SSL2129AT datasheet(5/21 Pages) NXP

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SSL2129AT

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Product data sheet

Rev. 2 — 23 October 2012

5 of 21

NXP Semiconductors

SSL2129AT

Dimmable LED controller IC

Functional description

8.1 Introduction

The SSL2129AT is a controller IC solution for small form factor mains phase-cut

dimmable LED lamps in isolated and non-isolated applications.

8.2 Converter operation

The converter in the SSL2129AT is a Boundary Conduction Mode (BCM), peak current

controlled system. See Figure 3 for the basic application diagram. See Figure 4 for the

waveforms.

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. The amplitude of the current build-up

in L is proportional to the voltage drop over the inductor and the time that the MOSFET

switch is on. When the MOSFET is switched off, the energy in the inductor is released

towards the output. The current then falls at a rate proportional to the value of VOUT. The

LED current ILED depends on the peak current through the inductor (SSL2129AT

controlled) and on the dimmer angle while it is optimized for a high-power factor. A new

cycle is started once the inductor current IL is zero. This quasi-resonant operation results

in higher efficiency.

8.3 Driver pin

The SSL2129AT is equipped with a driver output for controlling 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

a low level 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. The switching slope can be controlled further using an external

resistor between IC and gate.

At the lowest VCC voltage (VCC(stop)), the voltage of the driver is VO(DRIVER)min.

Fig 3.

SSL2129AT basic application diagram

TONMOD

VIN

VOUT

VCC

DRAIN

NTC

DRIVER

GND

NTC

LEDs

SOURCE

aaa-004042

Rsense

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