8.1.3 Special Considerations When Ramping Down V_IN and Enable

Care must be taken when ramping down voltage on the IN and EN pins to power-down the device when the operating free-air temperature is less than 15°C. The minimum ramp-down time for the IN pin is 10 ms. The minimum ramp-down time for the EN pin is 100 µs. Ramping at faster rates can cause the regulator to exhibit undesired startup behavior on the next power-on.

If V_IN is ramped down faster than 10 ms, the next startup may exhibit a partial startup, shutoff, followed by a normal soft-start startup. Figure 48 shows this response.

Figure 48. Partial Startup, Shutdown, Normal Startup With V_EN = V_IN

If the EN pin is ramped down faster than 100 µs, the next startup may exhibit a delay time of up to 130 ms before the output ramps up with a normal soft-start startup. Figure 49 shows this delay.

Figure 49. Long Delay to Startup With V_EN = V_IN

Fast ramp downs of V_IN and the EN pin charge internal high-impedance nodes in the device, which take extended time to discharge below 15°C. To avoid these startup behaviors, follow the recommended minimum ramp down times for V_IN and the EN pin.