CAT4238 [CATALYST]
High Efficiency 10 LED Boost Converter; 高效率10 LED升压转换器
| 型号： | CAT4238 |
| 厂家： | 
CATALYST SEMICONDUCTOR |
| 描述： | High Efficiency 10 LED Boost Converter |
| 文件： | 总14页 (文件大小：280K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
CAT4238
High Efficiency 10 LED Boost Converter
FEATURES
DESCRIPTION
Drives High Voltage LED strings (38V)
The CAT4238 is a DC/DC step-up converter that delivers
an accurate constant current ideal for driving LEDs.
Operation at a fixed 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 up to 5.5V, making
the device ideal for battery-powered applications. The
CAT4238 high-voltage output stage is perfect for driving
mid-size and large panel displays containing up to ten
white LEDs in series.
Up to 87% Efficiency
Low Quiescent Ground Current 0.6mA
Adjustable Output Current
1MHz Fixed Frequency Low noise Operation
Soft start “in-rush” current limiting
Shutdown current less than 1μA
Open LED Overvoltage Protection
Automatic Shutdown at 1.9V (UVLO)
Thermal overload protection
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
GPS Navigation Systems
Portable Media Players
Handheld Devices, Digital Cameras
Portable Game Machines
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.
ORDERING INFORMATION
Quantity Package
per Reel Marking
Part Number
Package
TSOT23-5
Green*
CAT4238TD-GT3
3000
MU
* NiPdAu Plated Finish
For Ordering Information details, see page 13.
TYPICAL APPLICATION CIRCUIT
PIN CONFIGURATION
L
D
VOUT
5-Lead Thin SOT23
(1mm max height)
VIN
47µH
C1
4.7µF
C2
1
2
3
5
SW
GND
FB
VIN
0.22µF
SW
VIN
CAT4238
SHDN FB
GND
4
SHDN
(300mV)
20mA
OFF ON
R1
15Ω
L: Sumida CDC5D23B-470
D: Central CMDSH05-4
C2: Taiyo Yuden UMK212BJ224 (rated 50V)
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1
Doc. No. 5019 Rev. A
CAT4238
ABSOLUTE MAXIMUM RATINGS
Parameters
Ratings
Units
V
VIN, FB voltage
-0.3 to +7
-0.3 to +7
-0.3 to 45
-65 to +160
-40 to +125
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
up to 5.5
0 to 38
Units
V
VIN
SW pin voltage
Ambient Temperature Range
V
-40 to +85
ºC
DC ELECTRICAL CHARACTERISTICS
VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise).
Typ
Symbol Parameter
Test Conditions
VFB = 0.2V
FB = 0.4V (not switching)
Min
Max
Units
IQ
Operating Current
0.6
0.1
1.5
0.6
mA
V
ISD
VFB
IFB
Shutdown Current
FB Pin Voltage
0.1
1
315
1
31.5
21
µA
mV
µA
VS¯¯H¯D¯N¯ = 0V
10 LEDs with ILED = 20mA
285
300
FB pin input leakage
Programmed LED Current
ILED
28.5
19
14.25
30
20
15
mA
R1 = 10Ω
R1 = 15Ω
R1 = 20Ω
15.75
¯¯¯¯¯
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
FSW
DC
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
1.0
92
1.3
MHz
%
VIN = 3V
ILIM
350
450
1.0
1
600
2.0
5
mA
RSW
ILEAK
ISW = 100mA
Ω
Switch Off, VSW = 5V
µA
ºC
ºC
V
150
20
Thermal Hysteresis
VUVLO Undervoltage Lockout (UVLO)
Threshold
1.9
VOV-SW Overvoltage Detection Threshold
40
42
V
V
VOCL
Output Voltage Clamp
“Open LED”
Doc. No. 5019 Rev. A
2
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
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 40V, 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 plane on the PCB.
ILED = 0.3V/R1
The lower LED cathode is connected to the FB pin.
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
47µH
VIN
C1
SW
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
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3
Doc. No. 5019 Rev. A
CAT4238
DEVICE OPERATION
The CAT4238 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
Under light load condition (under 2mA) and with input
voltage above 5.0V, the CAT4238 driving 10 LEDs,
the driver starts pulse skipping. Although the LED
current remains well regulated, some lower frequency
ripple may appear.
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).
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 operating from a Li-Ion battery, the device can
deliver 20mA of load current into a string of up to 10
white LEDs. For higher input voltages, the LED
current can be increased.
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 40V, 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 6μs and keeping it on
for about 1μs.
