White LED Step-Up Regulator
EC4513
Preliminary
PAGE
6 / 7
DR18EV9005-VER1.0
Detailed Description
The EC4513 is a constant current boost regulator specially designed for white LEDs. It can drive up to 4 LEDs in series
and achieves efficiency up to 90%.
The brightness of the LEDs is adjusted through a voltage level on CNTL pin. When the level falls below 0.2V, the chip
goes into shut-down mode and consumes less than 1µA of current for VIN less than 5.5V.
Steady-State Operation
EC4513 is operated in constant frequency PWM. The switching is around 1MHz. Depending on the input voltage, the
inductance, the type of LEDs driven, and the LED’s current, the converter operates at either continuous conduction
mode or discontinuous conduction mode (see waveforms). Both are normal.
Brightness Control
LED’s current is controlled by the voltage level on CNTL pin
(VCNTL). This voltage can be either a DC or a PWM signal with
frequency less than 200Hz (for C3=2200pF). When a higher
frequency PWM is used, an RC filter is recommended before the
CNTL pin (see Figure 11).
The relationship between the LED current and CNTL voltage level
is as follows:
When R1 is 5
&, 1V of VCNTL conveniently sets ILED to 15mA. The
FIGURE 11 : PWM Brightness Control
range of VCNTL is 250mV to 5.5V.
Shut-Down
When VCNTL is less than 200mV, the converter is in shutdown mode. The max current consumed by the chip is less than
1µA for VIN less than 5.5V.
Over-Voltage Protection
When an LED string is disconnected from the output, VO will continue to rise because of no current feedback. When VO
reaches 18.5V (nominal), the chip will shut down. The output voltage will drop. When VO drops bellow 18V (nominal), the
chip will boost output voltage again until it reaches 18.5V. This hiccough continues until LED is applied or converter is
shut down.
When designing the converter, caution should be taken to ensure the highest operating LED voltage does not exceed
18V, the minimum shut-down voltage. There is no external component required for this function.
Component Selection
The input and output capacitors are not very important for the converter to operate normally. The input capacitance is
normally 2.2µF - 4.7µF and output capacitance 0.47µF - 1µF. Higher capacitance is allowed to reduce the
oltage/current ripple, but at added cost. Use X5R or X7R type (for its good temperature characteristics) of ceramic
capacitors with correct voltage rating and maximum height.
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