SSL2109T datasheet(5/19 Pages) NXP

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SSL2109T

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Product data sheet

Rev. 2 — 26 April 2012

5 of 19

NXP Semiconductors

SSL2109T

GreenChip controller for LED lighting

Functional description

8.1 Introduction

The SSL2109T is an IC intended for small form factor retrofit SSL lamps and separate

LED drivers.

8.2 Converter operation

The converter in the SSL2109T is a Boundary Conduction Mode (BCM), peak current

controlled system. For the basic application diagram see Figure 3, for the waveforms see

Figure 4. 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 SSL2109T 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 3.

Basic application diagram SSL2109T

SSL2109

DVDT

VCC

DRAIN

NTC

DRIVER

GND

NTC

LEDs

SOURCE

aaa-001743

Rinrush

Rsense

Vsec

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