SSL2103T NXP [NXP Semiconductors], SSL2103T Datasheet - Page 5

• Manufacturer Part Number: SSL2103T
• Description: SMPS controller IC for dimmable LED lighting
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
8. Functional description
SSL2103
Product data sheet
8.1 Start-up and Under Voltage Lock Out (UVLO)
8.2 Oscillator
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.
Initially, the IC is self-supplying from the rectified mains voltage. The IC starts switching as
soon as the voltage on pin V
by the auxiliary winding of the transformer as soon as V
from the line is stopped for high efficiency operation. Alternatively the IC can be supplied
via a bleeder resistor connected to a high voltage.
Remark: The maximum V
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
and pin RC2. The external capacitor is charged rapidly to the V
from a new primary stroke, discharges to the V
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
frequency of the converter when V
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.
oscillator switches over from an RC curve with R1/R2, to R1 only. A low BRIGHTNESS
voltage will reduce the switching frequency.
RC
=
------ -
3.5
1



------- - t
f
osc
1
All information provided in this document is subject to legal disclaimers.
–
ch
arg
Rev. 2 — 25 November 2010
e


CC
CC
voltage rating of the IC must be considered.
passes the V
BRIGHTNESS
SMPS controller IC for dimmable LED lighting
CC(startup)
is high can be calculated using
RC(min)
level. The supply can be taken over
level. Because the discharge is
CC
is high enough and the supply
RC(max)
Figure 3
level and, starting
SSL2103
© NXP B.V. 2010. All rights reserved.
shows that the
Equation
5 of 21
(1)
1: