© Semiconductor Components Industries, LLC, 2011
November, 2011 − Rev. 3
1Publication Order Number:
CAT4137/D
CAT4137
CMOS Boost Converter -
White LED Driver
Description
The CAT4137 is a DC/DC step-up converter that delivers a
regulated output current. Operation at a constant switching frequency
of 1 MHz allows the device to be used with small value external
ceramic capacitors and inductor.
The device drives a string of white LEDs connected in series and
provides the regulated current to control the LEDs with inherent
uniform brightness and matching. An external resistor R1 sets the
output current and allows up to 30 mA current to be supported over a
wide range of input supply voltages from 2.2 V to 5.5 V, making the
device ideal for battery-powered applications.
LED dimming can be done by using a DC voltage, a logic signal, or
a pulse width modulation (PWM) signal. The shutdown control pin
allows the device to be placed in power-down mode with “zero”
quiescent current.
In addition to thermal protection and overload current limiting, the
device also enters a very low power operating mode during “Open
LED” fault conditions. The device is housed in a low profile (1 mm
max height) 5−lead thin SOT23 package for space critical
applications.
Features
•Drives up to 5 White LEDs from 3 V
•Power Efficiency up to 87%
•Low Quiescent Ground Current 0.1 mA
•Adjustable Output Current (up to 30 mA)
•High Frequency 1 MHz Operation
•“Zero” Current Shutdown Mode
•Operates Down to 2 V (from Two AA Batteries)
•Soft Start Power-up
•Open LED Low Power Mode
•Automatic Shutdown at 1.9 V (UVLO)
•Thermal Shutdown Protection
•Thin SOT23 5−lead (1 mm Max Height)
•These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS
Compliant
Applications
•LCD Backlighting
•Cellular Phones
•Handheld Devices
•Digital Cameras
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TSOT−23
TD SUFFIX
CASE 419AE
PIN CONNECTIONS
UEYM
MARKING DIAGRAMS
Device Package Shipping (Note 4)
ORDERING INFORMATION (Note 3)
CAT4137TD−T3
(Note 1)
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
LX = CAT4137TD−T3
UE = CAT4137TD−GT3
Y = Production Year (Last Digit)
M = Production Month (1−9, A, B, C)
1
5
(Top View)
VIN
SHDN
SW
GND
FB
1
LXYM
CAT4137TD−GT3
(Note 2)
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
1. Matte−Tin Plated Finish (RoHS−compliant).
2. NiPdAu Plated Finish (RoHS−compliant)
3. For detailed information and a breakdown of
device nomenclature and numbering systems,
please see the ON Semiconductor Device No-
menclature document, TND310/D, available at
www.onsemi.com
4. For information on tape and reel specifications, in-
cluding part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifica-
tions Brochure, BRD8011/D.
CAT4137
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2
Figure 1. Typical Application Circuit
VIN
CAT4137
LD
R1
15 W
1 mF
C1
0.22 mF
C2
FB
SW
GND
ON
22 mH
OFF
2.2 to
5.5 V
L: Murata LQH32CN220
D: Central CMDSH2-3 (rated 30 V)
VIN
VFB = 300 mV
SHDN
VOUT
Table 1. ABSOLUTE MAXIMUM RATINGS
Parameter Rating Unit
VIN, FB voltage −0.3 to +7 V
SHDN voltage −0.3 to +7 V
SW voltage −0.3 to +40 V
Storage Temperature Range −65 to +160 _C
Junction Temperature Range −40 to +150 _C
Lead Temperature 300 _C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
Table 2. RECOMMENDED OPERATING CONDITIONS
