AD5667 Analog Devices, AD5667 Datasheet - Page 27

• Manufacturer Part Number: AD5667
• Manufacturer: Analog Devices

Specifications of AD5667

• Resolution (bits): 16bit
• Dac Update Rate: 250kSPS
• Dac Settling Time: 4µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: I2C/Ser 2-wire,Ser

APPLICATION INFORMATION
USING A REFERENCE AS A POWER SUPPLY FOR
THE AD56x7R/AD56x7
Because the supply current required by the AD56x7R/AD56x7 is
extremely low, an alternative option is to use a voltage reference
to supply the required voltage to the part (see Figure 67). This is
especially useful if the power supply is quite noisy, or if the
system supply voltages are at some value other than 5 V or 3 V,
for example, 15 V. The voltage reference outputs a steady supply
voltage for the AD56x7R/AD56x7. If the low dropout
used, it must supply 450 μA of current to the AD56x7R/AD56x7
with no load on the output of the DAC. When the DAC output is
loaded, the REF195 also needs to supply the current to the load.
The total current required (with a 5 kΩ load on the DAC
output) is
The load regulation of the REF195 is typically 2 ppm/mA,
resulting in a 2.9 ppm (14.5 μV) error for the 1.45 mA current
drawn from it. This corresponds to a 0.191 LSB error.
BIPOLAR OPERATION USING THE
AD56x7R/AD56x7
The AD56x7R/AD56x7 has been designed for single-supply
operation, but a bipolar output range is also possible using the
circuit in Figure 68. The circuit gives an output voltage range of
±5 V. Rail-to-rail operation at the amplifier output is achieved
using an
The output voltage for any input code can be calculated as
follows:
where D represents the input code in decimal (0 to 65535).
With V
This is an output voltage range of ±5 V, with 0x0000 corre-
sponding to a −5 V output, and 0xFFFF corresponding to a
+5 V output.
450 μA + (5 V/5 kΩ) = 1.45 mA
V
V
O
O
Figure 67. REF195 as Power Supply to the AD56x7R/AD56x7
DD
INTERFACE
=
AD820
=
= 5 V, R1 = R2 = 10 kΩ,
SERIAL
⎡
⎢
⎣
⎛
⎜
⎝
2-WIRE
V
10
65
DD
,
×
536
×
D
or an
⎛
⎜
⎝
SDA
SCL
⎞
⎟
⎠
65
−
REF195
D
,
15V
536
OP295
5
V
⎞
× ⎟
⎠
5V
AD5627R/
AD5647R/
AD5667R/
⎛
⎜
⎝
AD5627/
AD5667
as the output amplifier.
R1
GND
V
DD
R1
+
R2
⎞
⎟
⎠
−
V
V
OUT
DD
= 0V TO 5V
⎛ ×
⎜
⎝
R2
R1
REF195
⎞
⎟
⎠
⎤
⎥
⎦
is
Rev. 0 | Page 27 of 32
AD5627R/AD5647R/AD5667R, AD5627/AD5667
POWER SUPPLY BYPASSING AND GROUNDING
When accuracy is important in a circuit, it is helpful to carefully
consider the power supply and ground return layout on the
board. The printed circuit board containing the AD56x7R/AD56x7
should have separate analog and digital sections, each having its
own area of the board. If the AD56x7R/AD56x7 are in a system
where other devices require an AGND to DGND connection, the
connection should be made at one point only. This ground point
should be as close as possible to the AD56x7R/AD56x7.
The power supply to the AD56x7R/AD56x7 should be bypassed
with 10 μF and 0.1 μF capacitors. The capacitors should be
located as close as possible to the device, with the 0.1 μF capacitor
ideally right up against the device. The 10 μF capacitor should be
the tantalum bead type. It is important that the 0.1 μF capacitor
have low effective series resistance (ESR) and effective series
inductance (ESI), for example, common ceramic types of
capacitors. This 0.1 μF capacitor provides a low impedance path
to ground for high frequencies caused by transient currents due
to internal logic switching.
The power supply line itself should have as large a trace as
possible to provide a low impedance path and to reduce glitch
effects on the supply line. Clocks and other fast switching
digital signals should be shielded from other parts of the board
by digital ground. Avoid crossover of digital and analog signals
if possible. When traces cross on opposite sides of the board,
ensure that they run at right angles to each other to reduce
feedthrough effects through the board. The best board layout
technique is the microstrip technique where the component
side of the board is dedicated to the ground plane only and the
signal traces are placed on the solder side. However, this is not
always possible with a two-layer board.
+5V
10µF
Figure 68. Bipolar Operation with the AD56x7R/AD56x7
0.1µF
GND
V
DD
AD5627R/
AD5647R/
AD5667R/
AD5627/
AD5667
R1 = 10kΩ
INTERFACE
SCL
SERIAL
2-WIRE
V
OUT
SDA
AD820/
OP295
R2 = 10kΩ
+5V
–5V
V
±5V
O