LM613 datasheet(17/22 Pages) NSC

17 / 22 page

Application Information (Continued)

Reference Hysteresis

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

tory of the die. Competitive micro-power products vary — al-

ways check the data sheet for any given device. Do not as-

sume that no specification means no hysteresis.

OPERATIONAL AMPLIFIERS AND COMPARATORS

Any amp, comparator, or the reference may be biased in any

way with no effect on the other sections of the LM613, ex-

cept when a substrate diode conducts, see Electrical Char-

acteristics (Note 1). For example, one amp input may be out-

side the common-mode range, another amp may be

operating as a comparator, and all other sections may have

all terminals floating with no effect on the others. Tying in-

verting input to output and non-inverting input to V

− on un-

used amps is preferred. Unused comparators should have

non-inverting input and output tied to V

+, and inverting input

tied 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 the 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:

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

the output within 300 mV of V

− over the military tempera-

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

output to V

− will help. Swing across any load may be im-

proved slightly if the load can be tied to V

+, at the cost of

poorer sinking open-loop voltage gain.

Cross-Over Distortion: The LM613 has lower cross-over

distortion (a 1 V

BE deadband versus 3 VBE for the

LM124), and increased slew rate as shown in the char-

acteristic curves. A resistor pull-up or pull-down will force

class-A operation with only the PNP or NPN output tran-

sistor conducting, eliminating cross-over distortion.

Capacitive Drive: Limited by the output pole caused by

the output resistance driving capacitive loads, a

pull-down resistor conducting 1 mA or more reduces the

output stage NPN r

e until the output resistance is that of

the current limit 25

Ω. 200 pF may then be driven without

oscillation.

Comparator Output Stage

The comparators, like the LM139 series, have open-collector

output stages. A pull-up resistor must be added from each

output pin to a positive voltage for the output transistor to

switch properly. When the output transistor is OFF, the out-

put voltage will be this external positive voltage.

For the output voltage to be under the TTL-low voltage

threshold when the output transistor is ON, the output cur-

rent must be less than 8 mA (over temperature). This im-

pacts the minimum value of pull-up resistor.

The offset voltage may increase when the output voltage is

low and the output current is less than 30 µA. Thus, for best

accuracy, the pull-up resistor value should be low enough to

allow the output transistor to sink more than 30 µA.

Op Amp and Comparator Input Stage

The lateral PNP input transistors, unlike those of most op

amps, have BV

EBO equal to the absolute maximum supply

voltage. Also, they have no diode clamps to the positive sup-

ply nor across the inputs. These features make the inputs

look like high impedances to input sources producing large

differential and common-mode voltages.

Typical Applications

DS009226-40

FIGURE 12. High Current, High Voltage Switch

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