Parameter Range Unit
VIN 2.2 to 5.5 V
SW pin voltage 0 to 24 V
Ambient Temperature Range −40 to +85 _C
LED Bias Current 1 to 30 mA
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Table 3. ELECTRICAL OPERATING CHARACTERISTICS
(VIN = 3.6 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified))
Symbol Parameter Conditions Min Typ Max Unit
IQOperating Current VFB = 0.3 V
VFB = 0.4 V (not switching)
0.4
0.1
1.5
0.3
mA
ISD Shutdown Current VSHDN = 0 V 0.1 1 mA
VFB FB Pin Voltage 3 LEDs with ILED = 20 mA 285 300 315 mV
IFB FB pin input leakage 0.1 1 mA
ILED Programmed LED Current R1 = 10 W
R1 = 15 W
R1 = 20 W
28.5
19
14.25
30
20
15
31.5
21
15.75
mA
VIH
VIL
SHDN Logic High
SHDN Logic Low
Enable Threshold Level
Shutdown Threshold Level 0.4
0.8
0.7
1.5 V
FSW Switching Frequency 0.7 1.0 1.3 MHz
ILIM Switch Current Limit 250 300 400 mA
RSW Switch “On” Resistance ISW = 100 mA 1.0 2.0 W
ILEAK Switch Leakage Current Switch Off, VSW = 5 V 1 5 mA
TSD Thermal Shutdown 150 °C
THYS Thermal Hysteresis 20 °C
hEfficiency Typical Application Circuit 86 %
VUVLO Undervoltage Lockout (UVLO) Threshold 1.9 V
VOV-SW Output Clamp Voltage “Open LED” fault 29 V
CAT4137
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TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
Figure 2. Quiescent Current vs. VIN
(Not Switching)
Figure 3. Quiescent Current vs. VIN
(Switching)
INPUT VOLTAGE (V) INPUT VOLTAGE (V)
5.04.54.03.53.02.5
0
20
40
60
80
100
120
5.04.54.03.53.02.5
0
0.25
0.50
0.75
1.00
Figure 4. FB Pin Voltage vs. Supply Voltage Figure 5. FB Pin Voltage vs. Output Current
INPUT VOLTAGE (V) OUTPUT CURRENT (mA)
4.5 5.04.03.53.02.5
290
295
300
305
310
302520151050
290
295
300
305
310
Figure 6. Switching Frequency vs. Supply
Voltage
Figure 7. Switch ON Resistance vs.
Input Voltage
INPUT VOLTAGE (V)
4.0 4.53.53.02.5
0.90
0.95
1.00
1.05
1.10
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
FB PIN VOLTAGE (mV)
FB PIN VOLTAGE (mV)
CLOCK FREQUENCY (MHz)
VFB = 0.4 V
3 LEDs
INPUT VOLTAGE (V)
4.54.0 5.03.53.02.5
0
0.5
1.0
1.5
2.0
SWITCH RESISTANCE (W)
3 LEDs
3 LEDs at 20 mA
CAT4137
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5
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
Figure 8. LED Current vs. Input Voltage
(3 LEDs)
Figure 9. LED Current Regulation
INPUT VOLTAGE (V) INPUT VOLTAGE (V)
5.04.54.03.53.02.5
0
5
10
15
20
25
30
35
5.54.54.03.53.02.52.0
−0.4
−0.2
0
0.2
0.4
Figure 10. Efficiency across Supply Voltage
(3 LEDs)
Figure 11. Efficiency across Load Current
(3 LEDs)
INPUT VOLTAGE (V) LED CURRENT (mA)
5.04.54.03.02.52.0
60
70
80
90
100
30201050
60
70
80
90
100
Figure 12. Efficiency across Supply Voltage
(4 LEDs)
Figure 13. Efficiency across Load Current
(4 LEDs)
INPUT VOLTAGE (V) LED CURRENT (mA)
5.04.03.53.02.52.0
60
70
80
90
100
30252015105
60
70
80
90
100
LED CURRENT (mA)
LED CURRENT VARIATION (%)
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
RFB = 10 W
RFB = 15 W
RFB = 20 W
VIN = 4.2 V
VIN = 3.6 V
5.02.0
3.5
15 mA
20 mA
VIN = 4.2 V
VIN = 3.6 V
15 25
15 mA
20 mA
4.5 0
CAT4137
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TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
Figure 14. FB Pin Voltage vs. Temperature Figure 15. Shutdown Voltage vs. Input Voltage
TEMPERATURE (°C) INPUT VOLTAGE (V)
4.54.03.53.0
0.2
0.4
0.6
0.8
1.0
Figure 16. Under Voltage Lock Out vs.
