CATALYST CAT4137

CAT4137
CMOS Boost Converter - White LED Driver
Features
Product Description
•
•
•
•
•
•
•
•
•
•
•
•
The CAT4137 is a DC/DC step-up converter that
delivers a regulated output current. Operation at
a constant switching frequency of 1MHz allows
the device to be used with small value external
ceramic capacitors and inductor.
Drives up to 5 White LEDs from 3V
Power Efficiency up to 87%
Low Quiescent Ground Current 0.1mA
Adjustable Output Current (up to 30mA)
High Frequency 1MHz Operation
“Zero” current shutdown mode
Operates down to 2V (from two AA batteries)
Soft start power-up
Open LED low power mode
Automatic shutdown at 1.9V (UVLO)
Thermal shutdown protection
Thin SOT23 5-Lead (1mm max height)
The device drives a string of white LEDs
connected in series and provides the regulated
current to control the LEDs with inherent uniform
brightness and matching. An external resistor R1
sets the output current and allows up to 30mA
current to be supported over a wide range of
input supply voltages from 2.2V to 5.5V, making
the device ideal for battery-powered applications.
Applications
•
•
•
•
LED dimming can be done by using a DC
voltage, a logic signal, or a pulse width
modulation (PWM) signal. The shutdown control
pin allows the device to be placed in power-down
mode with “zero” quiescent current.
LCD Backlighting
Cellular Phones
Handheld Devices
Digital Cameras
Ordering Information
Part Number
Package
CAT4137TS
CAT4137TD
TSOT23-5
TSOT23-5
1
Lead Free
Note 1: NiPdAu Lead Plating
Quantity
per Reel
3000
3000
Pin Configuration
Package
Marking
LW
LX
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.
Typical Application Circuit
Top View
5-Lead Thin SOT23
1mm max height
L: Murata LQH32CN220
D: Central CMDSH2-3 (rated 30V)
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1 of 14
Doc. 5012 , Rev. A
CAT4137
ABSOLUTE MAXIMUM RATINGS
Parameter
VIN, FB voltage
SHDN* voltage
SW voltage
Storage Temperature Range
Junction Temperature Range
Lead Temperature
Rating
-0.3 to +7
-0.3 to +7
-0.3 to 40
-65 to +160
-40 to +125
300
Unit
V
V
V
°C
°C
°C
RECOMMENDED OPERATING CONDITIONS
Parameter
VIN
SW pin voltage
Ambient Temperature Range
LED Bias Current
Range
2.2 to 5.5
0 to 24
-40 to +85
1 to 30
Unit
V
V
°C
mA
ELECTRICAL OPERATING CHARACTERISTICS
VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise)
Symbol Parameter
Conditions
Min
Typ
Max
Unit
IQ
Operating Current
VFB = 0.3V
0.4
1.5
mA
VFB = 0.4V (not switching)
0.1
0.3
ISD
Shutdown Current
VSHDN* = 0V
0.1
1
µA
VFB
FB Pin Voltage
3 LEDs with ILED=20mA
285
300
315
mV
IFB
FB pin input leakage
0.1
1
µA
31.5
30
28.5
R1 = 10Ω
mA
21
20
ILED
Programmed LED Current R1 = 15Ω
19
15.75
15
14.25
R1 = 20Ω
VIH
SHDN* Logic High
Enable Threshold Level
0.8
1.5
V
VIL
SHDN* Logic Low
Shutdown Threshold Level
0.4
0.7
V
FSW
ILIM
RSW
ILEAK
TSD
THYS
η
VUVLO
VOV-SW
Switching Frequency
Switch Current Limit
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
Thermal Hysteresis
Efficiency
Under-voltage lock out
(UVLO) threshold
Output Clamp Voltage
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
0.7
250
ISW = 100mA
Switch Off, VSW = 5V
Typical Application Circuit
“Open LED” fault
2 of 14
1
300
1.0
1
150
20
86
1.9
29
1.3
400
2.0
5
MHz
mA
Ω
µA
ºC
ºC
%
V
V
Doc. 5012 , Rev. A
CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22µF, L = 22µH with 3 LEDs at 20mA, TAMB=25ºC, unless otherwise specified.
