AD7834 Analog Devices, AD7834 Datasheet - Page 24

• Manufacturer Part Number: AD7834
• Description: LC2MOS Quad 14-Bit DAC
• Manufacturer: Analog Devices

Specifications of AD7834

• Resolution (bits): 14bit
• Dac Update Rate: 100kSPS
• Dac Settling Time: 10µs
• Max Pos Supply (v): +15.75V
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser

AD7834/AD7835
The other AD588 provides a reference voltage for DAC 3 and
DAC 4. These provide the reference voltages for the window
comparator shown in Figure 35. Pin 9 of this AD588 is con-
nected to DUT GND. This causes V
referenced to DUT GND. As DAC 3 and DAC 4 input codes vary
from 000 . . . 000 to 111 . . . 111, V
to +5 V with respect to DUT GND. DUT GND is also connected
to DSGB. When the AD7835 is cleared, V
cleared to 0 V with respect to DUT GND.
Care must be taken to ensure that the maximum and minimum
voltage specifications for the AD7835 reference voltages are
followed as shown in Figure 35.
POWER SUPPLY BYPASSING AND GROUNDING
In any circuit where accuracy is important, careful considera-
tion of the power supply and ground return layout helps to
ensure the rated performance. The printed circuit boards on
which the AD7834/AD7835 are mounted should be designed so
the analog and digital sections are separated and confined to
certain areas of the boards. This facilitates the use of ground
planes that can be easily separated. A minimum etch technique
is generally best for ground planes because it gives the best
shielding. Digital and analog ground planes should be joined at
only one place.
1µF
1
ADDITIONAL PINS OMITTED FOR CLARITY
13
10
12
1µF
13
11
4
6
8
7
4
6
8
+15V –15V
+15V –15V
AD588
10 11 12
AD588
7
2
2
16
9
16
DUT
GND
15
14
14
3
15
1
9
3
1
V
0.1µF
OFFSET
Figure 35. ATE Application
V
V
DSG A
V
V
REF
REF
REF
REF
AD7835
(+)A
(–)A
(+)B
(–)B
AGND
OUT
COMPARATOR
DSG B
REF
V
V
V
V
3 and V
1
OUT
OUT
OUT
OUT
WINDOW
(+)B and V
2
3
4
1
OUT
DRIVER
OUT
3 and V
DUT
GND
PIN
+15V
–15V
4 vary from −5 V
TO TESTER
REF
(−)B to be
OUT
4 are
GND
DUT
V
Rev. D | Page 24 of 28
DUT
If the AD7834/AD7835 are the only devices requiring an AGND
to DGND connection, then the ground planes should be connected
at the AGND and DGND pins of the AD7834/ AD7835. If the
AD7834/AD7835 are in a system where multiple devices require
an AGND to DGND connection, the connection can still be made
at one point only, a star ground point, which can be established as
close as possible to the AD7834/AD7835.
Digital lines running under the device must be avoided because
they couple noise onto the die. The analog ground plane can run
under the AD7834/AD7835 to avoid noise coupling. The power
supply lines of the AD7834/AD7835 can 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. These signals should never be
run near the analog inputs. 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
through the board. A microstrip method is best but not always
possible with a double-sided board. With this method, the
component side of the board is dedicated to ground plane while
signal traces are placed on the solder side.
The AD7834/AD7835 must have ample supply bypassing located
as close as possible to the package, ideally right up against the
device. Figure 36 shows the recommended capacitor values of
10 μF in parallel with 0.1 μF on each of the supplies. The 10 μF
capacitors are the tantalum bead type. The 0.1 μF capacitor can
have low effective series resistance (ESR) and effective series
inductance (ESI), such as the common ceramic types, which
provide a low impedance path to ground at high frequencies to
handle transient currents due to internal logic switching.
DGND
10μF
1
ADDITIONAL PINS OMITTED FOR CLARITY
Figure 36. Power Supply Decoupling
0.1μF
V
AD7834/
AD7835
CC
V
V
DD
1
SS
0.1μF
0.1μF
AGND
10μF
10μF