LED2000 datasheet(10/40 Pages) STMICROELECTRONICS

10 / 40 page

Functional description

LED2000

10/40

DocID023432 Rev 4

5.1

Power supply and voltage reference

The internal regulator circuit consists of a startup circuit, an internal voltage pre-regulator,

the BandGap voltage reference and the bias block that provides current to all the blocks.

The starter supplies the startup current to the entire device when the input voltage goes high

and the device is enabled. The pre-regulator block supplies the BandGap cell with a pre-

regulated voltage that has a very low supply voltage noise sensitivity.

5.2

Voltage monitor

An internal block continuously senses the VCC, Vref and Vbg. If the monitored voltages are

good, the regulator begins operating. There is also a hysteresis on the VCC (UVLO).

Figure 4. Internal circuit

5.3

Soft-start

The startup phase is implemented ramping the reference of the embedded error amplifier in

1 ms typ. time. It minimizes the inrush current and decreases the stress of the power

components at power-up.

During normal operation a new soft-start cycle takes place in case of:



Thermal shutdown event



UVLO event.

The soft-start is disabled when DIM input goes high in order to maximize the dimming

performance.

5.4

Error amplifier

The voltage error amplifier is the core of the loop regulation. It is a transconductance

operational amplifier whose non-inverting input is connected to the internal voltage

reference (100 mV), while the inverting input (FB) is connected to the output current sensing

resistor.

The error amplifier is internally compensated to minimize the size of the final application.

STARTER

PREREGULATOR

IC BIAS

BANDGAP

VREF

VREG

Vcc

D00IN126

AM12895v1

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