lm397-mdc National Semiconductor Corporation, lm397-mdc Datasheet - Page 5

• Manufacturer Part Number: lm397-mdc
• Description: Single General Purpose Voltage Comparator
• Manufacturer: National Semiconductor Corporation

Application Notes
(Continued)
Input Stage
The LM397 has a bipolar input stage. The input common
mode voltage range is from 0 to (V
– 1.5V).
S
Output Stage
The LM397 has an open collector grounded-emitter NPN
output transistor for the output stage. This requires an exter-
nal pull-up resistor connected between the positive supply
voltage and the output. The external pull-up resistor should
be high enough resistance so to avoid excessive power
dissipation. In addition, the pull-up resistor should be low
enough resistance to enable the comparator to switch with
the load circuitry connected. Because it is an open collector
output stage, several comparator outputs can be connected
together to create an OR’ing function output. With an open
collector, the output can be used as a simple SPST switch to
ground.The amount of current which the output can sink is
approximately 10mA. When the maximum current limit is
reached, the output transistor will saturate and the output will
rise rapidly (Figure 4).
20022107
FIGURE 4. Output Saturation Voltage vs. Output Sink
Current
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