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February 1993
LM1946 Over/Under Current Limit Diagnostic Circuit
LM1946 Over/Under Current Limit Diagnostic Circuit
General Description
The LM1946 provides the industrial or automotive system
designer with over or under current limit detection superior
to that of ordinary transistor or comparator-based circuits.
Each of the five independent comparators can be used to
monitor a separate load as either an over current or under
current limit detector. Two comparators monitoring a single
load can function as a current window monitor.
Current is sensed by monitoring the voltage drop across the
wiring harness, pc board trace, or external sense resistor
that feeds the load.
Provisions for compensating the user set limits for wiring
harness resistance variations over temperature and supply
voltage variations are also available.
When a limit is reached in one of the comparators, it turns
on its output which can drive an external LED or microprocessor.
One side of the load can be grounded (not possible with
Features
Y
Five independent comparators
Y
Capable of 20 mA per output
Y
Low power drain
Y
User set input threshold voltages
Y
Reverse battery protection
Y
60V load dump protection on supply and all inputs
Y
Input common mode range exceeds V
Y
Short circuit protection
Y
Thermal overload protection
Y
Prove-out test pin
Y
Available in plastic DIP and SO packages
Applications
Y
Lamp fault detector
Y
Motor stall detector
Y
Power supply bus monitoring
ordinary comparator designs), which is important for automotive systems.
Typical Application CircuitÐLamp Fault Detector (I
CC
l
1A)
L
FIGURE 1
TL/H/8707– 2
C
1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.
TL/H/8707
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Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Supply Voltage (V
Survival Voltage (T
and Input Pins)
CC
s
100 ms)
b
50V toa60V
Operational Voltage 9V to 26V
Internal Power Dissipation (Note 1) Internally Limited
s
Electrical Characteristics 9V
s
V
16V, Isete20 mA, T
CC
Parameter Conditions Min Typ Max Units
Quiescent Current All Outputs ‘‘Off’’ 1.40 3.00 mA
Reference Voltage I
Reference Voltage 9VsV
Line Regulation
e
10 mA 5.8 6.4 7.0 V
ref
CC
s
16V, I
e
ref
Iset Voltage Isete20 mA 1.20 1.40 1.60 V
Input Offset Voltage At Output Switch Point. V
Input Offset Current I
Input Bias Current I
9VsV
IN(a)
IN(a)
b
or I
CM
s
I
IN(b)
IN(b)
16V
,9VsV
,9VsV
CM
CM
Input Common Mode
Voltage Range
Maximum Positive Either Input. Ts100 ms
Input Transient
Maximum Negative Either Input. Ts100 ms
Input Transient
Output Saturation I
Voltage
Output Short Circuit V
Current
Output Leakage Current V
e
2 mA, 9VsV
O
e
I
10 mA, 9VsV
O
e
0Vdc, Comparator ‘‘ON’’
O
e
0Vdc. Comparator ‘‘Off’’ 0.01 1.00 mA
O
CC
CC
s
s
Test Threshold At Switch Point on Any Output
Voltage V
e
O
2V (Note 2)
Test Threshold
Current
Note 1: Thermal resistance from junction to ambient is typically 53§C/W (board mounted).
Note 2: The test pin is an active high input, i.e. all five will be forced high when this pin is driven high.
Note 3: C
ESD
e
100 pF, R
ESD
e
1.5k
Output Short Circuit to Ground or V
Operating Temperature Range (TA)
CC
Continuous
b
40§Ctoa85§C
Maximum Junction Temperature
Storage Temperature Range
b
65§Ctoa150§C
Lead Temperature (Soldering, 10 sec.)
ESD Susceptibility (Note 3) 600V
e
25§C (unless otherwise specified)
j
10 mA
e
2V
O
s
16V
s
16V 18.00 20.00 22.00 mA
g
5
g
1.0
g
0.10
g
50 mV
g
5.0 mV
g
1.00 mA
4.00 26.0 V
60 70 V
b
50
b
60 V
16V 0.80 1.00 V
16V 1.00 1.20 V
20 45 120.0 mA
0.80 1.25 2.00 V
0.2 mA
a
a
150§C
260§C
dc
dc
dc
dc
dc
dc
dc
dc
dc
dc
dc
dc
dc
dc
2
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Connection Diagram
Order Number LM1946N or LM1946M
See NS Package Number M20B or N20A
Typical Test Circuit
Simplified Comparator Schematic
TL/H/8707– 20
TL/H/8707– 23
TL/H/8707– 24
3
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Typical Performance Characteristics
V
sat
Peak I
vs I
Quiescent Current
O
vs V
O
CC
vs V
CC
V
vs Temperature V
set
Quiescent Current
vs V
CC
vs Temperature
ref
Iset vs Temperature Iset vs Temperature Iset vs Temperature
Test Threshold Common Mode Lower Limit
4
TL/H/8707– 4