DATASHEET

EL1848
®
Data Sheet
March 31, 2004
FN7427
White LED Step-Up Regulator
Features
The EL1848 is a constant current
boost regulator specially designed for
driving white LEDs. It can drive 3
LEDs in series or up to 9 LEDs in parallel/series
configuration and achieves efficiency up to 91%.
• 2.6V to 13.2V input voltage
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 supply current for VIN less than 5.5V.
• Up to 91% efficiency
The EL1848 is available in 8-pin TSOT and MSOP
packages. The TSOT is just 1mm high, compared to
1.45mm for the standard SOT-23 package.
• 8-pin TSOT and MSOP packages
PACKAGE
• Drives up to 9 LEDs, 3 in a series
• 1MHz switching frequency
• 1µA maximum shut-down current
• Dimming control
• Pb-free Available
Applications
Ordering Information
PART
NUMBER
• 14V maximum output voltage
• PDAs
TAPE & REEL PKG. DWG. #
• Cellular phones
EL1848IWT-T7
8-Pin TSOT
7” (3K pcs)
MDP0049
• Digital cameras
EL1848IWT-T7A
8-Pin TSOT
7” (250 pcs)
MDP0049
• White LED backlighting
EL1848IWTZ-T7
(See Note)
8-Pin TSOT
(Pb-free)
7” (3K pcs)
MDP0049
Typical Connection
EL1848IWTZT7A (See Note)
8-Pin TSOT
(Pb-free)
7” (250 pcs)
MDP0049
EL1848IY
8-Pin MSOP
-
MDP0043
EL1848IY-T7
8-Pin MSOP
7”
MDP0043
EL1848IY-T13
8-Pin MSOP
13”
MDP0043
NOTE: Intersil Pb-free products employ special Pb-free material
sets; molding compounds/die attach materials and 100% matte tin
plate termination finish, which is 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-020B.
D
L
2.6V TO
5.5V C1
C2
33µH
4.7µF
1µF
VIN
LX
VOUT
CS
VCTRL
C3
CNTL
PGND
COMP
SGND
R1
5Ω
0.1µF
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2004. All Rights Reserved. Elantec is a registered trademark of Elantec Semiconductor, Inc.
All other trademarks mentioned are the property of their respective owners.
EL1848
Pinouts
EL1848
(8-PIN MSOP)
TOP VIEW
EL1848
(8-PIN TSOT)
TOP VIEW
COMP 1
8 VIN
CS 1
8 CNTL
CNTL 2
7 CS
VIN 2
7 COMP
VOUT 3
6 SGND
PGND 3
6 LX
LX 4
5 PGND
SGND 4
5 VOUT
2
EL1848
Absolute Maximum Ratings (TA = 25°C)
SGND to PGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Ambient Operating Temperature . . . . . . . . . . . . . . . .-40°C to +85°C
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Curves
Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . 125°C
COMP, CNTL, CS to SGND. . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
VIN to SGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+14V
VOUT to SGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+14V
LX to PGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+16V
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. This part is ESD sensitive. Handle with care.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all tests areat
the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Electrical Specifications
VIN = 3V, VO = 12V, C1 = 4.7µF, L = 33µH, C 2 = 1µF, C3 = 0.1µF, R1 = 5Ω, TA = 25°C, unless otherwise
specified.
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
13.2
V
1
µA
VIN
Input Voltage
IQ1
Total Input Current at Shut-down
VCNTL = 0V
IQ1
Quiescent Supply Current at VO Pin
VCNTL = 1V, load disconnected
1
1.5
mA
ICOMP
COMP Pin Pull-up Current
COMP connected to SGND
11
20
µA
VCOMP
COMP Voltage Swing
1.5
2.5
V
ICNTL
CNTL Shut-down Current
1
µA
VCNTL1
Chip Enable Voltage
VCNTL2
Chip Disable Voltage
2.6
0.5
CNTL = 0V
240
mV
100
mV
IOUT_ACCURACY VCNTL = 1V
VCNTL = 1V
14
15
16
mA
VOUT1
Over-voltage Threshold
VOUT rising
13
14
15
V
VOUT2
Over-voltage Threshold
VOUT falling, with resistive load
11
12
13
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 Regulation
400
mA
Ω
0.7
VCNTL = 0V, VLX = 12V
VCNTL = 2V, IS = 0
800
1000
85
90
1
µA
1200
kHz
%
1
VIN = 2.6V - 5.5V
0.03
µA
%/V
Pin Descriptions
PIN NUMBER
PIN NAME
DESCRIPTION
1
COMP
Compensation pin. A compensation cap (4700pF to 1µF) is normally connected between this pin and SGND.
2
CNTL
Control pin for dimming and shut-down. A voltage between 250mV and 5.5V controls the brightness, and less
than 100mV shuts down the converter.
3
VOUT
Output voltage sense. Use for over voltage protection.
4
LX
Inductor connection pin. The drain of internal MOSFET.
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 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.
