AD5321 Analog Devices, AD5321 Datasheet - Page 13

• Manufacturer Part Number: AD5321
• Description: 2.5 V to 5.5 V, 120 µA, 2-Wire Interface, Voltage-Output 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of AD5321

• Resolution (bits): 12bit
• Dac Update Rate: 125kSPS
• Dac Settling Time: 8µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: I2C/Ser 2-wire,Ser

THEORY OF OPERATION
The AD5301/AD5311/AD5321 are single resistor-string DACs
fabricated on a CMOS process with resolutions of 8/10/12 bits,
respectively. Data is written via a 2-wire serial interface. The
devices operate from single supplies of 2.5 V to 5.5 V and the
output buffer amplifiers provide rail-to-rail output swing with
a slew rate of 0.7 V/μs. The power supply (V
reference to the DAC. The AD5301/AD5311/AD5321 have
three programmable power-down modes, in which the DAC
can be turned off completely with a high impedance output,
or the output can be pulled low by an on-chip resistor (see the
Power-Down Modes section).
DIGITAL-TO-ANALOG
The architecture of the DAC channel consists of a resistor string
DAC followed by an output buffer amplifier. The voltage at the
V
shows a block diagram of the DAC architecture. Since the input
coding to the DAC is straight binary, the ideal output voltage is
given by
where:
N = DAC resolution
D = decimal equivalent of the binary code that is loaded to the
DAC register:
DD
pin provides the reference voltage for the DAC. Figure 24
V
0–255 for AD5301 (8 bits)
0–1023 for AD5311 (10 bits)
0–4095 for AD5321 (12 bits)
OUT
=
REGISTER
V
DAC
DD
2
Figure 24. DAC Channel Architecture
N
×
D
RESISTOR
STRING
REF(+)
REF(–)
GND
V
DD
OUTPUT BUFFER
AMPLIFIER
DD
) acts as the
V
OUT
Rev. B | Page 13 of 24
RESISTOR STRING
The resistor string section is shown in Figure 25. It is simply
a string of resistors, each with a value of R. The digital code
loaded to the DAC register determines at what node on the
string the voltage is tapped off to be fed into the output ampli-
fier. 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 over all codes.
OUTPUT AMPLIFIER
The output buffer amplifier is capable of generating output volt-
ages to within 1 mV from either rail, which gives an output range
of 0.001 V to V
2 kΩ to GND and V
source and sink capabilities of the output amplifier can be seen
in Figure 14.
The slew rate is 0.7 V/μs with a half-scale settling time to
±0.5 LSB (at 8 bits) of 6 μs with the output unloaded.
POWER-ON RESET
The AD5301/AD5311/AD5321 are provided with a power-on
reset function, ensuring that they power up in a defined state.
The DAC register is filled with zeros and remains so until a
valid write sequence is made to the device. This is particularly
useful in applications where it is important to know the state
of the DAC output while the device is powering up.
DD
R
R
R
R
R
− 0.001 V. It is capable of driving a load of
DD
Figure 25. Resistor String
, in parallel with 500 pF to GND. The
AD5301/AD5311/AD5321
TO OUTPUT
AMPLIFIER