Catalyst CAT4238 High efficiency 10 led boost converter Datasheet

CAT4238
High Efficiency 10 LED Boost Converter
FEATURES
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DESCRIPTION
Drives High Voltage LED strings (38V)
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)
APPLICATIONS
„
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GPS Navigation Systems
Portable Media Players
Handheld Devices, Digital Cameras
Portable Game Machines
Package
CAT4238TD-GT3
TSOT23-5
Green*
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 (1mm max height) 5-lead
thin SOT23 package for space critical applications.
ORDERING INFORMATION
Part Number
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.
Quantity Package
per Reel Marking
3000
MU
* Lead Finish NiPdAu
For Ordering Information details, see page 13.
TYPICAL APPLICATION CIRCUIT
PIN CONFIGURATION
TSOT23 5-Lead
(1mm max height)
L
VIN
D
47µH
C1
SW
1
GND
2
FB
3
5
C2
4.7µF
VIN
VOUT
0.22µF
SW
VIN
CAT4238
4
SHDN
OFF ON
SHDN
FB
(300mV)
GND
Top View
20mA
R1
15Ω
L: Sumida CDC5D23B-470
D: Central CMDSH05-4
C2: Taiyo Yuden UMK212BJ224 (rated 50V)
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1
Doc. No. MD-5019 Rev. C
CAT4238
ABSOLUTE MAXIMUM RATINGS
Parameters
VIN, FB voltage
¯¯¯¯¯ voltage
SHDN
SW voltage(1)
Storage Temperature Range
Junction Temperature Range
Lead Temperature
Ratings
-0.3 to +7
-0.3 to +7
up to 60
-65 to +160
-40 to +150
300
Units
V
V
V
ºC
ºC
ºC
Note:
(1) The SW pin voltage is rated up to 39V for external continuous DC voltage.
RECOMMENDED OPERATING CONDITIONS
Typical application circuit with external components are shown on page 1.
Parameters
VIN
SW pin voltage
Ambient Temperature Range
Range
up to 5.5
0 to 38
-40 to +85
Units
V
V
ºC
DC ELECTRICAL CHARACTERISTICS
VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise).
Symbol Parameter
IQ
Operating Current
ISD
VFB
IFB
ILED
VIH
VIL
FSW
DC
ILIM
RSW
ILEAK
VUVLO
VOV-SW
VOCL
Shutdown Current
FB Pin Voltage
FB pin input leakage
Programmed LED Current
¯¯¯¯¯ Logic High
SHDN
¯¯¯¯¯ Logic Low
SHDN
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
Thermal Hysteresis
Undervoltage Lockout (UVLO)
Threshold
Test Conditions
VFB = 0.2V
VFB = 0.4V (not switching)
VSHDN
¯¯¯¯¯ = 0V
10 LEDs with ILED = 20mA
R1 = 10Ω
R1 = 15Ω
R1 = 20Ω
Enable Threshold Level
Shutdown Threshold Level
Max
1.5
0.6
Units
mA
285
0.1
300
28.5
19
14.25
30
20
15
1
315
1
31.5
21
15.75
µA
mV
µA
mA
1.5
V
V
MHz
%
mA
Ω
µA
ºC
ºC
V
0.4
0.8
VIN = 3V
350
ISW = 100mA
Switch Off, VSW = 5V
Overvoltage Detection Threshold
Output Voltage Clamp
“Open LED”
Doc. No. MD-5019 Rev. C
Typ
0.6
0.1
Min
2
0.8
0.7
1.0
92
450
1.0
1
150
20
1.9
40
42
1.3
600
2.0
5
V
V
© 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 overvoltage 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.
¯¯¯¯¯ is the shutdown logic input. When the pin is
SHDN
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
1
2
3
4
5
Function
SW
GND
FB
¯¯¯¯¯
SHDN
VIN
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.
BLOCK DIAGRAM
47µH
VIN
SW
C1
C2
4.7µF
0.22µF
A2
PWM &
Logic
300mV –
Thermal
Shutdown
& UVLO
+ A1
RC
+
–
Driver
LED
Current
N1
CC
RS
GND
–
Enable
SHDN
Over Voltage
Protection
+
VIN
Vref
1MHz
Oscillator
Current
Sense
FB
R1
15Ω
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3
Doc. No. MD-5019 Rev. C
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.
Doc. No. MD-5019 Rev. C
Switching Waveform VIN = 5.0V, ILED = 1.5mA
4
© 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 (Switching)
2.0
150
QUIESCENT CURRENT [mA]
QUIESCENT CURRENT [μA] .
Quiescent Current vs. VIN (Not Switching)
VFB = 0.4V
125
100
75
1.5
1.0
0.5
0.0
50
3.0
3.5
4.0
4.5
5.0
3.0
5.5
FB pin voltage vs. Temperature
4.5
5.0
5.5
FB Pin Voltage vs. Output Current
303
310
302
FB PIN VOLTAGE [mV]
FB PIN VOLTAGE [mV]
4.0
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
301
300
299
298
297
305
300
295
10 LEDs
290
-50
0
50
100
150
5
TEMPERATURE [ºC]
10
15
20
25
30
OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
SWITCHING FREQUENCY [MHz]
3.5
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]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. MD-5019 Rev. C
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
R1 = 10Ω
VOUT = 33.8V
35
LED CURRENT [mA]
LED CURRENT VARIATION [%] .
