SSL2109 datasheet(8/20 Pages) NXP

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SSL2109_SER

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Product data sheet

Rev. 3 — 4 June 2012

8 of 20

NXP Semiconductors

SSL2109 series

GreenChip controller for LED lighting

8.6 Protective features

The IC has the following protections:

• UnderVoltage LockOut (UVLO)

• Leading-Edge Blanking (LEB)

• OverCurrent Protection (OCP)

• Internal OverTemperature Protection (OTP)

• Brownout protection

• Short-Winding Protection (SWP) on SSL2109T only

• Output Short Protection (OSP)

• LED overtemperature control and protection

The SWP and the OSP are latched protections. These protections cause the IC to halt

until a reset (a result of power cycling) is executed. When VCC drops lower than VCC(rst),

the IC resets the latch protection mode. The internal OTP and LED over temperature

protections are safe-restart protections. The IC halts, causing VCC to fall lower than

VCC(stop), and instigates start-up. Switching starts only when no fault condition exists.

8.6.1 UnderVoltage LockOut (UVLO)

When the voltage on the VCC pin drops lower than VCC(stop), the IC stops switching. An

attempt is then made to restart by supplying VCC from the HV pin voltage.

8.6.2 Leading-Edge Blanking (LEB)

To prevent false detection of the short-winding or overcurrent, a blanking time following

switch-on is implemented. When the MOSFET switch turns on there can be a short

current spike due to capacitive discharge of voltage over the drain and source. During the

LEB time (tleb), the spike is disregarded.

8.6.3 OverCurrent Protection (OCP)

The SSL2109 series contains a highly accurate peak current detector. It triggers when the

voltage at the SOURCE pin reaches the peak-level Vth(ocp)SOURCE. The current through

the switch is sensed using a resistor connected to the SOURCE pin. The sense circuit is

activated following LEB time tleb. As the LED current is half the peak current (by design), it

automatically provides protection for maximum LED current during operation. There is a

propagation delay between overcurrent detection and the actual closure of the switch

td(ocp-swoff). Due to the delay, the actual peak current is slightly higher than the OCP level

set by the resistor in series to the SOURCE pin.

8.6.4 OverTemperature Protection (OTP)

When the internal OTP function is triggered at a certain IC temperature (Tth(act)otp), the

converter stops operating. The OTP safe-restart protection and the IC restarts again with

switching resuming when the IC temperature drops lower than Tth(rel)otp.

8.6.5 Brownout protection

Brownout protection is designed to limit the lamp power when the input voltage drops

close to the output voltage level. Since the input power has to remain constant, the input

current would otherwise increase to a level that is too large for the input circuitry. For the

SSL2109 series, there is a maximum limit on the on-time of switch ton(high).

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