CAT4137
CMOS Boost Converter – White LED Driver
FEATURES
Drives up to 5 White LEDs from 3V
Power Efficiency up to 87%
Low Quiescent Ground Current 0.1mA
Adjustable Output Current (up to 30mA)
High Frequency 1MHz Operation
“Zero” current shutdown mode
Operates down to 2V (from two AA batteries)
Soft start power-up
Open LED low power mode
Automatic shutdown at 1.9V (UVLO)
Thermal shutdown protection
Thin SOT23 5-Lead (1mm max height)
DESCRIPTION
The CAT4137 is a DC/DC step-up converter that
delivers a regulated output current. Operation at a
constant switching frequency of 1MHz 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 30mA current to be
supported over a wide range of input supply voltages
from 2.2V to 5.5V, 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 (1mm max
height) 5-lead thin SOT23 package for space critical
applications.
For Ordering Information details see page 15.
APPLICATIONS
LCD Backlighting
Cellular Phones
Handheld Devices
Digital Cameras
ORDERING INFORMATION
Part Number
CAT4137TD-T3
CAT4137TD-GT3
Package
TSOT23-5
(1)
TSOT23-5
(2)
Quantity
per Reel
3000
3000
Package
Marking
LX
UE
Notes:
(1) Matte-Tin Plated Finish (RoHS-compliant).
(2) NiPdAu Plated Finish (RoHS-compliant).
PIN CONFIGURATION
TSOT-23 5-Lead
1mm max height
SW
GND
FB
1
2
3
4
SHDN
5
VIN
TYPICAL APPLICATION CIRCUIT
V
IN
2.2 to
5.5V
C1
1µF
VIN
CAT4137
OFF ON
SHDN
GND
FB
V
FB
= 300mV
L
22µH
C2
SW
0.22µF
D
V
OUT
(Top View)
R1
15Ω
L: Murata LQH32CN220
D: Central CMDSH2-3 (rated 30V)
1
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
Doc. No. MD-5012 Rev. B
CAT4137
ABSOLUTE MAXIMUM RATINGS
Parameter
VIN, FB voltage
¯¯¯¯¯
SHDN voltage
SW voltage
Storage Temperature Range
Junction Temperature Range
Lead Temperature
Rating
-0.3 to +7
-0.3 to +7
-0.3 to 40
-65 to +160
-40 to +150
300
Unit
V
V
V
°C
°C
°C
RECOMMENDED OPERATING CONDITIONS
Parameter
VIN
SW pin voltage
Ambient Temperature Range
LED Bias Current
Range
2.2 to 5.5
0 to 24
-40 to +85
1 to 30
Unit
V
V
°C
mA
ELECTRICAL OPERATING CHARACTERISTICS
V
IN
= 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise)
Symbol Parameter
I
Q
I
SD
V
FB
I
FB
I
LED
V
IH
V
IL
F
SW
I
LIM
R
SW
I
LEAK
T
SD
T
HYS
η
V
UVLO
V
OV-SW
Operating Current
Shutdown Current
FB Pin Voltage
FB pin input leakage
Programmed LED Current
¯¯¯¯¯
SHDN Logic High
¯¯¯¯¯
SHDN Logic Low
Switching Frequency
Switch Current Limit
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
Thermal Hysteresis
Efficiency
Under-voltage lock out
(UVLO) threshold
Output Clamp Voltage
Typical Application Circuit
I
SW
= 100mA
Switch Off, V
SW
= 5V
R1 = 10Ω
R1 = 15Ω
R1 = 20Ω
Enable Threshold Level
Shutdown Threshold Level
28.5
19
14.25
0.4
0.7
250
Conditions
V
FB
= 0.3V
V
FB
= 0.4V (not switching)
V
SHDN
= 0V
¯¯¯¯¯
3 LEDs with I
LED
=20mA
Min
Typ
0.4
0.1
0.1
300
0.1
30
20
15
0.8
0.7
1
300
1.0
1
150
20
86
1.9
“Open LED” fault
29
Max
1.5
0.3
1
315
1
31.5
21
15.75
1.5
1.3
400
2.0
5
Unit
mA
µA
mV
µA
mA
V
V
MHz
mA
Ω
µA
ºC
ºC
%
V
V
285
Doc. No. MD-5012 Rev. B
2
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4137
TYPICAL CHARACTERISTICS
V
IN
= 3.6V, C
IN
= 1.0uF, C
OUT
= 0.22µF, L = 22µH with 3 LEDs at 20mA, T
AMB
=25ºC, unless otherwise specified.
