CATALYST CAT4237TD-T3

CAT4237
High Voltage CMOS Boost White LED Driver
FEATURES
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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
Thin SOT23 5-Lead (1mm max height)
APPLICATIONS
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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 highvoltage 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.
Color LCD and keypad Backlighting
Cellular Phones
Handheld Devices
Digital Cameras
PDAs
Portable Game Machine
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
CAT4237TD-T3
Package
TSOT23-5 (1)
Quantity
per Reel
3000
Package
Marking
LT
3000
UD
CAT4237TD-GT3 TSOT23-5 (2)
For Ordering Information details, see page 13.
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)
SW 1
5 VIN
L
VIN
3V to
4.2V
33µH
C1
4.7µF
GND 2
VOUT
C2
SW 0.22µF
VIN
CAT4237
4 SHDN
FB 3
D
OFF ON
Top View
SHDN
FB
VFB = 300mV
GND
20mA
R1
15Ω
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
VIN, FB voltage
¯¯¯¯¯ voltage
SHDN
SW voltage
Storage Temperature Range
Junction Temperature Range
Lead Temperature
Ratings
-0.3 to +7
-0.3 to +7
-0.3 to 55
-65 to +160
-40 to +150
300
Units
V
V
V
ºC
ºC
ºC
RECOMMENDED OPERATING CONDITIONS
Typical application circuit with external components are shown on page 1.
Parameters
VIN
SW pin voltage
Ambient Temperature Range
6, 7 or 8 LEDs
Range
2.8 to 5.5
0 to 30
-40 to +85
1 to 40
Units
V
V
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
IQ
Operating Current
ISD
Shutdown Current
Conditions
VFB = 0.2V
VFB = 0.4V (not switching)
VSHDN
¯¯¯¯¯ = 0V
VFB
FB Pin Voltage
8 LEDs with ILED=20mA
IFB
FB pin input leakage
ILED
Programmed LED Current
R1 = 10Ω
R1 = 15Ω
R1 = 20Ω
VIH
VIL
¯¯¯¯¯ Logic High
SHDN
¯¯¯¯¯ Logic Low
SHDN
Enable Threshold Level
Shutdown Threshold Level
FSW
Min
285
Typ
0.6
0.1
0.1
Max
1.5
0.6
1
Unit
300
315
mV
1
µA
mA
mA
µA
28.5
19
14.25
30
20
15
31.5
21
15.75
0.8
0.7
1.5
0.4
V
V
Switching Frequency
0.8
1.0
1.3
MHz
ILIM
Switch Current Limit
350
450
600
mA
RSW
Switch “On” Resistance
ISW = 100mA
1.0
2.0
Ω
ILEAK
Switch Leakage Current
Switch Off, VSW = 5V
1
5
µA
VUVLO
VOV-SW
Thermal Shutdown
150
ºC
Thermal Hysteresis
Undervoltage Lockout
(UVLO) Threshold
Overvoltage Threshold
20
ºC
1.9
V
35
V
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 overvoltage 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.
¯¯¯¯¯ 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 place on the PCB.
ILED = 0.3V/R1
The lower LED cathode is connected to the FB pin.
PIN DESCRIPTIONS
Pin #
1
2
3
4
5
Name
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
33µH
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-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
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.
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 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.
Doc. No. MD-5013, Rev. B
Figure 1. Switching Waveform VIN = 4.2V,
ILED = 4mA
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
SUPPLY CURRENT [mA]
2.0
INPUT CURRENT [uA]
120
100
80
60
40
VFB =0.4V
(not switching)
20
1.5
1.0
0.5
0.0
0
2.7
3.0
3.3
3.6
3.9
4.2
4.5
2.5
4.8
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
FB pin voltage vs. Supply Voltage
FB Pin Voltage vs. Output Current
315
315
FB PIN VOLTAGE [mV]
8LEDs at 20mA
VOUT= 26V
310
FEEDBACK [mV]
3.0
305
300
295
290
310
8 LEDs
305
300
295
290
285
285
2.7
3.0
3.3 3.6 3.9 4.2 4.5
INPUT VOLTAGE [V]
0
4.8
Switching Frequency vs. Supply Voltage
5
10
15
20
25
OUTPUT CURRENT [mA]
30
Switching Waveforms
1040
FREQUENCY [kHz]
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 Regulation (20mA)
LED Current vs. Input Voltage (8 LEDS)
35
1.0%
CURRENT VARIATION [%] .
