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SSL2109T Datasheet(PDF) 9 Page - NXP Semiconductors

Part No. SSL2109T
Description  GreenChip controller for LED lighting
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Maker  NXP [NXP Semiconductors]
Homepage  http://www.nxp.com
Logo NXP - NXP Semiconductors

SSL2109T Datasheet(HTML) 9 Page - NXP Semiconductors

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SSL2109T
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 2 — 26 April 2012
9 of 19
NXP Semiconductors
SSL2109T
GreenChip controller for LED lighting
8.9 VCC regulator
During supply dips, the input voltage can drop too low to supply the required IC current
through the DVDT pin. Under these conditions, if the VCC voltage drops lower than
VCC(swon)reg level, another regulator with a current capability of up to IHVhigh(oper) is started.
The job of the regulator is to fill in the required supply current, which the DVDT supply
does not deliver preventing the IC going into UVLO. When the VCC voltage is higher than
VCC(swon)reg level, the regulator is turned off.
8.10 NTC functionality and PWM dimming
The NTC pin can be used as a control method for LED thermal protection. Alternatively,
the pin can be used as an input to disable/enable light output using a digital signal (PWM
dimming). The pin has an internal current source that generates the current of Ioffset(NTC).
An NTC resistor to monitor the LED temperature can be directly connected to the NTC
pin. Depending on the resistance value and the corresponding voltage on the NTC pin,
the converter reacts as shown in Figure 5.
When the voltage on the NTC pin is higher than Vth(high)NTC see Figure 5 (4), the converter
delivers nominal output current. When the voltage is lower than this level, the peak current
is gradually reduced until Vth(low)NTC is reached, see Figure 5 (3). The peak current is now
half the peak current of nominal operation. When Vact(tmr)NTC is passed, see Figure 5 (2) a
timer starts to run to distinguish between the following situations:
If the low-level Vdeact(tmr)NTC is not reached within time tto(deact)NTC, Figure 5 (1) LED
overtemperature is detected. The IC stops switching and attempts to restart from the
HV pin voltage. Restart takes place when the voltage on NTC pin is higher than
Vth(high)NTC, see Figure 5 (4). It is assumed that the reduction in peak current did not
result in a lower NTC temperature and LED OTP is activated.
If the low-level Vdeact(tmr)NTC is reached within the time tto(deact)NTC, Figure 5 (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 Vdeact(tmr)NTC.
Fig 5.
NTC control curve
001aan700
2
3
4
5
Ipk
Peak current
Ipk / 2
Vth(ocp)SOURCE = 500 mV
Vth(ocp)SOURCE = 250 mV
VNTC
1


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