Quiescent Current vs. VIN (Not Switching)
Quiescent Current vs. VIN (Switching)
120
1.00
SUPPLY CURRENT [mA]
SUPPLY CURRENT [uA]
VFB = 0.4V
100
80
60
40
20
0
0.50
0.25
0.00
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
5.0
2.5
3.5
4.0
4.5
5.0
FB Pin Voltage vs. Output Current
310
310
FB PIN VOLTAGE [mV]
3 LEDs
305
300
295
290
3 LEDs
305
300
295
290
2.5
3.0
3.5
4.0
4.5
5.0
0
INPUT VOLTAGE [V]
5
10
15
20
25
30
OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
Switch ON Resistance vs. Input Voltage
2.0
SWITCH RESISTANCE [ohm]
1.10
CLOCK FREQUENCY [MHz].
3.0
INPUT VOLTAGE [V]
FB Pin Voltage vs. Supply Voltage
FB PIN VOLTAGE [mV]
0.75
1.05
3 LEDs at 20mA
1.00
0.95
1.5
1.0
0.5
0.0
0.90
2.5
3.0
3.5
4.0
2.5
4.5
INPUT VOLTAGE [V]
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3 of 14
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
5.0
Doc. 5012 , Rev. A
CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22µF, L = 22µH, with 3 LEDs at 20mA, TAMB=25ºC, unless otherwise specified.
LED Current vs. Input Voltage (3 LEDs)
LED Current Regulation
35
0.4
LED CURRENT VARIATION [%]
Rfb = 10O
LED CURRENT [mA]
30
25
Rfb = 15O
20
15
Rfb = 20O
10
5
0
2.0
2.5
3.0
3.5 4.0 4.5
INPUT VOLTAGE [V]
5.0
0.2
0.0
-0.2
-0.4
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
Efficiency across Supply Voltage (3 LEDs)
Efficiency across Load Current (3 LEDs)
100
100
VIN = 4.2V
EFFICIENCY [%]
EFFICIENCY [%]
15mA
90
80
20mA
70
60
90
80
VIN = 3.6V
70
60
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
5
INPUT VOLTAGE [V]
10
20
25
30
LED CURRENT [mA]
Efficiency across Supply Voltage (4 LEDs)
Efficiency across Load Current (4 LEDs)
100
100
VIN = 4.2V
15mA
90
EFFICIENCY [%]
EFFICIENCY [%]
15
80
20mA
70
90
VIN = 3.6V
80
70
60
60
2.0
2.5
3.0
3.5
4.0
4.5
0
5.0
© 2005 Catalyst Semiconductor, Inc.
10
15
20
25
30
LED CURRENT [mA]
INPUT VOLTAGE [V]
Characteristics subject to change without notice
5
4 of 14
Doc. 5012 , Rev. A
CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22µF, L = 22µH, with 3 LEDs at 20mA, TAMB=25ºC, unless otherwise specified.
Shutdown Voltage vs. Input Voltage
FB Pin Voltage vs. Temperature
1.0
SHUTDOWN VOLTAGE [V]
FB PIN VOLTAGE [mV]
304
302
300
298
3 LEDs at 20mA
296
294
25°C
0.8
0.6
85°C
0.4
0.2
-50
-25
0
25
50
75
100
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
TEMPERATURE [°C]
Under Voltage Lock Out vs. Temperature
5.0
Switching Frequency vs. Temperature
1.10
CLOCK FREQUENCY[MHz].
2.2
2.1
UVLO [V]
-40°C
2.0
1.9
1.8
1.7
20mA per LED
1.05
1.00
0.95
0.90
1.6
-50
-25
0
25
50
75
-50
100
TEMPERATURE [°C]
Switching Waveforms (3 LEDs in Series)
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
-25
0
25 50 75
TEMPERATURE [ºC]
100
Switching Waveforms (2 LEDs in Series)
5 of 14
Doc. 5012 , Rev. A
CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22µF, L = 22µH, with 3 LEDs at 20mA, TAMB=25ºC, unless otherwise specified.
Power-up with 3 LEDs at 20mA
Line Transient Response (3V – 5.5V)
Maximum Output Current vs. Input Voltage
MAX OUTPUT CURRENT [mA].
