SLUSCZ1 May 2017 TPS92518-Q1
PRODUCTION DATA.
If VIN and VLED are sufficiently close the duty cycle demand increases. Because of the TPS92518-Q1 hysteretic control method, the high-side FET attempts to remain ON until the programmed peak current is reached. Keeping the high-side FET ON requires energy from the BOOT capacitor which depletes the BOOT capacitor voltage. If the high-side FET is ON for sufficient duration, the BOOT capacitor voltage eventually reaches VBOOT-UVLO level at which point the high-side FET is turned off. This allows for long on-times and duty cycles >99.5%, since the time the high-side FET can remain ON is long (>1 ms) compared to the time required the recharge the BOOT capacitor (approximately 100 ns). The typical maximum on-time can be estimated by Equation 18