CYT 2506
Open-Circuit Protection
In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail,
the feedback voltage will be zero. The CYT2506 will then switch at a high duty cycle resulting in a high
output voltage, which may cause the SW pin voltage to exceed its maximum 30V rating. A zener diode can
be used at the output to limit the voltage on the SW pin. The zener voltage should be larger than the
maximum forward voltage of the LED string. The current rating of the zener should be larger than 0.1mA.
Dimming Control(There are two different types of dimming control circuits:)
1. Using a PWM Signal to EN Pin
With the PWM signal applied to the EN pin, the CYT2506 is turned on or off by the PWM signal. The
LEDs operate a either zero or full current. The average LED current increases proportionally with the duty
cycle of the PWM signal. A 0% duty cycle will turn off the CYT2506 and corresponds to zero LED current. A
100% duty cycle corresponds to full current. The typical frequency range o the PWM signal is 1kHz to 5kHz.
The magnitude of the PWM signal should be higher than the minimum EN voltage high. The switching
waveforms of the EN pin PWM control are shown below.
2. Using a DC Voltage
For some applications, the preferred method o brightness control is a variable DC voltage to adjust the
LED current. The dimming control using a DC voltage is shown below. As the DC voltage increases, the
voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases.
The selection of R2 and R3 will make the current from the variable DC source much smaller than the LED
current and much larger than the FB pin bias current. For Vcc range from 0V to 2V, the selection of
resistors gives dimming control of LED current from 0mA to 15mA
ShenZhen CYT IC Design CO ,Ltd
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