dac-1508a Analog Devices, Inc., dac-1508a Datasheet - Page 6

• Manufacturer Part Number: dac-1508a
• Description: 8-bit Multiplying D/a Converters
• Manufacturer: Analog Devices, Inc.

ACCURACY
Absolute
level with respect to its intended value, and is dependent
accuracy is the measure of each output current level as a
fraction of the full-scale current. The relative accuracy of the
the excellent temperature tracking of the monolithic resistor
causing a change in the absolute accuracy of output current.
drift with temperature.
The DAC-1508A-8/DAC-1408A series is guaranteed accurate
to within :t 1/2 LSB at a full-scale output current of 1.992mA.
This corresponds to a reference amplifier output current
drive to the ladder network of 2.0mA, with the loss of one LSB
The input current to Pin 14has a guaranteed value of between
source pair. Testing relative accuracy is accomplished by the
circuit labelled "Relative Accuracy Test Circuit". The 12-bit
converter is calibrated for a full-scale output current of
accuracy is essentially the same between 1.5 and 2.5mA.
Then the DAC-1508A-8 circuit's full-scale current is trimmed
to the same value with R14so that a zero value appears at the
error amplifier output. The counter is activated and the error
band may be displayed on an oscilloscope, detected by
comparators, or stored in a peak detector.
Two 8-bit D/A converters may not be used to construct a
16-bit accuracy D/A converter. 16-bit accuracy implies a
total errorof:t
is much more accurate
vided
upon relative accuracy and full-scale current drift. Relative
DAC-1508A-8 is essentially constant with temperature due to
ladder. The reference current may drift with temperature,
However, the DAC-1508A-8 has a very low full-scale current
(8.0pA), which is the ladder remainder shunted to ground.
1.9 and 2.1mA, allowing some mismatch in the NPN current
1.992mA. This is an optional step since the DAC-1508A-8
by the DAC-1508A-8.
accuracy is the measure of each output current
1/2 of one part in 65, 536, or:t0.00076% which
than the :to.19% specification pro-
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DAC-150aAl140aAa-BIT MULTIPLYING D/ACONVERTERS
--
11-120
tion for all
the dominant factor in satisfactory test results when measur-
frequencies, and a
The DAC-1508A-8 may be used
eight-bit accuracy when the reference current is varied
contributions are less
accuracy when referred to full scale.
current for each increment
SETTLING TIME
The "worst case" switching condition occurs when all bits are
switched
within:t 1/2 LSB, for 8-bit accuracy, and 200ns to 1/2 LSB for
7 and 6-bit accuracy.
These times apply when RL:5 500n and Co:5 25pF.
The slowest single switch is the least
applications
going
ing settling time.
mandatory.
MULTIPLYING ACCURACY
range of
mode ranges from
A monotonic converter is one which
DAC-1508A-8is monotonic
above 0.5mA. The recommended
DC reference current is 0.5 to 4.0mA.
not occur, and a settling time of less than 250ns may be
realized.
Extra care must be taken in
ramp mode, the "worst
256:1. If the reference current in the multiplying
"ON", which corresponds
bits. This time
where the D/A converter functions in a
Short leads,
16pA to 4.0mA, the additional error
minimum scope lead length are all
than 1.6pA. This
The turn off is typically under
in the binary word. Typically, the
is typically
for all values of reference current
board
case" switching condition does
100pF supply bypassing for low
in the multiplying
range for operation with a
layout since this is usually
to a low-to-high transi-
supplies
is well within eight-bit
250ns for settling to
significant bit. In
8/87, Rev. A1
an increasein
mode with
positive-
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1oon5.
overa
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