AD5064_15 Datasheet, PDF (19/28 Pages) Analog Devices – Fully Accurate, 12-/14-/16-Bit VOUT nanoDAC, Quad, SPI Interface, 4.5 V to 5.5 V in TSSOP

Data Sheet
AD5024/AD5044/AD5064
THEORY OF OPERATION
DIGITAL-TO-ANALOG CONVERTER
The AD5024/AD5044/AD5064/AD5064-1 are single 12-/14-/
16-bit, serial input, voltage output DACs with an individual
reference pin. The AD5064-1 model (see the Ordering Guide)
is a 16-bit, serial input, voltage output DAC that is identical to
other AD5064 models but with a single reference pin for all
DACs. The parts operate from supply voltages of 4.5 V to 5.5 V.
Data is written to the AD5024/AD5044/AD5064/AD5064-1 in a
32-bit word format via a 3-wire serial interface. The AD5024/
AD5044/AD5064/AD5064-1 incorporate a power-on reset circuit
that ensures that the DAC output powers up to a known output
state. The devices also have a software power-down mode that
reduces the typical current consumption to typically 400 nA.
Because the input coding to the DAC is straight binary, the ideal
output voltage when using an external reference is given by
V_OUT
= V_REFIN
×

D
2^N

where:
D is the decimal equivalent of the binary code that is loaded to
the DAC register (0 to 65,535 for the 16-bit AD5064).
N is the DAC resolution.
DAC ARCHITECTURE
The DAC architecture of the AD5064 consists of two matched
DAC sections. A simplified circuit diagram is shown in Figure 46.
The four MSBs of the 16-bit data word are decoded to drive
15 switches, E1 to E15. Each of these switches connects one of
15 matched resistors to either GND or the VREF buffer output.
The remaining 12 bits of the data-word drive the S0 to S11
switches of a 12-bit voltage mode R-2R ladder network.
V_OUT
2R 2R
2R
2R
2R
2R
2R
S0
S1
S11
E1 E2
E15
V_REF
12-BIT R-2R LADDER
FOUR MSBs DECODED INTO
15 EQUAL SEGMENTS
Figure 46. DAC Ladder Structure
REFERENCE BUFFER
The AD5024/AD5044/AD5064/AD5064-1 operate with an exter-
nal reference. For most models, each DAC has a dedicated voltage
reference pin. The AD5064-1 model has a single voltage reference
pin for all DACs. The reference input pin has an input range of
2.2 V to VDD. This input voltage is then buffered internally to
provide a reference for the DAC core.
OUTPUT AMPLIFIER
The output buffer amplifier can generate rail-to-rail voltages
on its output, which gives an output range of 0 V to VDD. The
amplifier is capable of driving a load of 5 kΩ in parallel with
200 pF to GND. The slew rate is 1.5 V/µs with a ¼ to ¾ scale
settling time of 5.8 µs.
SERIAL INTERFACE
The AD5024/AD5044/AD5064/AD5064-1 have a 3-wire serial
interface (SYNC, SCLK, and DIN) that is compatible with SPI,
QSPI, and MICROWIRE interface standards as well as most
DSPs. See Figure 4 for a timing diagram of a typical write
sequence. The AD5064-1 model contains an SDO pin to allow
the user to daisy-chain multiple devices together (see the Daisy-
Chaining section).
SHIFT REGISTER
The AD5024/AD5044/AD5064/AD5064-1 shift register is 32 bits
wide. The first four bits are don’t cares. The next four bits are the
command bits, C3 to C0 (see Table 8), followed by the 4-bit
DAC address bits, A3 to A0 (see Table 9), and finally the bit
data-word. The data-word comprises 12-bit, 14-bit, or 16-bit input
code, followed by eight, six, or four don’t care bits for the AD5024,
AD5044, and AD5064/AD5064-1, respectively (see Figure 47,
Figure 48, and Figure 49). These data bits are transferred to the
DAC register on the 32^nd falling edge of SCLK. Commands can be
executed on individually selected DAC channels or on all DACs.
Table 8. Command Definitions
Command
C3 C2 C1 C0 Description
0 0 0 0 Write to Input Register n
0 0 0 1 Update DAC Register n
0 0 1 0 Write to Input Register n, update all
(software LDAC)
0 0 1 1 Write to and update DAC Channel n
0 1 0 0 Power down/power up DAC
0 1 0 1 Load clear code register
0 1 1 0 Load LDAC register
0 1 1 1 Reset (power-on reset)
1 0 0 0 Set up DCEN register¹ (daisy-chain enable)
1 0 0 1 Reserved
1 1 1 1 Reserved
1 _{Available in the AD5064-1 14-lead TSSOP package only.}
Table 9. Address Commands
Address (n)
A3 A2 A1 A0 Selected DAC Channel
0
0
0
0
DAC A
0
0
0
1
DAC B
0
0
1
0
DAC C
0
0
1
1
DAC D
1
1
1
1
All DACs
Rev. F | Page 19 of 28