DATASHEET

EL7630
DESIGNS
FOR NEW
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PLACEME
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RECOMME
ISL97634
Data Sheet
February 22, 2006
FN7371.1
White LED Boost Regulator
Features
The EL7630 represents a high efficiency, constant frequency
PWM regulator for use in white LED driving applications.
With efficiencies up to 86%, the EL7630 operates at 1.35MHz
switching frequency while operating from an input voltage of
between 2.7V and 5.5V. The maximum output voltage of 27V
enables the EL7630 to drive up to 6 LEDs in series. It is also
possible to use the EL7630 to drive LEDs in series/parallel
combination for applications requiring up to 15 LEDs.
• Up to 6 LEDs in series
Available in the 6 Ld SC-70 and the 5 Ld TSOT packages, the
EL7630 features the same pinout as competitive products
but offers higher efficiency, constant frequency operation. It
is specified for operation over the -40°C to +85°C ambient
temperature range.
• Pb-free plus anneal available (RoHS compliant)
• 27V maximum output
• 2.7V to 5.5V input
• Up to 86% efficient
• 1.35MHz constant frequency
• Enable/PWM dimming control
Applications
• LED backlighting
• Cell phones
Pinouts
• PDAs
EL7630
(6 LD SC-70)
TOP VIEW
LX 1
• Handheld devices
Ordering Information
6 VIN
GND 2
5 PGND
FB 3
4 ENAB
EL7630
(5 LD TSOT)
TOP VIEW
LX 1
5 VIN
GND 2
FB 3
4 ENAB
1
PART NUMBER
PART
(See Note)
MARKING
TAPE &
REEL
PACKAGE
(Pb-free)
PKG.
DWG. #
EL7630ICZ-T7
BCA
7”
(3K pcs)
6 Ld SC-70
P6.049
EL7630ICZ-T7A
BCA
7”
(250 pcs)
6 Ld SC-70
P6.049
EL7630IWTZ-T7
BAAC
7”
(3K pcs)
5 Ld TSOT
MDP0049
EL7630IWTZ-T7A BAAC
7”
(250 pcs)
5 Ld TSOT
MDP0049
NOTE: Intersil Pb-free plus anneal products employ special Pb-free
material sets; molding compounds/die attach materials and 100%
matte tin plate termination finish, which are RoHS compliant and
compatible with both SnPb and Pb-free soldering operations. Intersil
Pb-free products are MSL classified at Pb-free peak reflow
temperatures that meet or exceed the Pb-free requirements of
IPC/JEDEC J STD-020.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2006. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
EL7630
Absolute Maximum Ratings (TA = 25°C)
Input Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
LX Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +27V
FB Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
ENAB Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
PGND to GND (SC-70 package) . . . . . . . . . . . . . . . . -0.3V to +0.3V
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . .-40°C to +85°C
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Lead Temperature (soldering, 10s) . . . . . . . . . . . . . . . . . . . . +300°C
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, VENAB = 3V, over temperature from -40°C to 85°C unless otherwise specified.
