ZXSC400EV2 ZXSC400EV2 USER GUIDE DESCRIPTION The ZXSC400 is voltage mode boost converter in SOT23-6 package. Its low feedback voltage allows the current in a chain of LEDs to be set and accurately monitored with a single resistor with minimal losses. The ZXSC400EV2 is configured for 25W LED Driver applications using the ZXSC400 boost converter. FEATURES • Drives strings of 23 serially connected R,G & B LEDs at 350mA • Typical efficiency of 85% • Over-voltage Protection APPLICATIONS • LCD TV RGB Backlight • High Power LED driving ORDERING INFORMATION ORDER NUMBER ZXSC400EV2 TYPICAL APPLICATION CIRCUIT L1 VIN D1 68uH/3.5A R4 VCC LED ANODE 10BQ100 1kohms Please note evaluation boards are subject to availability and qualified leads. Q1 U2 + C1 ZXMN10A09K D2 ZXT D6717E6 BZX84C47 + 100uF/25V U1 ZXSC400 VCC C2 C3 47uF/100V 100nF/100V DRIVE PWM ST DN GND SENSE D3 R1 VFB BZX84C47 10m Ohm C4 1uF/10V R3 D4 R5 BZX84C7V5 10k LED CATHODE 20k R2 0.75 Ohm ZXSC400EV2 ISSUE 8 - November 2005 1 ZXSC400EV2 REFERENCE DESIGN ZXSC400EV2 is configured to the reference design below. The target application is a 25W LED Driver typically White or RGB LED Driver for LCD TV backlighting. The supply voltage is: VIN=24V and VCC=12V for the ZXSC400EV2. For other reference designs or further applications information please refer to the ZXSC400 datasheet. Schematic Diagram L1 VIN R4 VCC D1 68uH/3.5A LED ANODE 10BQ100 1kohms Q1 ZXMN10A09K U2 + C1 D2 ZXT D6717E6 BZX84C47 + 100uF/25V U1 ZXSC400 VCC DRIVE ST DN SENSE C2 C3 47uF/100V 100nF/100V PWM GND D3 R1 VFB BZX84C47 10m Ohm C4 1uF/10V R3 D4 R5 BZX84C7V5 LED CATHODE 20k 10k R2 0.75 Ohm Materials List Ref Value Package Part Number Manufacturer Notes U1 U2 Q1 D1 D2 D3 D4 L1 R1 ZXSC400E6 ZXTD6717E6 ZXMN10A09K 10BQ100 BZX84C47 BZX84C47 BZX84C7V5 DO5022P-683 10mΩ SOT23-6 SOT23-6 DPAK SMB SOT23 SOT23 SOT23 N/A 1206 Zetex Zetex Zetex IR Philips Philips Philips Coilcraft Generic Boost converter MOSFET gate driver N-Channel MOSFET 100V 100V/1A Schottky diode 47V Zener diode 47V Zener diode 7V5 Zener diode 68uH/3.5A SMT Inductor 1206 5% tolerance R2 0.75Ω 1206 Generic 1205 1% tolerance R3 20kΩ 0805 Generic 0805 5% tolerance R4 1kΩ 0805 Generic 0805 5% tolerance Generic 0805 5% tolerance C1 C2 C3 10kΩ 100µF/25V 47µF/100V 100nF/100V 0805 E H13 1206 Panasonic Panasonic Generic C4 1µF/10V 0805 SMT Electrolytic capacitor SMT Electrolytic capacitor 100nF/100V/1206/Y5V Ceramic capacitor 1µF/10V/0805/Y5V Ceramic capacitor R5 N/A N/A N/A 100V/1A 47V 47V 7V5 68uH/3.5A EEVFK1E101P EEVFK2A470Q Generic ZXSC400EV2 ISSUE 8 - November 2005 2 ZXSC400EV2 ZXSC400EV2 OPERATION Connection diagram 25W LED DRIVER BOARD ZXSC400EV2 L1 ZDB246R2 VIN LED ANODE D1 U2 VCC C2 + + R3 R4 Q1 R5 LK1 PWM D3 U1 C4 D4 GND C1 R1 R2 D2 C3 LED CATHODE Copyright Zetex plc 2005 ZXSC400EV2 Set-up and Test 1. Connect VIN and GND to positive and zero volts of PSU1 supply respectively. 2. Connect VCC and GND to positive and zero volts of PSU2 supply respectively. 3. Connect LED chain to LED ANODE and LED CATHODE outputs on ZXSC400EV2 4. Set the PSU1 to 24V and PSU2 to 12V. 5. Turn on PSU1 and PSU2. 