CAT4237TD-T3 [CATALYST]
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： | 
CATALYST SEMICONDUCTOR |
| 描述： | High Voltage CMOS Boost White LED Driver |
| 文件： | 总14页 (文件大小：301K) |
| 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
FEATURES
DESCRIPTION
Drives 6 to 8 White LEDs in series from 3V
Up to 87% Efficiency
Low Quiescent Ground Current 0.6mA
Adjustable Output Current (up to 40mA)
High Frequency 1MHz Operation
High Voltage Power Switch
Shutdown current less than 1µA
Open LED low power mode
Automatic Shutdown at 1.9V (UVLO)
Thermal shutdown protection
RoHS-compliant
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
1MHz 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 external resistor R1. LED currents up to 40mA
can be supported over a wide range of input supply
voltages from 2.8V to 5.5V, 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.
Thin SOT23 5-Lead (1mm max height)
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.
APPLICATIONS
Color LCD and keypad Backlighting
Cellular Phones
Handheld Devices
Digital Cameras
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.
PDAs
Portable Game Machine
ORDERING INFORMATION
Quantity
per Reel
Package
Marking
For Ordering Information details, see page 13.
Part Number
Package
CAT4237TD-T3 TSOT23-5 (1)
CAT4237TD-GT3 TSOT23-5 (2)
3000
3000
LT
UD
Notes: (1) Matte-Tin Plated Finish (RoHS-compliant).
(2) NiPdAu Plated Finish (RoHS-compliant).
PIN CONFIGURATION
TYPICAL APPLICATION CIRCUIT
5-Lead Thin SOT23
(1mm max height)
L
D
V
OUT
V
IN
33µH
3V to
4.2V
C
C
2
1
1
2
3
5
SW
GND
FB
VIN
4.7µF
0.22µF
SW
VIN
CAT4237
SHDN FB
GND
4
SHDN
V
= 300mV
FB
20mA
OFF ON
R1
15Ω
Top View
L: Sumida CDRH3D16-330
D: Central CMDSH05-4 (rated 40V)
C2: Taiyo Yuden UMK212BJ224 (rated 50V)
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1
Doc. No. MD-5013, Rev. B
CAT4237
ABSOLUTE MAXIMUM RATINGS
Parameters
Ratings
Units
V
VIN, FB voltage
-0.3 to +7
-0.3 to +7
-0.3 to 55
-65 to +160
-40 to +150
300
¯¯¯¯¯
SHDN voltage
V
SW voltage
V
Storage Temperature Range
Junction Temperature Range
Lead Temperature
ºC
ºC
ºC
RECOMMENDED OPERATING CONDITIONS
Typical application circuit with external components are shown on page 1.
Parameters
Range
2.8 to 5.5
0 to 30
Units
V
VIN
SW pin voltage
Ambient Temperature Range
6, 7 or 8 LEDs
V
-40 to +85
1 to 40
ºC
mA
Note:
(1) Thin SOT23-5 package thermal resistance θJA = 135°C/W when mounted on board over a ground plane.
DC ELECTRICAL CHARACTERISTICS
VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise).
