ATMEL Corporation U643B-FP, U643B Datasheet

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ATMEL Corporation U643B-FP, U643B Datasheet

U643B

Flasher, 30-m Shunt

Description

The bipolar integrated circuit U643B is used in relaycontrolled 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

 

Temperature and supply voltage compensated

 

Minimum lamp load for flasher operation: 1 W

 

flashing frequency

Very low susceptibility to EMI

 

Frequency doubling indicates lamp outage

 

 

Protection according to ISO/TR 7637/1 level 4

 

 

 

Relay driver output with high current carrying capacity and low saturation voltage

Block Diagram

 

 

 

 

 

 

 

 

 

+ VS

 

 

 

 

 

 

 

 

 

+ 49

 

 

6

2

 

 

 

 

 

 

C1

 

Measuring comparator K 1

 

 

 

 

R3

30 m

 

 

 

 

 

 

 

Shunt

 

 

4

V6±81 mV

 

 

 

 

 

 

 

 

20 k

5 k

 

 

 

 

 

 

 

 

K1

7

 

 

 

 

 

 

 

 

K2

 

 

 

 

 

 

 

R1

 

Pulse

3

 

 

 

 

 

 

 

generator

 

 

 

 

 

 

 

 

 

49 a±Comparator K2

 

Relay

 

 

 

 

 

 

 

20 k

 

R2

 

 

 

 

 

 

 

49 a±Comparator K

8

 

 

 

 

 

 

 

3

 

 

 

 

 

49 a

 

 

 

 

 

 

 

 

 

 

 

5

K3

23 V

1.5...2.2 k

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

20 k

5 k

 

 

 

 

 

 

 

 

 

IC Ground

 

 

 

 

 

 

 

 

 

1

R4

 

 

 

 

 

 

95 9756

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

470

5 W

21 W

21 W

21 W

21 W 5 W

 

 

 

 

 

GND

 

Indicator lamps

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

± 31

 

 

 

 

Figure 1. Application circuit as a car flasher, Resistor R1 and R2: 1/4 Watt

R4 for protection against continuous reversed polarity: 0.5 Watt

Ordering Information

Extended Type Number

Package

Remarks

U643B

DIP8

 

U643B-FP

SO8

 

 

 

 

 

 

 

Rev. A3, 10-Apr-01

 

1 (5)

U643B

Pin Description

Pin

Symbol

 

Function

1

GND

IC ground

2

VS

Supply voltage VS

3

REL

Relay driver

4

OSC

C1

Oscillator

 

OSC

R1

Oscillator

5

6

VS

Supply voltage VS

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 R4 limits the current pulses in the IC.

Pin 2, Supply voltage, VS - 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 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):

 

 

1

 

 

f1

 

Hz

 

R1 C1 1.5

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 f2 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-

GND

1

8

SI

VS

2

7

LD

 

 

U643B

 

REL

3

6

Vs

OSC

4

5

OSC

94 9290

Figure 2. Pinning

mized layer resistance from point VS / shunt to Pin 6 is 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 (VS = 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 / (VS = 12 V):

Ilamp = 1.75 A

Nominal current of 2 lamps: 2 x 21 W / (VS = 12 V):

Ilamp = 3.5 A.

The detection threshold is recommended to be set in the

middle of the current range: Ioutage 2.7 A Thus the shunt resistor is calculated as:

R3 = VT (K1) / Ioutage

R3 = 81 mV/2.7 A = 30 m .

Comparator K1`s reference voltage is matched to the characteristics of filament lamps (see ªcontrol signal thresholdº 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 5 k 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.

2 (5)

Rev. A3, 10-Apr-01

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