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CAT4137
CMOS Boost Converter - White LED Driver
Features
* * * * * * * * * * * * 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)
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. 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. 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. 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.
Applications
* * * * LCD Backlighting Cellular Phones Handheld Devices Digital Cameras
Ordering Information
Part Number CAT4137TS CAT4137TD Package TSOT23-5 TSOT23-5 Green Quantity per Reel 3000 3000 Package Marking LW LX
Pin Configuration
Top View
Typical Application Circuit
5-Lead Thin SOT23 1mm max height
L: Murata LQH32CN220 D: Central CMDSH2-3 (rated 30V)
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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 25C (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 A VFB FB Pin Voltage 3 LEDs with ILED=20mA 285 300 315 mV IFB FB pin input leakage 0.1 1 A 28.5 30 31.5 R1 = 10 ILED Programmed LED Current R1 = 15 19 20 21 mA 14.25 15 15.75 R1 = 20 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 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 0.7 250 ISW = 100mA Switch Off, VSW = 5V 1 300 1.0 1 150 20 86 1.9 29 1.3 400 2.0 5 MHz mA A C C % V V
Typical Application Circuit
"Open LED" fault
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CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22F, L = 22H with 3 LEDs at 20mA, TAMB=25C, unless otherwise specified. Quiescent Current vs. VIN (Not Switching)
120 VFB = 0.4V SUPPLY CURRENT [uA] 100 80 60 40 20 0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0
Quiescent Current vs. VIN (Switching)
1.00 SUPPLY CURRENT [mA]
0.75 0.50
0.25
0.00 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
FB Pin Voltage vs. Supply Voltage
310 FB PIN VOLTAGE [mV] 3 LEDs 305
FB Pin Voltage vs. Output Current
310 FB PIN VOLTAGE [mV] 3 LEDs 305
300
300
295
295
290 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
290 0 5 10 15 20 25 30 OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
1.10 CLOCK FREQUENCY [MHz].
Switch ON Resistance vs. Input Voltage
2.0 SWITCH RESISTANCE [ohm]
1.05 3 LEDs at 20mA 1.00
1.5
1.0
0.95
0.5
0.90 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V]
0.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0
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CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22F, L = 22H, with 3 LEDs at 20mA, TAMB=25C, unless otherwise specified. LED Current vs. Input Voltage (3 LEDs)
35 30 LED CURRENT [mA] 25 20 15 10 5 0 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0 Rfb = 20 Rfb = 15
LED Current Regulation
0.4 LED CURRENT VARIATION [%]
Rfb = 10
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)
100 15mA EFFICIENCY [%] 90
Efficiency across Load Current (3 LEDs)
100 VIN = 4.2V EFFICIENCY [%] 90
80 20mA 70 60 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
80 70
VIN = 3.6V
60 0 5 10 15 20 25 30 LED CURRENT [mA]
Efficiency across Supply Voltage (4 LEDs)
100 15mA EFFICIENCY [%]
Efficiency across Load Current (4 LEDs)
100 VIN = 4.2V EFFICIENCY [%] 90 VIN = 3.6V 80
90 80 20mA 70 60 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
70 60 0 5 10 15 20 25 30 LED CURRENT [mA]
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Characteristics subject to change without notice
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CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22F, L = 22H, with 3 LEDs at 20mA, TAMB=25C, unless otherwise specified. FB Pin Voltage vs. Temperature
304 FB PIN VOLTAGE [mV]
SHUTDOWN VOLTAGE [V]
Shutdown Voltage vs. Input Voltage
1.0 25C -40C
302 300 298 296 294 -50 -25 0 25 50 75 100 TEMPERATURE [C]
0.8
0.6 85C 0.4
3 LEDs at 20mA
0.2 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0
Under Voltage Lock Out vs. Temperature
2.2 2.1
UVLO [V]
Switching Frequency vs. Temperature
1.10 CLOCK FREQUENCY[MHz]. 20mA per LED 1.05
2.0 1.9 1.8 1.7 1.6 -50 -25 0 25 50 75 100 TEMPERATURE [C]
1.00
0.95
0.90 -50 -25 0 25 50 75 TEMPERATURE [C] 100
Switching Waveforms (3 LEDs in Series)
Switching Waveforms (2 LEDs in Series)
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CAT4137
Typical Characteristics
VIN = 3.6V, CIN = 1.0uF, COUT = 0.22F, L = 22H, with 3 LEDs at 20mA, TAMB=25C, unless otherwise specified. Power-up with 3 LEDs at 20mA Line Transient Response (3V - 5.5V)
Maximum Output Current vs. Input Voltage
140 MAX OUTPUT CURRENT [mA] 120 100 80 60 40 20 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE [V] VOUT = 17V VOUT = 10V
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CAT4137
PIN DESCRIPTION VIN is the supply input for the internal logic. The device is compatible with supply voltages down to 2.2V and up to 5.5V. A small bypass ceramic capacitor of 1F 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. 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.
SW pin is the drain terminal of the internal low 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. 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: ILED = 0.3V/R1 The lower LED cathode is connected to the FB pin.
GND is the ground reference pin. This pin
should be connected directly to the ground plane on the PCB. Pin # 1 2 3 4 5 Name SW GND FB SHDN* VIN
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.
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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 150C. In the event of a thermal overload condition the device will automatically shutdown and wait till the junction temperatures cools to 130C before normal operation is resumed.
BLOCK DIAGRAM
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CAT4137
APPLICATION INFORMATION
External Component Selection Capacitors The CAT4137 only requires small ceramic capacitors of 1uF on the input and 0.22F on the output. Under normal condition, a 1F input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 2.2F or 4.7F may be appropriate. X5R and X7R capacitor types are ideal due to their stability across temperature range. Inductor A 22H 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.
100 3 LEDs VIN = 3.6V
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 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. LED Current Setting 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 () 5 60 10 30 15 20 20 15 25 12 30 10 Table 1. Resistor R1 and LED current
EFFICIENCY (%)
90
80 SUMIDA CDRH3D16-220 MURATA LQH32CN220 PANASONIC ELJ-EA220 PANASONIC ELJ-PC220 5 10 15 20 25 LED CURRENT [mA] 30
70
60
Figure 1. Efficiency for various inductors
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CAT4137
Dimming Control
There are several methods available to control the LED brightness. 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* 2. Filtered PWM signal 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.
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
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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.
Open LED Protection
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 Supply Current vs. VIN
2.5 SUPPLY CURRENT [mA]
2.0
1.5
1.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0
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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
closed
open
Figure 4. Closed-switch current loop
Figure 5. Open-switch current loop
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CAT4137
PACKAGE OUTLINES 5-LEAD SOT-23 All dimensions in millimeters
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CAT4137
REVISION HISTORY
Date 12/13/2005 Revision 00 Reason Initial issue
Copyrights, Trademarks and Patents Trademarks and registered trademarks of Catalyst Semiconductor include each of the following: DPP TM AE2 TM
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
Publication #: 25093 Revision: Rev. 00 Issue date: 12/13/05
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Characteristics subject to change without notice
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