CAT4238 D

CAT4238
High Efficiency 10 LED
Boost Converter
Description
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 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 external resistor
R1. LED currents up to 40 mA can be supported over a wide range of
input supply voltages up to 5.5 V, 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.
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.
Drives High Voltage LED Strings (38 V)
Up to 87% Efficiency
Low Quiescent Ground Current 0.6 mA
Adjustable Output Current
1 MHz Fixed Frequency Low Noise Operation
Soft Start “In−rush” Current Limiting
Shutdown Current Less than 1 mA
Open LED Overvoltage Protection
Automatic Shutdown at 1.9 V (UVLO)
Thermal Overload 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)
MUYM
MU = Specific Device Code
Y = Production Year (Last Digit)
M = Production Month
(1−9 (Jan−Sep), O, N, D (Oct−Dec))
ORDERING INFORMATION
Device
CAT4238TD−GT3
Package
Shipping
TSOT−23
(Pb−Free)
Green*
3,000/
Tape & Reel
* Lead Finish NiPdAu
Applications
•
•
•
•
5
MARKING DIAGRAM
Features
•
•
•
•
•
•
•
•
•
•
•
•
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GPS Navigation Systems
Portable Media Players
Handheld Devices, Digital Cameras
Portable Game Machines
© Semiconductor Components Industries, LLC, 2016
April, 2016 − Rev. 5
1
Publication Order Number:
CAT4238/D
CAT4238
L
VIN
D
VOUT
47 mH
C2
C1
4.7 mF
SW
0.22 mF
VIN
CAT4238
OFF ON
SHDN
GND
FB
VFB = 300 mV
20 mA
R1
15 W
L: Sumida CDC5D23B−470
D: Central CMDSH05−4
C2: Taiyo Yuden UMK212BJ224 (rated 50 V)
Figure 1. Typical Application Circuit
Table 1. ABSOLUTE MAXIMUM RATINGS
Ratings
Units
VIN, FB voltage
Parameters
−0.3 to +7
V
SHDN voltage
−0.3 to +7
V
up to 60
V
Storage Temperature Range
−65 to +160
_C
Junction Temperature Range
−40 to +150
_C
300
_C
SW voltage (Note 1)
Lead Temperature
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
1. The SW pin voltage is rated up to 39 V for external continuous DC voltage.
Table 2. RECOMMENDED OPERATING CONDITIONS
Parameters
VIN
SW pin voltage
Ambient Temperature Range
Range
Units
up to 5.5
V
0 to 38
V
−40 to +85
_C
Functional operation above the stresses listed in the Recommended Operating Ranges is not implied. Extended exposure to stresses beyond
the Recommended Operating Ranges limits may affect device reliability.
NOTE: Typical application circuit with external components is shown above.
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CAT4238
Table 3. DC ELECTRICAL CHARACTERISTICS
(VIN = 3.6 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified))
Symbol
Parameter
Test Conditions
Min
Typ
Max
Units
IQ
Operating Current
VFB = 0.2 V
VFB = 0.4 V (not switching)
0.6
0.1
1.5
0.6
mA
ISD
Shutdown Current
VSHDN = 0 V
0.1
1
mA
VFB
FB Pin Voltage
10 LEDs with ILED = 20 mA
300
315
mV
IFB
FB pin input leakage
1
mA
ILED
Programmed LED Current
VIH
VIL
R1 = 10 W
R1 = 15 W
R1 = 20 W
SHDN Logic High
SHDN Logic Low
Enable Threshold Level
Shutdown Threshold Level
FSW
Switching Frequency
DC
Maximum Duty Cycle
ILIM
Switch Current Limit
RSW
Switch “On” Resistance
ISW = 100 mA
ILEAK
Switch Leakage Current
Switch Off, VSW = 5 V
285
28.5
19
14.25
30
20
15
31.5
21
15.75
mA
0.8
0.7
1.5
V
0.4
0.8
1.0
1.3
MHz
VIN = 3 V
92
350
%
450
600
mA
1.0
2.0
W
1
5
mA
Thermal Shutdown
150
°C
Thermal Hysteresis
20
°C
VUVLO
Undervoltage Lockout (UVLO) Threshold
1.9
V
VOV-SW
Overvoltage Detection Threshold
40
V
VOCL
Output Voltage Clamp
“Open LED” with VIN = 5 V
43
45
48
V
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
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.
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.
GND is the ground reference pin. This pin should be
connected directly to the ground place on the PCB.
