U643

U643B Flasher, 30-mW 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 D Temperature and supply voltage compensated flashing frequency D Frequency doubling indicates lamp outage D Relay driver output with high current carrying capacity and low saturation voltage D Minimum lamp load for flasher operation: ≥ 1 W D Very low susceptibility to EMI D Protection according to ISO/TR 7637/1 level 4 Block Diagram + VS + 49 6 C1 4 Measuring comparator K 1 V6–81 mV 20 kW K1 2 R3 Shunt 5 kW 7 30 mW K2 R1 Pulse generator 3 49 a–Comparator K2 20 kW 49 a–Comparator K3 K3 23 V 20 kW 5 kW IC Ground 1 95 9756 Relay 8 R2 49 a 1.5...2.2 kW 5 R4 470 W 5 W 21 W 21 W 21 W 21 W 5 W Indicator lamps GND – 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 U643B U643B-FP Package DIP8 SO8 Remarks Rev. A3, 10-Apr-01 1 (5) U643B Pin Description Pin 1 2 3 4 5 6 7 8 Symbol GND VS REL OSC OSC VS LD SI IC ground Supply voltage VS Relay driver C1 Oscillator R1 Oscillator Supply voltage VS Lamp failure detection Start input (49a) Figure 2. Pinning OSC REL 3 4 VS 2 7 LD Function GND 1 8 SI U643B 6 Vs 5 OSC 94 9290 Functional Description Pin 1, GND The integrated circuit is p...