140
120
VOUT = 10V
100
80
60
40
VOUT = 17V
20
0
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
6 of 14
Doc. 5012 , Rev. A
CAT4137
PIN DESCRIPTION
VIN is the supply input for the internal logic.
SW pin is the drain terminal of the internal low
The device is compatible with supply voltages
down to 2.2V and up to 5.5V. A small bypass
ceramic capacitor of 1µF is recommended
between the VIN and GND pins near the
device. The under-voltage lockout (UVLO)
circuitry will place the device into an idle
mode (not switching) whenever the supply
falls below 1.9V.
resistance power switch. 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. This pin
contains over-voltage circuitry which becomes
active above 24V. In the event of an “Open-Led”
fault condition, the device will enter a low power
mode and the SW pin will be clamped to
approximately 30V.
SHDN* is the shutdown logic input. When the
pin voltage is taken below 0.4V, the device
immediately enters shutdown mode, drawing
nearly zero current. At voltages greater than
1.5V, the device becomes fully enabled and
operational.
FB feedback pin is regulated at 0.3V. A resistor
GND is the ground reference pin. This pin
should be connected directly to the ground
plane on the PCB.
The lower LED cathode is connected to the FB pin.
Pin #
1
2
3
4
5
Name
SW
GND
FB
SHDN*
VIN
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
connected between the FB pin and ground sets
the LED current according to the formula:
ILED = 0.3V/R1
Function
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.
7 of 14
Doc. 5012 , Rev. A
CAT4137
DEVICE OPERATION
The CAT4137 is a fixed frequency (1MHz),
low noise, inductive boost converter
providing constant current to the load. A high
voltage internal CMOS power switch is used
to energize the external inductor. When the
power switch is then turned off, the stored
energy inductor is released into the load via
the external Schottky diode.
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 external feedback resistor connected to
the feedback pin (FB). The value of external
resistor will accurately set the LED bias
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 will
comfortably deliver up to 30mA of bias current
into a string of up to 5 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 24V, an internal protection
circuit will become active and place the device
into a very low power safe operating mode. In
addition, an internal clamping circuit will limit the
peak output voltage to 29V. If this fault condition
is repaired, the device will automatically resume
normal operation.
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.
BLOCK DIAGRAM
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
8 of 14
Doc. 5012 , Rev. A
CAT4137
APPLICATION INFORMATION
External Component Selection
Schottky Diode
Capacitors
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
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 CMDSH2-3
(200mA rated) or the CMDSH-3 (100mA
rated)
are
recommended
for
most
applications.
The CAT4137 only requires small ceramic
capacitors of 1uF on the input and 0.22µF on
the output. Under normal condition, a 1µF
input capacitor is sufficient. For applications
with higher output power, a larger input
capacitor of 2.2µF or 4.7µF may be
appropriate. X5R and X7R capacitor types
are ideal due to their stability across
temperature range.
Inductor
LED Current Setting
A 22µH inductor is recommended for most of
the CAT4137 applications. In cases where
the efficiency is critical, inductances with
lower series resistance are preferred.
Several inductor types from various vendors
can be used. Figure 1 shows how different
inductor types affect the efficiency across
the load range.
EFFICIENCY (%)
100
The LED current is set by the external
resistor between the feedback pin (FB) and
ground. The formula below gives the
relationship between the resistor and the
current:
R1 = 0.3V/LED current
LED current (mA)
R1 (Ω)
5
60
10
30
15
20
20
15
25
12
30
10
Table 1. Resistor R1 and LED current
3 LEDs
VIN = 3.6V
90
80
SUMIDA CDRH3D16-220
MURATA LQH32CN220
PANASONIC ELJ-EA220
PANASONIC ELJ-PC220
70
60
5
10
15
20
25
LED CURRENT [mA]
30
Figure 1. Efficiency for various inductors
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
9 of 14
Doc. 5012 , Rev. A
CAT4137
Dimming Control
2. Filtered PWM signal
There are several methods available to
control the LED brightness.
A filtered PWM signal can be used as a
variable DC voltage that can be used to
control the LED current. Figure 4 shows the
PWM control circuitry connected to the
CAT4137 FB pin. The PWM signal has a
voltage swing of 0V to 2.5V. The LED current
can be dimmed within a range from 0 to
22mA. The PWM signal frequency can vary
from very low frequency up to 100kHz.