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 40 V,
the device enters a low power operating mode preventing the
SW voltage from exceeding the maximum rating.
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
Function
2
GND
Ground pin. Connect the pin to the ground plane.
3
FB
Feedback pin. Connect to the last LED cathode.
4
SHDN
5
VIN
Switch pin. This is the drain of the internal power switch.
Shutdown pin (Logic Low). Set high to enable the driver.
Power Supply input.
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CAT4238
Block Diagram
47 mH
VIN
SW
C1
C2
4.7 mF
0.22 mF
1 MHz
Oscillator
VREF
300 mV
–
A1
+
SHDN
Thermal
Shutdown
& UVLO
A2
RC
LED
Current
PWM &
Logic
–
N1
CC
+
Enable
Driver
+
RS
GND
Current
Sense
–
VIN
Over Voltage
Protection
FB
Figure 2. Block Diagram
Device Operation
The CAT4238 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
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 operating from a Li−Ion battery, the device can
deliver 20 mA 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 40 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 6 ms and
keeping it on for about 1 ms.
R1
15 W
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.
Light Load Operation
Under light load condition (under 2 mA) and with input
voltage above 5.0 V, the CAT4238 driving 10 LEDs, the
driver starts pulse skipping. Although the LED current
remains well regulated, some lower frequency ripple may
appear.
Figure 3. Switching Waveform VIN = 5.0 V,
ILED = 1.5 mA
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CAT4238
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 4.7 mF, COUT = 0.22 mF, L = 47 mH with 10 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
2.0
VFB = 0.4 V
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (mA)
150
125
100
75
1.5
1.0
0.5
0
50
3.0
3.5
4.0
4.5
5.0
3.0
5.5
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)
5.5
310
303
FB PIN VOLTAGE (mV)
FB PIN VOLTAGE (mV)
302
301
300
299
305
300
295
298
10 LEDs
297
−50
290
0
50
100
5
150
10
15
20
25
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
Figure 6. FB Pin Voltage vs. Temperature
Figure 7. FB Pin Voltage vs. Output Current
SWITCHING FREQUENCY (MHz)
1.2
SW
20V/div
1.1
Inductor
Current
100mA/div
1.0
0.9
VOUT
AC coupled
500mV/div
0.8
3.0
3.5
4.0
4.5
5.0
5.5
500 ns/div
INPUT VOLTAGE (V)
Figure 8. Switching Frequency vs. Supply
Voltage
Figure 9. Switching Waveforms
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30
CAT4238
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 4.7 mF, COUT = 0.22 mF, L = 47 mH with 10 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
40
1.0
LED CURRENT (mA)
LED CURRENT VARIATION (%)
R1 = 10 W
VOUT = 33.8 V
35
30
R1 = 15 W
VOUT = 33 V
25
20
15
R1 = 20 W
VOUT = 32.5 V
10
5
0
0
−0.5
10 LEDs @ 10 mA
−1.0
3.0
3.5
4.0
4.5
5.5
5.0
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 10. LED Current vs. Input Voltage
Figure 11. LED Current Regulation (10 mA)
5.5
100
100
90
90
EFFICIENCY (%)
VIN = 5 V
80
VIN = 3.6 V
70
VOUT = 32.5 V
10 LEDs @ 15 mA
80
VOUT = 33 V
10 LEDs @ 20 mA
70
60
60
5
10
15
20
25
3.0
30
3.5
4.0
4.5
5.0
LED CURRENT (mA)
INPUT VOLTAGE (V)
Figure 12. Efficiency vs. Load Current
(10 LEDs)
Figure 13. Efficiency vs. Input Voltage
(10 LEDs)
5.5
2.0
SWITCH RESISTANCE (W)
EFFICIENCY (%)
0.5
1.5
1.0
0.5
0
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 14. Power−up with 10 LEDs at 20 mA
Figure 15. Switch ON Resistance vs. Input
Voltage
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5.5
CAT4238
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, CIN = 4.7 mF, COUT = 0.22 mF, L = 47 mH with 10 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.)
