MSPS
• Dac Settling Time: 8µs
• Max Pos Supply (v): +16.5V
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

Data Sheet
THEORY OF OPERATION
The AD5744R is a quad, 14-bit, serial input, bipolar voltage output
DAC that operates from supply voltages of ±11.4 V to ±16.5 V and
has a buffered output voltage of up to ±10.5263 V. Data is written to
the AD5744R in a 24-bit word format via a 3-wire serial interface.
The AD5744R also offers an SDO pin that is available for daisy
chaining or readback.
The AD5744R incorporates a power-on reset circuit that ensures
that the data registers are loaded with 0x0000 at power-up. The
AD5744R features a digital I/O port that can be programmed via
the serial interface, an analog die temperature sensor, on-chip
10 ppm/°C voltage reference, on-chip reference buffers, and per
channel digital gain and offset registers.
DAC ARCHITECTURE
The DAC architecture of the AD5744R consists of a 14-bit current
mode segmented R-2R DAC. The simplified circuit diagram for
the DAC section is shown in Figure 39.
V
The four MSBs of the 14-bit data-word are decoded to drive
15 switches, E1 to E15. Each of these switches connects one of
the 15 matched resistors to either AGNDx or I
12 bits of the data-word drive Switch S0 to Switch S11 of the 12-bit
R-2R ladder network.
REFERENCE BUFFERS
The AD5744R can operate with either an external or an internal
reference. The reference inputs (REFAB and REFCD) have an
input range of up to 7 V. This input voltage is then used to provide
a buffered positive and negative reference for the DAC cores.
The positive reference is given by
The negative reference to the DAC cores is given by
These positive and negative reference voltages (along with the
gain register values) define the output ranges of the DACs.
REF
E15
4 MSBs DECODED INTO
+V
−V
15 EQUAL SEGMENTS
2R
REF
REF
E14
= 2 × V
= −2 × V
2R
E1
REFIN
Figure 39. DAC Ladder Structure
2R
REFIN
R
S11
12-BIT, R-2R LADDER
2R
R
S10
2R
R
S0
2R
OUT
2R
AGNDx
. The remaining
I
R/8
OUT
VOUTx
Rev. E | Page 21 of 32
SERIAL INTERFACE
The AD5744R is controlled over a versatile 3-wire serial interface
that operates at clock rates of up to 30 MHz and 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,
a reserved bit that must be set to 0, three register select bits, three
DAC address bits, and 16 data bits, as shown in Table 9. The timing
diagram for this operation is shown in Figure 2.
Upon power-up, the data registers are loaded with zero code
(0x0000), and the outputs are clamped to 0 V via a low impedance
path. The outputs can be updated with the zero code value by
asserting either LDAC or CLR . The corresponding output voltage
depends on the state of the BIN/ 2sCOMP pin. If the BIN/ 2sCOMP
pin is tied to DGND, the data coding is twos complement and the
outputs update to 0 V. If the BIN/ 2sCOMP pin is tied to DV
the data coding is offset binary and the outputs update to negative
full scale. To have the outputs power-up with zero code loaded
to the outputs, the CLR pin should be held low during power-up.
Standalone Operation
The serial interface works with both a continuous and noncon-
tinuous serial clock. A continuous SCLK source can be used only
if SYNC is held low for the correct number of clock cycles. In gated
clock mode, a burst clock containing the exact number of clock
cycles must be used, and SYNC must be taken high after the final
clock to latch the data. The first falling edge of SYNC starts the
write cycle. Exactly 24 falling clock edges must be applied to SCLK
before SYNC is brought high again. If SYNC is brought high before
the 24
than 24 falling SCLK edges are applied before SYNC is brought
high, the input data is also invalid. The input register addressed is
updated on the rising edge of SYNC . For another serial transfer to
take place, SYNC must be brought low again. After the end of
the serial data transfer, data is automatically transferred from the
input shift register to the addressed register.
When the data has been transferred into the chosen register of
the addressed DAC, all data registers and outputs can be
updated by taking LDAC low.
th
falling SCLK edge, the data written is invalid. If more
AD5744R
CC
,