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EN/SET Serial Interface (S2CwjreTM) The current source output magnitude is controlled by the EN/SET serial data interface. The interface records rising edges of the EN/SET pin, and decodes them int0 32 individual current level set- tings summarized in the above table. The modulo 32 interface wraps states back to state l after the 32nd clock, so the previous state is achieved by clocking the EN/SET pin 31 times. The counter can be clocked at speeds up t0 1MHz, so intermediate states are not visible. The first rising edge of EN/SET enables the lC and initially sets the output LED current to OdB. Once the final clock cycle is input for the desired brightness level, the EN/SET pin is held high to maintain the device output cur- rent at the programmed level. The device is dis- abled 500ps after the EN/SET pin transitions to a logic low state. The EN/SET timing is designed to accommodate a wide range of data rates. After the first rising edge of EN/SET, the charge pump is enabled and reaches full capacity after the soft start time (tss). During the soft start time, multiple clock pulses may be entered on the EN/SET pin to set the final output current level with a single burst of clocks. Alternatively, the EN/SET clock pulses may be entered one at a time to gradually increase the LED brightness over any desired time period. A constant current is sourced as long as EN/SET remains in a logic high state. The current source outputs are switched off after EN/SET has remained in a low state for at least the tOFF timeout period.