1. 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. Figures 2
and 3 show 1kHz and 4kHz signals with a
50% duty cycle applied to the SHDN* pin.
The PWM frequency range is from 100Hz to
10kHz. The recommended PWM frequency
range is from 100Hz to 4kHz.
Switching waveforms PWM on SHDN*
Figure 4. 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 100% duty cycle results
in an LED current of 0mA.
LED Current vs. Duty Cycle
25
Figure 2. PWM at 1kHz
LED CURRENT [mA]
20
15
10
5
0
0
20
40
60
80
DUTY CYCLE [%]
100
Figure 3. PWM at 4kHz
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
10 of 14
Doc. 5012 , Rev. A
CAT4137
Open LED Protection
In the event of an “Open LED” fault condition,
the CAT4137 will continue to boost the output
voltage with maximum power until the output
voltage reaches approximately 24V. Once the
output exceeds this level, internal circuitry
immediately places the device into a very low
power mode where the total input power
consumed is less than 10mW.
In low power mode, the input supply current
will typically drop to 2mA. An internal clamping
circuit will limit the subsequent output voltage to
approximately 29V. This operating mode
eliminates the need for any external protection
zener diode. This protection scheme also fully
protects the device against any malfunction in
the external Schottky diode (open-circuit).
Open LED Power-up Waveforms
Open LED Protection
Open LED Supply Current vs. VIN
SUPPLY CURRENT [mA]
2.5
2.0
1.5
1.0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE [V]
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5.0
11 of 14
Doc. 5012 , Rev. A
CAT4137
Board Layout
The CAT4137 is a high-frequency switching
regulator. Traces carrying 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
shown on Figure 4 indicate 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 4 corresponds to the
current path when the CAT4137 internal
switch is closed. On Figure 5 is shown the
current loop when the CAT4137 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 CAT4137 allows for direct connection of
the capacitors to ground. The resistor R1
must be connected directly to the GND pin of
the CAT4137 and not shared with the
switching current loops and any other
components.
Figure 5. Open-switch current loop
open
closed
Figure 4. Closed-switch current loop
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
Figure 5. Open-switch current loop
12 of 14
Doc. 5012 , Rev. A
CAT4137
PACKAGE OUTLINES
5-LEAD SOT-23
All dimensions in millimeters
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
13 of 14
Doc. 5012 , Rev. A
CAT4137
REVISION HISTORY
Date
10/14/2005
Revision
A
Reason
Initial issue
Copyrights, Trademarks and Patents
Trademarks and registered trademarks of Catalyst Semiconductor include each of the following:
DPP ™
AE2 ™
Catalyst Semiconductor has been issued U.S. and foreign patents and has patent applications pending that
protect its products. For a complete list of patents issued to Catalyst Semiconductor contact the Company’s
corporate office at 408.542.1000.
CATALYST SEMICONDUCTOR MAKES NO WARRANTY, REPRESENTATION OR GUARANTEE, EXPRESS
OR IMPLIED, REGARDING THE SUITABILITY OF ITS PRODUCTS FOR ANY PARTICULAR PURPOSE, NOR
THAT THE USE OF ITS PRODUCTS WILL NOT INFRINGE ITS INTELLECTUAL PROPERTY RIGHTS OR THE
RIGHTS OF THIRD PARTIES WITH RESPECT TO ANY PARTICULAR USE OR APPLICATION AND
SPECIFICALLY DISCLAIMS ANY AND ALL LIABILITY ARISING OUT OF ANY SUCH USE OR APPLICATION,
INCLUDING BUT NOT LIMITED TO, CONSEQUENTIAL OR INCIDENTAL DAMAGES.
Catalyst Semiconductor 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 Catalyst Semiconductor product could create a situation where
personal injury or death may occur.
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.
Catalyst Semiconductor, Inc.
Corporate Headquarters
1250 Borregas Avenue
Sunnyvale, CA 94089
Phone: 408.542.1000
Fax: 408.542.1200
www.catalyst-semiconductor.com
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
Publication #: 5012
Revision:
Rev. A
Issue date:
10/14/05
14 of 14
Doc. 5012 , Rev. A