U2481B/ U2482B
Rev. A5, 03-Apr-01 1 (12)
Multiple Automotive Lamp-Outage Monitor, VT = 3.5 mV
Description
The U2481B and the U2482B multicomparator circuits
are designed to monitor automotive illumination by
sensing the voltage drop across shunt resistors. Equipped
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
Extremely low comparator thresholds of typically
3.5 mV
Internal compensation for copper shunts
Internal compensation for voltage-dependent
bulb characteristic
Comparator input voltage may exceed supply voltage
Internal protection measures for pulses
according to ISO TR 7637/1
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
Extremely low threshold voltage gives low voltage
drop via shunt resistor. Power dissipation of the lamp
monitor module is minimized
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 safety and
add comfort features.
Ordering Information
Extended Type Number Package Remarks
U2481B–FL SO28
U2482B–FL SO28
U2481B/ U2482B
Rev. A5, 03-Apr-012 (12)
Block Diagram
Ref K2
E1
Ref K3
E1
E2
E3
Ref K5
E1
E2
Voltage drift
of comparator
threshold
IT= f (VB)
Power
on
Reset
Stabilized
voltage
Vstab = 5.2 V
Clock 1
2-TOsc
Clock 2
20-TOsc
Ref K4
E1
Ref K7
E1
E2
E3
Start
forward
Start
return
High at
counter end
High at
counter zero
Up down counter
T = 1.2 s
Cl2
Cl1
Start
forward
Start
return
High at
counter end
High at
counter zero
Up down counter
T = 1.2 sCl2
Cl1
28
REFK1
Set
Reset
Out
Oscillator
VB
POR
VS
VS
VB
Divider
Latch for
stoplamps
Out Reset
Set
POR
Cl1Cl2
K6 Ref
E1
3.5 mV
VS
3.5 mV
3.5 mV
3.5 mV
3.5 mV
13 mV
K1 13 mV
Ref
E1
26
1
2
7
6
8
9
24
25
16
4
3
5
23
11
10
12
13
27
IN1K1
REFK2
IN1K2
REFK3
IN1K3
IN2K3
IN3K3
INFK3
REFK4
IN1K4
INFK5
REFK5
IN1K5
IN2K5
INF
REFK7
IN1K7
IN2K7
IN3K7
VB
VS
20 19
15
14
17
22
21
18
OSC
OUT
INFK6
REFK6
IN1K6
GND
94 8833
ITIT
+
–
+
–
IT
* Connection to
GND only for
U2482B (latch
disabled)
*
Figure 1. Block diagram
U2481B/ U2482B
Rev. A5, 03-Apr-01 3 (12)
Pin Description
94 8831
REFK2 1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
IN1K2
In1K5
REFK5
IN2K5
IN1K3
REFK3
IN2K3
IN3K3
IN1K7
REFK7
IN2K7
IN3K7
OUT
REFK1
IN1K1
INFK3
IN1K4
REFK4
INF
REFK6
IN1K6
VB
VS
GND
INFK6
INFK5
OSC
Figure 2. Pinning
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 VSSupply voltage
20 VBReference voltage of compara-
tors
21 IN1K6 Input1; single comparator K6
22 REFK6 Reference for threshold voltage;
single comparator K6
23 INFInput; 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
U2481B/ U2482B
Rev. A5, 03-Apr-014 (12)
27
28
2 k
1 k
Fuse
16
2 k
4
1 k
3
2 k
Shunt
5
2 k
Shunt
20 19
15 F
C1
0.1 F
C2
R2
1000
R1
VBVS
150
VBatt
15 Osc
14 Out
Rosc
82 k
Cosc
10 nF
Kl 61
Pilot
lamp
1.2 W
GND
A
B
95 10689
U2481B
U2482B
A: Example of 2 “single comparators” using the fuses as shunt resistors. (Both comparators
are internally EXOR connected, see block diagram.)
B: Example of a “double comparator” using copper shunts and additional fuse monitoring
2
2 k
1
100 k
100 k
Fuse
18
Figure 3. Basic application diagram
U2481B/ U2482B
Rev. A5, 03-Apr-01 5 (12)
Functional Description
Power Supply, Pins 19 and 20
The ICs have two supply pins. The IC itself is supplied via
Pin 19 (stabilized voltage, POR-circuitry). Pin 20
supplies only the current sources of the comparators. Both
pins have an an internal 21-V Zener diode for protection.
For reasons of interference protection, and surge
immunity, the supply voltage pins have to be provided
with RC-circuitries as shown in figure 3. The resistors
limit the current in the case of overvoltage, whereas the
capacitors smooth the supply voltage.
