CAT4137 CMOS Boost Converter – White LED Driver FEATURES DESCRIPTION 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 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. APPLICATIONS LCD Backlighting Cellular Phones Handheld Devices Digital Cameras 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 CAT4137TD-T3 Package TSOT23-5(1) Quantity per Reel 3000 Package Marking LX CAT4137TD-GT3 TSOT23-5(2) 3000 UE For Ordering Information details see page 15. Notes: (1) Matte-Tin Plated Finish (RoHS-compliant). (2) NiPdAu Plated Finish (RoHS-compliant). PIN CONFIGURATION TYPICAL APPLICATION CIRCUIT TSOT-23 5-Lead 1mm max height SW 1 GND 2 FB 3 5 L VIN 2.2 to 5.5V C1 VIN D VOUT 22µH C2 SW 1µF VIN 0.22µF CAT4137 4 SHDN OFF ON SHDN GND (Top View) FB VFB = 300mV R1 15Ω L: Murata LQH32CN220 D: Central CMDSH2-3 (rated 30V) © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 1 Doc. No. MD-5012 Rev. B CAT4137 ABSOLUTE MAXIMUM RATINGS Parameter Rating Unit VIN, FB voltage -0.3 to +7 V ¯¯¯¯¯ voltage SHDN -0.3 to +7 V SW voltage -0.3 to 40 V Storage Temperature Range -65 to +160 °C Junction Temperature Range -40 to +150 °C 300 °C Lead Temperature RECOMMENDED OPERATING CONDITIONS Parameter VIN SW pin voltage Ambient Temperature Range LED Bias Current Range Unit 2.2 to 5.5 V 0 to 24 V -40 to +85 °C 1 to 30 mA ELECTRICAL OPERATING 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 = 0.3V VFB = 0.4V (not switching) VSHDN ¯¯¯¯¯ = 0V VFB FB Pin Voltage 3 LEDs with ILED=20mA IFB FB pin input leakage R1 = 10Ω R1 = 15Ω R1 = 20Ω Enable Threshold Level Shutdown Threshold Level Min Typ 0.4 0.1 0.1 Max 1.5 0.3 1 Unit 285 300 315 mV 1 31.5 21 15.75 1.5 µA 0.4 0.1 30 20 15 0.8 0.7 28.5 19 14.25 mA µA ILED Programmed LED Current VIH VIL ¯¯¯¯¯ Logic High SHDN ¯¯¯¯¯ Logic Low SHDN FSW Switching Frequency 0.7 1 1.3 MHz ILIM Switch Current Limit 250 300 400 mA RSW Switch “On” Resistance ISW = 100mA 1.0 2.0 Ω ILEAK Switch Leakage Current Switch Off, VSW = 5V 1 5 µA TSD Thermal Shutdown 150 ºC THYS Thermal Hysteresis 20 ºC 86 % 1.9 V 29 V η VUVLO VOV-SW Efficiency Under-voltage lock out (UVLO) threshold Output Clamp Voltage Doc. No. MD-5012 Rev. B Typical Application Circuit “Open LED” fault 2 mA V V © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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 (Switching) Quiescent Current vs. VIN (Not 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 2.5 3.0 3.5 4.0 4.5 3 LEDs 305 300 295 290 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] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 3 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0 Doc. No. MD-5012 Rev. B 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 Regulation LED Current vs. Input Voltage (3 LEDs) 35 0.4 LED CURRENT VARIATION [%] Rfb = 10Ω LED CURRENT [mA] 30 25 Rfb = 15Ω 20 15 Rfb = 20Ω 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 10 15 20 25 30 LED CURRENT [mA] INPUT VOLTAGE [V] Doc. No. MD-5012 Rev. B 5 4 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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] 5.0 Switching Frequency vs. Temperature Under Voltage Lock Out 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] 100 Switching Waveforms (2 LEDs in Series) Switching Waveforms (3 LEDs in Series) © Catalyst Semiconductor, Inc. Characteristics subject to change without notice -25 0 25 50 75 TEMPERATURE [ºC] 5 Doc. No. MD-5012 Rev. B CAT4137 TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 1.0uF, COUT = 0.22µF, L = 22µH, with 3 LEDs at 20mA, TAMB=25ºC, unless otherwise specified. Line Transient Response (3V – 5.5V) Power-up with 3 LEDs at 20mA 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] Doc. No. MD-5012 Rev. B 6 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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 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. 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. ¯¯¯¯¯ is the shutdown logic input. When the pin SHDN 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 connected between the FB pin and ground sets the LED current according to the formula: ILED = 0.3V/R1 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 # Name 1 SW 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 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice Function Switch pin. This is the drain of the internal power switch. Shutdown pin (Logic Low). Set high to enable the driver. Power Supply input. 7 Doc. No. MD-5012 Rev. B 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. 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. 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). 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. 