STLDC08 STMicroelectronics, STLDC08 Datasheet - Page 13

• Manufacturer Part Number: STLDC08
• Description: Step-up controller for LED supply
• Manufacturer: STMicroelectronics

STLDC08
7
7.1
7.2
Detailed description
Main control loop
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
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.
Start up
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
pin. When the 2V
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
rather than from V
zero. When V
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.
OUT
voltage exceeds 1.9 V, the chip starts drawing its supply current from V
OUT
CC
exceeds the forward voltage of LED V
CC
pin reaches 1.7 V a soft-start cycle begins. The external main MOSFET
, the charge pump is turned off and the voltage on the 2V
Doc ID 18476 Rev 1
LED
, the current starts flowing trough
Detailed description
CC
pin goes to
FB
OUT
CC
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