AD588TQ Analog Devices, AD588TQ Datasheet - Page 10

• Manufacturer Part Number: AD588TQ
• Description: High Precision Voltage Reference
• Manufacturer: Analog Devices

AD588
Attempts to drive a large capacitive load (in excess of 1,000 pF)
may result in ringing or oscillation, as shown in the step response
photo (Figure 19a). This is due to the additional pole formed by
the load capacitance and the output impedance of the amplifier,
which consumes phase margin. The recommended method of
driving capacitive loads of this magnitude is shown in Figure 19b.
The 150 Ω resistor isolates the capacitive load from the output
stage, while the 10 kΩ resistor provides a dc feedback path and
preserves the output accuracy. The 1 µF capacitor provides a
high frequency feedback loop. The performance of this circuit is
shown in Figure 19c.
Figure 19a. Output Amplifier Step Response, C
Figure 19b. Compensation for Capacitive Loads
Figure 19c. Output Amplifier Step Response
Using Figure 19b Compensation
+
–
V
IN
10k
1 F
150
C
1 F
L
V
OUT
L
= 1 µ F
–10–
USING THE AD588 WITH CONVERTERS
The AD588 is an ideal reference for a wide variety of A/D and
D/A converters. Several representative examples follow.
14-Bit Digital-to-Analog Converter—AD7535
High resolution CMOS D/A converters require a reference voltage
of high precision to maintain rated accuracy. The combination
of the AD588 and AD7535 takes advantage of the initial accu-
racy, drift, and full Kelvin output capability of the AD588 as
well as the resolution, monotonicity, and accuracy of the AD7535
to produce a subsystem with outstanding characteristics. See
Figure 20.
16-Bit Digital-to-Analog Converter—AD569
Another application that fully utilizes the capabilities of the
AD588 is supplying a reference for the AD569, as shown in
Figure 21. Amplifier A2 senses system common and forces V
to assume this value, producing +5 V and –5 V at Pin 6 and
Pin 8, respectively. Amplifiers A3 and A4 buffer these voltages
out to the appropriate reference force-sense pins of the AD569.
The full Kelvin scheme eliminates the effect of the circuit traces
or wires and the wire bonds of the AD588 and AD569 them-
selves, which would otherwise degrade system performance.
SUBSTITUTING FOR INTERNAL REFERENCES
Many converters include built-in references. Unfortunately,
such references are the major source of drift in these converters.
By using a more stable external reference like the AD588, drift
performance can be improved dramatically.
REV. D
CT