3
EL1848
Block Diagram
2.6V TO
5.5V
CIN
VIN
4.7µF
REFERENCE
GENERATOR
1MHz
OSCILLATOR
THERMAL
SHUTDOWN
OVER-VOLTAGE
PROTECTION
L
33µH
VOUT
LX
COMP
+
+
+
CCOMP
COUT
PWM
LOGIC
1µF
BOOST
I-SENSE
0.1µF
I(LED)
START-UP
CONTROL
PWM
SIGNAL
VCNTL
ERROR AMP
+
-
617K
CNTL
PGND
CS
5Ω
50K
SGND
Typical Performance Curves
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, 3 LEDs in a
series; unless otherwise specified.
1.05
3.5
3
1.04
VCNTL=0V, 0.1V
WHITE LEDs DISCONNECTED
1.03
IIN (µA)
FS (MHz)
2.5
1.02
2
1.5
1
1.01
1
2.5
0.5
3
4
3.5
4.5
5
VIN (V)
FIGURE 1. SWITCHING FREQUENCY vs VIN
4
5.5
0
2.5
4.5
6.5
8.5
10.5
12.5
VIN (V)
FIGURE 2. QUIESCENT CURRENT
14.5
EL1848
Typical Performance Curves (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, 3 LEDs in a
series; unless otherwise specified.
VCNTL=1V
35
16
15.8
30
15.6
15.4
20
ILED (mA)
ILED (mA)
25
15
10
15
14.8
14.6
14.4
5
0
15.2
14.2
0
0.5
1
1.5
2
2.5
14
2.5
VCNTL (V)
FIGURE 3. ILED vs VCNTL
3.5
4.5
4
VIN (V)
5
5.5
FIGURE 4. ILED vs VIN
BAT54HT1
L
VIN
3
90
33µH
4.7µF
2 LEDs IN A SERIES
1µF
VIN=4.2V
8
VIN
LX
VOUT
CS
VCTRL
2
1
CNTL PGND
COMP SGND
EFFICIENCY (%)
85
4
3
7
VIN=2.7V
80
75
5Ω
5
70
6
L=COILCRAFT LPO1704-333CM
5
10
15
0.1µF
FIGURE 5A. 2 LEDs IN A SERIES
3 LEDs IN A SERIES
33µH
90
1µF
VIN=4.2V
LX
VOUT
CS
VCTRL
2
1
CNTL PGND
COMP SGND
EFFICIENCY (%)
85
VIN
30
FIGURE 5B. EFFICIENCY vs IO
FIGURE 5.
4.7µF
8
25
BAT54HT1
L
VIN
20
IO (mA)
4
3
7
5
VIN=2.7V
80
75
5Ω
70
6
L=COILCRAFT LPO1704-333CM
5
10
15
20
25
IO (mA)
0.1µF
FIGURE 6A. 3 LEDs IN A SERIES
5
FIGURE 6.
FIGURE 6B. EFFICIENCY vs IO
30
EL1848
Typical Performance Curves (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, 3 LEDs in a
series; unless otherwise specified.
BAT54HT1
L
VIN
90
33µH
4.7µF
2 LEGS OF 2 LEDs IN A SERIES
1µF
VIN=4.2V
8
VIN
LX
VOUT
CS
2
VCTRL
1
CNTL PGND
COMP SGND
EFFICIENCY (%)
85
4
3
7
5Ω
5
VIN=2.7V
80
75
5Ω
70
10
6
L=COILCRAFT LPO1704-333CM
20
30
40
50
60
IO (mA)
0.1µF
FIGURE 7A. 2 LEGS OF 2 LEDs IN A SERIES
BAT54HT1
L
VIN
FIGURE 7B. EFFICIENCY vs IO
FIGURE 7.
2 LEGS OF 3 LEDs IN A SERIES
33µH
90
4.7µF
1µF
VIN=4.2V
VIN
LX
VOUT
CS
2
VCTRL
1
CNTL PGND
COMP SGND
EFFICIENCY (%)
85
8
4
3
7
5Ω
5
VIN=2.7V
80
75
5Ω
70
10
6
L=SUMIDA CMD13D13-33µH
20
30
FIGURE 8A. 2 LEGS OF 3 LEDs IN A SERIES
VIN
50
60
FIGURE 8B. EFFICIENCY vs IO
FIGURE 8.
BAT54HT1
L
3 LEGS OF 2 LEDs IN A SERIES
95
15µH
1µF
8
VIN
LX
VOUT
CS
2
1
CNTL PGND
COMP SGND
EFFICIENCY (%)
4.7µF
VCTRL
40
IO (mA)
0.1µF
4
3
7
90
VIN=4.2V
85
VIN=2.7V
80
75
5Ω
5
5Ω
5Ω
70
15
6
L=SUMIDA CMD13D13-15µH
35
55
75
IO (mA)
0.1µF
FIGURE 9A. 3 LEGS OF 2 LEDs IN A SERIES
6
FIGURE 9.
FIGURE 9B. EFFICIENCY vs IO
95
EL1848
Typical Performance Curves (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, 3 LEDs in a
series; unless otherwise specified.