DESCRIPTION
CONDITION
VIN-MIN
Minimum Operating Voltage
VOUT = 16V, ILED = 20mA
VIN-MAX
Maximum Operating Voltage
VOUT = 25V, ILED = 20mA
Feedback Voltage
TA = 25°C
VFB
IFB
FB Pin Bias Current
IIN
Supply Current
MIN
TYP
2.7
DMAX
ILIM
rDS(ON)
ILEAK
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
104
mV
80
95
115
mV
100
nA
1.0
mA
1
µA
0.6
0.8
1.35
1.8
MHz
0.8
1.35
1.9
MHz
85
90
%
82
90
%
280
350
mA
250
350
mA
m
ILX = 100mA
750
Switch Leakage Current
VLX = 27V
0.01
ENAB Voltage High
VENAB-LO
ENAB Voltage Low
ILED/VIN
TA = 25°C
2
1
2.5
VIN = 2.7V to 5V
µA
V
ENAB Pin Bias Current
Line Regulation
V
95
Switch On Resistance
VENAB-HI
IENAB
TA = 25°C
5.5
86
ENAB = 3V, output not switching
TA = 25°C
UNIT
V
ENAB = 0V
FOSC
MAX
0.2
0.6
V
1
µA
%/V
February 22, 2006
EL7630
Typical Application
90
L1
22µH
VDD
LEDs
LX
2.7V~5.5V
C1
1µF
C2
0.22µF
EL7630
ENAB FB
GND
OFF/ON
EFFICIENCY (%)
85
D1
VIN
80
75
70
RSET
4.75
65
0
5
10
15
20
25
30
LED CURRENT (mA)
FIGURE 1. TYPICAL APPLICATION CIRCUIT AND EFFICIENCY vs LED CURRENT
0.7
24.6
0.6
24.595
LED CURRENT (mA)
QUIESCENT CURRENT (mA)
Typical Performance Curves
0.5
0.4
0.3
0.2
0.1
24.59
24.585
24.58
24.575
24.57
24.565
0
24.56
0
1
2
3
4
5
6
0
5
10
VOUT (V)
VIN (V)
20
FIGURE 3. LOAD REGULATION (VIN=4V)
FIGURE 2. QUIESCENT CURRENT (ENABLE)
1.34
SWITCHING FREQUENCY (MHz)
24.7
24.68
LED CURRENT (mA)
15
24.66
24.64
24.62
24.6
24.58
24.56
2.5
3
3.5
4
4.5
VIN (V)
FIGURE 4. LINE REGULATION
3
5
5.5
1.32
1.3
1.28
1.26
1.24
1.22
1.2
-40
10
60
TEMPERATURE (°C)
FIGURE 5. SWITCHING FREQUENCY vs TEMPERATURE
February 22, 2006
EL7630
Typical Performance Curves
22
20
IOUT (mA)
16
12
8
4
0
0
20
40
60
80
100
DUTY-CYCLE (D)
FIGURE 6. PWM DIMMING CURVE (400Hz)
Block Diagram
Vin
Enable
EL7630
1.2MHz Oscillator and Ramp
Generator
LX
PWM
Comparator
PWM Logic
Controller
FET
Driver
Current
Sense
PGND
GM Amp
Compensation
GM
Amplifier
(shared with PGND
in TSOT5 package) GND
FB
95mV
Bandgap
Reference
Generator
FIGURE 7. EL7630 BLOCK DIAGRAM
Pin Functions
LX (Pin 1) - Switching Pin. Connect to inductor and diode.
GND (Pin 2) - Ground Pin. Connect to local ground.
PGND (Pin 5, SC-70 Package) - Ground Pin. Connect to
Pin 2 and to local ground.
VIN (Pin5/Pin6 SC-70 Package) - Input Supply Pin.
Connect to the input supply voltage.
FB (Pin 3) - Feedback Pin. Connect to the cathode of lowest
LED and the sense resistor.
ENAB (Pin 4) - Enable Pin. Connect to enable signal to
turn-on or off the device.
4
February 22, 2006
EL7630
Detailed Description
Steady-State Operation
EL7630 operates with constant frequency PWM. The
switching frequency is around 1.2MHz. Depending on the
input voltage, inductance, number of LEDs and the LED
current, the converter operates in either continuous
conduction mode or discontinuous conduction mode. Both
are normal. The forward current of the LED is set using the
RSET resistor. In steady state mode, this current is given by
the equation:
V FB
I LED = --------------R SET
(EQ. 1)
Shut-Down
The ENAB pin, when taken low places EL7630 into power
down mode. When in power down, the supply current
reduced to less than 1µA.
Dimming Control
The ENAB pin also doubles as a brightness control. There
are two different types of dimming control methods. The first
dimming control is controlled through the duty-cycle of the
ENAB input PWM waveform, which can operate at
frequencies of 400Hz to 1kHz. The LEDs operate at either
zero or full current. This is called PWM dimming control
method. The relationship between the average LED current
and the duty-cycle (D) of the ENAB pin’s waveform is as
follows:
V FB
average I LED = ---------------  D
R SET
25
20
IOUT (mA)
EL7630 uses a constant frequency, current mode control
scheme to provide excellent line and load regulation. It
can drive up to 6 LEDs in series or 15 LEDs in
parallel/series configuration, with efficiencies of up 86%.
