SSL21081AT Datasheet, PDF (11/22 Pages) NXP Semiconductors – Compact non-dimmable LED driver IC

NXP Semiconductors
Peak current
I_pk
I_pk / 2
SSL21082AT
Mains dimmable LED driver IC
V_{th(ocp)SOURCE} = 500 mV
V_{th(ocp)SOURCE} = 250 mV
1
23
4
5 _VNTC
001aan700
Fig 6. NTC control curve
When the voltage on the NTC pin exceeds V_th(high)NTC (see Figure 6 (4)), the converter
delivers nominal output current. When the voltage is lower than this level, the peak current
is gradually reduced until V_th(low)NTC is reached (see Figure 6 (3)). The peak current is
now half the peak current of nominal operation. When V_act(tmr)NTC is passed (see Figure 6
(2)) a timer starts to run to distinguish between the following situations:
• If the low-level V_{deact(tmr)NTC} is not reached within time t_to(deact)NTC (see Figure 6 (1))
LED overtemperature is detected. The IC stops switching and attempts to restart from
the HV pin voltage. The converter restarts from an NTC protection shutdown when the
voltage on the NTC pin exceeds V_th(high)NTC (see Figure 6 (4)). It is assumed that the
reduction in peak current does not result in a lower NTC temperature and LED OTP is
activated.
• If the low-level V_{deact(tmr)NTC} is reached within the time t_to(deact)NTC (see Figure 6 (1)) it
is assumed that the pin is pulled down externally. The restart function is not triggered.
Instead, the output current is reduced to zero. PWM dimming can be implemented this
way. The output current rises again when the voltage is higher than V_th(low)NTC.
8.7.1 Soft-start function
The NTC pin can be used to make a soft start function. During switch-on, the level on the
NTC pin is low. By connecting a capacitor (in parallel with the NTC resistor), a time
constant can be defined. The time constant causes the level on the NTC pin to increase
slowly. When passing level V_th(low)NTC (see Figure 6 (3)), the convertor starts with half of
the maximum current. The output current slowly increases to maximum when V_th(high)NTC
(see Figure 6 (4)) is reached.
SSL21082AT
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 6 — 3 October 2013
© NXP B.V. 2013. All rights reserved.
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