U6808B Datasheet | Atmel

Features - - - - - Digital Self-supervising Watchdog with Hysteresis One 250-m A Output Driver for Relay Enable Output Open Collector 8 m A Over/Undervoltage Detection ENABLE and RELAY Outputs Protected Against Standard Transients and 40V Load Dump - ESD Protection According to MIL-STD-883 D Test Method 3015.7 - Human Body Model: ±2 k V (100 p F, 1.5 kΩ) - Machine Model: ±200 V (200 p F, 0Ω) Special Fail-safe IC U6808B 1. Description The U6808B is designed to support the fail-safe function of a safety critical system (e.g., ABS). It includes a relay driver, a watchdog controlled by an external R/C-network and a reset circuit initiated by an over and undervoltage condition of the 5-V supply providing a low-level reset signal. Figure 1-1. Block Diagram VS VS Bandgap reference 2.44 V Power-on reset .. + - RESET Reset debounce Reset delay + RELAY Under/ overvoltage detection ENABLE RIN + + - Internal oscillator Watchdog RC oscillator Current limitation Rev. 4707B- AUTO- 10/05 2. Pin Configuration Figure 2-1. Pinning SO8 RELAY ENABLE RESET Table 2-1. Pin 1 2 3 4 5 6 7 8 Pin Description Symbol RELAY GND ENABLE WDC RESET WDI RIN VS Type Open collector driver output Supply Digital output Analog input Digital output Digital input Digital input Supply Function Fail-safe relay driver Standard ground Negative reset signal External RC for watchdog timer Negative reset signal Watchdog trigger signal Activation of relay driver 5-V supply Logic No signal: driver off Low: driver on No signal Low: reset No signal Low: reset Pulse sequence High: driver on Low: driver off - 2 4707B- AUTO- 10/05 3. Fail-safe Functions A fail-safe IC has to maintain its monitoring function even if there is a fault condition at one of the pins (e.g., short circuit). This ensures that a microcontroller system is not brought into a critical status. A critical status is reached if the system is not able to switch off the...