LM612 National Semiconductor, LM612 Datasheet - Page 8

• Manufacturer Part Number: LM612
• Description: Dual-Channel Comparator and Reference
• Manufacturer: National Semiconductor

Application Information
of hysteresis can substantially reduce the accuracy of the
comparator since the offset voltage is effectively being in-
creased by the hysteresis when the comparator output is
high
It is often a good idea to decrease the amount of hysteresis
until oscillations are observed then use three times that
minimum hysteresis in the final circuit Note that the amount
of hysteresis needed is greatly affected by layout The
amount of hysteresis should be rechecked each time the
layout is changed such as changing from a breadboard to a
P C board
Input Stage
The input stage uses lateral PNP input transistors which
unlike those of many op amps have breakdown voltage
BV
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
Typical Applications
EBO
equal to the absolute maximum supply voltage Also
(Continued)
Power Supply Monitor with Indicator
8
The guaranteed common-mode input voltage range for an
LM612 is V
This is the voltage range in which the comparisons must be
made If both inputs are within this range the output will be
at the correct state If one input is within this range and the
other input is less than (V
than V
either or both inputs are driven below V
current exceeds 10
to be correct If both inputs are above (V
output state is also not guaranteed to be correct
Output Stage
The comparators have a common open-collector output
stage which requires a pull-up resistor to a positive supply
voltage for the output to switch properly When the internal
output transistor is off the output (HIGH) voltage will be
pulled up to this external positive voltage
To ensure that the LOW output voltage is under the TTL-low
threshold the output transistor’s load current must be less
than 0 8 mA (over temperature) when it turns on This im-
pacts the minimum value of the pull-up resistor
a
the output will be at the correct state If however
b
s
V
CM s
A the output state is not guaranteed
(V
b
a
a
b
32V) even if this is greater
1 8V) over temperature
b
TL H 11058 – 12
a
and either input
b
1 8V) the