SSL2108 datasheet(6/20 Pages) NXP

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SSL2109_SER

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Product data sheet

Rev. 3 — 4 June 2012

6 of 20

NXP Semiconductors

SSL2109 series

GreenChip controller for LED lighting

Functional description

8.1 Introduction

The SSL2109 series is a range of products for small form factor retrofit SSL lamps and

separate LED drivers.

8.2 Converter operation

The converter in the SSL2109 series is a Boundary Conduction Mode (BCM), peak

current controlled system. For the basic application diagram see Figure 4, for the

waveforms see Figure 5. This converter type operates at the boundary between

continuous and discontinuous mode. Energy is stored in inductor L each period that the

switch is on. The inductor current IL is zero when the MOSFET is switched on. Thereafter,

the amplitude of the current build-up in L is proportional to VIN

−VOUT and the time that the

MOSFET switch is on. When the MOSFET switch is switched off, the current continues to

flow through the freewheel diode and the output capacitor. The current then falls at a rate

proportional to the value of VOUT. The LED current ILED is almost equal to half the peak

switch current. A new cycle is started, as soon as the inductor current IL is zero.

8.3 Conversion frequency

The conversion frequency must be limited to below 200 kHz. Therefore, select an

inductance value so that the conversion frequency is always within limits, given the supply

voltage, LED voltage and component spread.

8.4 Driver pin

The SSL2109 series is equipped with an external driver that can control an external

switch. The voltage on the driver output pin is increased towards Vo(DRIVER)max to open the

switch during the first cycle (t0 to t1). The voltage on the driver output pin is pulled down

towards Vo(DRIVER)min from the start of the secondary stroke until the next cycle starts (t0 to

t00). During transition from low to high and back, there is a controlled switching slope

steepness. This controlled condition limits the high frequency radiation from the circuit to

the surrounding area.

Fig 4.

Basic application diagram SSL2109 series

SSL2109

DVDT

VCC

DRAIN

NTC

DRIVER

GND

NTC

LEDs

SOURCE

aaa-001743

Rinrush

Rsense

Vsec

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