OP297FS datasheet(9/12 Pages) AD

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REV. E

OP297

–9–

CIN

IOS

–IN

EREF

RIN2

+IN

RIN1

EOS

R16

R17

ISYS

28 29

D5 26

R18

R19

D10

R10

R11

R13

R12

R14

R15

Figure 15. Macro Model

In these circuits, IREF is a function of the negative power supply.

To maintain accuracy, the negative supply should be well regu-

lated. For applications where very high accuracy is required, a

voltage reference may be used to set IREF. An important consider-

ation for the squaring circuit is that a sufficiently large input voltage

can force the output beyond the operating range of the output

op amp. Resistor R4 can be changed to scale IREF, or R1, and R2

can be varied to keep the output voltage within the usable range.

Unadjusted accuracy of the square-root circuit is better than 0.1%

over an input voltage range of 100 mV to 10 V. For a similar

input voltage range, the accuracy of the squaring circuit is better

than 0.5%.

OP297 SPICE MACRO MODEL

Figures 14 and 15 show the node end net list for a SPICE macro

model of the OP297. The model is a simplified version of the

actual device and simulates important dc parameters such as VOS,

IOS, IB, AVO, CMR, VO, and ISY. AC parameters such as slew

rate, gain and phase response, and CMR change with frequency

are also simulated by the model.

The model uses typical parameters for the OP297. The poles

and zeros in the model were determined from the actual open-

and closed-loop gain and phase response of the OP297. In this

way, the model presents an accurate ac representation of the actual

device. The model assumes an ambient temperature of 25

°C.

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