Symbol Parameter
Conditions
FB = 0.2V
VFB = 0.4V (not switching)
Min
Typ
Max
Unit
V
0.6
0.1
1.5
0.6
IQ
Operating Current
mA
ISD
VFB
IFB
Shutdown Current
FB Pin Voltage
0.1
1
315
1
µA
mV
µA
VS¯¯H¯D¯N¯ = 0V
8 LEDs with ILED=20mA
285
300
FB pin input leakage
R1 = 10Ω
28.5
19
14.25
30
20
15
31.5
21
15.75
ILED
Programmed LED Current R1 = 15Ω
R1 = 20Ω
mA
¯¯¯¯¯
SHDN Logic High
¯¯¯¯¯
SHDN Logic Low
VIH
VIL
Enable Threshold Level
Shutdown Threshold Level
0.8
0.7
1.5
V
V
0.4
0.8
350
FSW
ILIM
Switching Frequency
Switch Current Limit
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
1.0
450
1.0
1
1.3
600
2.0
5
MHz
mA
Ω
RSW
ILEAK
ISW = 100mA
Switch Off, VSW = 5V
µA
ºC
150
20
Thermal Hysteresis
ºC
Undervoltage Lockout
(UVLO) Threshold
VUVLO
1.9
35
V
V
VOV-SW
Overvoltage Threshold
Doc. No. MD-5013, Rev. B
2
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4237
PIN DESCRIPTION
VIN is the supply input for the internal logic The
device is compatible with supply voltages down to
2.8V and up to 5.5V. It is recommended that a small
bypass ceramic capacitor (4.7µF) be placed between
the VIN and GND pins near the device. If the supply
voltage drops below 1.9V, 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 35V, 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 0.4V, the device is in
shutdown mode, drawing nearly zero current. When
the pin is connected to a voltage higher than 1.5V, the
device is enabled.
FB feedback pin is regulated at 0.3V. 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.
ILED = 0.3V/R1
The lower LED cathode is connected to the FB pin.
PIN DESCRIPTIONS
Pin #
Name
SW
Function
1
2
3
4
5
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.
GND
FB
¯¯¯¯¯
SHDN
VIN
BLOCK DIAGRAM
33µH
VIN
SW
C1
C2
0.22µF
4.7µF
1MHz
Oscillator
Over Voltage
Protection
300mV
–
+
VREF
Driver
LED
Current
VIN
A1
+
–
PWM &
Logic
A2
R
Enable
C
N
1
CC
Thermal
Shutdown
& UVLO
+
–
RS
SHDN
GND
FB
Current
Sense
R1
15Ω
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3
Doc. No. MD-5013, Rev. B
CAT4237
DEVICE OPERATION
The CAT4237 is a fixed frequency (1MHz), 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.
Thermal overload protection circuitry has been
included to prevent the device from operating at
unsafe junction temperatures above 150ºC. In the
event of a thermal overload condition the device will
automatically shutdown and wait till the junction
temperatures cools to 130ºC before normal operation
is resumed.
Light Load Operation
The on/off duty cycle of the power switch is internally
adjusted and controlled to maintain a constant
regulated voltage of 0.3V across the feedback resistor
connected to the feedback pin (FB). The value of the
resistor sets the LED current accordingly (0.3V/R1).
Under light load condition (under 4mA) and with input
voltage above 4.2V, the CAT4237 driving 6 LEDs, the
driver starts pulse skipping. Although the LED current
remains well regulated, some lower frequency ripple
may appear.
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
40mA of load current into a string of up to 8 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 35V, 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 60µs and keep it on for
about 1μs only.
Figure 1. Switching Waveform VIN = 4.2V,
ILED = 4mA
Doc. No. MD-5013, Rev. B
4
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4237
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
Quiescent Current vs. VIN (Not Switching)
Quiescent Current vs. VIN (Switching)
140
120
100
80
2.0
1.5
1.0
0.5
0.0
60
40
VFB =0.4V
(not switching)
20
0
2.5
3.0
3.5
4.0
4.5
5.0
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
FB pin voltage vs. Supply Voltage
FB Pin Voltage vs. Output Current
315
315
8LEDs at 20mA
VOUT= 26V
310
310
305
300
295
290
285
8 LEDs
305
300
295
290
285
0
5
10
15
20
25
30
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