VIN
BAT54HT1
L
3 LEGS OF 3 LEDs IN A SERIES
95
15µH
4.7µF
1µF
VIN=4.2V
8
VIN
LX
VOUT
CS
VCTRL
2
1
CNTL PGND
COMP SGND
EFFICIENCY (%)
90
4
3
7
85
VIN=2.7V
80
75
5Ω
5
5Ω
5Ω
70
15
6
L=SUMIDA CMD13D13-15µH
35
55
75
95
IO (mA)
0.1µF
FIGURE 10A. 3 LEGS OF 3 LEDs IN A SERIES
JEDEC JESD51-7 HIGH EFFECTIVE
THERMAL CONDUCTIVITY TEST BOARD
0.6
0.9
0.8 870mW
POWER DISSIPATION (W)
POWER DISSIPATION (W)
1
MSOP8/10
0.7
θJA=115°C/W
0.6
0.5
0.4
0.3
0.2
0.1
0
FIGURE 10B. EFFICIENCY vs IO
FIGURE 10.
0.5
486mW
25
50
75 85
100
125
AMBIENT TEMPERATURE (°C)
FIGURE 11. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
7
MSOP8/10
0.4
θJA=206°C/W
0.3
0.2
0.1
0
0
JEDEC JESD51-3 LOW EFFECTIVE
THERMAL CONDUCTIVITY TEST BOARD
0
25
50
75 85
100
125
AMBIENT TEMPERATURE (°C)
FIGURE 12. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
EL1848
Waveforms
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.
C3=4700pF
50mA/DIV
IIN
VIN
2V/DIV
IIN
50mA/DIV
VCNTL
1V/DIV
ILED
VCNTL
1V/DIV
ILED
10mA/DIV
10mA/DIV
0.1ms/DIV
10ms/DIV
FIGURE 14. SHUT-DOWN
FIGURE 13. START-UP
ILED=15mA
2V
VCNTL
1V
14.2V
12.9V
VO
ILED
10mV/DIV
∆VIN
IL
100mA/DIV
30mA
VLX
10V/DIV
15mA
∆VO
50mV/DIV
1µs/DIV
20ms/DIV
FIGURE 15. TRANSIENT RESPONSE
FIGURE 16. CONTINUOUS CONDUCTION MODE
VCTRL=0.34V, ILED=5mA
∆VIN
10mV/DIV
VO (5V/DIV)
IL
100mA/DIV
VLX
10V/DIV
∆VO
50mV/DIV
VCOMP (1V/DIV)
1µs/DIV
FIGURE 17. DISCONTINUOUS CONDUCTION MODE
8
FIGURE 18. OVER VOLTAGE PROTECTION (LED
DISCONNECTED)
EL1848
Detailed Description
The EL1848 is a constant current boost regulator specially
designed for driving white LEDs. It can drive up to 3 LEDs in
series or 9 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
EL1848 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 17).
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
13V, 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.
When choosing an inductor, make sure the inductor can
handle the average and peak currents giving by following
formulas (80% efficiency assumed):
IO × VO
I LAVG = ----------------------0.8 × V IN
1
I LPK = I LAVG + --- × ∆I L
2
V IN × ( V O – V IN )
∆I L = -------------------------------------------L × VO × FS
where:
PWM
SIGNAL
100K
0.1µF
CNTL
• ∆IL is the peak-to-peak inductor current ripple in Ampere
COMP
• L inductance in µH
• FS switching frequency, typical 1MHz
FIGURE 19. PWM BRIGHTNESS CONTROL
The relationship between the LED current and CNTL voltage
level is as follows:
V CNTL
I LED = ---------------------------13.33 × R 1
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 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 14V (nominal), the chip will shut down. The output
voltage will drop. When VO drops below 11V (nominal), the
chip will boost output voltage again until it reaches 14V. This
9
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 9
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.
EL1848
For the same inductance, higher overall efficiency can be
obtained by using lower DCR inductor.
85
EFFICIENCY vs IO
EFFICIENCY (%)
VIN=3.3V FOR
DIFFERENT L
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.
L=22µH
83
L=33µH
L=15µH
81
L=10µH
79
77
L=Coilcraft
LPO1704 SERIES
1mm HEIGHT
5
10
15
20
25
30
IO (mA)
FIGURE 20. EFFICIENCY OF DIFFERENT INDUCTANCE
(4 LEDs IN A SERIES)
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:
I DRMS =
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.
The trace connected to the CS pin 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 EL1848 Application Brief for the
layout.
I LAVG × I O
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. 14V maximum voltage enables
3 LEDs can be placed in series.
10
EL1848
TSOT Package Outline Drawing
11
EL1848
MSOP Package Outline Drawing
NOTE: The package drawing shown here may not be the latest version. To check the latest revision, please refer to the Intersil website at
<http://www.intersil.com/design/packages/index.asp>
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
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.
For information regarding Intersil Corporation and its products, see www.intersil.com
12
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