AD5346/AD5347/AD5348
COARSE AND FINE ADJUSTMENT USING
THE AD5346/AD5347/AD5348
POWER SUPPLY BYPASSING AND GROUNDING
In any circuit where accuracy is important, careful consideration
of the power supply and ground return layout helps to ensure
the rated performance.
Two of the DACs in the AD5346/AD5347/AD5348 can be
paired together to form a coarse and fine adjustment function,
as shown in Figure 47. As with the window comparator
previously described, the description refers to DACs A and B.
The printed circuit board on which the AD5346/AD5347/
AD5348 is mounted should be designed so that the analog and
digital sections are separated and are confined to certain areas
of the board. This facilitates the use of ground planes that can
be separated easily. A minimum etch technique is generally best
for ground planes because it gives the best shielding. Digital and
analog ground planes should be joined in one place only. If the
AD5346/AD5347/AD5348 is the only device requiring an
AGND-to-DGND connection, then the ground planes should
be connected at the AGND and DGND pins of the AD5346/
AD5347/AD5348. If the AD5346/AD5347/AD5348 is in a
system where multiple devices require AGND-to-DGND
connections, the connection should be made at one point only, a
star ground point that should be established as close as possible
to the AD5346/AD5347/AD5348.
DAC A provides 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 shown, the output amplifier has unity gain for
the DAC A output, so the output range is 0 V to (VREF – 1 LSB).
For DAC B, the amplifier has a gain of 7.6 × 10–3, giving DAC B
a range equal to 2 LSBs of DAC A.
The circuit is shown with a 2.5 V reference, but reference
voltages up to VDD may be used. The op amps indicated allow a
rail-to-rail output swing.
V
= 5V
DD
R4
R3
390Ω
51.2kΩ
0.1µF
10µF
5V
The AD5346/AD5347/AD5348 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 effective series inductance (ESI), such as the
common ceramic types that provide a low impedance path to
ground at high frequencies to handle transient currents due to
internal logic switching.
V
DD
V
V
OUT
IN
V
A
OUT
EXT
REF
R1
390Ω
V
V
AB
OUT
REF
0.1µF
AD5346/AD5347/
AD5348
GND
R2
51.2kΩ
V
B
OUT
AD780/ADR381/REF192
WITH V = 5V
DD
GND
Figure 47. Coarse and Fine Adjustment
The power supply lines of the device should use the largest trace
possible to provide low impedance paths and to 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 should
never be run near the reference inputs. Avoid crossover of
digital and analog signals. Traces on opposite sides of the board
should run at right angles to each other to reduce the effects of
feedthrough through the board. A microstrip technique is by far
the best, but not always possible with a double-sided board. In
this technique, the component side of the board is dedicated to
ground plane, while signal traces are placed on the solder side.
Rev. 0 | Page 21 of 24
5秒后页面跳转
资料手册解读：UC3842参数和管脚说明
一文带你了解无源晶振的负载电容为何要加两颗谐振电容CL1和CL2
玻璃管保险丝与陶瓷管保险丝：区别与替代性探讨
PCF8574资料解读：主要参数分析、引脚说明
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
数据手册
如果您发现信息不准确，