Temperature
Figure 17. Switching Frequency vs.
Temperature
TEMPERATURE (°C) TEMPERATURE (°C)
10075500−50
1.6
1.7
1.8
1.9
2.0
2.1
2.2
10050250−50
0.90
0.95
1.00
1.05
1.10
Figure 18. Switching Waveforms
(3 LEDs in Series)
SHUTDOWN VOLTAGE (V)
UVLO (V)
CLOCK FREQUENCY (MHz)
25°C
−40°C
85°C
Figure 19. Switching Waveforms
(2 LEDs in Series)
10075500−50
294
296
298
300
302
304
FB PIN VOLTAGE (mV)
3 LEDs at 20 mA
20 mA per LED
−25 25
25−25 −25 75
5.0
CAT4137
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TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
Figure 20. Power−up with 3 LEDs at 20 mA Figure 21. Line Transient Response
(3 V − 5.5 V)
Figure 22. Maximum Output Current vs. Input
Voltage
INPUT VOLTAGE (V)
5.54.03.53.02.0
0
20
40
60
80
120
140
MAX OUTPUT CURRENT (mA)
2.5 4.5 5.0
100
VOUT = 10 V
VOUT = 17 V
CAT4137
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Pin Description
VIN is the supply input for the internal logic. The device is
compatible with supply voltages down to 2.2 V and up to
5.5 V. A small bypass ceramic capacitor of 1 mF is
recommended between the VIN and GND pins near the
device. The under−voltage lockout (UVLO) circuitry will
place the device into an idle mode (not switching) whenever
the supply falls below 1.9 V.
SHDN is the shutdown logic input. When the pin voltage is
taken below 0.4 V, the device immediately enters shutdown
mode, drawing nearly zero current. At voltages greater than
1.5 V, the device becomes fully enabled and operational.
GND is the ground reference pin. This pin should be
connected directly to the ground plane on the PCB.
SW pin is the drain terminal of the internal low resistance
power switch. The inductor and the Schottky diode anode
should be connected to the SW pin. Traces going to the SW
pin should be as short as possible with minimum loop area.
This pin contains over-voltage circuitry which becomes
active above 24 V. In the event of an “Open−Led” fault
condition, the device will enter a low power mode and the
SW pin will be clamped to approximately 30 V.
FB feedback pin is regulated at 0.3 V. A resistor connected
between the FB pin and ground sets the LED current
according to the formula:
ILED +
0.3 V
R1
The lower LED cathode is connected to the FB pin.
Table 4. PIN DESCRIPTIONS
Pin # Name Function
1 SW Switch pin. This is the drain of the internal power switch.
2 GND Ground pin. Connect the pin to the ground plane.
3 FB Feedback pin. Connect to the last LED cathode.
4 SHDN Shutdown pin (Logic Low). Set high to enable the driver.
5 VIN Power Supply input.
CAT4137
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Device Operation
The CAT4137 is a fixed frequency (1 MHz), low noise,
inductive boost converter providing constant current to the
load. A high voltage internal CMOS power switch is used to
energize the external inductor. When the power switch is
then turned off, the stored energy inductor is released into
the load via the external Schottky diode.
The on/off duty cycle of the power switch is internally
adjusted and controlled to maintain a constant regulated
voltage of 0.3 V across the external feedback resistor
connected to the feedback pin (FB). The value of external
resistor will accurately set the LED bias current accordingly
(0.3 V/R1).
During the initial power-up stage, the duty cycle of the
internal power switch is limited to prevent excessive in-rush
currents and thereby provide a “soft-start” mode of
operation.
While in normal operation, the device will comfortably
deliver up to 30 mA of bias current into a string of up to 5
white LEDs.
In the event of a “Open-Led” fault condition, where the
feedback control loop becomes open, the output voltage will
continue to increase. Once this voltage exceeds 24 V, an
internal protection circuit will become active and place the
device into a very low power safe operating mode. In
addition, an internal clamping circuit will limit the peak
output voltage to 29 V. If this fault condition is repaired, the
device will automatically resume normal operation.
