SSL2109T datasheet(8/19 Pages) NXP | GreenChip controller for LED lighting

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SSL2109T

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Product data sheet

Rev. 2 — 26 April 2012

8 of 19

NXP Semiconductors

SSL2109T

GreenChip controller for LED lighting

rise in the coil during the on-phase is proportional to the difference between input voltage

and output voltage. Therefore, the peak current cannot be reached before ton(high) and as

a result the average output current to the LEDs is reduced.

8.6.6 Short-Winding Protection (SWP)

SWP activates if there is a steep rising current through the MOSFET and thus the external

resistor connected to the SOURCE pin. This current can occur when there is a short from

the freewheel diode. Additionally, it occurs due to a small/shorted inductor between the

input voltage and the DRAIN pin. If the voltage on the SOURCE pin is greater than 1.5 V,

latched protection is triggered following LEB time tleb. In addition, if VCC drops lower than

VCC(rst) the IC resets the latched protection mode.

8.6.7 Output Short Protection (OSP)

During the second stroke (switch-off time), if a valley is not detected within the off-time

limit (toff(high)), then typically the output voltage is less than the minimum limit allowed in

the application. This condition can occur either during starting up or due to a short. A timer

is 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.

8.7 VCC supply

The SSL2109T 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 switching) 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 SSL2109T 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.

8.8 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 prevent the additional high-power losses, which would result if a regulator were used for

continuously powering the IC. Unlike an auxiliary supply, additional inductor windings are

not needed.

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