Recommended values:
Pin 19: R1 = 150 ;C
1
= 15 F
Pin 20: R2 = 1000 ;C2 = 0.1 F
An external diode protects the IC against battery reversal.
Power-on Reset
When the supply voltage is switched on, a power-on-reset
pulse is generated internally which resets the brake lamp
monitor latch and the counter stages.
Oscillator, Pin 15
The RC-oscillator is the time base for clock 1 and clock 2
(see block diagram) which are desired from a divider
stage and fed to the two upward and downward counters.
The oscillator frequency fosc is mainly determined by the
external R/C components and an integrated resistor. The
capacitor Cosc is charged by the external resistor and
discharged by the integrated one. Because of the temper-
ature characteristic and the tolerances of the integrated
2 k-resistor, the external one has to have considerable
higher value in order to achieve a stable frequency.
Calculation of the frequency:
fosc 1
tosc 1
cosc (0.74 Rosc 2260 )
With the recommended values
Rosc = 82 k and Cosc = 10 nF
fosc ≈1.58 kHz
Comparators
Comparators K1 and K2: threshold voltage of typically
Vth = 13 mV; designed to monitor high- and low-beam
bulbs, where the fuses can be used as shunt resistors.
Comparators K3 to K7: threshold voltage of typically
Vth = 3.5 mV; designed for all other monitor purposes.
Due to the integrated compensation circuitry, these
comparators are suitable for pc layer copper shunts.
A bulb is detected as “good” as long as the voltage drop
via the shunt resistor exceeds the threshold voltage. If the
pilot lamp is off, a failed bulb is detected if the voltage
drop via the shunt resistor is smaller than the threshold
voltage. If the pilot lamp is on, an external transistor is
necessary to drive the pilot lamp.
Monitoring is disabled when the lamps are switched off,
therefore the comparator outputs are disabled if the refe-
rence voltage Vref < VMin with VMin = 0.33VB.
As protection against transients on the supply, all
comparator inputs require external resistors. Their
tolerances directly influence the comparator threshold
accuracy. Resistors with a 1% tolerance are
recommended.
Single comparators: The inputs (K1, K2, K4, K6) sink
currents of typically 10 A each. During switch-over, the
currents of reference and input pins are identical.
Therefore, identical external protection resistors
(R = 1 k) are required.
Double comparator: The reference input (K5) sinks a
current of typically 20 A; its inputs sink currents of
typically 10 A each during switch-over. Therefore, the
external protection resistors must provide R = 1 k for
REFK5 and R = 2 k each for IN1K5 and IN2K5.
Triple comparators: The reference inputs (K3 and K7)
sink currents of typically 30 A. All inputs (IN1K3, IN2K3
IN3K3, and IN 1K7, IN2K7, IN3K7) sink the identical typical
current of 10 A during switch-over. Therefore, the
external protection resistor must provide R = 1 k for
REFK3 and REFK7 and R = 3 k at each input.
Fuse Monitoring
The internal EXOR conjunction of comparators K1 and
K2 allows fuse monitoring for both lamps. Even a
simultaneous blowout of both fuses is detected.
The pins INFK3, INFK5 and INFK6 with their EXOR gates
can be used for additional fuse monitoring.
Detection threshold for a blown fuse is Vref < VMin with
VMin = 0.33 VB (VB = reference voltage of comparators).
Pin INF is used for brake fuse monitoring. With a voltage
drop VF > 4.8 V across the fuse, the comparator detects
a blown fuse. A voltage drop VF < 2.8 V represents a
“good” fuse. U2481B’s comparator, K7, is connected to
a latch, thus a brake lamp outage is memorized.
U2481B/ U2482B
Rev. A5, 03-Apr-016 (12)
Integrated Delay, Debouncing, Failure
Display
As soon as a comparator detects a failure, a slow upward
counter is started in order to generate the delay time,
tdel = 1.2 s. During consistent failure, the output stage is
enabled after tdel. If the failure disappears during tdel, a
fast downward counter is started in order to generate the
reset time treset 135 ms. The upward counter is reset,
the output stage stays disabled.
Benefits: Intermittent contacts in the wire harness do not
activate the pilot lamp! Even cyclical intermittent
contacts are screened out as long as the pulse/pause ratio
is smaller than 10:1. In the case of higher duty cycles the
upward counter may reach its trigger threshold for the
output activation after t > tdel.
Individual delay- and reset times can be adjusted with
external R/C components according to (see “oscillator”)
–t
del = 1930 x tosc
–t
reset = 198 x tosc
Latch for Brake Lamp Monitor
A failure of a brake lamp detected by comparator K7 or
a blown fuse in the brake circuitry is memorized after the
delay time has expired.
A reset of the latch can only be performed with a “power-
on-reset”.
