LM397MF Datasheet, PDF (6/14 Pages) Texas Instruments – LM397 Single General Purpose Voltage Comparator

LM397
SNOS977D – MAY 2001 – REVISED MARCH 2013
V_CC
R₁
V_IN
R_PULL-UP
-
V_O
V_T
+
R
R₃
2
V_O
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V_T2
V_T1
0
V_IN
Figure 10. Inverting Configured Comparator - LM397
Input Stage
The LM397 has a bipolar input stage. The input common mode voltage range is from 0 to (V_S – 1.5V).
Output Stage
The LM397 has an open collector grounded-emitter NPN output transistor for the output stage. This requires an
external 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 11).
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
1
-40°C
85°C
25°C
10
100
OUTPUT SINK CURRENT (mA)
Figure 11. Output Saturation Voltage vs. Output Sink Current
6
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