Thermal overload protection circuitry has been included
to prevent the device from operating at unsafe junction
temperatures above 150°C. In the event of a thermal
overload condition the device will automatically shutdown
and wait till the junction temperatures cools to 130°C before
normal operation is resumed.
Enable
Current
Sense
300 mV
R1
15 W
C1
Thermal
Shutdown
& UVLO
1 MHz
Oscillator
Over Voltage
Protection
PWM &
Logic
Driver
C2
GND
SW
FB
+
–
+
–
+
–
VIN
VIN
VREF
SHDN
RC
CC
RS
N1
Figure 23. Block Diagram
VOUT
ILED
A1
A2
CAT4137
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Application Information
External Component Selection
Capacitors
The CAT4137 only requires small ceramic capacitors of
1mF on the input and 0.22 mF on the output. The output
capacitor should be rated at 30 V or greater. Under normal
conditions, a 1 mF input capacitor is sufficient. For
applications with higher output power, a larger input
capacitor of 2.2 mF or 4.7 mF may be appropriate. X5R and
X7R capacitor types are ideal due to their stability across
temperature range.
Inductor
A 22 mH inductor is recommended for most of the
CAT4137 applications. In cases where the efficiency is
critical, inductances with lower series resistance are
preferred. Several inductor types from various vendors can
be used. Figure 24 shows how different inductor types affect
the efficiency across the load range.
SUMIDA CDRH3D16−220
MURATA LQH32CN220
PANASONIC ELJ−EA220
PANASONIC ELJ−PC220
Figure 24. Efficiency for Various Inductors
LED CURRENT (mA)
3025155
60
70
80
90
100
EFFICIENCY (%)
2010
3 LEDs
VIN = 3.6 V
Schottky Diode
The current rating of the Schottky diode must exceed the
peak current flowing through it. The Schottky diode
performance is rated in terms of its forward voltage at a
given current. In order to achieve the best efficiency, this
forward voltage should be as low as possible. The response
time is also critical since the driver is operating at 1 MHz.
Central Semiconductor Schottky CMDSH2−3 (200 mA
rated) or the CMDSH−3 (100 mA rated) is recommended
for most applications.
LED Current Setting
The LED current is set by the external resistor between the
feedback pin (FB) and ground. The formula below gives the
relationship between the resistor and the current:
R1 +
0.3 V
LED current
Table 5. RESISTOR R1 AND LED CURRENT
LED Current (mA) R1 (W)
5 60
10 30
15 20
20 15
25 12
30 10
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Typical Applications
Figure 25. CAT4137 Driving Two LEDs
VIN
CAT4137
LD
1 mF
2.2 V to
5.0 V
C1
1 mF
C2
R1
15 W
FB
SW
GND
ON
33 mH
OFF
20 mA
VIN VOUT
SHDN
VFB = 300 mV
L: Sumida CDRH3D16−330
D: Central CMDSH2-3 (rated 30 V)
C2: Taiyo Yuden GMK212BJ105KG-T (rated 35 V)
For best performance, a 33 mH inductor and a 1 mF output
capacitor are recommended for 2−LED applications.
In 2−LED configuration, the CAT4137 can be powered
from two AA alkaline cells or from a Li−ion battery.
Figure 26. Efficiency vs. LED Current, Two LEDs
LED CURRENT (mA)
403020100
70
75
80
90
100
EFFICIENCY (%)
85
95
VIN = 3.6 V
VIN = 3.0 V
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Dimming Control
There are several methods available to control the LED
brightness.
PWM Signal on the SHDN Pin
LED brightness dimming can be done by applying a PWM
signal to the SHDN input. The LED current is repetitively
turned on and off, so that the average current is proportional
to the duty cycle. A 100% duty cycle, with SHDN always
high, corresponds to the LEDs at nominal current.
Figures 27 and 28 show 1 kHz and 4 kHz signals with a 50%
duty cycle applied to the SHDN pin. The PWM frequency
range is from 100 Hz to 10 kHz. The recommended PWM
frequency range is from 100 Hz to 4 kHz.
