U643B
Rev. A3, 10-Apr-01
1 (5)
Flasher, 30-m
W Shunt
Description
The bipolar integrated circuit U643B is used in relay-
controlled automotive flashers where a high-level EMC
is required.
Lamp outage is indicated by frequency doubling during
hazard warning as well as direction mode.
Features
D Temperature and supply voltage compensated
flashing frequency
D Frequency doubling indicates lamp outage
D Relay driver output with high current
carrying capacity and low saturation voltage
D Minimum lamp load for flasher operation:
1 W
D Very low susceptibility to EMI
D Protection according to ISO/TR 7637/1 level 4
Block Diagram
V
6
81 mV
20 k
W
5 k
W
20 k
W
5 k
W
23 V
Pulse
generator
IC Ground
20 k
W
1.5...2.2 k
W
Relay
7
3
8
1
+ V
S
+ 49
R
3
470
W
R
4
49 a
4
5
K
2
K
1
K
3
C
1
R
1
6
2
95 9756
49 aComparator K
3
49 aComparator K
2
21 W 21 W 5 W
21 W
21 W
5 W
GND
31
R
2
Indicator lamps
Measuring comparator K
1
Shunt
30 m
W
Figure 1. Application circuit as a car flasher, Resistor R
1
and R
2
: 1/4 Watt
R
4
for protection against continuous reversed polarity: 0.5 Watt
Ordering Information
Extended Type Number
Package
Remarks
U643B
DIP8
U643B-FP
SO8
U643B
Rev. A3, 10-Apr-01
2 (5)
Pin Description
Pin
Symbol
Function
1
GND
IC ground
2
V
S
Supply voltage V
S
3
REL
Relay driver
4
OSC
C
1
Oscillator
5
OSC
R
1
Oscillator
6
V
S
Supply voltage V
S
7
LD
Lamp failure detection
8
SI
Start input (49a)
1
2
3
4
8
7
6
5
GND
REL
OSC
SI
LD
Vs
OSC
94 9290
U643B
V
S
Figure 2. Pinning
Functional Description
Pin 1, GND
The integrated circuit is protected against damage via
resistor R
4
to ground (31) in the case of battery reversal.
An integrated protection circuit together with external
resistances R
2
and R
4
limits the current pulses in the IC.
Pin 2, Supply voltage, V
S
- Power
The arrangement of the supply connections to Pin 2 must
be so as to ensure that, on the connection printed circuit
board (PCB), the resistance of V
S
to Pin 6 is lower than
that to Pin 2.
Pin 3, Relay control output (driver)
The relay control output is a high-side driver with a low
saturation voltage and capable to drive a typical automo-
tive relay with a minimum coil resistance of 60
W.
Pin 4 and 5 Oscillator
Flashing frequency, f
1
, is determined by the R
1
C
1
compo-
nents as follows (see figure 1):
f
1
[
1
R
1
C
1
1.5
Hz
where
C
1
47
mF
R
1
+ 6.8 kW to 510 kW
In the case of a lamp outage (see Pin 7) the oscillator
frequency is switched to the lamp outage frequency f
2
with f
2
[ 2.2 f
1
.
Duty cycle in normal flashing mode: 50%
Duty cycle in lamp outage mode: 40% (bright phase)
Pin 6, Supply voltage, Sense
For accurate monitoring via the shunt resistor, a mini-
mized layer resistance from point V
S
/ shunt to Pin 6 is
recommended.
Pin 7, Lamp outage detection
The lamp current is monitored via an external shunt
resistor R
3
and an internal comparator K1 with its
reference voltage of typ. 81 mV (V
S
=
12 V). The outage
of one lamp out of two lamps is detected according to the
following calculation:
Nominal current of 1 lamp: 21 W / (V
S
= 12 V):
I
lamp
= 1.75 A
Nominal current of 2 lamps: 2 x 21 W / (V
S
= 12 V):
I
lamp
= 3.5 A.
The detection threshold is recommended to be set in the
middle of the current range: I
outage
[ 2.7 A
Thus the shunt resistor is calculated as:
R
3
= V
T
(K1) / I
outage
R
3
= 81 mV/2.7 A = 30 m
W.
Comparator K1`s reference voltage is matched to the
characteristics of filament lamps (see "control signal
threshold" in the data part).
The combination of shunt resistor and resistance of wire
harness prevents Pin 7 from a too high voltage in the case
of shorted lamps.
Pin 8, Start input
Start condition for flashing: the voltage at Pin 8 has to be
below K3 threshold (flasher switch closed).
Humidity and dirt may decrease the resistance between
49 a and GND. If this leakage resistance is
u 5 kW the IC
is still kept in its off-condition. In this case the voltage at
Pin 8 is between the thresholds of comparators K2 and
K3.
During the bright phase the voltage at Pin 8 is above the
K2
threshold, during the dark phase it is below the K3
threshold. For proper start conditions a minimum lamp
wattage of 1 W is required.
U643B
Rev. A3, 10-Apr-01
3 (5)
Absolute Maximum Ratings
Reference point Pin 1
Parameters
Symbol
Value
Unit
Supply voltage
Pin 2 and 6
V
S
16.5
V
Surge forward current
t
P
= 0.1 ms
Pin 2 and 6
I
FSM
1.5
A
t
P
= 0.1 ms
Pin 2 and 6
t
P
= 300 ms Pin 2 and 6
I
FSM
I
FSM
1.5
1.0
A
A
t
P
= 300 ms Pin 2 and 6
t
P
= 300 ms
Pin 8
I
FSM
I
FSM
1.0
50
A
mA
Output current
Pin 3
I
O
0.3
A
Power dissipation
T
amb
= 95
C
DIP 8
SO 8
P
tot
P
tot
420
340
mW
mW
SO 8
T
amb
= 60
C
DIP 8
SO 8
P
tot
P
tot
P
tot
340
690
560
mW
mW
mW
Junction temperature
T
J
150
C
Ambient temperature range
T
amb
40 ... + 95
C
Storage temperature range
T
stg
55 ... + 150
C
Thermal Resistance
Parameters
Symbol
Value
Unit
Junction ambient
DIP8
SO8
R
thJA
R
thJA
110
160
K/W
K/W
Electrical Characteristics
Typical values under normal operation in application circuit (see figure 1), V
S
(+49, Pin 2 and 6) = 12 V.
Reference point ground (31), T
amb
= 25
C, unless otherwise specified
Parameters
Test Conditions / Pins
Symbol
Min.
Typ.
Max.
Unit
Supply voltage range
Pin 2 and 6
V
S
(+49)
9 to 15
V
Supply current:
Pin 2 and 6
Dark phase
I
4 5
8
mA
Dark phase
Bright phase
I
S
I
S
4.5
7.0
8
11
mA
mA
Relay output:
saturation voltage
Pin 3
I
O
= 150 mA, V
S
= 9 V
saturation voltage
reverse current
I
O
150 mA, V
S
9 V
with resistance = 60
W
V
O
I
O
1.0
0.1
V
mA
Start delay
First bright phase
t
on
10
ms
Frequency tolerance
df
1
5
+5
%
Bright period
Basic frequency f
1
Control frequency f
2
f
1
f
2
47
37
53
45
%
%
Frequency increase
Lamp outage
f
2
2.15 f
1
2.3 f
1
Hz
Control signal threshold
V
S
= 15 V
Pin 7
V
S
= 9 V
Pin 7
V
S
= 12 V
Pin 7
V
R3
V
R3
V
R3
85
66
76
91
71
81
97
76
87
mV
mV
mV
Leakage resistance
49a to GND
R
P
4
5
k
W
Lamp load
P
L
1
W
U643B
Rev. A3, 10-Apr-01
4 (5)
Package Information
13021
9.8
9.5
Package DIP8
Dimensions in mm
1.64
1.44
4.8 max
0.5 min
3.3
0.58
0.48
7.62
2.54
6.4 max
0.36 max
9.8
8.2
7.77
7.47
8
5
1
4
technical drawings
according to DIN
specifications
13034
technical drawings
according to DIN
specifications
Package SO8
Dimensions in mm
5.00
4.85
0.4
1.27
3.81
1.4
0.25
0.10
5.2
4.8
3.7
3.8
6.15
5.85
0.2
8
5
1
4
U643B
Rev. A3, 10-Apr-01
5 (5)
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