Техническая Спецификация для Nxp Semiconductors SSL2101 Evaluation Boards SSL2101T/DB/FBCB230V,598 SSL2101T/DB/FBCB230V,598

SSL2101

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© NXP B.V. 2011. All rights reserved.

The SSL2101 is an LED driver IC that operates directly from the rectified mains.

The SSL2101 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.

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

CC

 passes the V

CC(startup)

 level. The supply can be taken over 

by the auxiliary winding of the transformer as soon as V

CC

 is high enough and the supply 

from the line is stopped for high efficiency operation. Alternatively the IC can be supplied 
via a bleeder resistor connected to a high voltage. Note however the maximum V

CC

 

voltage rating of the IC.

If for some reason the auxiliary supply is not sufficient, the high-voltage supply can also 
supply the IC. As soon as the voltage on pin V

CC

 drops below the V

CC(UVLO)

 level, the IC 

stops switching and will restart from the rectified mains voltage, if the internal current 
delivered is sufficient.

An internal 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 
and pin RC2. The external capacitor is charged rapidly to the V

RC(max)

 level and, starting 

from a new primary stroke, it discharges to the V

RC(min)

 level. Because the discharge is 

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 Phase Width Modulated (PWM) systems with 
a linear sawtooth oscillator. Stable operation at low duty factors is easily realized. The 
frequency of the converter when V

BRIGHTNESS

 is high can be estimated using 

(1)

R equals the parallel resistance of both oscillator resistors. C is the capacitor connected at 
the RC pin (pin 8).

The BRIGHTNESS input controls the frequency reduction mode. 

 shows that the 

oscillator switches over from an RC curve with R1 in parallel with R2 to R1 only. A low 
BRIGHTNESS voltage will reduce the switching frequency.

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