CAT4237TD-T3 [ONSEMI]
High Voltage CMOS Boost White LED Driver; 高电压CMOS升压型白光LED驱动器
| 型号： | CAT4237TD-T3 |
| 厂家： | 
ONSEMI |
| 描述： | High Voltage CMOS Boost White LED Driver |
| 文件： | 总13页 (文件大小：269K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
CAT4237
High Voltage CMOS Boost
White LED Driver
Description
The CAT4237 is a DC/DC step−up converter that delivers an
accurate constant current ideal for driving LEDs. Operation at a
constant switching frequency of 1 MHz allows the device to be used
with small value external ceramic capacitors and inductor. LEDs
connected in series are driven with a regulated current set by the
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external resistor R . LED currents up to 40 mA can be supported over
1
1
a wide range of input supply voltages from 2.8 V to 5.5 V, making the
device ideal for battery−powered applications. The CAT4237
high−voltage output stage is perfect for driving six, seven or eight
white LEDs in series with inherent current matching in LCD backlight
applications.
LED dimming can be done by using a DC voltage, a logic signal, or
a pulse width modulation (PWM) signal. The shutdown input 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.
TSOT−23
TD SUFFIX
CASE 419AE
PIN CONNECTIONS
1
VIN
SW
GND
FB
SHDN
(Top View)
MARKING DIAGRAMS
Features
• Drives 6 to 8 White LEDs in Series from 3 V
• Up to 87% Efficiency
LTYM
UDYM
• Low Quiescent Ground Current 0.6 mA
• Adjustable Output Current (up to 40 mA)
• High Frequency 1 MHz Operation
• High Voltage Power Switch
LT = CAT4237TD−T3
UD = CAT4237TD−GT3
Y = Production Year (Last Digit)
M = Production Month (1−9, A, B, C)
• Shutdown Current Less than 1 mA
• Open LED Low Power Mode
ORDERING INFORMATION
• Automatic Shutdown at 1.9 V (UVLO)
• Thermal Shutdown Protection
Device
Package
Shipping
CAT4237TD−T3
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
• Thin SOT23 5−lead (1 mm Max Height)
(Note 1)
• These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS
CAT4237TD−GT3
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
Compliant
(Note 2)
Applications
1. Matte−Tin Plated Finish (RoHS−compliant).
2. NiPdAu Plated Finish (RoHS−compliant)
• Color LCD and Keypad Backlighting
• Cellular Phones
• Handheld Devices
• Digital Cameras
• PDAs
• Portable Game Machine
© Semiconductor Components Industries, LLC, 2010
1
Publication Order Number:
February, 2010 − Rev. 2
CAT4237/D
CAT4237
L
D
V
OUT
V
IN
33 mH
3 V to
4.2 V
C
2
C
1
4.7 mF
0.22 mF
SW
VIN
CAT4237
V
FB
= 300 mV
20 mA
OFF
ON
FB
SHDN
GND
R
1
15 W
L: Sumida CDRH3D16−330
D: Central CMDSH05−4 (rated 40 V)
C2: Taiyo Yuden UMK212BJ224 (rated 50 V)
Figure 1. Typical Application Circuit
Table 1. ABSOLUTE MAXIMUM RATINGS
Parameters
Ratings
−0.3 to +7
−0.3 to +7
−0.3 to +55
−65 to +160
−40 to +150
300
Units
V
V
IN
, FB voltage
SHDN voltage
V
SW voltage
V
Storage Temperature Range
Junction Temperature Range
Lead Temperature
_C
_C
_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
Parameters
Range
2.8 to 5.5
0 to 30
Units
V
V
IN
SW pin voltage
V
Ambient Temperature Range
6, 7 or 8 LEDs
−40 to +85
1 to 40
_C
mA
NOTE: Typical application circuit with external components is shown above.
