LM1946N National Semiconductor, LM1946N Datasheet - Page 7

• Manufacturer Part Number: LM1946N
• Description: IC DIAGNOSTIC CIRCUIT 20 DIP
• Manufacturer: National Semiconductor

Specifications of LM1946N

• Function: Current Sense
• Voltage - Input: 9 ~ 26 V
• Current - Output: 20mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 20-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Accuracy: -
• Sensing Method: -
• Other names: *LM1946N; LM1946

Application Hints
One solution is to use a low cost thermistor in conjunction
with some low-TC resistors (see Figure 8 )
There are three fixed resistors and one thermistor This is
an NTC thermistor since it has a negative temperature co-
efficient This is what is required in order to have Iset in-
crease as the temperature rises The data sheet with the
thermistor described a number of ways to establish different
final TC’s The thermistor itself has a very large TC which is
somewhat difficult to describe mathematically But if it is
used with some other fixed resistors such as Rmin and
Rmax definite end point limits can be established and an
(Continued)
FIGURE 9 Iset vs Temperature with Figure 8 Circuit
FIGURE 8 Thermistor Resistor Network
7
approximate staight line TC generated See Figure 9 for a
graphic representation of the ideal calculated values of Iset
and the actual measured values generated Notice that
there is very close agreement between the two graphs The
circuit actually creates an S-shaped curve around the ideal
The low-cost thermistor is available from Keystone and is
listed as follows RL2008-52 3K-155-D1
OVER-CURRENT LIMIT DETECTOR
Other applications include an over-current detector as
shown in Figure 10 The load represented here can be ei-
ther a single component or an entire system Resistors R3
TL H 8707 – 11
TL H 8707 – 12
Thermistor
Keystone
RL2008-52 3K-155-D1
100k
25 C