LED CURRENT [mA]
30
RFB = 10Ω
25
RFB = 15Ω
20
15
RFB = 20Ω
10
5
0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
0.5%
0.0%
-0.5%
-1.0%
3.0
5.0
3.3 3.6 3.9 4.2 4.5
INPUT VOLTAGE [V]
8 LED Efficiency vs. Input Voltage
8 LED Efficiency vs. Load Current
90
90
20mA
85
80
EFFICIENCY [%]
EFFICIENCY [%]
VIN = 4.2V
VIN = 3.6V
75
8 LEDs
VOUT ~ 27V at 20mA
L = 33uH
70
5
10
15
85
15mA
80
75
8 LEDs
VOUT ~ 27V at 20mA
L = 33uH
70
65
65
20
25
3.0
30
3.5
4.0
4.5
5.0
LED CURRENT [mA]
INPUT VOLTAGE [V]
7 LED Efficiency vs. Load Current
6 LED Efficiency vs. Load Current
90
90
VIN = 4.2V
85
EFFICIENCY [%]
EFFICIENCY [%]
4.8
VIN = 3.6V
80
75
7 LEDs
VOUT ~ 23V at 20mA
L = 33uH
70
65
VIN = 4.2V
85
VIN = 3.6V
80
75
6 LEDs
VOUT ~ 20V at 20mA
L = 33uH
70
65
5
10
15
20
25
30
5
LED CURRENT [mA]
Doc. No. MD-5013, Rev. B
10
15
20
25
30
LED CURRENT [mA]
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.
Switch ON Resistance vs. Input Voltage
Power-up with 8 LEDs at 20mA
SWITCH RESISTANCE [ohm]
2.0
1.5
1.0
0.5
0.0
2.5
4.5
Shutdown Voltage vs. Input Voltage
FB pin voltage vs. Temperature
1.0
303
302
SHUTDOWN VOLTAGE [V]
FEEDBACK VOLTAGE [mV]
3.0
3.5
4.0
INPUT VOLTAGE [V]
301
300
299
V IN =3.6V, 8LEDs
298
ILED =20mA
297
25°C
0.8
-40°C
0.6
125° C
85°C
0.4
0.2
-50
0
50
100
150
3.0
TEMPERATURE [ºC]
3.5
4.0
4.5
INPUT VOLTAGE [V]
5.0
Maximum Output Current vs. Input Voltage
MAX OUTPUT CURRENT [mA]
140
120
VOUT = 15V
100
80
60
40
VOUT = 20V
20
0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5.0
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
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 given current. In order to achieve the best
Doc. No. MD-5013, Rev. B
8
LED current (mA)
R1 (Ω)
5
60
10
30
15
20
20
15
25
12
30
10
© 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 Switching waveforms
without Zener
Open LED Protection without Zener
Schottky 100V
(Central CMSH1-100)
L
VIN
VOUT
33µH
C1
C2
0.22µF
4.7µF
SW
VIN
CAT4237
OFF ON
SHDN
FB
VFB = 300mV
R1
15Ω
Open LED Supply Current vs. VIN
without Zener
Open LED Output Voltage vs. VIN
without Zener
2.0
50
OUTPUT VOLTAGE [V]
SUPPLY CURRENT [mA]
GND
1.5
1.0
0.5
45
40
35
30
0.0
2.5
3.0
3.5
4.0
4.5
2.5
5.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE [V]
INPUT VOLTAGE [V]
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3.0
9
Doc. No. MD-5013, Rev. B
CAT4237
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 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.
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
CAT4237
SHDN
GND
PWN
Signal
2.5V
3.73kΩ
3.1kΩ
RA
RB
FB
VFB = 300mV
1kΩ
VIN
0V
C1
R2
i
LED
Current
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]
25
LED CURRENT [mA]
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
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
Figure 4. Open-switch Current Loop
11
Doc. No. MD-5013, Rev. B
CAT4237
PACKAGE OUTLINES DRAWING
TSOT-23 5-Lead (TD)
(1)(2)
SYMBOL
D
MIN
NOM
A
e
E1
E
MAX
1.00
A1
0.01
0.05
0.10
A2
0.80
0.87
0.90
0.15
0.20
b
0.30
c
0.12
0.45
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
0º
0.50
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-229.
Doc. No. MD-5013, Rev. B
12
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT4237
EXAMPLE OF ORDERING INFORMATION 1
Prefix
CAT
Device #
Suffix
4237
TD
Product Number
4237
Optional
Company ID
–
G
T3
Lead Finish
G: NiPdAu
Blank: Matte-Tin(4)
Tape & Reel
T: Tape & Reel
3: 3000/Reel
Package
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
12/13/2005
Rev.
00
01/31/2007
A
Update Absolute Maximum Ratings
Update Recommended Operating Conditions
Change document number from 25094 to 5013, Rev. A
B
Add NiPdAu lead finish
Add Extended Temperature range
Update Package Outline Drawing
Add Example of Ordering Information
Add “MD-“ to Document Number
01/07/2008
Reason
Initial Issue
Copyrights, Trademarks and Patents
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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
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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
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:
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Document No: MD-5013
Revision:
B
Issue date:
01/07/08