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.
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
1
TSOT−23
TD SUFFIX
CASE 419AE
PIN CONNECTIONS
1
VIN
SW
GND
SHDN
FB
(Top View)
LXYM
UEYM
LX = CAT4137TD−T3
UE = CAT4137TD−GT3
Y = Production Year (Last Digit)
M = Production Month (1−9, A, B, C)
ORDERING INFORMATION (Note 3)
Package
Shipping (Note 4)
CAT4137TD−T3
(Note 1)
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
CAT4137TD−GT3
(Note 2)
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
Device
1. Matte−Tin Plated Finish (RoHS−compliant).
2. NiPdAu Plated Finish (RoHS−compliant)
Applications
•
•
•
•
5
MARKING DIAGRAMS
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
http://onsemi.com
LCD Backlighting
Cellular Phones
Handheld Devices
Digital Cameras
3. For detailed information and a breakdown of
device nomenclature and numbering systems,
please see the ON Semiconductor Device Nomenclature document, TND310/D, available at
www.onsemi.com
4. For information on tape and reel specifications, including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D.
© Semiconductor Components Industries, LLC, 2011
November, 2011 − Rev. 3
1
Publication Order Number:
CAT4137/D
CAT4137
L
VIN
D
VOUT
22 mH
2.2 to
5.5 V
C2
C1
1 mF
SW
VIN
0.22 mF
CAT4137
OFF ON
SHDN
FB
GND
VFB = 300 mV
R1
15 W
L: Murata LQH32CN220
D: Central CMDSH2-3 (rated 30 V)
Figure 1. Typical Application Circuit
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
300
_C
Lead Temperature
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
VIN
SW pin voltage
Ambient Temperature Range
LED Bias Current
http://onsemi.com
2
Range
Unit
2.2 to 5.5
V
0 to 24
V
−40 to +85
_C
1 to 30
mA
CAT4137
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
IQ
Operating 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
300
315
mV
IFB
FB pin input leakage
0.1
1
mA
ILED
Programmed LED Current
28.5
19
14.25
30
20
15
31.5
21
15.75
mA
0.4
0.8
0.7
1.5
V
VIH
VIL
R1 = 10 W
R1 = 15 W
R1 = 20 W
SHDN Logic High
SHDN Logic Low
Enable Threshold Level
Shutdown Threshold Level
285
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
THYS
Thermal Hysteresis
h
Efficiency
Typical Application Circuit
VUVLO
Undervoltage Lockout (UVLO) Threshold
VOV-SW
Output Clamp Voltage
“Open LED” fault
http://onsemi.com
3
150
°C
20
°C
86
%
1.9
V
29
V
CAT4137
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.)
120
1.00
100
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
VFB = 0.4 V
80
60
40
20
0
2.5
3.0
3.5
4.0
4.5
0.75
0.50
0.25
0
5.0
2.5
3.0
3.5
INPUT VOLTAGE (V)
Figure 2. Quiescent Current vs. VIN
(Not Switching)
Figure 3. Quiescent Current vs. VIN
(Switching)
FB PIN VOLTAGE (mV)
FB PIN VOLTAGE (mV)
3 LEDs
305
300
295
2.5
3.0
3.5
4.0
4.5
305
300
295
290
5.0
0
5
10
15
20
25
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
Figure 4. FB Pin Voltage vs. Supply Voltage
Figure 5. FB Pin Voltage vs. Output Current
30
2.0
1.10
3 LEDs at 20 mA
SWITCH RESISTANCE (W)
CLOCK FREQUENCY (MHz)
5.0
310
3 LEDs
1.05
1.00
0.95
0.90
4.5
INPUT VOLTAGE (V)
310
290
4.0
2.5
3.0
3.5
4.0
1.5
1.0
0.5
0
4.5
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 6. Switching Frequency vs. Supply
Voltage
Figure 7. Switch ON Resistance vs.
Input Voltage
http://onsemi.com
4
5.0
CAT4137
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.)
