SSL21081AT datasheet(8/22 Pages) PHILIPS

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SSL21081AT

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Product data sheet

Rev. 6 — 3 October 2013

8 of 21

NXP Semiconductors

SSL21081AT

Compact non-dimmable LED driver IC

8.3 Protective features

The IC has the following protective features:

• UnderVoltage LockOut (UVLO)

• Leading-Edge Blanking (LEB)

• OverCurrent Protection (OCP)

• Internal OverTemperature Protection (OTP)

• Brownout protection

• Output Short Protection (OSP)

• LED overtemperature control and protection

The OSP is a latched protection. This protection causes the IC to halt until a reset (a result

of power cycling) is executed. When VCC drops to below VCC(rst), the IC resets the latch

protection mode. The internal OTP and LED overtemperature protections are safe-restart

protections. The IC halts, causing VCC to drop to below VCC(stop), triggering a start-up.

When VCC drops to below VCC(rst), the IC resets the latch protection mode. Switching

starts only when a no fault condition exists.

8.3.1 UnderVoltage LockOut (UVLO)

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

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

8.3.2 Leading-Edge Blanking (LEB)

To prevent false detection of overcurrent, a blanking time following switch-on is

implemented. When the internal MOSFET switch switches on, there can be a short

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

charging of the gate to source capacitance. During the LEB time (tleb), the spike is

disregarded.

8.3.3 OverCurrent Protection (OCP)

The SSL21081AT contains a highly accurate built-in 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 (td(ocp-swoff)) between the overcurrent detection and the

actual switching off of the switch. 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.

8.3.4 OverTemperature Protection (OTP)

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

converter stops operating. The safe-restart protection is triggered and the IC restarts with

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

8.3.5 Brownout protection

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

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

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

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