3. Thin SOT23−5 package thermal resistance q = 135°C/W when mounted on board over a ground plane.
JA
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CAT4237
Table 3. DC ELECTRICAL CHARACTERISTICS
(V = 3.6 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified))
IN
Symbol
Parameter
Operating Current
Conditions
Min
Typ
Max
Unit
I
Q
V
FB
V
FB
= 0.2 V
= 0.4 V (not switching)
0.6
0.1
1.5
0.6
mA
I
Shutdown Current
FB Pin Voltage
V
= 0 V
0.1
1
315
1
mA
mV
mA
SD
SHDN
V
8 LEDs with I
= 20 mA
285
300
FB
LED
I
FB pin input leakage
Programmed LED Current
FB
I
R1 = 10 W
R1 = 15 W
R1 = 20 W
28.5
19
14.25
30
20
15
31.5
21
15.75
mA
LED
V
SHDN Logic High
SHDN Logic Low
Enable Threshold Level
0.8
0.7
1.5
V
IH
IL
V
Shutdown Threshold Level
0.4
0.8
F
Switching Frequency
1.0
450
1.0
1
1.3
600
2.0
5
MHz
mA
W
SW
LIM
I
Switch Current Limit
350
R
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
I
= 100 mA
SW
SW
I
Switch Off, V
= 5 V
mA
°C
°C
V
LEAK
SW
150
20
Thermal Hysteresis
V
Undervoltage Lockout (UVLO) Threshold
Overvoltage Threshold
1.9
35
UVLO
V
V
OV-SW
Pin Description
VIN is the supply input for the internal logic. The device is
compatible with supply voltages down to 2.8 V and up to
5.5 V. It is recommended that a small bypass ceramic
capacitor (4.7 mF) be placed between the VIN and GND pins
near the device. If the supply voltage drops below 1.9 V, the
device stops switching.
SW pin is connected to the drain of the internal CMOS
power switch of the boost converter. 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. An over-voltage detection circuit
is connected to the SW pin. When the voltage reaches 35 V,
the device enters a low power operating mode preventing the
SW voltage from exceeding the maximum rating.
SHDN is the shutdown logic input. When the pin is tied to
a voltage lower than 0.4 V, the device is in shutdown mode,
drawing nearly zero current. When the pin is connected to a
voltage higher than 1.5 V, the device is enabled.
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:
GND is the ground reference pin. This pin should be
connected directly to the ground place on the PCB.
0.3 V
R1
ILED
+
The lower LED cathode is connected to the FB pin.
Table 4. PIN DESCRIPTIONS
Pin #
Name
SW
Function
1
2
3
4
5
Switch pin. This is the drain of the internal power switch.
GND
FB
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.
SHDN
VIN
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CAT4237
Block Diagram
33 mH
V
IN
SW
C2
C1
4.7 mF
0.22 mF
1 MHz
Oscillator
Over Voltage
Protection
300 mV
–
+
V
REF
Driver
V
IN
LED
Current
A1
+
–
PWM &
Logic
A2
R
Enable
C
N
1
C
C
Thermal
Shutdown
& UVLO
+
–
SHDN
R
S
GND
FB
Current
Sense
R1
15 W
Figure 2. Block Diagram
Device 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.
The CAT4237 is a fixed frequency (1 MHz), low noise,
inductive boost converter that provides a constant current
with excellent line and load regulation. The device uses a
high-voltage CMOS power switch between the SW pin and
ground to energize the inductor. When the switch is turned
off, the stored energy in the inductor is released into the load
via the 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 feedback resistor connected to the
feedback pin (FB). The value of the resistor sets the LED
Light Load Operation
Under light load condition (under 4 mA) and with input
voltage above 4.2 V, the CAT4237 driving 6 LEDs, the
driver starts pulse skipping. Although the LED current
remains well regulated, some lower frequency ripple may
appear.
current accordingly (0.3 V/R ).
1
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 can deliver up to
40 mA of load current into a string of up to 8 white LEDs.
In the event of an “Open LED” fault condition, where the
feedback control loop becomes open, the output voltage will
continue to increase. Once this voltage exceeds 35 V, an
internal protection circuit will become active and place the
device into a very low power safe operating mode where
only a small amount of power is transferred to the output.
This is achieved by pulsing the switch once every 60 ms and
keep it on for about 1 ms only.
Figure 3. Switching Waveform VIN = 4.2 V,
ILED = 4 mA
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CAT4237
TYPICAL CHARACTERISTICS
(V = 3.6 V, C = 4.7 mF, C
= 0.22 mF, L = 33 mH with 8 LEDs at 20 mA, T
= 25°C, unless otherwise specified.)
IN
IN
OUT
AMB
140
120
2.0
1.5
1.0
100
80
60
VFB = 0.4 V
(not switching)
40
0.5
0
20
0
2.7
2.7
2.7
3.0
3.3
3.6
3.9
4.2
4.5
4.8
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 4. Quiescent Current vs. VIN
(Not Switching)
Figure 5. Quiescent Current vs. VIN
(Switching)
315
310
315
310
8 LEDs at 20 mA
VOUT = 26 V
8 LEDs
305
300
295
305
300
295
290
285
290
285
3.0
3.3
3.6
3.9
4.2
4.5
4.8
0
5
10
15
20
25
30
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
Figure 6. FB Pin Voltage vs. Supply Voltage
Figure 7. FB Pin Voltage vs. Output Current
1040
1020
1000
SW pin
20V/div
Inductor
Current
100mA/div
980
960
VOUT
AC coupled
200mV/div
3.0
3.3
3.6
3.9
4.2
4.5
4.8
0.5 msec/div
INPUT VOLTAGE (V)
Figure 8. Switching Frequency vs. Supply
Voltage
Figure 9. Switching Waveforms
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CAT4237
TYPICAL CHARACTERISTICS
(V = 3.6 V, C = 4.7 mF, C
= 0.22 mF, L = 33 mH with 8 LEDs at 20 mA, T
= 25°C, unless otherwise specified.)