Switching Waveforms PWM on SHDN
Figure 27. PWM at 1 kHz
Figure 28. PWM at 4 kHz
Filtered PWM Signal
A filtered PWM signal can be used as a variable DC
voltage that can be used to control the LED current.
Figure 29 shows the PWM control circuitry connected to the
CAT4137 FB pin. The PWM signal has a voltage swing of
0 V to 2.5 V. The LED current can be dimmed within a range
from 0 to 22 mA. The PWM signal frequency can vary from
very low frequency up to 100 kHz.
Figure 29. Circuit for Filtered PWM Signal
VIN SW
CAT4137
0 V
2.5 V
R1
15 W
R2
1 kW
3.3 kW
4.02 kW
C1
0.22 μF
LED
Current
PWM
Signal
FBGND
SHDN
RB
RAVFB = 300 mV
A PWM signal at 0 V DC, or a 0% duty cycle, results in
a max LED current of about 22 mA. A PWM signal with a
100% duty cycle results in an LED current of 0 mA.
Figure 30. LED Current vs. Duty Cycle
LED CURRENT (mA)
25
20
15
10
5
0
0 20 40 60 80 100
DUTY CYCLE (%)
CAT4137
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Open LED Protection
In the event of an “Open LED” fault condition, the
CAT4137 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 24 V. Once the output exceeds this level,
internal circuitry immediately places the device into a very
low power mode where the total input power consumed is
less than 10 mW.
In low power mode, the input supply current will typically
drop to 2 mA. An internal clamping circuit will limit the
subsequent output voltage to approximately 29 V. This
operating mode eliminates the need for any external
protection zener diode. This protection scheme also fully
protects the device against any malfunction in the external
Schottky diode (open-circuit).
Figure 31. Open LED Protection Figure 32. Open LED Power−up Waveforms
Figure 33. Open LED Supply Current vs. VIN
VIN
CAT4137
L
(Central CMDSH2−3)
D
1 μF
C1
0.22 μF
C2
R1
15 W
FB
SW
GND
ON
22 μH
OFF
INPUT VOLTAGE (V)
5.04.53.53.02.5
1.0
1.5
2.0
2.5
SUPPLY CURRENT (mA)
4.0
VFB = 300 mV
SHDN
VIN
VOUT
CAT4137
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Board Layout
The CAT4137 is a high-frequency switching regulator.
Traces carrying high-frequency switching current have to be
carefully layout on the board in order to minimize EMI,
ripple and noise in general. The thicker lines shown on
Figure 34 indicate the switching current path. All these
traces have to be short and wide enough to minimize the
parasitic inductance and resistance. The loop shown on
Figure 34 corresponds to the current path when the
CAT4137 internal switch is closed. On Figure 35 is shown
the current loop when the CAT4137 switch is open. Both
loop areas should be as small as possible.
Capacitor C1 has to be placed as close as possible to the
VIN pin and GND. The capacitor C2 has to be connected
separately to the top LED anode. A ground plane under the
CAT4137 allows for direct connection of the capacitors to
ground. The resistor R1 must be connected directly to the
GND pin of the CAT4137 and not shared with the switching
current loops and any other components.
Figure 34. Closed−switch Current Loop Figure 35. Open−switch Current Loop
VIN
CAT4137
LD
R1
FB
Switch
Closed
SW
GND
VIN
CAT4137
LD
R1
FB
Switch
Open
SW
GND
C2
VIN
C1
VOUT
SHDN
C1C2
SHDN
VOUT
VIN
CAT4137
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PACKAGE DIMENSIONS
TSOT−23, 5 LEAD
CASE 419AE−01
ISSUE O
E1 E
A2
A1
e
b
D
c
A
TOP VIEW
SIDE VIEW END VIEW
L1
LL2
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC MO-193.
SYMBOL
θ
MIN NOM MAX
q
A
A1
A2
b
c
D
E
E1
e
L
0º 8º
L1
L2
0.01
0.80
0.30
0.12
0.30
0.05
0.87
0.15
2.90 BSC
2.80 BSC
1.60 BSC
0.95 TYP
0.40
0.60 REF
0.25 BSC
1.00
0.10
0.90
0.45
0.20
0.50
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
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CAT4137/D
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