EL7630 operates from an input voltage of 2.7V to 5.5V and
can boost up to 27V.
15
1kHz
10
400Hz
5
0
0 10 20 30 40 50 60 70 80 90 10
DUTY-CYCLE (%)
FIGURE 8. PWM DIMMING LINEAR RANGE (FOR 400Hz AND
1kHz PWM FREQUENCIES CONDITION,
COUT = 0.22µF)
The second dimming control is to apply a variable DC
voltage to adjust the LED current. This is called analog
dimming control. The dimming control using a DC voltage is
shown in Figure 9. As the DC dimming signal voltage
increases, the voltages drop on R1 and R2 increases and
the voltage drop on RSET decreases. Thus, the LED current
decreases. The DC dimming signal voltage can be a variable
DC voltage or a DC voltage generated from a PWM control
signal. For some application areas, the PWM control signal
is a high frequency signal. To make dimming controllable
with these high frequency PWM signals, the high frequency
components of the PWM control signal should be filtered to
get the equivalent DC voltage. The equivalent DC voltage is
then used as the variable DC voltage for dimming LED
current.
V FB R 1 + R 2 V Dim  R 1
I LED = ---------------  --------------------- – --------------------------R SET
R2
R SET  R 2
(EQ. 3)
R2
R1


V Dim = -------  V FB   1 + ------- – F
R1
R2


(EQ. 4)
(EQ. 2)
The magnitude of the PWM signal should be higher than the
minimum ENAB voltage high. The bench PWM dimming test
results are shown in Figure 8. In the test, two PWM
frequencies 400Hz and 1kHz are chosen to compare the
linear dimming range. It is clear that for lower PWM
frequency, the linear dimming range is wider than one for
higher PWM frequency. In the PWM dimming test, the output
capacitor is 0.22µF.
5
where F is the brightness with respect to the undimmed
value.
February 22, 2006
EL7630
Components Selection
L1
22µH
D1
VIN
VDD
2.7V~5.5V
C1
1µF
OFF/ON
LEDs
LX
C2
0.22µF
EL7630
ENAB FB
GND
R2
R1
RSET
4.75
DIMMING SIGNAL
FIGURE 9. ANALOG DIMMING CONTROL APPLICATION
CIRCUIT
For a required LED current ILED and chosen values of R1
and R2, the dimming DC voltage VDim can be expressed as:
R2
V Dim = V FB +  V FB – I LED  R SET   ------R1
(EQ. 5)
The input capacitance is normally 0.22µF~4.7µF and the
output capacitor is 0.22µF~1µF. X5R or X7R type of ceramic
capacitor with the correct voltage rating is recommended.
The output capacitor value will affect PWM dimming
performance. For lower output capacitor values, the range of
PWM dimming is wider than for higher values of output
capacitor.
When choosing an inductor, make sure the inductor can
handle the average and peak currents given by the following
formulas (80% efficiency assumed):
I LED  V OUT
I LAVG = --------------------------------0.8  V IN
(EQ. 6)
1
I LPK = I LAVG + ---  I L
2
(EQ. 7)
V IN   V OUT – V IN 
I L = --------------------------------------------------L  V OUT  f OSC
(EQ. 8)
It is clear that as the required LED current ILED is closed to
the rate current VFB/RSET, VDim is closed to VFB. As the
required LED current is lower than the rate current, the
dimming DC voltage VDim is increased in R2/R1 factor.
Where:
Open-Voltage Protection
• L inductance in H.
In some applications, it is possible that the output is
opened, e.g. when the LEDs are disconnected from the
circuit or the LEDs fail. In this case the feedback voltage
will be zero. The EL7630 will then switch to a high duty
cycle resulting in a high output voltage, which may cause
the LX pin voltage to exceed its maximum 27V rating. To
implement overvoltage protection, a zener diode Dz and a
resistor R1 can be used at the output and FB pin to limit the
voltage on the LX pin as shown in Figure 10. It is clear that
as the zener is turned on, due to the overvoltage, the zener
diode’s current will set up a voltage on R1 and RSET and this
voltage is applied on FB pin as the feedback node. This
feedback will prevent the output from reaching the
overvoltage condition. In the overvoltage protection circuit
design, the zener voltage should be larger than the
maximum forward voltage of the LED string.