35
0.4
LED CURRENT (mA)
30
LED CURRENT VARIATION (%)
RFB = 10 W
25
RFB = 15 W
20
RFB = 20 W
15
10
5
0
2.0
2.5
3.0
3.5
4.0
4.5
3.0
3.5
4.0
4.5
5.0
Figure 9. LED Current Regulation
5.5
100
90
EFFICIENCY (%)
EFFICIENCY (%)
2.5
Figure 8. LED Current vs. Input Voltage
(3 LEDs)
15 mA
20 mA
VIN = 4.2 V
VIN = 3.6 V
80
70
2.0
2.5
3.0
3.5
4.0
4.5
60
5.0
0
5
10
15
20
25
INPUT VOLTAGE (V)
LED CURRENT (mA)
Figure 10. Efficiency across Supply Voltage
(3 LEDs)
Figure 11. Efficiency across Load Current
(3 LEDs)
100
90
90
EFFICIENCY (%)
100
15 mA
80
20 mA
30
VIN = 4.2 V
VIN = 3.6 V
80
70
70
60
2.0
INPUT VOLTAGE (V)
70
EFFICIENCY (%)
−0.2
INPUT VOLTAGE (V)
90
60
0
−0.4
5.0
100
80
0.2
2.0
2.5
3.0
3.5
4.0
4.5
60
5.0
0
5
10
15
20
25
INPUT VOLTAGE (V)
LED CURRENT (mA)
Figure 12. Efficiency across Supply Voltage
(4 LEDs)
Figure 13. Efficiency across Load Current
(4 LEDs)
http://onsemi.com
5
30
CAT4137
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.)
1.0
SHUTDOWN VOLTAGE (V)
FB PIN VOLTAGE (mV)
304
302
300
298
3 LEDs at 20 mA
296
294
−50
−25
0
25
50
75
0.4
3.0
3.5
4.0
5.0
4.5
INPUT VOLTAGE (V)
Figure 14. FB Pin Voltage vs. Temperature
Figure 15. Shutdown Voltage vs. Input Voltage
1.10
CLOCK FREQUENCY (MHz)
2.1
2.0
UVLO (V)
85°C
0.6
TEMPERATURE (°C)
2.2
1.9
1.8
1.7
1.6
−50
25°C
0.2
100
−40°C
0.8
−25
0
25
50
75
20 mA per LED
1.05
1.00
0.95
0.90
−50
100
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 16. Under Voltage Lock Out vs.
Temperature
Figure 17. Switching Frequency vs.
Temperature
Figure 18. Switching Waveforms
(3 LEDs in Series)
Figure 19. Switching Waveforms
(2 LEDs in Series)
http://onsemi.com
6
100
CAT4137
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)
MAX OUTPUT CURRENT (mA)
140
120
VOUT = 10 V
100
80
60
VOUT = 17 V
40
20
0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 22. Maximum Output Current vs. Input
Voltage
http://onsemi.com
7
5.5
CAT4137
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:
I LED +
0.3 V
R1
The lower LED cathode is connected to the FB pin.
Table 4. PIN DESCRIPTIONS
Pin #
Name
1
SW
2
GND
3
FB
4
SHDN
5
VIN
Function
Switch pin. This is the drain of the internal power switch.
Ground pin. Connect the pin to the ground plane.
Feedback pin. Connect to the last LED cathode.
Shutdown pin (Logic Low). Set high to enable the driver.
Power Supply input.
http://onsemi.com
8
CAT4137
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.
VIN
VOUT
SW
C2
C1
1 MHz
Oscillator
300 mV
–
+
Enable
SHDN
Thermal
Shutdown
& UVLO
A1
Driver
+
RC
–
ILED
PWM &
Logic
A2
N1
CC
Current
Sense
RS
GND
–
VREF
+
VIN
Over Voltage
Protection
FB
Figure 23. Block Diagram
http://onsemi.com
9
R1
15 W
CAT4137
Application Information
External Component Selection
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.
Capacitors
The CAT4137 only requires small ceramic capacitors of
1 mF 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.
