SSL21081AT datasheet(6/22 Pages) PHILIPS

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SSL21081AT

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Product data sheet

Rev. 6 — 3 October 2013

6 of 21

NXP Semiconductors

SSL21081AT

Compact non-dimmable LED driver IC

Functional description

8.1 Converter operation

The converter in the SSL21081AT is a Boundary Conduction Mode (BCM), peak current

controlled system. Figure 3 shows the basic application diagram. Figure 4 shows 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 internal MOSFET switch is switched on. Thereafter,

the amplitude of the current build-up in L is proportional to VIN VOUT and the time that

the internal MOSFET switch is on. When the internal 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. As soon as the inductor current IL is zero, a

new cycle is started.

Fig 3.

Basic SSL21081AT application diagram

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