Features
•
Temperature and Voltage Compensated Frequency
•
Warning Indication of Lamp Failure by Means of Frequency Doubling only in Direction
•
•
•
•
•
•
•
Mode
Voltage Dependence of the Car Indicator Lamps also Compensated for Lamp Failure
Relay Output with High Current-carrying Capacity and Low Saturation Voltage
Load-dump Protection
Minimum Lamp Load for Flasher Operation
³
1 W
Low Susceptibility to EMI
Extremely Low Standby Current of 10 µA
Protection According to ISO/TR 7637/1 Level 4 with External Capacitor (C
2
)
Description
The U6432B is an advanced automotive flasher IC which provides low standby cur-
rent. Its basic function is equal to Atmel’s flasher IC U6043B but low current
consumption and frequency doubling disabling make outstanding differences.
Low-power
Flasher IC with
18-mW Shunt
U6432B
4725A–AUTO–06/03
1
Functional Description
Pin 1, GND
The U6432B is protected against damage in case of battery reversal via resistor R
4
to
ground (-31). An integrated protection circuit together with external resistances R
2
and
R
4
limits the current pulses in the IC.
The arrangement of the supply connections to Pin 2 (and 6) 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.
The relay control output is a high-side driver with a low saturation voltage. It is capable
of driving a typical automotive relay with a minimum coil resistance of 60
W
.
The flashing frequency, f
1
, is determined by the R
1
C
1
components as given by the for-
mula below (see Figure 1):
1
-
f
1
»
----------------------------------
Hz
R
1
´
C
1
´
1.5
Pin 2, Supply Voltage,
V
S
power
Pin 3, Relay Control
Output (Driver)
Pin 4 and 5, Oscillator
where C
1
£
47 µF, R
1
= 6.8 k
W
to 510 k
W
In case of a lamp outage (see Pin 7) the oscillator frequency is switched to the lamp out-
age 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
Pin 7
Control Signal Threshold
(49 mV Comparator)
For accurate monitoring via the shunt resistor, a minimized layer resistance from point
V
S
/shunt to Pin 6 is recommended.
The detection point for lamp failure can be calculated from the control signal threshold,
typically 49 mV with V
S
= 12 V. With a measuring resistance of R
3
= 18 m
W
, the fre-
quency change-over is reached at a lamp load of 21 W + 11.4 W. The variation of the
control signal threshold supply voltage takes into account the PTC characteristic of fila-
ment lamps.
A voltage drop at the shunt resistor R
3
between 49 mV and 15 mV lets the flasher work
in frequency doubling mode.
If the voltage drop decreases to a value below V
R3MAX
= 15 mV, frequency doubling is
disabled.
This can be achieved either with a switch which by-passes the shunt resistor (e.g., a
special hazard warning switch) or with a small lamp load.
Flasher operation starts with a lamp load of P
L
³
1 W.
Control Signal Threshold 2
(15-mV Comparator)
4
U6432B
4725A–AUTO–06/03
U6432B
Pin 8, Start Input
Start condition for flashing:
•
•
Voltage at Pin 8 (see Figure 1)
V
8
£
V
S
- (V
BE(T1)
+ V
Z(D2)
)
The resistor R
2
betwen V
S
and Pin 8 provides an extremly low standby current
(I
S
£
10 µA). The leakage current depends on the pull-up resistor R
2
according to
the following formula:
I
Leak
»
(V
BE(T1)
+ V
Z(D2)
)/R
2
Condition for standby:
Application Hint
In order to achieve a high-level immunity against "electrical interference by conduction
and coupling" according to ISO/TR 7637/1 test level 4, an electrolythic capacitor
C
2
= 10 µF (25 V) between Pin 1 and 2 – mounted close to the IC – is highly
recommended.
Absolute Maximum Ratings
Reference point Pin 1
Parameters
Supply voltage
Surge Forward Current
t
P
= 0.1 ms
t
P
= 300 ms
t
P
= 300 ms
Output current
Power Dissipation
T
amb
= 95°C
T
amb
= 60°C
Junction temperature
Ambient temperature range
Storage temperature range
DIP 8
SO8
DIP 8
SO8
P
tot
P
tot
P
tot
P
tot
T
J
T
amb
T
stg
420
340
690
560
150
-40 to +105
-55 to +150
mW
mW
mW
mW
°C
°C
°C
Pin 2 and 6
Pin 2 and 6
Pin 8
Pin 3
I
FSM
I
FSM
I
FSM
I
O
1.5
1.0
30
0.3
A
A
mA
A
Pin 2 and 6
Symbol
V
S
Value
18
Unit
V
5
4725A–AUTO–06/03
RF/Wirelessly
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