SSL21084T datasheet(8/24 Pages) PHILIPS

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SSL21081T_2T_3T_4T

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Preliminary data sheet

Rev. 2 — 6 December 2011

8 of 24

NXP Semiconductors

SSL21081T/2T/3T/4T

GreenChip drivers for LED lighting

secondary stroke starts. When no capacitor is connected to the pin, VTONMAX is reached

quickly, shorter than the minimum limit of one microsecond. In this case, or in case the

TONMAX pin is grounded, the internal time constant, ton(high) determines the maximum

on-time.

8.4.6 Short-Winding Protection (SWP)

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

8.4.7 Output Short Protection (OSP)

During the second stroke (switch-of 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 of the PWM signal.

8.5 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 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 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.

8.6 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

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