SSL2103

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© NXP B.V. 2010. All rights reserved.

Product data sheet

Rev. 2 — 25 November 2010

5 of 21

NXP Semiconductors

SSL2103

SMPS controller IC for dimmable LED lighting

8.

Functional description

The SSL2103 is a LED driver IC that operates directly from the rectified mains. The

SSL2103 uses on-time mode control and frequency control to control the LED brightness.

The BRIGHTNESS and PWMLIMIT input of the IC can be used to control the LED light

output in combination with an external dimmer. The PWMLIMIT input can also be used for

Thermal Lumen Management (TLM) and for precision LED current control.

8.1 Start-up and Under Voltage Lock Out (UVLO)

Initially, the IC is self-supplying from the rectified mains voltage. The IC starts switching as

from the line is stopped for high efficiency operation. Alternatively the IC can be supplied

via a bleeder resistor connected to a high voltage.

8.2 Oscillator

An oscillator inside the IC provides the timing for the switching converter logic.

The frequency of the oscillator is set by the external resistors and the capacitor on pin RC

exponential, the relative sensitivity of the duty factor to the regulation voltage at low duty

factor, is almost equal to the sensitivity at high duty factors. This results in a more constant

gain over the duty factor range, compared to Pulse Width Modulated (PWM) systems with

a linear sawtooth oscillator. Stable operation at low duty factors is easily achieved. The

(1)

R equals the parallel resistance of both oscillator resistors. C is the capacitor connected at

the RC pin (pin 7).

The BRIGHTNESS input controls the frequency reduction mode. Figure 3 shows that the

oscillator switches over from an RC curve with R1/R2, to R1 only. A low BRIGHTNESS

voltage will reduce the switching frequency.

RC

1

3.5

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1

f

osc

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t

ch

e

arg

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