Connecting a resistor across Cathode-to-FEEDBACK cre-

ates a 0 TC current source, but a range of TCs may be

synthesized.

Hysteresis

The reference voltage depends, slightly, on the thermal his-

tory

of

the

die.

Competitive

micro-power

products

vary — always check the data sheet for any given device. Do

not assume that no specification means no hysteresis.

OPERATIONAL AMPLIFIERS

Any amp or the reference may be biased in any way with no

effect on the other amps or reference, except when a sub-

strate diode conducts (see Guaranteed Electrical Character-

istics (Note 1)). One amp input may be outside the

common-mode range, another amp may be operated as a

comparator, another with all terminals floating with no effect

on

the

others

(tying

inverting

input

to

output

and

non-inverting input to V

Choosing operating points that cause oscillation, such as

driving too large a capacitive load, is best avoided.

Op Amp Output Stage

These op amps, like their LM124 series, have flexible and

relatively wide-swing output stages. There are simple rules

to optimize output swing, reduce cross-over distortion, and

optimize capacitive drive capability:

1.

Output Swing: Unloaded, the 42 µA pull-down will bring

the output within 300 mV of V

ture range. If more than 42 µA is required, a resistor from

output to V

proved slightly if the load can be tied to V

poorer sinking open-loop voltage gain

DS009326-14

FIGURE 6. Output Voltage has Negative Temperature

Coefficient (TC) if R2 has Negative TC

DS009326-15

FIGURE 7. Output Voltage has Positive TC

if R1 has Negative TC

DS009326-16

FIGURE 8. Diode in Series with R1 Causes Voltage

across R1 and R2 to be Proportional to Absolute

Temperature (PTAT)

DS009326-17

I = Vr/R1 = 1.24/R1

FIGURE 9. Current Source is Programmed by R1

DS009326-18

FIGURE 10. Proportional-to-Absolute-Temperature

Current Source

DS009326-19

FIGURE 11. Negative-TC Current Source

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