Features
•
Temperature and Supply Voltage Compensated Flashing Frequency
•
Frequency Doubling Indicates Lamp Outage
•
Two Relay Driver Outputs with High Current-carrying Capacity and Low Saturation
•
•
•
•
•
•
Voltage
Minimum Lamp Load for Flasher Operation:
≥
1W
Very Low Susceptibility to EMI
Protection According to ISO/TR7637/1 Level 4
Extremely Low Current Consumption < 10 µA (with Switches Open)
Reverse Polarity Protection
Three Control Inputs: Left, Right and Hazard Warning
Dual Output
Flasher
U2044B
1. Description
The integrated circuit U2044B is used in relay-controlled automotive flashers. With
two output stages, each side of the vehicle is controlled separately. A left and a right
direction indicator input with only a small control current makes switch contacts for
small loads possible.
The separate hazard warning input simplifies the construction of the hazard switch.
Lamp outage is indicated by frequency doubling during direction mode. Thanks to
extreme low current consumption the U2044B can be directly connected to the
battery.
Rev. 4721B–AUTO–09/05
Figure 1-1.
Block Diagram
30
9
5
R
Shunt
C
1
4.7 µF
K1
Contact
1
14
R
1
82 k
Ω
1
+
-
7
+
-
-
+
V
S
-6 V
27.5 V
11
13
GND
R
2
220
Ω
Hazard warning
R
4
4.7 k
Ω
R
6
4.7 k
Ω
right
10
3
2
4
R
3
4.7 k
Ω
R
10
1.2 k
Ω
-
+
12
V
Ref2
V
S
/2
+
-
V
Ref1
6
R
9
47 k
Ω
R
8
47 k
Ω
2
+
-
V
S
-81 mV
8
30 m
Ω
30
30
Relay
1
2
15
left
31
12700
R
5
1.2 k
Ω
R
7
1.2 k
Ω
2
U2044B
4721B–AUTO–09/05
U2044B
2. Pin Configuration
Figure 2-1.
Pinning DIP14/SO14
OSC 1
SIL 2
SIR
3
14 OSC
13 OR2
12
VS
SIHW 4
VS
5
U2044B
11 OR1
10 GND
9
8
VS
LD
CR1 6
CR2 7
Table 2-1.
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Pin Description
Symbol
OSC
SIL
SIR
SIHW
VS
CR1
CR2
LD
VS
GND
OR1
VS
OR2
OSC
Function
Oscillator
Start input left
Start input right
Start input hazard warning
V
S
Control input relay 1
Control input relay 2
Lamp failure detection
V
S
IC ground
Output relay 1
V
S
Output relay 2
Oscillator
3
4721B–AUTO–09/05
3. Functional Description
3.1
Oscillator (Pin 1 and 14)
Flashing frequency, f
1
, is determined by the R
1
C
1
components as follows (see
Figure 1-1 on
page 2):
1
-
f
1
≈
------------------------------------
Hz
R
1
×
C
1
×
1.5
where
C
1
≤
47 µF
R
1
= 6.8 kΩ to 180 kΩ
In the case of a lamp outage, 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:
Duty cycle in lamp outage mode:
50%
40% (bright phase)
3.2
Start Input Right and Left (Pin 2 and 3)
Flashing is disabled as long as the input comparator is tied to GND (pull-down resistor R
7
or R
5
).
The high-side flasher switch left or right changes the comparator status and enables the output
stage at pin 11 or pin 13. R
6
and R
4
are protection resistors for the input stage.
With an open flasher switch the current consumption is only I < 10 µA. The IC is kept in stand-by
mode until there is a voltage drop of V
≈
6.9V at the pull-down resistor.
Direction mode can only be activated when the ignition switch is in the ON-position as shown in
Figure 1-1 on page 2.
3.3
Start Input Hazard Warning (Pin 4)
In contrast to the direction switches, the hazard input is a low-side type. The pull-up resistor R
10
provides the off-state. R
3
is a protection resistor for the input stage. Hazard warning can be acti-
vated independent of the ignition switch position.
3.4
Supply Voltage Sense (Pin 5)
This pin supplies the lamp outage comparator at pin 8 and is externally connected to the battery
(Kl 30).
3.5
Control Input Relay 1 and 2 (Pin 6 and 7)
The feedback detects the bright phase and the dark phase and enables the oscillator.
4
U2044B
4721B–AUTO–09/05
U2044B
3.6
Lamp Outage Detection (Pin 8)
The lamp current is monitored via an external shunt resistor, R
Shunt
and an internal comparator,
K1, with its reference voltage of typically 81 mV (V
S
= 12V). The outage of one lamp out of two
lamps is detected according to the following calculation:
Nominal current of 1 lamp: 21W/(V
S
= 12V):
Nominal current of 2 lamps: 2
×
21W/(V
S
= 12V):
I
lamp
= 1.75A
I
lamp
= 3.5A
We recommend setting the detection threshold in the middle of the current range: I
outage
≈
2.7A
Thus the shunt resistor is calculated as:
R
Shunt
= V
T
(K1)/I
outage
R
Shunt
= 81 mV/2.7 A = 30 mΩ
Comparator K1’s reference voltage is matched to the characteristics of filament lamps (see sec-
tion “Control Signal Threshold”).
The combination of the shunt resistor and the resistance of the wire harness prevents pin 8 from
a too high voltage in the case of shorted lamps.
3.7
Supply Voltage (Pin 9)
This pin supplies the oscillator, the comparators and the logic parts of the IC.
3.8
GND (Pin 10)
The integrated circuit is protected against transients according to ISO-TR 7637-3 level 3 via
resistor R
2
to ground (–31). An integrated protection circuit together with external resistors R
2,
R
3,
R
4,
R
6,
R
8
and R
9
limits the current pulses in the IC. The IC is also protected against reversed
battery.
3.9
Control Output Relay 1 and 2 (Pin 11 and 13)
The relay control outputs are high-side drivers with a low saturation voltage and capable of driv-
ing a typical automotive relay with a coil resistance of 60Ω.
3.10
Supply Voltage Power (Pin 12)
This pin supplies the relay drivers connected directly to the battery (Kl 30). It is internally
clamped by a 27-V Z-diode.
5
4721B–AUTO–09/05
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