SSL2102_1

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 01 — 29 June 2009

6 of 21

NXP Semiconductors

SSL2102

SMPS IC for dimmable LED lighting

A typical RC waveform is given in Figure 4. The RC switch-over threshold is controlled by

the BRIGHTNESS pin.

To ensure that the capacitor can be charged within the charge time, the value of the

oscillator capacitor should be limited to 1 nF. Leakage current limits the value of the

resistor connected between the RC pin and the ground should be limited to a maximum of

220 k

Ω.

8.3 Duty factor control

The duty factor is controlled by an internally regulated voltage and the oscillator signal on

pin RC. The internal regulation voltage is set by the voltage on the PWMLIMIT pin.

A low PWMLIMIT voltage will results in a low on-time for the internal power switch. The

minimum duty factor of the switched mode power supply can be set to 0 %. The maximum

duty factor is set to 75 %.

Fig 3.

Brightness control block

Fig 4.

Brightness timing waveform.

STARplug

OSCILLATOR

24

µA

5 V

rc_threshold

Comparator

R2

10 k

Ω

R1

220 k

Ω

C1

330 pF

BRIGHTNESS

RC

RC2

V

V

014aaa574

time

014aaa582

rc_threshhold

75 mV

RC voltage

Voltage

(mV)