CONSONANCE

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5

REV 1.0

The wide operating voltage range helps protect the CN5501 against large transients such as those found in

load-dump situations up to 32V.

compared to a fixed reference voltage, and the error is amplified to serve as the drive to the internal power

Application Information

Input Voltage Considerations

The operating voltage range of the CN5501 is ＋4V to ＋32V . The device may operate below +4V, however,

LED current may not meet the full regulation specification. For proper operation, the minimum input voltage

must always be higher than the worst-case sum of the forward drops of all series-connected LEDs at the output

of the CN5501.

+5V Regulator

The CN5501 includes a fixed +5V output regulator that delivers up to 3mA of load current for low-power

applications throughout the +5.5V to +32V input voltage range. Connect a 2.2μF to 10uF compensation

capacitor from VCC pin to GND.

The

+5V output can be used to power the external circuitry.

Thermal Regulation

The CN5501 features thermal regulation instead of thermal shutdown. If the voltage drop across LED pin and

CS pin is high, or the LED current is large, or both the voltage drop and LED current are large, CN5501 will

become heater, when the silicon temperature reaches 125℃, the on-chip thermal regulation circuit begins to

function, the LED current will be decreased to keep the silicon temperature at 125℃(typical). This typically

occurs in overload or LED short-circuit conditions.

Setting the LED Current

The CN5501 uses a current sense resistor between CS pin and GND to set the LED current. The LED current is

given by the equation below:

PWM Dimming

The CN5501 provides pulsed or chopped current dimming. Generally, high-brightness LEDs are binned to match

at their full-rated current. However, LEDs from the same bin exhibit poor matching at currents other than

full-rated current. To achieve uniformity, high brightness LED manufacturers recommend PWM pulsing of the

LED current at their full-rated value. This can be achieved by pulsing the enable input (EN) while having a

constant voltage at VIN, as shown in Figure 2. The PWM signal frequency should be less than 300Hz.