Datasheet

LM613
www.ti.com SNOSC11B –AUGUST 2000–REVISED MARCH 2013
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, except when a substrate diode conducts, see
(1)
in Electrical Characteristics. For example, one amp
input may be outside 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 inverting input to output and non-
inverting input to V
−
on unused 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:
1. Output Swing: Unloaded, the 42 μA pull-down will bring the output within 300 mV of V
−
over the military
temperature range. If more than 42 μA is required, a resistor from output to V
−
will help. Swing across any
load may be improved slightly if the load can be tied to V
+
, at the cost of poorer sinking open-loop voltage
gain.
2. Cross-Over Distortion: The LM613 has lower cross-over distortion (a 1 V
BE
deadband versus 3 V
BE
for the
LM124), and increased slew rate as shown in the characteristic curves. A resistor pull-up or pull-down will
force class-A operation with only the PNP or NPN output transistor conducting, eliminating cross-over
distortion.
3. 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 25Ω. 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 output 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
current must be less than 8 mA (over temperature). This impacts 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 supply nor across the inputs. These features
make the inputs look like high impedances to input sources producing large differential and common-mode
voltages.
(1) Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply
when operating the device beyond its rated operating conditions.
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