Switching Waveforms
1040
1020
1000
980
960
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. MD-5013, Rev. B
CAT4237
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
LED Current vs. Input Voltage (8 LEDS)
LED Current Regulation (20mA)
35
1.0%
0.5%
0.0%
-0.5%
-1.0%
30
RFB = 10
Ω
25
20
15
10
5
RFB = 15
Ω
RFB = 20
Ω
0
3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
8 LED Efficiency vs. Load Current
8 LED Efficiency vs. Input Voltage
90
85
80
75
70
65
90
85
80
75
70
65
20mA
VIN = 4.2V
15mA
VIN = 3.6V
8 LEDs
8 LEDs
VOUT ~ 27V at 20mA
L = 33uH
VOUT ~ 27V at 20mA
L = 33uH
3.0
3.5
4.0
4.5
5.0
5
10
15
20
25
30
INPUT VOLTAGE [V]
LED CURRENT [mA]
7 LED Efficiency vs. Load Current
6 LED Efficiency vs. Load Current
90
85
80
75
70
65
90
85
80
75
70
65
VIN = 4.2V
VIN = 4.2V
VIN = 3.6V
VIN = 3.6V
7 LEDs
6 LEDs
VOUT ~ 23V at 20mA
L = 33uH
VOUT ~ 20V at 20mA
L = 33uH
5
10
15
20
25
30
5
10
15
20
25
30
LED CURRENT [mA]
LED CURRENT [mA]
Doc. No. MD-5013, Rev. B
6
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4237
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
Power-up with 8 LEDs at 20mA
Switch ON Resistance vs. Input Voltage
2.0
1.5
1.0
0.5
0.0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
FB pin voltage vs. Temperature
Shutdown Voltage vs. Input Voltage
1.0
303
302
301
300
299
298
297
-40°C
25°C
0.8
0.6
0.4
0.2
C
125°
4.5
85°C
VIN=3.6V, 8LEDs
ILED=20mA
3.0
3.5
4.0
5.0
-50
0
50
100
150
INPUT VOLTAGE [V]
TEMPERATURE [ºC]
Maximum Output Current vs. Input Voltage
140
120
VOUT = 15V
100
80
60
40
VOUT = 20V
20
0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
7
Doc. No. MD-5013, Rev. B
CAT4237
APPLICATION INFORMATION
External Component Selection
efficiency, this forward voltage should be as low as
possible. The response time is also critical since the
driver is operating at 1MHz. Central Semiconductor
Schottky diode CMDSH05-4 (500mA rated) is recom–
mended for most applications.
Capacitors
The CAT4237 only requires small ceramic capacitors
of 4.7µF on the input and 0.22µF on the output. Under
normal condition, a 4.7µF input capacitor is sufficient.
For applications with higher output power, a larger
input capacitor of 10µF 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 R1
connected between the feedback pin (FB) and
ground. The formula below gives the relationship
between the resistor and the current:
Inductor
A 33µH 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 300mA or
higher are recommended for most applications.
Sumida CDRH3D16-330 33µH inductor has a rated
current of 320mA and a series resistance (D.C.R.) of
520mΩ typical.
R1 = 0.3V/LED current
Table 1. Resistor R1 and LED current
LED current (mA)
R1 (Ω)
60
5
10
15
20
25
30
30
20
Schottky Diode
15
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
12
10
Doc. No. MD-5013, Rev. B
8
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4237
OPEN LED PROTECTION
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 35V. 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 4mW (about 1mA input
current with a 3.6V supply). The SW pin clamps at a
voltage below its maximum rating of 60V. There is no
need to use an external zener diode between Vout
and the FB pin. A 50V rated C2 capacitor is required to
prevent any overvoltage damage in the open LED
condition.
Open LED Protection without Zener
Open LED Switching waveforms
without Zener
Schottky 100V
(Central CMSH1-100)
L
VOUT
V
IN
33µH
C
1
C
2
4.7µF
0.22µF
SW
VIN
CAT4237
SHDN FB
GND
V
FB = 300mV
OFF ON
R1
15Ω
Open LED Supply Current vs. VIN
without Zener
Open LED Output Voltage vs. VIN
without Zener
2.0
1.5
1.0
0.5
0.0
50
45
40
35
30
2.5
3.0
3.5
4.0
4.5
5.0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
9
Doc. No. MD-5013, Rev. B
CAT4237
DIMMING CONTROL
Filtered PWM Signal
There are several methods available to control the
LED brightness.