Output Stage
The output is a PNP Darlington stage with protection
diodes to VS and IC ground. The output is designed to
drive an external pilot lamp with an external NPN
transistor.
At the end of the delay time, the output stage is switched
on and can source a current of Iout = –10 mA with a typical
saturation voltage of Vsat = 1 V.
Test Mode
With VTEST = 23 V (20 mA) applied to Pin osc, via a
200 resistor the delay time stage can be bypassed for
test purposes. A failure detection will be displayed
immediately to save time during threshold testing.
U2481B/ U2482B
Rev. A5, 03-Apr-01 7 (12)
Application Hints
Layout Recommendations for Copper
Layer Shunts
Lamp-outage monitor systems can be produced most
cost-efficiently if stamped shunt resistors are replaced by
copper layer shunts which are generated with the pc board
layout.
The U2481B and the U2482B are suitable for this
application because of their comparator thresholds,
which are compensated in reference to the temperature
characteristic of copper.
A constant lamp current, ILAMP = VTh/Rsh with threshold
voltage VTh = f(T) and shunt resistor Rsh = f(T), is
achieved if the comparator threshold and the shunt
resistor have identical temperature characteristics. With
the temperature coefficient of copper acu = 3.910–3
1/K, a copper shunt changes its nominal value by 52% if
the automotive ambient temperature range of tamb = –40
to +95C is taken into consideration.
Examples for sheet resistances of copper shunts
(Tamb = 25C):
RA = 0.5 m/square (35.1 m layer thickness)
RA = 0.25 m/square (70 m layer thickness)
How to Lay Out Copper Shunts (figure 4)
The width of the copper trace has to be selected in
reference to a low-current-effected temperature increase.
The copper trace must be capable of peak currents which
do not blow the fuse. The peak currents are specified by
the car manufacturers.
Example:
A 7.5-A fuse allows a peak current of 26 A (1 s), 15 A
(10 s) or 10 A (60 s).
The copper shunt length has to be calculated between the
two sense connections to the comparator. The connection
of the common reference input of double and triple
comparators has to be considered carefully.
There is calculation example for a copper shunt used with
a 4-W bulb.
ILAMP = 0.325 A
Failure criterion: I = 1/2ILAMP
10-A fuse is capable of I = 13.5 A
Copper layer thickness: 70 m
Comparator threshold voltage (U2481B, U2482B):
VTh = 3.5 mV
Assumed copper width for temperature increase
Tcu < 50C:
Wcu = 2.5 mm (13.5 A, 70 m)
Two equations for calculation of the shunt resistance:
Rshunt = RAL/Wcn
(with RA = Cu sheet resistance)
Rshunt = VTh / 1/2 ILAMP
Therefore, the length of copper shunt is calculated as:
L = 2VThWcn / RAILAMP
L = 215 mm
For a reasonable pc-layout, a meander-shaped shunt
resistor is recommended. The high lamp currents may
cause hot spots at sharp edges of the copper shunts. That
may deteriorate accuracy of the measurement. Therefore
it is recommended to layout the copper shunts with
smoothed curves.
According to figure 4, the meander may be formed by 4
straight tracks (length LS each) and 3 connecting 180°
ares (length L are each). If the mean arc radius is selected
to r = Wcn the are length becomes Lare = Wcn.
Therefore, the total length is
L= 4L
S
+ 3Lare
= 4LS + 3Wcn
With L = 215 mm, the track length becomes
LS1
4(L 3Wcn)
LS = 47.8 mm
Using Fuses as Shunt Resistors
This cost-saving method can be used if the following
assumptions are fulfilled:
– Each lamp needs a dedicated fuse
– The fuse socket is mounted within the monitor
module to connect the sense lines are suitable for
this monitor
– Both integrated circuits are suitable for this
monitor task because of their comparator
thresholds arecompensated for the fuse
temperature coefficient of aF = 4.110–3 1/K
Calculation Example for a 55-W Bulb and a
7.5-A fuse:
Measured voltage drop across the fuse: VF = 52 mV
Measured current: ILAMP = 4.2 A
Calculated resistance: RF = 12.4 m
Selected comparatore threshold:
VTh = 1/4 VF = 13 mV (typically);
With a lamp current ILAMP < VTh/RF =< 1.05 A
the comparator detects a blown fuse.