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. BLOCK DIAGRAM VOUT VIN SW C1 C2 1MHz Oscillator 300mV + Enable SHDN – Thermal Shutdown & UVLO A1 PWM & Logic + RC A2 – Driver ILED N1 CC RS GND – VREF + VIN Over Voltage Protection Current Sense FB R1 15Ω Doc. No. MD-5012 Rev. B 8 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4137 APPLICATION INFORMATION EXTERNAL COMPONENT SELECTION 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) is recommended for most applications. Capacitors The CAT4137 only requires small ceramic capacitors of 1uF on the input and 0.22µF on the output. The output capacitor should be rated at 30V or greater. Under normal conditions, 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 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 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 3 LEDs VIN = 3.6V 90 80 SUMIDA CDRH3D16-220 MURATA LQH32CN220 PANASONIC ELJ-EA220 PANASONIC ELJ-PC220 70 LED current (mA) R1 (Ω) 5 60 10 30 15 20 20 15 25 12 30 10 Table 1. Resistor R1 and LED current 60 5 10 15 20 25 LED CURRENT [mA] 30 Figure 1. Efficiency for various inductors © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 9 Doc. No. MD-5012Rev. B CAT4137 TYPICAL APPLICATIONS Efficiency vs. LED Current, Two LEDs CAT4137 Driving Two LEDs L VIN 1µF 100 VOUT 95 33µH C2 SW 1µF VIN CAT4137 OFF ON SHDN FB 20mA VFB = 300mV GND EFFICIENCY [%] 2.2V to 5.0V C1 D VIN = 3.6V 90 85 80 R1 75 15Ω 70 VIN = 3V 0 10 20 30 40 LED CURRENT [mA] L: Sumida CDRH3D16-330 D: Central CMDSH2-3 (rated 30V) C2: Taiyo Yuden GMK212BJ105KG-T (rated 35V) For best performance, a 33µH inductor and a 1µF output capacitor are recommended for 2-LED applications. In 2-LED configuration, the CAT4137 can be powered from two AA alkaline cells or from a Li-ion battery. Doc. No. MD-5012 Rev. B 10 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4137 DIMMING CONTROL There are several methods available to control the LED brightness. 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. ¯¯¯¯¯ pin 1. 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. Figures 2 and 3 show 1kHz and 4kHz signals with a 50% duty cycle applied to the ¯¯¯¯¯ pin. The PWM frequency range is from 100Hz SHDN to 10kHz. The recommended PWM frequency range is from 100Hz to 4kHz. VIN SW CAT4137 SHDN GND ¯¯¯¯¯ Switching waveforms PWM on SHDN RA 4.02kΩ PWM 2.5V Signal 0V VIN C1 0.22µF LED Current FB VFB = 300mV RB 3.3kΩ R2 1kΩ R1 15Ω 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 Figure 2. PWM at 1kHz 25 LED CURRENT [mA] 20 15 10 5 0 0 20 40 60 80 DUTY CYCLE [%] 100 Figure 3. PWM at 4kHz © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 11 Doc. No. MD-5012Rev. B 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 (opencircuit). Open LED Power-up Waveforms Open LED Protection (Central CMDSH2-3) L VIN D VOUT 22µH C1 C2 1µF 0.22µF SW VIN CAT4137 OFF ON SHDN FB VFB = 300mV GND R1 15Ω Open LED Supply Current vs. VIN SUPPLY CURRENT [mA] 2.5 2.0 1.5 1.0 2.5 Doc. No. MD-5012 Rev. B 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0 12 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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. L D 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. L VOUT D VOUT VIN VIN SW SW VIN VIN CAT4137 Switch Closed SHDN C1 CAT4137 FB SHDN C2 R1 FB C2 C1 R1 GND GND Figure 5. Open-switch current loop Figure 4. Closed-switch current loop © Catalyst Semiconductor, Inc. Characteristics subject to change without notice Switch Open 13 Doc. No. MD-5012Rev. B CAT4137 PACKAGE OUTLINE DRAWING TSOT-23 5-Lead (TD) (1)(2) SYMBOL D MIN NOM 0.01 0.05 0.10 A2 0.80 0.87 0.90 b 0.30 c 0.12 0.15 0.20 A e 1.00 A1 E1 E MAX 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 L1 SIDE VIEW L2 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-5012 Rev. B 14 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4137 EXAMPLE OF ORDERING INFORMATION1 Prefix CAT Device # Suffix 4137 TD – Product Number 4137 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 CAT4137TD–GT3 (TSOT-23, NiPdAu Plated Finish, Tape & Reel 3000). (4) For Matte-Tin package option, please contact your nearest Catalyst Semiconductor Sales office. © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 15 Doc. No. MD-5012 Rev. B REVISION HISTORY Date Rev. 12/13/2005 00 Initial Issue B Add NiPdAu lead finish Add Extended Temperature range Update Package Outline Drawing Add Example of Ordering Information Change Document Number from 25093, Rev. 00 to MD-5016, Rev. B 01/11/2008 Reason Copyrights, Trademarks and Patents © Catalyst Semiconductor, Inc. Trademarks and registered trademarks of Catalyst Semiconductor include each of the following: Adaptive Analog™, Beyond Memory™, DPP™, EZDim™, LDD™, MiniPot™, Quad-Mode™ and Quantum Charge Programmable™ Catalyst Semiconductor has been issued U.S. and foreign patents and has patent applications pending that protect its products. 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 2975 Stender Way Santa Clara, CA 95054 Phone: 408.542.1000 Fax: 408.542.1200 www.catsemi.com Document No: MD-5012 Revision: B Issue date: 01/11/08