Switching Waveform VIN = 5.0V, ILED = 1.5mA
Doc. No. 5019 Rev. A
4
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
Quiescent Current vs. VIN (Not Switching)
Quiescent Current vs. VIN (Switching)
150
2.0
VFB = 0.4V
1.5
1.0
0.5
0.0
125
100
75
50
3.0
3.5
4.0
4.5
5.0
5.5
3.0 3.5
4.0 4.5
5.0 5.5
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
FB pin voltage vs. Temperature
FB Pin Voltage vs. Output Current
303
302
301
300
299
298
297
310
305
300
295
10 LEDs
290
-50
0
50
100
150
5
10
15
20
25
30
TEMPERATURE [ºC]
OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
Switching Waveforms
1.2
1.1
1.0
0.9
0.8
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE [V]
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. 5019 Rev. A
CAT4238
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
LED Current vs. Input Voltage
LED Current Regulation (10mA)
1.0
40
R1 = 10Ω
VOUT = 33.8V
35
0.5
0.0
30
R1 = 15Ω
25
VOUT = 33V
20
15
R1 = 20Ω
VOUT = 32.5V
5
-0.5
10
10 LEDs @ 10mA
-1.0
0
3.0
3.5 4.0
4.5 5.0
5.5
3.0
3.5
4.0 4.5
5.0
5.5
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
Efficiency vs. Load Current (10 LEDs)
Efficiency vs. Input Voltage (10 LEDs)
100
100
VOUT = 32.5V
10 LEDs @ 15mA
VIN = 5V
90
80
70
60
90
80
VIN = 3.6V
VOUT = 33V
10 LEDs @ 20mA
70
60
5
10
15
20
25
30
3.0 3.5
4.0 4.5
5.0 5.5
INPUT VOLTAGE [V]
LED CURRENT [mA]
Power-up with 10 LEDs at 20mA
Switch ON Resistance vs. Input Voltage
2.0
1.5
1.0
0.5
0.0
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE [V]
Doc. No. 5019 Rev. A
6
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
Maximum Output Current vs. Input Voltage
Shutdown Voltage vs. Input Voltage
60
50
40
30
20
1.0
-40°C
-25°C
0.8
0.6
125°C
0.4
10
85°C
VOUT = 35V
0
0.2
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
7
Doc. No. 5019 Rev. A
CAT4238
APPLICATION INFORMATION
External Component Selection
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 1MHz. Central Semiconductor
Schottky diode CMDSH05-4 (500mA rated) is
recommended for most applications.
Capacitors
The CAT4238 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 47µH inductor is recommended for most of the
CAT4238 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 CDC5D23B-470 47µH inductor has a rated
current of 490mA and a series resistance (D.C.R.) of
420mΩ typical.
R1 = 0.3V/LED current
LED current (mA)
R1 (Ω)
60
5
10
15
20
25
30
30
20
15
Schottky Diode
12
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
10
Table 1. Resistor R1 and LED current
Doc. No. 5019 Rev. A
8
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
OPEN LED PROTECTION
In the event of an “Open LED” fault condition, the
CAT4238 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 40V. 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 6mW (about 1.6mA
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
VIN
47µH
C1
4.7µF
C2
0.22µF
SW
VIN
CAT4238
SHDN FB
GND
V
FB = 300mV
OFF ON
R1
15Ω
Open LED Output Voltage vs. VIN
without Zener
Open LED Supply Current vs. VIN
without Zener
55
50
45
40
35
5.0
4.0
3.0
2.0
1.0
0.0
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
9
Doc. No. 5019 Rev. A
CAT4238
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 CAT4238 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.
CAT4238
The recommended PWM frequency range is from
100Hz to 2kHz.
SHDN
GND
FB
VFB = 300mV
LED
3.73kΩ
3.1kΩ
1kΩ
25V
0V
PWN
Signal
Current
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]
Figure 1. Switching Waveform
25
¯¯¯¯¯
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. 5019 Rev. A
10
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
BOARD LAYOUT
The CAT4238 is a high-frequency switching regulator.
The traces that carry the high-frequency switching
current have to be carefully laid out 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 CAT4238 internal switch
is closed. On Figure 4 is shown the current loop, when
the CAT4238 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 CAT4238 allows for direct connection
of the capacitors to ground. The resistor R1 must be
connected directly to the GND pin of the CAT4238
and not shared with the switching current loops and
any other components.
Figure 4. Open-switch Current Loop
Figure 3. Closed-switch Current Loop
Figure 5. Recommended PCB Layout
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11
Doc. No. 5019 Rev. A
CAT4238
PACKAGE OUTLINES
5-LEAD SOT-23
e
e
E
E1
e1
D
GAUGE
PLANE
A2
c
A
L2
θ
L
A1
b
L1
SYMBOL
MIN
—
NOM
MAX
1.0
A
A1
A2
b
—
0.01
0.80
0.30
0.12
0.05
0.1
0.87
0.9
—
0.45
0.20
c
0.15
D
2.90 BSC
2.80 BSC
1.60 BSC
1.95 BSC
1.90 BSC
0.40
E
E1
e
e1
L
0.30
0º
0.50
8º
L1
L2
q
0.60 REF
0.25 BSC
Notes:
(1) All dimensions are in millimeters, angles in degrees.
(2) Refer JEDEC MO-193.
Doc. No. 5019 Rev. A
12
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
EXAMPLE OF ORDERING INFORMATION
Prefix
Device #
Suffix
CAT
4238
TD
–
G
T3
Product Number
Lead Finish
G: NiPdAu
Tape & Reel
T: Tape & Reel
3: 3000/Reel
4238
Optional
Company ID
Package
TD: Thin SOT-23 (Lead-free, Halogen-free)
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 CAT4238–GT3 (TSOT-23, NiPdAu, Tape & Reel).
(4) For additional package and temperature options, please contact your nearest Catalyst Semiconductor Sales office.
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
13
Doc. No. 5019 Rev. A
REVISION HISTORY
Date
Rev. Reason
Initial Issue
06/14/2006
A
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applications intended to support or sustain life, or for any other application in which the failure of the Catalyst Semiconductor product could create a situation where personal
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Catalyst Semiconductor advises customers to obtain the current version of the relevant product information before placing orders. Circuit diagrams illustrate typical
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Corporate Headquarters
1250 Borregas Avenue
Sunnyvale, CA 94089
Phone: 408.542.1000
Fax: 408.542.1200
www.catsemi.com
Document No: 5019
Revision:
A
Issue date:
06/14/06
相关型号：
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