STMicroelectronics STLDC08 Demo Board STEVAL-ILL039V1/2 STEVAL-ILL039V2 STEVAL-ILL039V2 Fiche De Données

Doc ID 18476 Rev 1

13/29

The STLDC08 is an LED driver step-up controller dedicated to handheld equipment, having 
a typical voltage ranging from 0.8 V to 1.5 V. The controller drives an N-channel Power 
MOSFET and implements a hysteretic current mode control with constant OFF time. 
Hysteretic operation eliminates the need for small signal control loop compensation. The 
control loop adapts the value of the inductor peak current as needed to deliver the desired 
current on the LED branch. The LED current is set by an external sense resistor R

FB

 

inserted between the feedback pin (FB) and GND. When the current mode control system 
operates in continuous mode the control peak current is almost equivalent to the average 
current control.

At the startup phase, when the device is connected to the battery or when the EN pin is 
pulled high, the internal 2x charge pump starts to work, boosting the voltage on the 2V

CC

 

pin. When the 2V

CC

 pin reaches 1.7 V a soft-start cycle begins. The external main MOSFET 

is switched on/off allowing the charging of the output capacitor.

If the optional PWMOUT MOSFET is used for the dimming operation, the PWMOUT pin is 
held low, further assuring that no current is flowing. The PWMOUT pin starts to follow the 
PWM input when the soft-start cycle is ended. 

When V

OUT

 voltage exceeds 1.9 V, the chip starts drawing its supply current from V

OUT

 

rather than from V

CC

, the charge pump is turned off and the voltage on the 2V

CC

 pin goes to 

zero. When V

OUT

 exceeds the forward voltage of LED V

LED

, the current starts flowing trough 

the LED, but, at this point, the voltage on the DRV pin is high enough to allow the main 
MOSFET to carry the necessary current.