U643B

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 Minimum Lamp Load for Flasher Operation: ≥ 1W Very Low Susceptibility to EMI Protection According to ISO/TR 7637/1 Level 4 Flasher IC with 30-mΩ Shunt 1. Description The bipolar integrated circuit U643B is used in relay-controlled automotive flashers where a high-level EMC is required. Lamp outage is indicated by frequency doubling during hazard warning as well as direction mode. U643B Rev. 4727B–AUTO–09/05 2. Block Diagram Figure 2-1. Car Flasher Application Circuit, Resistor R1 and R2: 0.25W; R4 for Protection Against Continuous Reversed Polarity: 0.5W C1 4 6 Measuring comparator K 1 V 6-81 mV 20 kΩ K1 2 5 kΩ 7 R3 Shunt 30 mΩ + VS + 49 K2 Pulse R1 generator 49 a-Comparator K 2 20 kΩ 49 a-Comparator K 3 K3 5 20 kΩ 3 Relay 8 R2 23 V 5 kΩ IC Ground 1 1.5...2.2 kΩ R4 470 Ω 49 a 5 W 21 W 21 W 21 W 21 W 5 W GND - 31 Indicator lamps 2 U643B 4727B–AUTO–09/05 3. Pin Configuration Figure 3-1. Pinning GND 1 8 SI VS 2 REL 3 U643B 7 LD 6 VS OSC 4 5 OSC Table 3-1. Pin 1 2 3 4 5 6 7 8 Pin Description Symbol Function GND IC ground VS Supply voltage VS REL Relay driver OSC OSC VS LD C1 Oscillator R1 Oscillator Supply voltage VS Lamp failure detection SI Start input (49a) U643B 4727B–AUTO–09/05 3 4. Functional Description 4.1 Pin 1, GND The ...