1.0
50
SHUTDOWN VOLTAGE (V)
OUTPUT CURRENT (mA)
60
40
30
20
VOUT = 35 V
10
−40°C
0.8
−25°C
85°C
0.6
125°C
0.4
0.2
0
3.0
3.5
4.0
4.5
5.0
3.0
5.5
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 16. Maximum Output Current vs. Input
Voltage
Figure 17. Shutdown Voltage vs. Input Voltage
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 CAT4238 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 R1
connected between the feedback pin (FB) and ground. The
formula below gives the relationship between the resistor
and the current:
R1 +
Inductor
A 47 mH 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 300 mA or higher
are recommended for most applications. Sumida
CDC5D23B−470 47 mH inductor has a rated current of
490 mA and a series resistance (D.C.R.) of 420 mW typical.
0.3 V
current
LED
Table 5. RESISTOR R1 AND LED CURRENT
LED Current (mA)
R1 (W)
5
60
10
30
15
20
20
15
25
12
30
10
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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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 40 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 6 mW (about 1.6 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
between Vout and the FB pin. A 50 V rated C2 capacitor is
required to prevent any overvoltage damage in the open
LED condition.
SUPPLY CURRENT (mA)
3.0
2.0
1.0
0
3.0
C1
4.0
4.5
5.0
5.5
Figure 20. Open LED Supply Current vs. VIN without
Zener
C2
4.7 mF
3.5
INPUT VOLTAGE (V)
VOUT
47 mH
0.22 mF
55
SW
VIN
SHDN
GND
FB
OUTPUT VOLTAGE (V)
CAT4238
OFF ON
4.0
Schottky 100 V
(Central CMSH1−100)
L
VIN
5.0
VFB = 300 mV
R1
15 W
Figure 18. Open LED Protection without Zener
50
45
40
35
3.0
3.5
4.0
4.5
5.0
5.5
SW 10 V/div
INPUT VOLTAGE (V)
Figure 21. Open LED Output Voltage vs. VIN without
Zener
2 ms/div
Figure 19. Open LED Switching Waveforms without
Zener
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CAT4238
Dimming Control
There are several methods available to control the LED
brightness.
VIN
SW
CAT4238
PWM Signal on the SHDN Pin
SHDN
GND FB
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 22
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.
PWM
Signal
2.5 V
3.73 kW
3.1 kW
RA
RB
0V
C1
VFB = 300 mV
1 kW
LED
Current
R2
i
R1
15 W
0.22 mF
Figure 23. 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.
LED CURRENT (mA)
25
20
15
10
5
Figure 22. Switching Waveform with 1 kHz PWM on
SHDN
0
0
10
20
30
40
50
60
70
80
90 100
PWM DUTY CYCLE (%)
Filtered PWM Signal
A filtered PWM signal used as a variable DC voltage can
control the LED current. Figure 23 shows the PWM control
circuitry connected to the CAT4238 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 24. Filtered PWM Dimming (0 V to 2.5 V)
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CAT4238
Board Layout
The CAT4238 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 25 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 25
corresponds to the current path when the CAT4238 internal
switch is closed. On Figure 26 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 25. Closed−switch Current Loop
Figure 26. Open−switch Current Loop
Figure 27. Recommended PCB Layout
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CAT4238
PACKAGE DIMENSIONS
TSOT−23, 5 LEAD
CASE 419AE
ISSUE O
SYMBOL
D
MIN
NOM
A
e
E1
MAX
1.00
A1
0.01
0.05
0.10
A2
0.80
0.87
0.90
b
0.30
c
0.12
E
0.45
0.15
D
2.90 BSC
E
2.80 BSC
E1
1.60 BSC
e
0.95 TYP
0.30
L
L1
0.40
0.20
0.50
0.60 REF
L2
0.25 BSC
0º
θ
8º
TOP VIEW
A2 A
b
q
L
A1
c
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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L2
CAT4238
Example of Ordering Information (Note 4)
Prefix
Device #
Suffix
CAT
4238
TD
Company ID
(Optional)
Product Number
4238
−G
T3
Lead Finish
G: NiPdAu
Tape & Reel (Note 6)
T: Tape & Reel
3: 3,000 / Reel
Package
TD: Thin SOT−23 (Lead−free, Halogen−free)
2.
3.
4.
5.
6.
All packages are RoHS−compliant (Lead−free, Halogen−free).
The standard lead finish is NiPdAu.
The device used in the above example is a CAT4238TD−GT3 (TSOT−23, NiPdAu, Tape & Reel, 3,000/Reel).
For additional package and temperature options, please contact your nearest ON Semiconductor Sales office.
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 the
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries.
SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed
at www.onsemi.com/site/pdf/Patent−Marking.pdf. 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
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For additional information, please contact your local
Sales Representative
CAT4238/D
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