• fOSC switching frequency, typically 1.2MHz
D1
L1
22µH
VIN
VDD
LEDs
LX
2.7V~5.5V
C1
EL7630
Dz
1µF
OFF/ON
ENAB FB
GND
R1
RSET
4.75
C2
0.22µF
• IL is the peak-to-peak inductor current ripple in Ampere
The boost inductor can be chosen in a wide range of
inductance (10µH~82µH). For 10µH inductor value, the
boost inductor current will be in discontinuous mode. As the
inductor value decreases further, the ripple of the boost
inductor current is increased and can even trigger
overcurrent protection. For high boost inductor value, the
boost inductor current will be in continuous mode. For
general boost converter, as the converter operates in
continuous mode, there is right half plane zero (RHPZ). If
RHPZ frequency is less than or close to the control loop
crossover frequency, there is a stability issue. In EL7630, the
compensation network is well designed and there is no
RHPZ stability issue even if the inductor value is over 82µH.
For the same series of inductors, a lower inductance has
lower DC resistance (DCR), which causes less conducting
loss, but higher peak to peak current variation, which
generates more RMS current loss. Figure 11 shows the
efficiency of the demo board with different LED load for a
specific series of inductor.
The diode used should be a schottky type with minimum
reverse voltage of 28V. The diode’s peak current is the same
as the inductor’s peak current. The schottky RMS current is:
I RMS =
2
2
1
D   2  I LAVG + ---  I L


6
(EQ. 9)
FIGURE 10. LED DRIVER WITH OVERVOLTAGE
PROTECTION CIRCUIT
6
February 22, 2006
EL7630
The efficiency bench test results are shown in Figure 11. In
the test, the input voltage is 4V and 2, 3, 4, 5 and 6 LEDs are
used as the load (boost inductor L = 22µH Sumida
CDRH5D28R-220NC).
90
22µH,VIN=4V
EFFICIENCY (%)
85
2LED
80
5LED
75
4LED
70
6LED
65
3LED
60
55
0
10
20
30
LED CURRENT (mA)
FIGURE 11. EFFICIENCY CURVE WITH 2, 3, 4, 5 AND 6 LEDs
LOAD
White LED Connections
One leg of LEDs connected in series will ensure brightness
uniformity. The 27V maximum output voltage specification
enables up to 6 LEDs to be placed in series.
In order to output more power to drive more LEDs, LEDs
should be in series/parallel connection. Due to the LED's
negative temperature coefficient, in each parallel branch, the
driving source should be high impedance, to balance the
LED current in each branch. One of the ways to ensure the
brightness uniformity is to add mirror current balance circuit,
built up with three transistors for the 15 LEDs series/parallel
connection application shown in Figure 12.
PCB Layout Considerations
The PCB layout is very important for the converter to
function properly. For the SC-70 6 pin package, Power
Ground and Signal Ground should be separated to ensure
the high pulse current in the power ground does not interfere
with the sensitive signals connected to Signal Ground. Both
grounds should only be connected at one point right at the
chip. The heavy current loops (VIN-L1-LX-PGND, and VIN L1-D1-C2-PGND) should be as short as possible. For the
TSOT 5 pin package, there is no separated GND. All return
GNDs should be connected in GND pin but with no sharing
branch. Based on the signal level on each branch, the lower
power level of the branch, the closer the branch to GND pin
in order to minimize the branch interactive.
The FB pin is most important. The current sense resistor
RS ET should be very close to this pin. If a long trace is
required to the LEDs, a small decoupling capacitor should be
placed at this pin.
The heat of the IC is mainly dissipated through the PGND
pin. Maximizing the copper area connected to this pin 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 EL7630 Application Brief for the
layout.
D1
L1
VIN
2.7V~5.5V
C1
OFF/ON
VDD
LX
C2
EL7630
ENAB FB
ENAB FB
GND
LEDs
RSET
FIGURE 12. LEDs IN SERIES/PARALLEL WITH MIRROR
CURRENT BALANCE
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Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
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7
February 22, 2006