EL7513 查看數據表（PDF） - Renesas Electronics

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EL7513

White LED Step-Up Regulator

Renesas Electronics 

EL7513

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 = 5, 4 LEDs in a

series; unless otherwise specified.

VCTRL = 0.34V, ILED = 5mA

VIN

10mV/DIV

IL

100mA/DIV

VLX

10V/DIV

VO

50mV/DIV

1µs/DIV

FIGURE 18. DISCONTINUOUS CONDUCTION MODE

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).

PWM

SIGNAL

100k

0.1µF

CNTL

COMP

FIGURE 20. PWM BRIGHTNESS CONTROL

VO (5V/DIV)

VCOMP (1V/DIV)

FIGURE 19. OVER VOLTAGE PROTECTION (LED

DISCONNECTED)

The relationship between the LED current and CNTL voltage

level is as follows:

ILED = -1---3-V--.--3-C--3--N----T----LR----1--

(EQ. 1)

When R1 is 5, 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.

FN7112 Rev 5.00

December 22, 2008

Page 9 of 12

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