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AN10876 Datasheet(PDF) 10 Page - NXP Semiconductors |
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AN10876 Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 20 page  SSL2109_SER All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved. Product data sheet Rev. 3 — 4 June 2012 10 of 20 NXP Semiconductors SSL2109 series 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 6. When the voltage on the NTC pin is higher than Vth(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 Vth(low)NTC is reached, see Figure 6 (3). The peak current is now half the peak current of nominal operation. When Vact(tmr)NTC is passed, see Figure 6 (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 6 (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 6 (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 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 Vdeact(tmr)NTC. Fig 6. 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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