SSL3401HN Datasheet, PDF (10/29 Pages) NXP Semiconductors – Low voltage dimmable controller for LED lighting

NXP Semiconductors
SSL3401HN
Low voltage dimmable controller for LED lighting
During the initialization phase, the PWM signal has a 100 % duty cycle. When the
initialization phase is completed, the PWM duty cycle is set according to the required
output power. The setting depends on the dimmer conduction angle in the event of a
phase cut dimmed AC supply.
A properly designed application causes the duty cycle, defined as T_LOW/T_period, to
increase when LED current increases.
7_SHULRG
7_/2:
Fig 5. PWM duty cycle definition
DDD
8.6 Output load control
The SSL3401HN provides a Pulse Width Modulation (PWM) signal to control the output
load resistor (R_LOAD). The signal is continuously HIGH for the maximum output load
power setting (lowest resistor value) and LOW for the minimum output load power setting
(open resistor).
A properly designed application causes the duty cycle, defined as T_LOW/T_period (Figure 5),
to decrease when the output load power increases.
The output load resistor (R_LOAD) is aimed at limiting the boost output voltage (V_BST)
overshoot in case of a sudden increase in input power. The optimum total R_LOAD value is
R_LOAD = V_BST / (I_LEDMAX * 0.3).
8.7 Feedback loop control
The SSL3401HN incorporates three independent proportional-integral (PI) feedback loop
controllers. All of them act on an error signal, as a result of the difference between the
minimum voltage on the FB pin and a predefined setpoint (0.625 V). The minimum voltage
is computed during a time interval equal to the supply time period: 10 ms for a rectified
50 Hz supply and 8.3 ms for a rectified 60 Hz supply. The PI controller output value is then
updated once per supply time period or 10 ms in a DC supply.
The first PI controller sets an analog signal at the ACMPREF pin to control the coil current
of the hysteretic boost converter.
The second PI controller adjusts the duty cycle of the LED current PWM signal
(LEDPWM).
The third PI controller output is a PWM signal (LOADPWM). It can be used to improve the
line rejection and thus the LED current stability.
SSL3401HN
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 2 — 28 January 2014
© NXP B.V. 2014. All rights reserved.
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