ATMEL U643B-FP, U643B Datasheet
Flasher, 30-m Shunt
Description
The bipolar integrated circuit U643B is used in relaycontrolled automotive flashers where a high-level EMC
is required.
Features
Temperature and supply voltage compensated
flashing frequency
Frequency doubling indicates lamp outage
Relay driver output with high current
carrying capacity and low saturation voltage
Block Diagram
6
C
1
4
Measuring comparator K
V6–81 mV
K
1
1
20 k 5 k
U643B
Lamp outage is indicated by frequency doubling during
hazard warning as well as direction mode.
Minimum lamp load for flasher operation: ≥ 1 W
Very low susceptibility to EMI
Protection according to ISO/TR 7637/1 level 4
2
R
3
Shunt
7
30 m
+ V
+ 49
S
K
2
1
3
8
1.5...2.2 k
Relay
R
2
R
4
470
GND
– 31
5
95 9756
Pulse
generator
49 a–Comparator K
49 a–Comparator K
K
3
2
20 k
3
23 V
20 k 5 k
IC Ground
R
1
Figure 1. Application circuit as a car flasher , Resistor R1 and R2: 1/4 W att
for protection against continuous reversed polarity: 0.5 Watt
R
4
Ordering Information
Extended Type Number Package Remarks
U643B DIP8
U643B-FP SO8
49 a
21 W 21 W 5 W21 W21 W5 W
Indicator lamps
Rev. A3, 10-Apr-01 1 (5)
U643B
Pin Description
Pin Symbol Function
1 GND IC ground
2 V
3 REL Relay driver
4 OSC C1 Oscillator
5 OSC R1 Oscillator
6 V
7 LD Lamp failure detection
8 SI Start input (49a)
Functional Description
Pin 1, GND
The integrated circuit is protected against damage via
resistor R4 to ground (–31) in the case of battery reversal.
An integrated protection circuit together with external
resistances R2 and R
Pin 2, Supply voltage, V
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 VS 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 automotive relay with a minimum coil resistance of 60 .
Pin 4 and 5 Oscillator
Flashing frequency, f1, is determined by the R1C1 components as follows (see figure 1):
f
Supply voltage V
S
Supply voltage V
S
limits the current pulses in the IC.
4
- Power
S
1
1
R1 C1 1.5
S
S
Hz
1
GND
V
2
S
SI
8
7
LD
U643B
3
REL
4
OSC
Figure 2. Pinning
mized layer resistance from point V
recommended.
Pin 7, Lamp outage detection
The lamp current is monitored via an external shunt
resistor R3 and an internal comparator K1 with its
reference voltage of typ. 81 mV (V
of one lamp out of two lamps is detected according to the
following calculation:
Nominal current of 1 lamp: 21 W / (V
I
= 1.75 A
lamp
Nominal current of 2 lamps: 2 x 21 W / (V
I
= 3.5 A.
lamp
The detection threshold is recommended to be set in the
middle of the current range: I
outage
Thus the shunt resistor is calculated as:
R
= V
(K1) / I
3
T
R
= 81 mV/2.7 A = 30 m.
3
outage
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.
6
Vs
OSC
5
94 9290
/ shunt to Pin 6 is
S
= 12 V). The outage
S
= 12 V):
S
= 12 V):
S
2.7 A
where C1 47 F
R1 6.8 k to 510 k
In the case of a lamp outage (see Pin 7) the oscillator
frequency is switched to the lamp outage frequency f
with f2 2.2 f1.
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-
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 5 k the IC
2
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.
Rev. A3, 10-Apr-012 (5)
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