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EL7513IYZ Datasheet(PDF) 9 Page - Intersil Corporation |
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EL7513IYZ Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 12 page 9 Detailed Description The EL7513 is a constant current boost regulator specially designed for driving white LEDs. It can drive up to 4 LEDs in series or 12 LEDs in parallel/series configuration and achieves efficiency up to 91%. The brightness of the LEDs is adjusted through a voltage level on the CNTL pin. When the level falls below 0.1V, the chip goes into shut-down mode and consumes less than 1µA of current for VIN less than 5.5V. Steady-State Operation EL7513 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=4700pF). When a higher frequency PWM is used, an RC filter is recommended before the CNTL pin (see Figure 20). The relationship between the LED current and CNTL voltage level is as follows: When R1 is 5Ω, 1V of VCNTL conveniently sets ILED to 15mA. The range of VCNTL is 250mV to 5.5V. Shut-Down When VCNTL is less than 100mV, the converter is in shut- down 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 18V (nominal), the chip will shut down. The output voltage will drop. When VO drops below 16V (nominal), the chip will boost output voltage again until it reaches 18V. 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 17V, 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 0.22µF - 4.7µF and output capacitance 0.22µF - 1µF. Higher capacitance is allowed to reduce the voltage/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. FIGURE 18. DISCONTINUOUS CONDUCTION MODE FIGURE 19. OVER VOLTAGE PROTECTION (LED DISCONNECTED) Waveforms (Continued) All performance curves and waveforms are taken with C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, L = 33µF, VIN = 3.3V, VCNTL = 1V, R1 =5Ω, 4 LEDs in a series; unless otherwise specified. VCTRL=0.34V, ILED=5mA ∆VIN IL VLX ∆VO 10mV/DIV 100mA/DIV 10V/DIV 50mV/DIV 1µs/DIV VO (5V/DIV) VCOMP (1V/DIV) FIGURE 20. PWM BRIGHTNESS CONTROL CNTL COMP PWM SIGNAL 0.1µF 100K I LED V CNTL 13.33 R 1 × ---------------------------- = EL7513 |
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