Q: In the plot below, the TPS61175's EN pin (orange) is taken low but the TPS61175 SW pin keeps switching (blue) and so the output voltage (black) does start to fall for 17ms.  Why is that?


A:

The TPS61175 was spun from the TPS61500 LED driver.  On the LED driver the EN pin is used for PWM dimming at frequencies down to 200Hz, hence the delay before true shutdown.  The delay before the IC stops switching can be between 15ms at colder ambient temperatures and 20 ms at hotter ambient temperatures.  If you use a switch to actively pull down the COMP pin or the SS pin, which will indirectly pull COMP low, the IC will stop switching immediately.