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 VCCattains the minimum voltage of 1 V during power up, the RESET\ output becomes active (low). As VCCapproaches 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:td20 × 103× capacitance

where tdis 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.Read more