40
LED Current Regulation (10mA)
30
R1 = 15Ω
VOUT = 33V
25
20
15
R1 = 20Ω
VOUT = 32.5V
10
5
0
3.0
3.5
4.0
4.5
5.0
5.5
1.0
0.5
0.0
-0.5
10 LEDs @ 10mA
-1.0
3.0
4.5
5.0
5.5
Efficiency vs. Input Voltage (10 LEDs)
Efficiency vs. Load Current (10 LEDs)
100
100
VIN = 5V
EFFICIENCY [%]
EFFICIENCY [%]
4.0
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
90
3.5
80
VIN = 3.6V
70
60
VOUT = 32.5V
10 LEDs @ 15mA
90
80
VOUT = 33V
10 LEDs @ 20mA
70
60
5
10
15
20
25
30
3.0
LED CURRENT [mA]
Power-up with 10 LEDs at 20mA
3.5
4.0 4.5
5.0
INPUT VOLTAGE [V]
5.5
Switch ON Resistance vs. Input Voltage
SWITCH RESISTANCE [Ω]
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. MD-5019 Rev. C
6
© 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
1.0
SHUTDOWN VOLTAGE [V]
OUTPUT CURRENT [mA]
60
50
40
30
20
10
VOUT = 35V
0
-40°C
-25°C
0.8
0.6
125°C
0.4
85°C
0.2
3.0
3.5
4.0
4.5
5.0
5.5
3.0
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
7
Doc. No. MD-5019 Rev. C
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)
5
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
Doc. No. MD-5019 Rev. C
R1 (Ω)
60
30
20
15
12
10
Table 1. Resistor R1 and LED current
8
© 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
L
VIN
Open LED Switching Waveforms
without Zener
Schottky 100V
(Central CMSH1-100)
VOUT
47µH
C1
C2
4.7µF
0.22µF
SW
VIN
CAT4238
OFF ON
SHDN
FB
VFB = 300mV
R1
15Ω
GND
Open LED Output Voltage vs. VIN
without Zener
Open LED Supply Current vs. VIN
without Zener
55
OUTPUT VOLTAGE [V]
SUPPLY CURRENT [mA]
5.0
4.0
3.0
2.0
1.0
0.0
50
45
40
35
3.0
3.5
4.0
4.5
5.0
5.5
3.0
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE [V]
9
Doc. No. MD-5019 Rev. C
CAT4238
DIMMING CONTROL
Filtered PWM Signal
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.
There are several methods available to control the
LED brightness.
¯¯¯¯¯ Pin
PWM signal on the SHDN
LED brightness dimming can be done by applying a
¯¯¯¯¯ input. The LED current is
PWM signal to the SHDN
repetitively turned on and off, so that the average
current is proportional to the duty cycle. A 100% duty
¯¯¯¯¯ always high, corresponds to the
cycle, with SHDN
LEDs at nominal current. Figure 1 shows a 1kHz
¯¯¯¯¯ pin.
signal with a 50% duty cycle applied to the SHDN
The recommended PWM frequency range is from
100Hz to 2kHz.
VIN
SW
CAT4238
SHDN
FB
VFB = 300mV
GND
PWM
Signal
2.5V
0V
3.73kΩ
3.1kΩ
RA
RB
C1
LED
Current
1kΩ
R2
i
R1
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
¯¯¯¯¯
with 1kHz PWM on SHDN
LED CURRENT [mA]
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
90
100
PWM DUTY CYCLE [%]
Doc. No. MD-5019 Rev. C
10
© 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 3. Closed-switch Current Loop
Figure 4. Open-switch Current Loop
Figure 5. Recommended PCB Layout
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11
Doc. No. MD-5019 Rev. C
CAT4238
PACKAGE OUTLINE DRAWING
TSOT-23 5-Lead (TD) (1)(2)
SYMBOL
D
MIN
NOM
MAX
0.01
0.05
0.10
A2
0.80
0.87
b
0.30
c
0.12
A
e
1.00
A1
E1
E
0.15
D
2.90 BSC
E
2.80 BSC
E1
1.60 BSC
e
0.95 TYP
L
0.30
0.40
L1
0.60 REF
L2
0.25 BSC
θ
0.90
0.45
0.20
0.50
0º
8º
TOP VIEW
A2 A
b
θ
L
A1
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-193.
Doc. No. MD-5019 Rev. C
12
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4238
EXAMPLE OF ORDERING INFORMATION
Prefix
CAT
Device #
4238
Product Number
4238
(1)(2)(3)
Suffix
TD
–
G
Lead Finish
G: NiPdAu
T3
Tape & Reel
T: Tape & Reel
3: 3000/Reel
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.
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
13
Doc. No. MD-5019 Rev. C
REVISION HISTORY
Date
06/14/2006
Rev.
A
Reason
Initial Issue
03/16/2007
B
Update Absolute Maximum Ratings
Update Figure 2.
Update SOT-23 5 Lead package outline
10-17-07
C
Update Absolute Maximum Ratings
Update Package Outline Drawing
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OF ANY SUCH USE OR APPLICATION, INCLUDING BUT NOT LIMITED TO, CONSEQUENTIAL OR INCIDENTAL DAMAGES.
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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 reserves the right to make changes to or discontinue any product or service described herein without notice. Products with data sheets labeled
"Advance Information" or "Preliminary" and other products described herein may not be in production or offered for sale.
Catalyst Semiconductor advises customers to obtain the current version of the relevant product information before placing orders. Circuit diagrams illustrate typical
semiconductor applications and may not be complete.
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Corporate Headquarters
2975 Stender Way
Santa Clara, CA 95054
Phone: 408.542.1000
Fax:
408.542.1200
www.catsemi.com
Document No: MD-5019
Revision:
C
Issue date:
10/17/07