CAT4238 High Efficiency 10 LED Boost Converter FEATURES DESCRIPTION Drives High Voltage LED strings (38V) Up to 87% Efficiency Low Quiescent Ground Current 0.6mA Adjustable Output Current 1MHz Fixed Frequency Low noise Operation Soft start “in-rush” current limiting Shutdown current less than 1μA Open LED Overvoltage Protection Automatic Shutdown at 1.9V (UVLO) Thermal overload protection Thin SOT23 5-Lead (1mm max height) APPLICATIONS GPS Navigation Systems Portable Media Players Handheld Devices, Digital Cameras Portable Game Machines Package CAT4238TD-GT3 TSOT23-5 Green* 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 (1mm max height) 5-lead thin SOT23 package for space critical applications. ORDERING INFORMATION Part Number 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 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 up to 5.5V, 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. Quantity Package per Reel Marking 3000 MU * Lead Finish NiPdAu For Ordering Information details, see page 13. TYPICAL APPLICATION CIRCUIT PIN CONFIGURATION TSOT23 5-Lead (1mm max height) L VIN D 47µH C1 SW 1 GND 2 FB 3 5 C2 4.7µF VIN VOUT 0.22µF SW VIN CAT4238 4 SHDN OFF ON SHDN FB (300mV) GND Top View 20mA R1 15Ω L: Sumida CDC5D23B-470 D: Central CMDSH05-4 C2: Taiyo Yuden UMK212BJ224 (rated 50V) © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 1 Doc. No. MD-5019 Rev. C CAT4238 ABSOLUTE MAXIMUM RATINGS Parameters VIN, FB voltage ¯¯¯¯¯ voltage SHDN SW voltage(1) Storage Temperature Range Junction Temperature Range Lead Temperature Ratings -0.3 to +7 -0.3 to +7 up to 60 -65 to +160 -40 to +150 300 Units V V V ºC ºC ºC Note: (1) The SW pin voltage is rated up to 39V for external continuous DC voltage. RECOMMENDED OPERATING CONDITIONS Typical application circuit with external components are shown on page 1. Parameters VIN SW pin voltage Ambient Temperature Range Range up to 5.5 0 to 38 -40 to +85 Units V V ºC DC ELECTRICAL CHARACTERISTICS VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise). Symbol Parameter IQ Operating Current ISD VFB IFB ILED VIH VIL FSW DC ILIM RSW ILEAK VUVLO VOV-SW VOCL Shutdown Current FB Pin Voltage FB pin input leakage Programmed LED Current ¯¯¯¯¯ Logic High SHDN ¯¯¯¯¯ Logic Low SHDN Switching Frequency Maximum Duty Cycle Switch Current Limit Switch “On” Resistance Switch Leakage Current Thermal Shutdown Thermal Hysteresis Undervoltage Lockout (UVLO) Threshold Test Conditions VFB = 0.2V VFB = 0.4V (not switching) VSHDN ¯¯¯¯¯ = 0V 10 LEDs with ILED = 20mA R1 = 10Ω R1 = 15Ω R1 = 20Ω Enable Threshold Level Shutdown Threshold Level Max 1.5 0.6 Units mA 285 0.1 300 28.5 19 14.25 30 20 15 1 315 1 31.5 21 15.75 µA mV µA mA 1.5 V V MHz % mA Ω µA ºC ºC V 0.4 0.8 VIN = 3V 350 ISW = 100mA Switch Off, VSW = 5V Overvoltage Detection Threshold Output Voltage Clamp “Open LED” Doc. No. MD-5019 Rev. C Typ 0.6 0.1 Min 2 0.8 0.7 1.0 92 450 1.0 1 150 20 1.9 40 42 1.3 600 2.0 5 V V © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4238 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 40V, 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 plane on the PCB. ILED = 0.3V/R1 The lower LED cathode is connected to the FB pin. Pin # Name 1 2 3 4 5 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 47µH 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-5019 Rev. C CAT4238 DEVICE OPERATION The CAT4238 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 2mA) and with input voltage above 5.0V, the CAT4238 driving 10 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 operating from a Li-Ion battery, the device can deliver 20mA 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 40V, 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 6μs and keeping it on for about 1μs. Doc. No. MD-5019 Rev. C Switching Waveform VIN = 5.0V, ILED = 1.5mA 4 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4238 TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified. Quiescent Current vs. VIN (Switching) 2.0 150 QUIESCENT CURRENT [mA] QUIESCENT CURRENT [μA] . Quiescent Current vs. VIN (Not Switching) VFB = 0.4V 125 100 75 1.5 1.0 0.5 0.0 50 3.0 3.5 4.0 4.5 5.0 3.0 5.5 FB pin voltage vs. Temperature 4.5 5.0 5.5 FB Pin Voltage vs. Output Current 303 310 302 FB PIN VOLTAGE [mV] FB PIN VOLTAGE [mV] 4.0 INPUT VOLTAGE [V] INPUT VOLTAGE [V] 301 300 299 298 297 305 300 295 10 LEDs 290 -50 0 50 100 150 5 TEMPERATURE [ºC] 10 15 20 25 30 OUTPUT CURRENT [mA] Switching Frequency vs. Supply Voltage SWITCHING FREQUENCY [MHz] 3.5 Switching Waveforms 1.2 1.1 1.0 0.9 0.8 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 5 Doc. No. MD-5019 Rev. C CAT4238 TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified. LED Current vs. Input Voltage R1 = 10Ω VOUT = 33.8V 35 LED CURRENT [mA] LED CURRENT VARIATION [%] . 