SSL21083AT datasheet(9/23 Pages) PHILIPS

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SSL21083AT

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Product data sheet

Rev. 6 — 4 October 2013

9 of 22

NXP Semiconductors

SSL21083AT

Compact non-dimmable LED driver IC

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

SSL21083AT, there is a maximum limit on the on-time ton(high). The rate of current 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). As a result

the average output current to the LEDs is reduced.

8.3.6 Output Short-circuit Protection (OSP)

During the secondary 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 start-up or due to a short-circuit. A

timer tdet(sc) is started when toff(high) is detected. Timer tdet(sc) is reset when a valid valley

detection occurs in one of the subsequent cycles or when VCC drops to below VCC(stop).

The timer can also be reset if the maximum limit on the on-time of the switch (ton(high)) is

reached, which is usually the case at start-up (brownout protection). If no valley is

detected and (ton(high)) is not reached before tdet(sc), then it is concluded that a real

short-circuit exists. The IC enters latched protection. If VCC drops to below VCC(rst), the IC

resets the latched protection mode (see Figure 5).

Fig 5.

OSP logic diagram

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