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TELEFUNKEN Semiconductors
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Automotive Lamp Outage Monitor
U2481B/ U2482B
Description
The U2481B and the U2482B multicomparator circuits
are designed to monitor automotive illumination by
sensing the voltage drop across shunt resistors. Provided
with extremely low comparator thresholds, these ICs can
be used together as a chip set to build an entire lamp
monitor system. Single operation of both circuits is also
possible.
As a special feature for brake lamp monitoring, the
U2481B contains a latch stage connected to one of its
triple comparators.
With
– 4 single comparators
– 1 double comparator and
– 2 triple comparators
each of the integrated circuits monitors up to 12 lamps
and up to 6 fuses.
All comparator stages are combined together to control
the common output stage.
Features
D Extremely low comparator thresholds of typically
3.5 mV
D Internal compensation for copper shunts
D Internal compensation for voltage-dependent
bulb characteristic
D Comparator input voltage may exceed supply voltage
D Internal protection measures for pulses
according to ISO TR 7637/1
D ESD according to MIL-SID-883 C test method 3015.7
– Human body model: 4 kV
– Machine model:
200 V
EMI protection (TEM cell up to 100 V/m)
Benefits
D Extremely low threshold voltage gives low voltage
drop via shunt resistor. Power dissipation of the lamp
monitor module is minimized
D Perfect EMC in conjunction with an appropriate
pc board layout
Applications
Both ICs can be used in any kind of vehicle with a 12 V
supply. It is sufficient to insert small resistors into the
lamp wiring and to provide the dashboard instrument
cluster with a pilot lamp. These ICs increase the safety
and add comfort features.
Rev. A1: 21.08.1995
Preliminary Information
1 (11)

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U2481B/ U2482B
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Block Diagram
28 Ref
REFK1
27
IN1K1
E1
K1 13 mV
+
IT
IT
REFK2
IN1K2
1
2
Ref K2 13 mV
E1
TELEFUNKEN Semiconductors
VB
20
VB
Voltage drift
of comparator
threshold
IT = f (VB)
Power
on
Reset
VS Stabilized
voltage
Vstab = 5.2 V
POR
IT
Divider
Oscillator
Clock 1 Clock 2
2-TOsc 20-TOsc
Cl1 Cl2
19
VS
15 OSC
REFK3
IN1K3
IN2K3
IN3K3
7
6
8
9
26
INFK3
REFK4
IN1K4
24
25
INFK5 16
REFK5
IN1K5
IN2K5
INF
4
3
5
VB
23
Ref K3 3.5 mV
E1
E2
E3
Ref K4 3.5 mV
E1
Ref K5 3.5 mV
E1
E2
+
REFK7
IN1K7
IN2K7
IN3K7
11
10
12
13
Ref K7 3.5 mV
E1
E2
E3
Up down counter
Cl2 T = 1.2 s
Start High at
Set
VS
forward counter end
Out
Start High at
return counter zero
Reset
Cl1
14
OUT
Out Reset
Latch for
stoplamps
Set
POR
K6 Ref
3.5 mV E1
17
INFK6
22
REFK6
21
IN1K6
Up down counter
Cl2 T = 1.2 s
Start High at
forward counter end
Start High at
return counter zero
Cl1
VS
* Connection to
GND only for
U2482B (latch
disabled
18
*
GND
94 8833
Figure 1.
2 (11)
Preliminary Information
Rev. A1: 21.08.1995

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Pin Description
REFK2 1
28 REFK1
IN1K2 2
27 IN1K1
In1K5 3
REFK5 4
26 INFK3
25 IN1K4
IN2K5 5
24 REFK4
IN1K3 6
REFK3 7
23 INF
22 REFK6
IN2K3 8
IN3K3 9
21 IN1K6
20 VB
IN1K7 10
19 VS
REFK7 11
18 GND
IN2K7 12
17 INFK6
IN3K7 13
16 INFK5
OUT 14
15 OSC
94 8831
Figure 2. Pin configuration
U2481B/ U2482B
Pin Symbol
Function
1 REFK2 Reference for threshold voltage
single comparator K2
2 IN1K2 Input 1; single comparator K2
3 IN1K5 Input 1; double comparator K5
4 REFK5 Reference for threshold voltage;
double comparator K5
5 IN2K5 Input 2; double comparator K5
6 IN1K3 Input 1; triple comparator K3
7 REFK3 Reference for threshold voltage;
triple comparator K3
8 IN2K3 Input 2; triple comparator K3
9 IN3K3 Input 3; triple comparator K3
10 IN1K7 Input 1; triple comparator K7
(U2481B with latch)
11 REFK7 Reference for threshold voltage;
triple comparator K7
(U2481B with latch)
12 IN2K7 Input 2; triple comparator K7
(U2481B with latch)
13 IN3K7 Input 3; triple comparator K7
(U2481B with latch)
14 OUT Output for pilot lamp
15 OSC R/C combination for oscillator
16 INFK5 Fuse monitor input ; double
comparator K5
17 INFK6 Fuse monitor input; single
comparator K6
18 GND Ground
19 VS Supply voltage
20 VB Reference voltage of compara-
tors
21 IN1K6 Input1; single comparator K6
22 REFK6 Reference for threshold voltage;
single comparator K6
23 INF Input; brake fuse comparator
24 REFK4 Reference for threshold voltage;
single comparator K4
25 IN1K4 Input 1; single comparator K4
26 INFK3 Fuse monitor input; triple
comparator K3
27 IN1K1 Input 1; single comparator K1
28 REFK1 Reference for threshold voltage;
single comparator K1
Rev. A1: 21.08.1995
Preliminary Information
3 (11)