Quiescent Current vs. VIN (Not Switching)
120
VFB = 0.4V
SUPPLY CURRENT [uA]
100
80
60
40
20
0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
5.0
Quiescent Current vs. VIN (Switching)
1.00
SUPPLY CURRENT [mA]
0.75
0.50
0.25
0.00
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
FB Pin Voltage vs. Supply Voltage
310
FB PIN VOLTAGE [mV]
3 LEDs
305
FB Pin Voltage vs. Output Current
310
FB PIN VOLTAGE [mV]
3 LEDs
305
300
300
295
295
290
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
290
0
5
10
15
20
25
30
OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
1.10
CLOCK FREQUENCY [MHz].
Switch ON Resistance vs. Input Voltage
2.0
SWITCH RESISTANCE [ohm]
1.05
3 LEDs at 20mA
1.00
1.5
1.0
0.95
0.5
0.90
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
0.0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
5.0
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3
Doc. No. MD-5012 Rev. B
CAT4137
TYPICAL CHARACTERISTICS
V
IN
= 3.6V, C
IN
= 1.0uF, C
OUT
= 0.22µF, L = 22µH, with 3 LEDs at 20mA, T
AMB
=25ºC, unless otherwise specified.
LED Current vs. Input Voltage (3 LEDs)
35
30
LED CURRENT [mA]
25
20
15
10
5
0
2.0
2.5
3.0
3.5 4.0 4.5
INPUT VOLTAGE [V]
5.0
Rfb = 20Ω
Rfb = 15Ω
LED Current Regulation
0.4
LED CURRENT VARIATION [%]
Rfb = 10Ω
0.2
0.0
-0.2
-0.4
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
Efficiency across Supply Voltage (3 LEDs)
100
15mA
EFFICIENCY [%]
90
Efficiency across Load Current (3 LEDs)
100
VIN = 4.2V
EFFICIENCY [%]
90
80
20mA
70
60
2.0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
80
70
VIN = 3.6V
60
0
5
10
15
20
25
30
LED CURRENT [mA]
Efficiency across Supply Voltage (4 LEDs)
100
15mA
EFFICIENCY [%]
Efficiency across Load Current (4 LEDs)
100
VIN = 4.2V
EFFICIENCY [%]
90
VIN = 3.6V
80
90
80
20mA
70
60
2.0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
70
60
0
5
10
15
20
25
30
LED CURRENT [mA]
Doc. No. MD-5012 Rev. B
4
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4137
TYPICAL CHARACTERISTICS
V
IN
= 3.6V, C
IN
= 1.0uF, C
OUT
= 0.22µF, L = 22µH, with 3 LEDs at 20mA, T
AMB
=25ºC, unless otherwise specified.
FB Pin Voltage vs. Temperature
304
FB PIN VOLTAGE [mV]
SHUTDOWN VOLTAGE [V]
Shutdown Voltage vs. Input Voltage
1.0
25°C
-40°C
302
300
298
296
294
-50
-25
0
25
50
75
100
TEMPERATURE [°C]
0.8
0.6
85°C
0.4
3 LEDs at 20mA
0.2
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
5.0
Under Voltage Lock Out vs. Temperature
2.2
2.1
UVLO [V]
Switching Frequency vs. Temperature
1.10
CLOCK FREQUENCY[MHz].
20mA per LED
1.05
2.0
1.9
1.8
1.7
1.6
-50
-25
0
25
50
75
100
TEMPERATURE [°C]
1.00
0.95
0.90
-50
-25
0
25 50 75
TEMPERATURE [ºC]
100
Switching Waveforms (3 LEDs in Series)
Switching Waveforms (2 LEDs in Series)
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. MD-5012 Rev. B
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