ad5066bruz-1reel7 Analog Devices, Inc., ad5066bruz-1reel7 Datasheet - Page 12

• Manufacturer Part Number: ad5066bruz-1reel7
• Description: Fully Accurate 16-bit Unbuffered Vout Dac Spi Interface 2.7 V To 5.5 V In A Tssop
• Manufacturer: Analog Devices, Inc.

AD5066
THEORY OF OPERATION
D/A SECTION
DACs. The parts operate from supply voltages of 2.7 V to 5.5 V.
Data is written to the AD5066 in a 32-bit word format via a 3-
wire serial interface. The AD5066 incorporates a power-on reset
circuit that ensures the DAC output powers up to a known out-
put state (midscale or zero-scale, see the Ordering Guide). The
devices also have a software power-down mode that reduces the
typical current consumption to less than 1 µa.
Because the input coding to the DAC is straight binary, the ideal
output voltage when using an external reference is given by
The ideal output voltage when using and internal reference is
given by
where:
D = decimal equivalent of the binary code that is loaded to the
DAC register. 0 to 65,535 for AD5066 (16 bits). N = the DAC
resolution.
DAC ARCHITECTURE
The DAC architecture of the AD5066 consists of two matched
DAC sections. A simplified circuit diagram is shown in Figure
5. 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 V
remaining 12 bits of the data word drive switches S0 to S11 of a
12-bit voltage mode R-2R ladder network.
V
REFERENCE BUFFER
The AD5066 operates with an external reference. Each of the
four onboard dac’s will have a dedicated voltage reference pin.
In either case the reference input pin has an input range of 2 V
to V
reference for the DAC core.
The AD5066 are Quad 16-bit, serial input, voltage output
REF
DD
V
V
. This input voltage is then used to provide a buffered
OUT
OUT
2R
12-BIT R-2R LADDER
V
2
2R
S0
u
REFIN
V
REFOUT
Figure 6. Dac Ladder Structure
§ u
2R
S1
¨
©
2
D
N
§ u
¨
©
·
¸
¹
2
D
N
S11
2R
·
¸
¹
FOUR MSBs DECODED INTO
15 EQUAL SEGMENTS
2R
E1
REF
2R
E2
buffer output.
2R
E15
V
OUT
The
Rev. PrB | Page 12 of 20
SERIAL INTERFACE
The AD5066 has 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 3 for a
timing diagram of a typical write sequence.
STANDALONE MODE
The write sequence begins by bringing the SYNC line low. Data
from the DIN line is clocked into the 32-bit shift register on the
falling edge of SCLK. The serial clock frequency can be as high
as 50 MHz, making the AD5066 compatible with high speed
DSPs. On the 32
in and the programmed function is executed, that is, a change
in DAC register contents and/or a change in the mode of
operation. At this stage, the SYNC line can be kept low or be
brought high. In either case, it must be brought high for a
minimum of 15 ns before the next write sequence so that a
falling edge of SYNC can initiate the next write sequence.
Because the SYNC buffer draws more current when V
than it does when V
between write sequences for even lower power operation of the
part. As is mentioned previously, however, SYNC must be
brought high again just before the next write sequence.
R
R
R
R
R
nd
falling clock edge, the last data bit is clocked
Preliminary Technical Data
IN
= 0.8 V, SYNC should be idled low
Figure 7. Resistor String
TO OUTPUT
AMPLIFIER
IN
= 2 V