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SSL21084T/1,118

GreenChip drivers for LED lighting

NXP Semiconductors. 

NXP Semiconductors

SSL2108X

Drivers for LED lighting

started when toff(high) is detected, and is stopped only if a valid valley-detection occurs in

one of the subsequent cycles. If no valley is detected for tdet(sc), it is concluded that a real

short-circuit exists and not start-up. The IC enters latched protection. If Vcc drops lower

than VCC(rst), the IC resets the latched protection mode. During PWM dimming, the OSP

timer is paused during the off-cycle.

8.6 VCC supply

The SSL2108X can be supplied using three methods:

• Under normal operation, the voltage swing on the DVDT pin is rectified within the IC

providing current towards the VCC pin

• At start-up, there is an internal current source connected to the HV pin. The current

source provides internal power until either the dV/dt supply or an external current on

the VCC pin provides the supply

• An external voltage source can be connected to the VCC pin

The IC starts up when the voltage at the VCC pin is higher than VCC(startup). The IC locks

out (stops oscillating) when the voltage at the VCC pin is lower than VCC(stop). The

hysteresis between the start and stop levels allows the IC to be supplied by a buffer

capacitor until the dV/dt supply is settled. The SSL2108X has an internal Vcc clamp, which

is an internal active Zener (or shunt regulator). This internal active Zener limits the voltage

on the supply VCC pin to the maximum value of Vcc. If the maximum current of the dV/dt

supply minus the current consumption of the IC (determined by the load on the gate

drivers), is lower than the maximum value of IDD no external Zener diode is needed in the

dV/dt supply circuit.

8.7 DVDT supply

The DVDT pin is connected to an internal single-sided rectification stage. When an

alternating voltage with sufficient amplitude is supplied to the pin, the IC can be powered

without any other external power connection. This solution provides an effective method

to stop the introduction of high-power losses, without the need for additional inductor

windings.

8.8 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.

8.9 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. However, depending on the resistance value and the corresponding voltage on the

NTC pin, the converter reacts as shown in Figure 6.

SSL2108X

Preliminary data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 1 — 9 September 2011

© NXP B.V. 2011. All rights reserved.

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