NSC LM1851N, LM1851MX, LM1851M Datasheet
TL/H/5177
LM1851 Ground Fault Interrupter
June 1992
LM1851 Ground Fault Interrupter
General Description
The LM1851 is designed to provide ground fault protection
for AC power outlets in consumer and industrial environments. Ground fault currents greater than a presettable
threshold value will trigger an external SCR-driven circuit
breaker to interrupt the AC line and remove the fault condition. In addition to detection of conventional hot wire to
ground faults, the neutral fault condition is also detected.
Full advantage of the U.S. UL943 timing specification is taken to insure maximum immunity to false triggering due to
line noise. Special features include circuitry that rapidly resets the timing capacitor in the event that noise pulses introduce unwanted charging currents and a memory circuit that
allows firing of even a sluggish breaker on either half-cycle
of the line voltage when external full-wave rectification is
used.
Features
Y
Internal power supply shunt regulator
Y
Externally programmable fault current threshold
Y
Externally programmable fault current integration time
Y
Direct interface to SCR
Y
Operates under line reversal; both load vs line and hot
vs neutral
Y
Detects neutral line faults
Block and Connection Diagram
TL/H/5177– 1
Order Number LM1851M or LM1851N
See NS Package Number M08A or N08E
C
1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Supply Current 19 mA
Power Dissipation (Note 1) 1250 mW
Operating Temperature Range
b
40§Ctoa70§C
Storage Temperature Range
b
55§Ctoa150§C
Soldering Information
Dual-In-Line Package (10 sec.) 260
§
C
Small Outline Package
Vapor Phase (60 sec.) 215
§
C
Infrared (15 sec.) 220
§
C
See AN-450 ‘‘Surface Mounting and Their Effects on Product Reliability’’ for other methods of soldering surface
mount devices.
DC Electrical Characteristics T
A
e
25§C, I
SS
e
5mA
Parameter Conditions Min Typ Max Units
Power Supply Shunt Pin 8, Average Value
22 26 30 V
Regulator Voltage
Latch Trigger Voltage Pin 7 15 17.5 20 V
Sensitivity Set Voltage Pin 8 to Pin 6 6 7 8.2 V
Output Drive Current Pin 1, With Fault 0.5 1 2.4 mA
Output Saturation Voltage Pin 1, Without Fault 100 240 mV
Output Saturation Resistance Pin 1, Without Fault 100 X
Output External Current Pin 1, Without Fault,
2.0 5 mA
Sinking Capability V
pin 1
Held to 0.3V (Note 4)
Noise Integration Pin 7, Ratio of Discharge
Sink Current Ratio Currents Between No Fault 2.0 2.8 3.6 mA/mA
and Fault Conditions
AC Electrical Characteristics T
A
e
25§C, I
SS
e
5mA
Parameter Conditions Min Typ Max Units
Normal Fault Current
Figure 1
(Note 3) 3 5 7 mA
Sensitivity
Normal Fault Trip Time 500X Fault,
Figure 2
(Note 2) 18 ms
Normal Fault with 500X Normal Fault, 18 ms
Grounded Neutral Fault 2X Neutral,
Figure 2
(Note 2)
Trip Time
Note 1: For operation in ambient temperatures above 25§C, the device must be derated based on a 125§C maximum junction temperature and a thermal resistance
of 80
§
C/W junction to ambient for the DIP and 162§C/W for the SO Package.
Note 2: Average of 10 trials.
Note 3: Required UL sensitivity tolerance is such that external trimming of LM1851 sensitivity will be necessary.
Note 4: This externally applied current is in addition to the internal ‘‘output drive current’’ source.
TL/H/5177– 2
FIGURE 1. Normal Fault Sensitivity Test Circuit
2
Internal Schematic Diagram
TL/H/5177– 3
3
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