IN
IN
OUT
AMB
35
30
1.0
R
= 10 W
FB
0.5
0
25
20
15
10
R
R
= 15 W
= 20 W
FB
FB
−0.5
−1.0
5
0
2.5
3.0
3.5
4.0
4.5
5.0
30
30
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.0
30
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 10. LED Current vs. Input Voltage
(8 LEDs)
Figure 11. LED Current Regulation (20 mA)
90
85
90
85
20 mA
15 mA
VIN = 4.2 V
VIN = 3.6 V
80
75
80
75
8 LEDs
8 LEDs
VOUT ~ 27 V at 20 mA
L = 33 mH
70
65
70
65
VOUT ~ 27 V at 20 mA
L = 33 mH
5
10
15
20
25
3.0
3.5
4.0
4.5
LED CURRENT (mA)
INPUT VOLTAGE (V)
Figure 12. 8 LED Efficiency vs. Load Current
Figure 13. 8 LED Efficiency vs. Input Voltage
90
85
90
85
VIN = 4.2 V
VIN = 3.6 V
VIN = 4.2 V
VIN = 3.6 V
80
75
80
75
6 LEDs
VOUT ~ 20 V at 20 mA
L = 33 mH
7 LEDs
VOUT ~ 23 V at 20 mA
L = 33 mH
70
65
70
65
5
10
15
20
25
5
10
15
20
25
LED CURRENT (mA)
LED CURRENT (mA)
Figure 14. 7 LED Efficiency vs. Load Current
Figure 15. 6 LED Efficiency vs. Load Current
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CAT4237
TYPICAL CHARACTERISTICS
(V = 3.6 V, C = 4.7 mF, C
= 0.22 mF, L = 33 mH with 8 LEDs at 20 mA, T
= 25°C, unless otherwise specified.)
IN
IN
OUT
AMB
2.0
EN
5V/div
1.5
1.0
0.5
VOUT
10V/div
Input
Current
100mA/
div
0
2.5
3.0
3.5
4.0
4.5
50 msec/div
INPUT VOLTAGE (V)
Figure 16. Power−up with 8 LEDs at 20 mA
Figure 17. Switch ON Resistance vs. Input
Voltage
303
302
1.0
0.8
0.6
−40°C
25°C
301
300
299
85°C
125°C
0.4
0.2
V
= 3.6 V, 8 LEDs
= 20 mA
IN
298
297
I
LED
−50
0
50
100
150
3.0
3.5
4.0
4.5
5.0
TEMPERATURE (°C)
INPUT VOLTAGE (V)
Figure 18. FB Pin Voltage vs. Temperature
Figure 19. Shutdown Voltage vs. Input Voltage
140
120
100
VOUT = 15 V
80
60
40
VOUT = 20 V
20
0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 20. Maximum Output Current vs. Input
Voltage
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CAT4237
Application Information
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 diode CMDSH05−4
(500 mA rated) is recommended for most applications.
External Component Selection
Capacitors
The CAT4237 only requires small ceramic capacitors of
4.7 mF on the input and 0.22 mF on the output. Under normal
condition, a 4.7 mF input capacitor is sufficient. For
applications with higher output power, a larger input
capacitor of 10 mF may be appropriate. X5R and X7R
capacitor types are ideal due to their stability across
temperature range.
LED Current Setting
The LED current is set by the external resistor R
1
connected between the feedback pin (FB) and ground. The
formula below gives the relationship between the resistor
and the current:
0.3 V
LED
R1 +
current
Inductor
A 33 mH inductor is recommended for most of the
CAT4237 applications. In cases where the efficiency is
critical, inductances with lower series resistance are
preferred. Inductors with current rating of 300 mA or higher
are recommended for most applications. Sumida
CDRH3D16−330 33 mH inductor has a rated current of
320 mA and a series resistance (D.C.R.) of 520 mW typical.
Table 5. RESISTOR R1 AND LED CURRENT
LED Current (mA)
R (W)
1
5
60
30
20
15
12
10
10
15
20
25
30
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
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CAT4237
Open LED Protection
2.0
1.5
1.0
In the event of an “Open LED” fault condition, the
CAT4237 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 35 V. Once the output exceeds this level, the
internal circuitry immediately places the device into a very
low power mode where the total input power is limited to
about 4 mW (about 1 mA input current with a 3.6 V supply).
