The TL7770 is an integrated-circuit system supervisor designed for use as a reset controller in microcomputer and microprocessor power-supply systems. This device contains two independent supply-voltage supervisors that monitor the supplies for overvoltage and undervoltage conditions at the VSO and VSU terminals, respectively. When VCC attains the minimum voltage of 1 V during power up, the RESET\ output becomes active (low). As VCC approaches 3.5 V, the time-delay function activates, latching RESET and RESET\ active (high and low, respectively) for a time delay (td) after system voltages have achieved normal levels. Above VCC = 3.5 V, taking RESIN\ low activates the time-delay function during normal system-voltage levels. To ensure that the microcomputer system has reset, the outputs remain active until the voltage at VSU exceeds the threshold value, VIT+, for a time delay, which is determined by an external timing capacitor such that: td 20 × 103 × capacitance

where td is in seconds and capacitance is in farads.

The overvoltage-detection circuit is programmable for a wide range of designs. During an overvoltage condition, an internal silicon-controlled rectifier (SCR) is triggered, providing 250-mA peak instantaneous current and 25-mA continuous current to the SCR gate drive terminal, which can drive an external high-current SCR gate or an overvoltage-warning circuit.

The TL7770C series is characterized for operation from 0°C to 70°C. The TL7770I series is characterized for operation from -40°C to 85°C.

• Power-On Reset Generator
• Automatic Reset Generation After Voltage Drop
• RESET\ Defined When VCC Exceeds 1 V
• Wide Supply-Voltage Range...3.5 V to 18 V
• Precision Overvoltage and Undervoltage Sensing
• 250-mA Peak Output Current for Driving SCR Gates
• 2-mA Active-Low SCR Gate Drive for False-Trigger Protection
• Temperature-Compensated Voltage Reference
• True and Complementary Reset Outputs
• Externally Adjustable Output Pulse Duration