Power-Down Mode

During a rapid power-down condition (as would occur with a power-supply short circuit with a poorly filtered power supply), the energy stored in C_X could discharge into pin 2 or pin 14. To avoid possible device damage in this mode when C_X is \u0001 0.5 µF, a protection diode with a 1-A rating or higher (1N5395 or equivalent) and a separate ground return for C_X should be provided. Rapid-Power-Down Protection Circuit

An alternate protection method is shown in Alternative Rapid-Power-Down Protection Circuit, where a 51-Ω current-limiting resistor is inserted in series with C_X . Note that a small pulse-duration decrease occurs, however, and R_X must be increased appropriately to obtain the originally desired pulse duration.

Figure 7-1 Rapid-Power-Down Protection Circuit

Figure 7-2 Alternative Rapid-Power-Down Protection Circuit