AD5338 Analog Devices, AD5338 Datasheet - Page 21

• Manufacturer Part Number: AD5338
• Description: 2.5 V to 5.5 V, 250 µA, 2-Wire Interface, Dual Voltage Output, 10-Bit DACs
• Manufacturer: Analog Devices

Specifications of AD5338

• Resolution (bits): 10bit
• Dac Update Rate: 14.8kSPS
• Dac Settling Time: 7µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: I2C/Ser 2-wire

PRODUCT AS A DIGITALLY PROGRAMMABLE
WINDOW DETECTOR
Figure 39 shows a digitally programmable upper/lower limit
detector using the two DACs in the AD5337/AD5338/AD5339.
The upper and lower limits for the test are loaded into DAC A
and DAC B, which, in turn, set the limits on the CMP04. If the
signal at the V
an LED indicates the fail condition.
V
COARSE AND FINE ADJUSTMENT CAPABILITIES
The two DACs in the AD5337/AD5338/AD5339 can be paired
together to form a coarse and fine adjustment function, as
shown in Figure 40. DAC A is used to provide the coarse
adjustment while DAC B provides the fine adjustment. Varying
the ratio of R1 and R2 changes the relative effect of the coarse
and fine adjustments. With the resistor values and external
reference shown, the output amplifier has unity gain for the
DAC A output, thus, the output range is 0 V to 2.5 V − 1 LSB.
For DAC B, the amplifier has a gain of 7.6 × 10
a range equal to 19 mV.
The circuit is shown with a 2.5 V reference, but reference
voltages up to V
a rail-to-rail output swing.
AD780/REF192/ADR391
5V
SCL
EXT
REF
DIN
REF
GND
WITH V
V
1
1
ADDITIONAL PINS OMITTED FOR CLARITY.
IN
ADDITIONAL PINS OMITTED FOR CLARITY.
V
OUT
0.1µF
DD
REFIN
SDA
SCL
0.1µF
= 5V
AD5337/
AD5338/
AD5339
IN
1µF
DD
GND
input is not within the programmed window,
10µF
Figure 40. Coarse/Fine Adjustment
10µF
can be used. The op amps indicated allow
Figure 39. Window Detection
V
1
REFIN
V
V
DD
OUT
OUT
A
B
AD5337/
AD5338/
AD5339
V
DD
V
GND
= 5V
DD
V
IN
V
V
1
OUT
OUT
51.2kΩ
CMP04
A
B
R3
1/2
51.2kΩ
390Ω
R1
R2
390Ω
R4
–3
FAIL
PASS/FAIL
1kΩ
1/6 74HC05
, giving DAC B
5V
AD820/
OP295
PASS
1kΩ
V
OUT
Rev. C | Page 21 of 28
POWER SUPPLY DECOUPLING
In any circuit where accuracy is important, careful consideration
of the power supply and ground return layout helps to ensure
the rated performance. The printed circuit board on which the
AD5337/AD5338/AD5339 are mounted should be designed so
that the analog and digital sections are separated and confined
to certain areas of the board. If the AD5337/AD5338/AD5339
are in a system where multiple devices require an AGND-to-
DGND connection, the connection should be made at one
point only. The star ground point should be established as close
as possible to the device. The AD5337/AD5338/AD5339 should
have ample supply bypassing of 10 μF in parallel with 0.1 μF on
the supply located as close to the package as possible, ideally
right up against the device. The 10 μF capacitors are the tantalum
bead type. The 0.1 μF capacitor should have low effective series
resistance (ESR) and low effective series inductance (ESI) to
provide a low impedance path to ground at high frequencies to
handle transient currents due to internal logic switching. The
power supply lines of the AD5337/AD5338/AD5339 should use
as large a trace as possible to provide low impedance paths and
reduce the effects of glitches on the power supply line. Fast
switching signals such as clocks should be shielded with digital
ground to avoid radiating noise to other parts of the board, and
they should never be run near the reference inputs. A ground
line routed between the SDA and SCL lines helps to reduce
crosstalk between them. This is not required on a multilayer
board because there is a separate ground plane, but separating
the lines does help.
Avoid crossover of digital and analog signals. Traces on opposite
sides of the board should run at right angles to each other. This
reduces the effects of feedthrough on the board. Using a microstrip
technique is the best solution, but its use is not always possible
with a double-sided board. In this technique, the component
side of the board is dedicated to the ground plane, while signal
traces are placed on the solder side.
AD5337/AD5338/AD5339