The SW pin clamps at a voltage below its maximum rating
of 60 V. There is no need to use an external zener diode
0.5
0
between Vout and the FB pin. A 50 V rated C capacitor is
required to prevent any overvoltage damage in the open
LED condition.
2
2.5
3.0
3.5
4.0
4.5
5.0
Schottky 100 V
(Central CMSH1−100)
L
INPUT VOLTAGE (V)
V
IN
V
OUT
33 mH
Figure 23. Open LED Supply Current vs. VIN without
Zener
C
1
C
2
4.7 mF
0.22 mF
50
45
40
SW
CAT4237
VIN
V
FB
= 300 mV
OFF
SHDN
GND
FB
ON
R1
15 W
Figure 21. Open LED Protection without Zener
35
30
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 24. Open LED Output Voltage vs. VIN without
Zener
SW PIN
10 V/div
10 msec/div
Figure 22. Open LED Switching Waveforms without
Zener
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CAT4237
Dimming Control
There are several methods available to control the LED
brightness.
VIN
CAT4237
SW
PWM Signal on the SHDN Pin
SHDN
GND
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. Figure 25
shows a 1 kHz signal with a 50% duty cycle applied to the
SHDN pin. The recommended PWM frequency range is
from 100 Hz to 2 kHz.
FB
PWN
V
= 300 mV
1 kW
Signal
2.5 V
FB
LED
Current
3.73 kW
3.1 kW
VIN
0 V
R
R
R
2
A
B
C1
i
R
1
15 W
0.22 mF
Figure 26. 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
93% duty cycle or more, results in an LED current of 0 mA.
25
20
15
10
5
0
Figure 25. Switching Waveform with 1 kHz PWM on
SHDN
0
10 20 30 40 50 60
PWM DUTY CYCLE (%)
70 80 90 100
Filtered PWM Signal
A filtered PWM signal used as a variable DC voltage can
control the LED current. Figure 26 shows the PWM control
circuitry connected to the CAT4237 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 mA to 20 mA. The
PWM signal frequency can vary from very low frequency up
to 100 kHz.
Figure 27. Filtered PWM Dimming (0 V to 2.5 V)
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CAT4237
Board Layout
The CAT4237 is a high−frequency switching regulator.
The traces that carry the 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 on
Figure 28 show 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 28
corresponds to the current path when the CAT4237 internal
switch is closed. On Figure 29 is shown the current loop,
when the CAT4237 switch is open. Both loop areas should
be as small as possible.
Capacitor C has to be placed as close as possible to the
1
V
IN
pin and GND. The capacitor C has to be connected
2
separately to the top LED anode. A ground plane under the
CAT4237 allows for direct connection of the capacitors to
ground. The resistor R must be connected directly to the
1
GND pin of the CAT4237 and not shared with the switching
current loops and any other components.
Open
Closed
Figure 28. Closed−switch Current Loop
Figure 29. Open−switch Current Loop
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CAT4237
PACKAGE DIMENSIONS
TSOT−23, 5 LEAD
CASE 419AE−01
ISSUE O
SYMBOL
MIN
NOM
MAX
1.00
0.10
0.90
0.45
0.20
D
A
A1
A2
b
e
0.01
0.80
0.30
0.12
0.05
0.87
c
0.15
D
2.90 BSC
2.80 BSC
1.60 BSC
0.95 TYP
0.40
E1
E
E
E1
e
L
0.30
0.50
L1
L2
θ
0.60 REF
0.25 BSC
0º
8º
TOP VIEW
A2 A
q
L
b
c
A1
L2
L1
SIDE VIEW
END VIEW
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC MO-193.
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CAT4237
Example of Ordering Information (Note 6)
Prefix
Device #
Suffix
CAT
4237
TD
− G
T3
Company ID
(Optional)
Product Number
Package
TD: TSOT−23
Lead Finish
G: NiPdAu
Blank: Matte−Tin (Note 7)
Tape & Reel (Note 8)
T: Tape & Reel
3: 3,000 / Reel
4237
4. All packages are RoHS−compliant (Lead−free, Halogen−free).
5. The standard lead finish is NiPdAu.
6. The device used in the above example is a CAT4237TD−GT3 (TSOT−23, NiPdAu Plated Finish, Tape & Reel, 3,000/Reel).
7. For Matte−Tin package option, please contact your nearest ON Semiconductor Sales office.
8. 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.
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
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PUBLICATION ORDERING INFORMATION
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Email: orderlit@onsemi.com
For additional information, please contact your local
Sales Representative
CAT4237/D
相关型号：
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