AD7841AS Analog Devices Inc, AD7841AS Datasheet - Page 11

• Manufacturer Part Number: AD7841AS
• Description: IC DAC 14BIT OCTAL VOUT 44-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7841AS

• Rohs Status: RoHS non-compliant
• Settling Time: 31µs
• Number Of Bits: 14
• Data Interface: Parallel
• Number Of Converters: 8
• Voltage Supply Source: Analog and Digital, Dual ±
• Power Dissipation (max): 303mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-MQFP, 44-PQFP
• For Use With: EVAL-AD7841EBZ - BOARD EVAL FOR AD7841

REV. B
TRIMDAC is a registered trademark of Analog Devices, Inc.
The AD7841 should have ample supply bypassing located as
close to the package as possible, ideally right up against the
device. Figure 11 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
should 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 frequen-
cies to handle transient currents due to internal logic switching.
Automated Test Equipment
The AD7841 is particularly suited for use in an automated test
environment. Figure 12 shows the AD7841 providing the neces-
sary voltages for the pin driver and the window comparator in a
typical ATE pin electronics configuration. AD588s are used to
provide reference voltages for the AD7841. In the configuration
shown, the AD588s are configured so that the voltage at Pin 1 is
5 V greater than the voltage at Pin 9 and the voltage at Pin 15 is
5 V less than the voltage at Pin 9.
One of the AD588s is used as a reference for DACs A and B.
These DACs are used to provide high and low levels for the pin
driver. The pin driver may have an associated offset. This can
be nulled by applying an offset voltage to Pin 9 of the AD588.
First, the code 1000 . . . 0000 is loaded into the DACA latch
and the pin driver output is set to the DACA output. The
V
driver output and DUTGND. This causes both V
V
OFFSET
REF
13
10
12
11
13
10
11
12
4
6
8
4
6
8
(–) to be offset with respect to GND by an amount equal to
1 F
1 F
+15V –15V
+15V –15V
AD588
AD588
2
2
voltage is adjusted until 0 V appears between the pin
7
7
0.1 F
16
16
1
15
14
15
14
3
9
1
3
9
ADDITIONAL PINS OMITTED FOR CLARITY
V
0.1 F
DEVICE
GND
10 F
OFFSET
V
V
V
V
DUTGND_AB
REF
REF
REF
REF
V
AD7841
(+)AB
(–)AB
(+)GH
(–)GH
CC
AD7841
DUTGND_GH
GND
V
V
V
V
COMPARATOR
V
V
OUT
OUT
OUT
OUT
DD
SS
WINDOW
G
H
A
B
10 F
10 F
DRIVER
DEVICE
GND
+15V
–15V
PIN
TO TESTER
0.1 F
0.1 F
REF
(+) and
DEVICE
GND
V
OUT
V
–10 V to +10 V with respect to DUTGND as the DAC input
code varies from 000 . . . 000 to 111 . . . 111. The V
voltage is also applied to the DUTGND pins. When a clear is
performed on the AD7841, the output of the pin driver will be
0 V with respect to DUTGND.
The other AD588 is used to provide a reference voltage for
DACs G and H. These provide the reference voltages for the
window comparator shown in the diagram. Note that Pin 9 of
this AD588 is connected to Device GND. This causes V
and V
and DAC H input codes vary from 000 . . . 000 to 111 . . . 111,
V
Device GND. Device GND is also connected to DUTGND.
When the AD7841 is cleared, V
0 V with respect to Device GND.
Programmable Reference Generation for the AD7841 in an
ATE Application
The AD7841 is particularly suited for use in an automated test
environment. The reference input for the AD7841 octal 14-bit
DAC requires three differential references for the eight DACs.
Programmable references may be a requirement in some ATE
applications as the offset and gain errors at the output of a DAC
can be adjusted by varying the voltages on the reference pins of
the DAC. To trim offset errors, the DAC is loaded with the
digital code 000 . . . 000 and the voltage on the V
adjusted until the desired negative output voltage is obtained.
To trim out gain errors, first the offset error is trimmed. Then
the DAC is loaded with the code 111 . . . 111 and the voltage
on the V
minus one LSB is obtained.
It is not uncommon in ATE design, to have other circuitry at
the output of the AD7841 that can have offset and gain errors of
up to say ± 300 mV. These offset and gain errors can be easily
removed by adjusting the reference voltages of the AD7841.
The AD7841 uses nominal reference values of ± 5 V to achieve
an output span of ± 10 V. Since the AD7841 has a gain of two
from the reference inputs to the DAC output, adjusting the
reference voltages by ± 150 mV will adjust the DAC offset and
gain by ± 300 mV.
There are a number of suitable 8- and 10-bit DACs available
that would be suitable to drive the reference inputs of the AD7841,
such as the AD7804, a quad 10-bit digital-to-analog converter
with serial load capabilities. The voltage output from this DAC
is in the form of V
achievable. The voltage reference for this DAC can be inter-
nally generated or provided externally. This DAC also contains
an 8-bit SUB DAC which can be used to shift the complete trans-
fer function of each DAC around the V
used as a fine trim on the output voltage. In this application two
AD7804s are required to provide programmable reference capabil-
ity for all eight DACs. One AD7804 is used to drive the V
pins and the second package used to drive the V
Another suitable DAC for providing programmable reference
capability is the AD8803. This is an octal 8-bit TRIMDAC
and provides independent control of both the top and bottom
ends of the TRIMDAC. This is helpful in maximizing the reso-
lution of devices with a limited allowable voltage control range.
OFFSET
OUT
G and V
REF
. However, the output of the pin driver will vary from
REF
(–)GH to be referenced to Device GND. As DAC G
(+) pin is adjusted until the desired full-scale voltage
OUT
H vary from –10 V to +10 V with respect to
BIAS
± V
SWING
OUT
and rail-to-rail operation is
G and V
BIAS
point. This can be
OUT
AD7841
H are cleared to
REF
REF
(–) pins.
OFFSET
(–) pin is
REF
(+)GH
REF
(+)
®