LED Current Setting
Inductor
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:
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.
R1 +
Table 5. RESISTOR R1 AND LED CURRENT
100
3 LEDs
VIN = 3.6 V
LED Current (mA)
R1 (W)
5
60
10
30
15
20
20
15
25
12
30
10
EFFICIENCY (%)
90
80
SUMIDA CDRH3D16−220
MURATA LQH32CN220
PANASONIC ELJ−EA220
PANASONIC ELJ−PC220
70
60
0.3 V
LED current
5
10
15
20
25
30
LED CURRENT (mA)
Figure 24. Efficiency for Various Inductors
http://onsemi.com
10
CAT4137
Typical Applications
L
VIN
C1
1 mF
33 mH
C2
SW
VIN
SHDN
FB
100
1 mF
CAT4137
OFF ON
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.
VOUT
20 mA
95
VFB = 300 mV
GND
EFFICIENCY (%)
2.2 V to
5.0 V
D
R1
15 W
L: Sumida CDRH3D16−330
D: Central CMDSH2-3 (rated 30 V)
C2: Taiyo Yuden GMK212BJ105KG-T (rated 35 V)
90
VIN = 3.6 V
85
VIN = 3.0 V
80
75
Figure 25. CAT4137 Driving Two LEDs
70
0
10
20
30
LED CURRENT (mA)
Figure 26. Efficiency vs. LED Current, Two LEDs
http://onsemi.com
11
40
CAT4137
Dimming Control
There are several methods available to control the LED
brightness.
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.
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.
VIN
SW
CAT4137
Switching Waveforms PWM on SHDN
2.5 V
PWM
Signal
SHDN
GND
RA
4.02 kW
FB
RB
0V
VFB = 300 mV
R2
1 kW
3.3 kW
C1
0.22 μF
LED
Current
R1
15 W
Figure 29. Circuit for Filtered PWM Signal
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.
LED CURRENT (mA)
25
Figure 27. PWM at 1 kHz
20
15
10
5
0
0
20
40
60
80
DUTY CYCLE (%)
Figure 30. LED Current vs. Duty Cycle
Figure 28. PWM at 4 kHz
http://onsemi.com
12
100
CAT4137
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.
L
VIN
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).
(Central CMDSH2−3)
D
V
OUT
22 μH
C1
1 μF
C2
0.22 μF
SW
VIN
CAT4137
OFF ON
SHDN
FB
VFB = 300 mV
GND
R1
15 W
Figure 31. Open LED Protection
Figure 32. Open LED Power−up Waveforms
SUPPLY CURRENT (mA)
2.5
2.0
1.5
1.0
2.5
3.0
4.0
3.5
4.5
INPUT VOLTAGE (V)
Figure 33. Open LED Supply Current vs. VIN
http://onsemi.com
13
5.0
CAT4137
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
L
D
VIN
VOUT
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.
L
D
VOUT
VIN
SW
SW
VIN
VIN
CAT4137
SHDN
C1
Switch
Closed
CAT4137
FB
SHDN
C2
R1
C1
GND
GND
Figure 34. Closed−switch Current Loop
Switch
Open
FB
C2
Figure 35. Open−switch Current Loop
http://onsemi.com
14
R1
CAT4137
PACKAGE DIMENSIONS
TSOT−23, 5 LEAD
CASE 419AE−01
ISSUE O
SYMBOL
D
MIN
NOM
A1
0.01
0.05
0.10
A2
0.80
0.87
0.90
b
0.30
c
0.12
A
e
E1
1.00
0.45
0.15
D
2.90 BSC
E
2.80 BSC
E1
1.60 BSC
E
MAX
e
0.20
0.95 TYP
L
0.30
0.40
L1
0.60 REF
L2
0.25 BSC
0º
θ
0.50
8º
TOP VIEW
A2 A
b
q
L
A1
c
L2
L1
SIDE VIEW
END VIEW
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC MO-193.
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,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: [email protected]
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5817−1050
http://onsemi.com
15
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
CAT4137/D
Similar pages