6. The LED chain should illuminate and be regulated at 350mA - THIS IS A FUNCTIONAL EVAL BOARD. ZXSC400EV2 ISSUE 8 - November 2005 3 ZXSC400EV2 LED Dimming using the PWM Input. By injecting a PWM signal on the PWM input and varying the duty cycle, LED current and hence LED brightness can be adjusted. To implement this method of brightness control on the ZXLD1100EV2: 1. Connect a 10kΩ resistor between the drive pin of the ZXSC400 and GND (see diagram below). 2. Apply PWM signal with amplitude of between 0.7V and Vcc at a frequency of 100Hz to 1kHz (to eliminate LED flicker). The LED current and hence LED brightness is linearly proportional to the duty cycle ratio, so for brightness control adjust duty cycle ratio as necessary. For example, a 10% duty cycle equates to 10% of full LED brightness. L1 VIN VCC D1 68uH/3.5A R4 LED ANODE 10BQ100 1kohms Q1 ZXMN10A09K U2 + C1 D2 ZXT D6717E6 BZX84C47 + 100uF/25V U1 ZXSC400 VCC DRIVE ST DN SENSE C2 C3 47uF/100V 100nF/100V PWM GND D3 R1 VFB BZX84C47 10m Ohm C4 1uF/10V R3 D4 BZX84C7V5 R5 LED CATHODE 20k 10k R2 0.75 Ohm Note: It may be necessary to reduce to value of the output capacitor, C2, to optimize for a 1kHz PWM dimming signal. We recommend a value of 10µF/100V for the best compromise between PWM switching and LED current ripple at full power. ZXSC400EV2 ISSUE 8 - November 2005 4 ZXSC400EV2 Layout considerations PCB tracks should be kept as short as possible to minimise ground bounce, and the ground pin of the device should be soldered directly to the ground plane. It is particularly important to mount the coil and the input/output capacitors close to the device to minimise parasitic resistance and inductance, which will degrade efficiency. The FB pin is a high impedance input, so PCB track lengths to this should also be kept as short as possible to reduce noise pickup. Excess capacitance from the FB pin to ground should be avoided. Below is the recommended layout of the ZXSC400EV2. 25W LED DRIVER BOARD ZXSC400EV2 L1 ZDB246R2 VIN LED ANODE LK1 C2 + R3 + PWM D3 U1 C4 D4 GND D1 U2 VCC R4 Q1 R5 C1 R1 D2 R2 C3 LED CATHODE Copyright Zetex plc 2005 Top Silk Top Copper Bottom Copper Drill File ZXSC400EV2 ISSUE 8 - November 2005 5 ZXSC400EV2 © Zetex Semiconductors plc 2005 Europe Zetex GmbH Streitfeldstraße 19 D-81673 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 email: [email protected] The Americas Zetex Inc 700 Veterans Memorial Hwy Hauppauge, NY 11788 USA Telephone: (1) 631 360 2222 Fax: (1) 631 360 8222 email: [email protected] Asia Zetex (Asia) Ltd 3701-04 Metroplaza Tower 1 Hing Fong Road, Kwai Fong Hong Kong Telephone: (852) 26100 611 Fax: (852) 24250 494 email: [email protected] Corporate Headquarters Zetex Semiconductors plc Zetex Technology Park, Chadderton, OL9 9LL United Kingdom Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 email: [email protected] These offices are supported by agents and distributors in major countries world-wide. This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. For the latest product information, log on to www.zetex.com ZXSC400EV2 ISSUE 8 - November 2005 6