ETC EC4513

White LED Step-Up Regulator
EC4513
Preliminary
The EC4513 is a constant current boost regulator specially designed for driving white LEDs. It can drive 4
LEDs in series and achieves efficiency up to 90%. The brightness of the LEDs is adjusted through a voltage
level on the CNTL pin. When the level falls below 0.2V, the chip goes into shut-down mode and consumes
less than 1µA of supply current for VIN less than 5.5V. The EC4513 is available in the 8-pin MSOP packages.
Features
Applications
• 2.6V to 13.2V input voltage
• PDAs
• 18V maximum output voltage
• Cellular phones
•
• Digital cameras
• 1MHz switching frequency
• White LED backlighting
• Up to 90% efficiency
• 1µA maximum shut-down current
• Dimming control
• 8-pin MSOP packages
Pinouts
Application Circuit
MSOP 8-PIN
TOP VIEW
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DR18EV9005-VER1.0
White LED Step-Up Regulator
EC4513
Preliminary
Absolute Maximum Ratings (TA = 25°C)
COMP, CNTL, IS to SGND. . . . . . . .. . . . . .. . . . . -0.3V to +6V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C
VOUT, VIN to SGND. . . . . . . . . . . . . . . . . . . . . . . . . . . . +19.5V
Lead Temperature . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 300°C
LX to PGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+20V
Operating Temperature . . . . . . . . . . . . . . . . . . . . . -40°C to +85°C
SGND to PGND . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation
of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all
tests are
at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Electrical Specifications
PARAMETER
VIN = 3V, VO = 12V, C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, R1 = 5&, TA = 25°C, unless otherwise specified.
DESCRIPTION
CONDITIONS
VIN
Input Voltage
IQ1
Shut-down Supply Current
VCNTL = 0V, Vin=3V
ICOMP
COMP Pin Pull-up Current
COMP connected to SGND
VCOMP
COMP Voltage Swing
ICNTL
CNTL shut-down Current
VCNTL1
Chip Enable Voltage
MIN
TYP
2.6
MAX
UNIT
13.2
V
1
uA
10
0.5
2.5
CNTL = 0V
uA
3.5
V
1
uA
270
mV
Chip Disable Voltage
14
15
200
mV
16
mA
IOUT_ACCURACY
VCNTL =1V
VCNTL =1V
VOUT1
Over-voltage Threshold
VOUT rising
17
V
VOUT2
Over-voltage Threshold
VOUT falling
15
V
ILX
MOSFET Current Limit
RDS_ON
MOSFET On-resistance
ILEAK
MOSFET leakage Current
FS
Switching Frequency
DMAX
Maximum Duty Ratio
ICS
CS Input Bias Current
△IO/△VIN
Line Requlation
500
mA
Ω
0.7
VCNTL = 0V , VLX = 12V
800
VCNTL = 2V , IS = 0
1000
1
uA
1200
KHz
%
85
1
VIN = 2.6V - 5.5V
PAGE 2 / 7
0.05
uA
%/V
DR18EV9005-VER1.0
White LED Step-Up Regulator
EC4513
Preliminary
PIN Desription
PIN NUMBER
PIN NAME
DECRIPTION
1
COMP
Compensation pin. A compensation cap (2200pF to 0.1uF) is normally between this pin and SGND
2
CNTL
Control pin for dimming and shut-down. A voltage between 270mV and 5.5V
controls the brightness, and less then 200mV shuts down the converter.
Output voltage sense. Use for over voltage protection
3
VOUT
4
LX
5
PGND
Power Ground pin. The source of internal MOSFET.
6
SGND
Signal Ground. Ground pin for internal control circuitry. Needs to connect to PGND at only
Inductor connection pin. The drain of internal MOSFET.
one point
7
CS
Current sense pin. Connect to sensing resistor to set the LED bias current.
8
VIN
Power supply for internal control circuitry
Block Diagram
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DR18EV9005-VER1.0
White LED Step-Up Regulator
EC4513
Preliminary
Typical Performance Curves
ILED VS. VCNTL
Application Circuit
FIGURE 1A : 2 LEDS in a series
FIGURE 2A : 3 LEDS in a series
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DR18EV9005-VER1.0
White LED Step-Up Regulator
EC4513
Preliminary
FIGURE 3A : 4 LEDs in a series
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DR18EV9005-VER1.0
White LED Step-Up Regulator
EC4513
Preliminary
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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DR18EV9005-VER1.0
White LED Step-Up Regulator
EC4513
Preliminary
When choosing an inductor, make sure the inductor can handle the average and peak currents
giving by following formulas (80% efficiency assumed):
where:
•△IL is the peak-to-peak inductor current ripple in Ampere
• L inductance in µH
A wide range of inductance (6.8µH - 68µH) can be used for the converter to function correctly.
For the same series of inductors, the lower inductance has lower DC resistance (DCR), which has less conducting loss.
But the ripple current is bigger, which generates more RMS current loss. Figure 12 shows the efficiency of the demo
board under different inductance for a specific series of inductor. For optimal efficiency in an application, it is a good
exercise to check several adjacent inductance values of your preferred series of inductors.
For the same inductance, higher overall efficiency can be obtained by using lower DCR inductor.
The diode should be Schottky type with minimum reverse voltage of 20V. The diode's peak current is the same as
inductor's peak current, the average current is IO, and RMS current is:
Ensure the diode's ratings exceed these current requirements.
White LED Connections
One leg of LEDs connected in series will ensure the uniformity
of the brightness. 18V maximum voltage enables 4 LEDs can
be placed in series. When placing 4 LEDs in series, make sure the worst total forward voltage does not exceed 18V.
However, placing LEDs into series/parallel connection can give higher efficiency as shown in the efficiency curves. One
of the ways to ensure the brightness uniformity is to prescreen the LEDs.
PCB Layout Considerations
The layout is very important for the converter to function properly. Power Ground ( ) and Signal Ground ( ) should be
separated to ensure the high pulse current in the power ground does not interference with the sensitive signals
connected to Signal Ground. Both grounds should only be connected at one point right at the chip. The heavy current
paths (VIN-L-LX pin-PGND, and VIN-L-D-C2-PGND) should be as short as possible.
The trace connected to pin (CS) is most important. The current sense resister R1 should be very close to the pin When
the trace is long, use a small filter capacitor close to the CS pin.
The heat of the IC is mainly dissipated through the PGND pin. Maximizing the copper area around the plane is preferable.
In addition, a solid ground plane is always helpful for the EMI performance.
The demo board is a good example of layout based on the principle. Please refer to the EC4513 Application Brief for the
layout.
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DR18EV9005-VER1.0