SSL2103

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© NXP B.V. 2010. All rights reserved.

Product data sheet

Rev. 2 — 25 November 2010

6 of 21

NXP Semiconductors

SSL2103

SMPS controller IC for dimmable LED lighting

A typical RC waveform is shown 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. Due to leakage current, the value of the

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

220 k

.

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 external 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

.

8.4 Bleeder for dimming applications

The SSL2103 IC contains some circuitry intended for mains dimmer compatibility. This

circuitry can drive two external current sinks, called bleeders. A strong bleeder is used for

zero-cross reset of the dimmer and TRIAC latching. A weak bleeder is added to maintain

the hold current through the dimmer.

Fig 3.

Brightness control block

Fig 4.

Brightness timing waveform

OSCILLATOR

24

μA

5 V

rc_threshold

Comparator

R2

10 k

Ω

R1

220 k

Ω

C1

330 pF

BRIGHTNESS

RC

RC2

V

V

001aam657

time

014aab108

rc_threshold

75 mV

RC voltage

Voltage

(mV)