U2481B/ U2482B
Rev. A5, 03-Apr-018 (12)
94 8832
1234567
89
10 11 12 13 14
28 27 26 25 24 23 22 21 20 19 18 17 16 15
U2481B
U2482B
Wcn = 2.5 mm
to lamp switch
to lamp
R1
R2
Wcn
LS
Larc
Figure 4. Design example for a copper shunt with meander shape
Absolute Maximum Ratings
Parameters Symbol Value Unit
Supply voltage VS, VBatt 16.5 V
Pulse current (2 ms) IS1.1 A
Short circuit current (reversed battery) ISC 170 mA
Output current Iout –12 mA
Ambient temperature range Tamb –40 to +100 °C
Storage temperature range Tstg –55 to +125 °C
Junction temperature Tj150 °C
Thermal Resistance
Parameters Symbol Value Unit
Thermal resistance SO 28 RthJA 110 K/W
U2481B/ U2482B
Rev. A5, 03-Apr-01 9 (12)
Electrical Characteristics
VBatt (Kl. 15) = 10 to 15 V, Tamb = –40 to +100C, supply series resistors and input protection resistors connected
(see figure 1 “Block diagram” and figure 3 “Basic application schematic”) unless otherwise specified.
Parameters Test Conditions / Pins Symbol Min. Typ. Max. Unit
Supply
Operating voltage VBatt 916 V
Supply current VBatt = 13 V, V14 = low
Pin 20
Pin 19 0.3
30.7
51.1
7mA
mA
Power on reset (POR) Tamb = 25°C Pin 19
VBatt (Kl. 15) 3.0
3.7 4.2
5.0 V
V
Comparators
Comparator input current
during switch over VBatt = 13 V Pins 27, 28
Pins 1, 2
Pins 24, 25
Pins 21, 22
Pin 7
Pins 6, 8, 9
Pin 11
Pins 10,12,13
Pin 4
Pins 3,5
I27, I28
I1, I2
I24, I25
I21, I22
I7
I6, I8, I9
I11
I10,I12,I13
I4
I3, I5
10
10
10
10
30
10
30
10
20
10
A
Comparator thresholds VT1
of comparators K1 and K2
(VT1 = VRef... – VIN...)
VS = 10 V Pins 1, 2, 27, 28
VS = 13 V
VS = 15 V VT1x
x = Pin No.
8.5
10.0
11.0
11.5
13.0
14.0
14.5
16.0
17.0 mV
Voltage characteristic VT1 0.5 mV/V
Temperature characteristic TT1 3900 ppm/°K
Comparator thresholds VT2
of comparators K3 to K7
(VT2 = VRef... – VIN...)
Pins 6, 7, 8, 9
Pins 24, 25
Pins 3, 4, 5
Pins 21, 22
Pins 10, 11, 12, 13
VS = 10 V
VS = 13 V
VS = 15 V
VT1x
x = Pin No.
1.5
2.0
2.3
3.0
3.5
3.8
4.5
5.0
5.3 mV
Voltage characteristic VT2 0.17 mV/V
Temperature characteristic TT2 3900 ppm/°K
Min. comparator input
voltage for detection all Ref-pins VMin 0.33
VBatt
V
Output
Output current VBatt = 13 V Pin 14 I14 –10.0 mA
Output saturation voltage Iout = –10 mA ,Pin 19–14 VSat 1.0 1.5 V
U2481B/ U2482B
Rev. A5, 03-Apr-0110 (12)
Electrical Characteristics (continued)
VBatt (Kl. 15) = 10 to 15 V, T amb = –40 to +100C, supply series resistors and input protection resistors connected (see
figure 1 “Block diagram” and figure 3 “Basic application schematic”) unless otherwise specified.
Parameters Test Conditions / Pins Symbol Min. Typ. Max. Unit
Protection
Voltage of Zener diodes Pin 19
Pin 20
all Ref... and IN... pins
VS
VB
VRef...,
VIN...
21
19
19
V
Oscillator
Oscillator frequency Rosc = 82 k,
Cosc = 10 nF, Pin 15 fosc 1.58 kHz
Delay time Rosc = 82 k, Cosc = 10 nF t d1.1 1.2 1.3 s
Debounce time Rosc = 82 k, Cosc = 10 nF tdb 115 125 135 ms
Break fuse
Brake fuse detection
threshold Pin 23 VTB 2.8 3.8 4.8 V
Input current V23 = 13 V Pin 23 I23 100 A
Trigger threshold (internal
pull-down resistor) Pins 16, 17, 26 VTTx
x=16,17,26
0.33
VBatt
V
Input current VBatt = 13 V Pin 16, 17, 26 Ix100 A
Test
Test voltage for delay time
override I = 20 mA Pin 15 V15 23 V
U2481B/ U2482B
Rev. A5, 03-Apr-01 11 (12)
Package Information
13033
technical drawings
according to DIN
specifications
0.25
0.10
Package SO28
Dimensions in mm
0.4
1.27 16.51
18.05
17.80
2.35
7.5
7.3
9.15
8.65
10.50
10.20
0.25
28 15
114
U2481B/ U2482B
Rev. A5, 03-Apr-0112 (12)
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