40 LED Current Regulation (10mA) 30 R1 = 15Ω VOUT = 33V 25 20 15 R1 = 20Ω VOUT = 32.5V 10 5 0 3.0 3.5 4.0 4.5 5.0 5.5 1.0 0.5 0.0 -0.5 10 LEDs @ 10mA -1.0 3.0 4.5 5.0 5.5 Efficiency vs. Input Voltage (10 LEDs) Efficiency vs. Load Current (10 LEDs) 100 100 VIN = 5V EFFICIENCY [%] EFFICIENCY [%] 4.0 INPUT VOLTAGE [V] INPUT VOLTAGE [V] 90 3.5 80 VIN = 3.6V 70 60 VOUT = 32.5V 10 LEDs @ 15mA 90 80 VOUT = 33V 10 LEDs @ 20mA 70 60 5 10 15 20 25 30 3.0 LED CURRENT [mA] Power-up with 10 LEDs at 20mA 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V] 5.5 Switch ON Resistance vs. Input Voltage SWITCH RESISTANCE [Ω] 2.0 1.5 1.0 0.5 0.0 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE [V] Doc. No. MD-5019 Rev. C 6 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4238 TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified. Maximum Output Current vs. Input Voltage Shutdown Voltage vs. Input Voltage 1.0 SHUTDOWN VOLTAGE [V] OUTPUT CURRENT [mA] 60 50 40 30 20 10 VOUT = 35V 0 -40°C -25°C 0.8 0.6 125°C 0.4 85°C 0.2 3.0 3.5 4.0 4.5 5.0 5.5 3.0 INPUT VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V] 7 Doc. No. MD-5019 Rev. C CAT4238 APPLICATION INFORMATION External Component Selection 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 diode CMDSH05-4 (500mA rated) is recommended for most applications. Capacitors The CAT4238 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 47µH 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 300mA or higher are recommended for most applications. Sumida CDC5D23B-470 47µH inductor has a rated current of 490mA and a series resistance (D.C.R.) of 420mΩ typical. R1 = 0.3V/LED current LED current (mA) 5 10 15 20 25 30 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 Doc. No. MD-5019 Rev. C R1 (Ω) 60 30 20 15 12 10 Table 1. Resistor R1 and LED current 8 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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 40V. 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 6mW (about 1.6mA 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 Protection without Zener L VIN Open LED Switching Waveforms without Zener Schottky 100V (Central CMSH1-100) VOUT 47µH C1 C2 4.7µF 0.22µF SW VIN CAT4238 OFF ON SHDN FB VFB = 300mV R1 15Ω GND Open LED Output Voltage vs. VIN without Zener Open LED Supply Current vs. VIN without Zener 55 OUTPUT VOLTAGE [V] SUPPLY CURRENT [mA] 5.0 4.0 3.0 2.0 1.0 0.0 50 45 40 35 3.0 3.5 4.0 4.5 5.0 5.5 3.0 INPUT VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE [V] 9 Doc. No. MD-5019 Rev. C CAT4238 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 CAT4238 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 CAT4238 SHDN FB VFB = 300mV GND PWM Signal 2.5V 0V 3.73kΩ 3.1kΩ RA RB C1 LED Current 1kΩ R2 i 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] Figure 1. Switching Waveform ¯¯¯¯¯ with 1kHz PWM on SHDN LED CURRENT [mA] 25 20 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 PWM DUTY CYCLE [%] Doc. No. MD-5019 Rev. C 10 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4238 BOARD LAYOUT The CAT4238 is a high-frequency switching regulator. The traces that carry the high-frequency switching current have to be carefully laid out 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 CAT4238 internal switch is closed. On Figure 4 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 3. Closed-switch Current Loop Figure 4. Open-switch Current Loop Figure 5. Recommended PCB Layout © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 11 Doc. No. MD-5019 Rev. C CAT4238 PACKAGE OUTLINE DRAWING TSOT-23 5-Lead (TD) (1)(2) SYMBOL D MIN NOM MAX 0.01 0.05 0.10 A2 0.80 0.87 b 0.30 c 0.12 A e 1.00 A1 E1 E 0.15 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 0.90 0.45 0.20 0.50 0º 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-193. Doc. No. MD-5019 Rev. C 12 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4238 EXAMPLE OF ORDERING INFORMATION Prefix CAT Device # 4238 Product Number 4238 (1)(2)(3) Suffix TD – G Lead Finish G: NiPdAu T3 Tape & Reel T: Tape & Reel 3: 3000/Reel Optional Company ID Package TD: Thin SOT-23 (Lead-free, Halogen-free) 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 CAT4238–GT3 (TSOT-23, NiPdAu, Tape & Reel). (4) For additional package and temperature options, please contact your nearest Catalyst Semiconductor Sales office. © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 13 Doc. No. MD-5019 Rev. C REVISION HISTORY Date 06/14/2006 Rev. A Reason Initial Issue 03/16/2007 B Update Absolute Maximum Ratings Update Figure 2. Update SOT-23 5 Lead package outline 10-17-07 C Update Absolute Maximum Ratings Update Package Outline Drawing Copyrights, Trademarks and Patents Trademarks and registered trademarks of Catalyst Semiconductor include each of the following: Beyond Memory™, DPP™, EZDim™, LDD™, MiniPot™ and Quad-Mode™ 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-5019 Revision: C Issue date: 10/17/07