U643 ATMEL Corporation, U643 Datasheet - Page 2

• Manufacturer Part Number: U643
• Description: Flasher/ 30-mohm Shunt
• Manufacturer: ATMEL Corporation

Pin Description
Functional Description
Pin 1, GND
The integrated circuit is protected against damage via
resistor R
An integrated protection circuit together with external
resistances 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 V
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
nents as follows (see figure 1):
where
In the case of a lamp outage (see Pin 7) the oscillator
frequency is switched to the lamp outage frequency f
with f
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-
U643B
2 (5)
Pin
1
2
3
4
5
6
7
8
2
[ 2.2
4
Symbol
to ground (–31) in the case of battery reversal.
GND
REL
OSC
OSC
LD
V
V
2
SI
f
C
R
and R
S
S
1
1
1
[
 47 mF
+ 6.8 kW to 510 kW
f
1
R
.
4
1
1
IC ground
Supply voltage V
Relay driver
C
R
Supply voltage V
Lamp failure detection
Start input (49a)
, is determined by the R
limits the current pulses in the IC.
1
1
S
Oscillator
Oscillator
C
- Power
1
1
1.5
S
Function
to Pin 6 is lower than
Hz
S
S
1
C
1
compo-
2
mized layer resistance from point V
recommended.
Pin 7, Lamp outage detection
The lamp current is monitored via an external shunt
resistor R
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
Nominal current of 2 lamps: 2 x 21 W / (V
I
The detection threshold is recommended to be set in the
middle of the current range: I
Thus the shunt resistor is calculated as:
R
R
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.
lamp
lamp
3
3
= V
= 81 mV/2.7 A = 30 mW.
= 1.75 A
= 3.5 A.
T
GND
(K1) / I
OSC
REL
V
3
S
and an internal comparator K1 with its
1
2
3
4
outage
Figure 2. Pinning
U643B
outage
S
[ 2.7 A
= 12 V). The outage
Rev. A3, 10-Apr-01
S
8
7
6
5
/ shunt to Pin 6 is
S
= 12 V):
OSC
LD
Vs
SI
S
= 12 V):
94 9290