AD588TQ Просмотр технического описания (PDF) - Analog Devices

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AD588TQ

High Precision Voltage Reference

Analog Devices 

AD588

Figure 11 displays the output amplifier characteristics driving a

5 mA to 10 mA load, a common situation found when the refer-

ence is shared among multiple converters or is used to provide a

bipolar offset current.

Figure 13 displays the crosstalk between output amplifiers. The

top trace shows the output of A4, dc-coupled and offset by 10

volts, while the output of A3 is subjected to a 0 mA-to-10 mA

load current step. The transient at A4 settles in about 1 µs, and

the load-induced offset is about 100 µV.

Figure 11a. Transient and Constant Load Test Circuit

Figure 13a. Load Crosstalk Test Circuit

Figure 11b. Transient Response 5 mA–10 mA Load

In some applications, a varying load may be both resistive and

capacitive in nature, or be connected to the AD588 by a long

capacitive cable.

Figure 12 displays the output amplifier characteristics driving a

1,000 pF, 0 mA-to-10 mA load.

Figure 13b. Load Crosstalk

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 14a). 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

14b. 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 pro-

vides a high frequency feedback loop. The performance of this

circuit is shown in Figure 14c.

Figure 12a. Capacitive Load Transient Response Test

Circuit

Figure 14a. Output Amplifier Step Response, CL = 1 µF

Figure 12b. Output Response with Capacitive Load

REV. B

–8–

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