TL7705 Datasheet PDF - TI

●Introduction

●After power-on a digital system must normally be forced into a definite initial state. For microcomputers and microprocessors a reset input is provided to which, in simple applications, an R/C network is connected. After power-on, this circuitry maintains the logic level at this input high (or low), until the supply voltage has reached its nominal value, and the internal logic of the microcomputer has executed the initialization of the system.

●However, this circuit does not work well during short drops of the supply voltage. In this case, the capacitor C must be quickly discharged via the diode D, which will occur only if the supply voltage V cc goes below the threshold voltage (1 … 2 Volt) of the Reset input. A small decrease of V cc under the recommended minimum supply voltage can destroy the content of the memory and registers and yet not activate the reset circuit. This may have catastrophic consequences.