artisan DAC128V, Hardware Reference Manual

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PRODUCT OVERVIEW
Copyright 2001 2-7 DAC128V HARDWARE REFERENCE
ratiometric tolerance of ±0.05% (very important) that track at 5 ppm/
°
C, in the worst
case.
All four reference voltages are buffered by the four Operational Amplifiers at U4, U5,
U6, and U9 to provide the user with outputs at the I/O connector for the voltages of
+10.00 V, -5.00 V, +5.00 V, and -10.00 V, respectively.
2.9 External Analog Supply
The DAC128V has provisions for running all of its analog circuitry off of an external
power source. There are at least two reasons for taking this action. First, some
applications may require “quieter” performance than is possible using the carrier’s power
sources. These are usually developed using noisier “switcher” technology than the older
“linear” techniques.
Second, and more importantly, the external power source provides greater accuracy.
While the reference circuitry is capable of running well from the +12 V provided by a
carrier, the DAC128V will not be able to maintain accuracy specifications when using
either of the +10 V rails to drive loads.
The DAC128V is shipped with the analog power selections configured for running from
the carrier's ±12 V supplies. This is implemented by the placement of the shunt H2 at the
two-by-two jumper block designated J3, and the shunt H3 at the jumper block J4 at the
top (towards the IP Module logic connector J1, away from the I/O connector J2) pair of
jumper pins. The printed circuit board’s silk-screen has these positions labeled as “+12v”
and “-12v”, respectively.
To operate the DAC128V from external (±12
→
) ±15 V supplies:
•
First ensure that the +15 V is wired to pin 48 of the I/O connector, and that -15 V
is wired to pin 45 of the I/O connector.
•
Ensure its power supply ground is well connected to the DAC128V’s ground
connections at J2.
•
Then, move jumper H2 to the bottom connections of J3, and move jumper H3 to
the bottom connections of J4 (bottom
≡
away from the logic connector J1,
towards the I/O connector J2).
These positions are silk-screen labeled on the printed circuit board as “+15v” and “-15v",
respectively.
2.10 The Buffers
There are eleven analog buffers used on the DAC128V, located at U4, U5, U6, U9, U10,
U11, U12, U13, U14, U15, and U16. They are all configured as unity-gain (non-
inverting) voltage followers, all using the ultra-precision Operational Amplifier
#OP177GS. This device was selected because it provides performance characteristics that
approach those typically only possible with chopper-stabilized amplifiers, without the
usual “chopper” problems of noise and spikes, large size with mandatory external storage
capacitors, limited common-mode input ranges, and high expense.
The 60
µ
V maximum input offset voltage (over temperature) is so small that offset
voltage reduction circuitry implemented with trim-potentiometers would fail to provide
significant accuracy improvements over temperature due to the tracking problems of
dissimilar temperature coefficients between the Operational Amplifiers and the
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