A filtered PWM signal used as a variable DC voltage
can control the LED current. Figure 2 shows the PWM
control circuitry connected to the CAT4237 FB pin.
The PWM signal has a voltage swing of 0V to 2.5V.
The LED current can be dimmed within a range from
0mA to 20mA. The PWM signal frequency can vary
from very low frequency up to 100kHz.
¯¯¯¯¯
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. Figure 1 shows a 1kHz
VIN
SW
¯¯¯¯¯
signal with a 50% duty cycle applied to the SHDN pin.
CAT4237
The recommended PWM frequency range is from
100Hz to 2kHz.
SHDN
GND
FB
VFB = 300mV
LED
3.73kΩ
3.1kΩ
1kΩ
Current
2.5V
0V
PWN
Signal
VIN
RA
RB
R2
i
C1
R
1
15Ω
0.22µF
Figure 2. Circuit for Filtered PWM Signal
A PWM signal at 0V DC, or a 0% duty cycle, results
in a max LED current of about 22mA. A PWM signal
with a 93% duty cycle or more, results in an LED
current of 0mA.
FILTERED PWM DIMMING [0V to 2.5V]
25
Figure 1. Switching Waveform
¯¯¯¯¯
with 1kHz PWM on SHDN
20
15
10
5
0
0
10 20 30 40 50 60 70 80 90 100
PWM DUTY CYCLE [%]
Doc. No. MD-5013, Rev. B
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
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 3 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 3 corresponds
to the current path when the CAT4237 internal switch
is closed. On Figure 4 is shown the current loop, when
the CAT4237 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 CAT4237 allows for direct connection
of the capacitors to ground. The resistor R1 must be
connected directly to the GND pin of the CAT4237
and not shared with the switching current loops and
any other components.
open
closed
Figure 3. Closed-switch Current Loop
Figure 4. Open-switch Current Loop
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11
Doc. No. MD-5013, Rev. B
CAT4237
PACKAGE OUTLINES DRAWING
TSOT-23 5-Lead (TD) (1)(2)
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
0.95TYP
0.40
E1
E
E
E1
e
L
0.30
0º
0.50
8º
L1
L2
θ
0.60 REF
0.25 BSC
TOP VIEW
A2 A
A1
θ
L
b
c
L2
L1
SIDE VIEW
END VIEW
For current Tape and Reel information, download the PDF file from:
http://www.catsemi.com/documents/tapeandreel.pdf.
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC standard MO-229.
Doc. No. MD-5013, Rev. B
12
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4237
EXAMPLE OF ORDERING INFORMATION1
Prefix
CAT
Device #
4237
Suffix
TD
–
G
T3
Product Number
Lead Finish
Tape & Reel
T: Tape & Reel
3: 3000/Reel
4237
G: NiPdAu
Blank: Matte-Tin(4)
Optional
Package
Company ID
TD: TSOT-23
Notes:
(1) All packages are RoHS-compliant (Lead-free, Halogen-free).
(2) The standard lead finish is NiPdAu.
(3) The device used in the above example is a CAT4237TD–GT3 (TSOT-23, NiPdAu Plated Finish, Tape & Reel 3000).
(4) For Matte-Tin package option, please contact your nearest Catalyst Semiconductor Sales office.
Doc. No. MD-5013, Rev. B
13
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
REVISION HISTORY
Date
Rev. Reason
12/13/2005
00
A
Initial Issue
Update Absolute Maximum Ratings
Update Recommended Operating Conditions
Change document number from 25094 to 5013, Rev. A
01/31/2007
01/07/2008
Add NiPdAu lead finish
Add Extended Temperature range
Update Package Outline Drawing
Add Example of Ordering Information
Add “MD-“ to Document Number
B
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Phone: 408.542.1000
Fax: 408.542.1200
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Document No: MD-5013
Revision:
B
Issue date:
01/07/08
相关型号：
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