LED6000 datasheet(20/49 Pages) STMICROELECTRONICS

20 / 49 page

Functional description

LED6000

20/49

DocID027777 Rev 2

Figure 12. ISKIP typical current and RILIM value

However, due to the current sensing comparator delay, the actual inductor charge current is

slightly impacted by the VIN and selected inductor value.

In order to let the bootstrap capacitor recharge, in case of an extremely light-load the

LED6000 is able to pull-down the LX net through an integrated small LS MOS. In this way

the bootstrap recharge current can flow from the VIN through the CBOOT, LX and LS MOS.

This mechanism is activated if the HS MOS has been kept turned-off for more than 3 ms

(typ.).

4.5

Low VIN operation

In normal operation (i.e.: VOUT programmed lower than input voltage) when the HS MOS is

turned off, a minimum off time (TOFFMIN) interval is performed.

In case the input voltage falls close or below the programmed output voltage (low dropout,

LDO) the LED6000 control loop is able to increase the duty cycle up to 100%. However, in

order to keep the boot capacitor properly recharged, a maximum HS MOS on-time is limited

(TONMAX). When this limit is reached the HS MOS is turned-off and an integrated switch

working as a pull-down resistor between the LX and GND is turned on, until one of the

following conditions is met:



A negative current limit (300 mA typ.) is reached



A timeout (1 µs typ.) is reached.

So doing the LED6000 device is able to work in the low dropout operation, due to the

advanced boot capacitor management, and the effective maximum duty cycle is about

s / 13 s = 92%.

LED6000 Datasheet(PDF) 20 Page - STMicroelectronics