STLD20D

Functional description

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5

Functional description

5.1

Boost converter

The STLD20D is a PWM mode control boost converter operating at 500kHz.

An automatic compensation of the oscillation ramp allows rejection of the battery voltage

transient. The LED current regulation (see

Figure 3.) is done by sensing the LED current

controller (FB pin).

5.2

Peak inductor current limitation and soft start function

An integrated current sensor limits the switching current at 640 mA maximum.

turn off the switch SW. During start up, this peak drain current limitation acts like a soft start

function.

5.3

Peak inductor current programmability (STLD20D-C8 only)

The converter peak current must be always below the inductor saturation current. For

flexibility reasons, the maximum peak inductor current can be programmed by connecting a

The

5.4

Shutdown

The SHDN pin is a low logic input signal and allows turning off the controller without cutting

the input voltage from the boost regulator circuit.

An integrated Load Disconnect Switch LDS disconnects the LEDs branch in shutdown

mode.This arrangement allows eliminating the DC current path that normally exists with

traditional boost regulator in shutdown mode.

5.5

Brightness control

The brightness of the LED is adjusted by pulsing the shutdown pin with a PWM signal as

high as 10kHz.

By using such a PWM signal the controller is alternatively ON and OFF and the LED current

changes from full current to zero.

The duty cycle allows regulating the average LED current. This scheme ensures that when

the LEDs are ON, they are driven at the full current without risk of color change.