Not Recommended For New Design Evaluation Board information LXE1684 EVALUATION BOARD USER’S GUIDE LX1684 BUCK PWM CONTROLLER Manufactured by: Microsemi Power Management Division Garden Grove Telephone: 714-898-8121 www.Microsemi.com More than solutions – enabling possibilities LXE1684 Evaluation Board Installation Guide Not Recommended For New Design GENERAL DESCRIPTION QUICK INSTALLATION GUIDE It is recommended that you use laboratory power supply with adjustable current limit. Ground and power wires used to connect power supply to LX1684 should be 4 inches or less each. Wires should be at least 18 Gauge wire or larger, we recommend 16 or 14 Gauge stranded wires for all power wires and ground wires. Additional through hole power and ground pads are provided in order to reduce connector resistance. See silkscreen for more details. WWW . Microsemi .C OM The LXE1684 evaluation board is a switching Buck power supply which provides a 3.3V output from a 12V power supply utilizing the LX1684 Microsemi’s integrated controller. It can source 0A to 10A and requires no minimum load for proper voltage regulation. The LXE1684 uses 12V as its main power source and 5V to bias the LX1684 IC. 1. Turn off power to 5V and 12V power supplies. 2. Connect 5V,12V, and GND from power supplies to 5V,12V and GND connectors of LXE1684. 3. Connect GND and 3.3V output to test load. 4. Turn on power supply. ENVIRONMENTAL Ambient Temperature: <70°C INPUT VOLTAGE REQUIREMENTS 12V / 10A ± 10% 5V / 100mA ±5% ELECTRICAL SPECIFICATIONS Parameter Value Output voltage 3.3V, 0A to 10A ±5% Output Current 10A Short Circuit protected. Switching Frequency 175kHZ 75% at 500mA 92% at 1A LXE1684 USER GUIDE Typical Efficiencies 90% at 5A 87% at 10A Copyright © 2001 Rev. 0.1 6/2/06 Page 2 New Product Information LXE1684 Evaluation Board Installation Guide Not Recommended For New Design DETAILED DESCRIPTION Utilizing synchronous Logic Level MOSFET rectification, the LXE1684 features high efficiency conversion (typically 87% at full load of 10A for 12V to 3.3V application). With a switching frequency of about 200KHz, it provides an optimum efficiency and low ripple output voltage over a full range of output current load. WWW . Microsemi .C OM With Both 5V and 12V power supplies readily available on an AT or ATX desktop power supply, the LX1684 provides a flexible option for choosing either 5V or 12V as power source. Differential current sensing allows more accurate current sensing from 12V which is unavailable in the earlier LX1681/LX1682 controllers. The LXE1684 provides lossless HICCUP mode current limiting eliminating the need for an expensive current sense resistor. The unit can survive an output short circuit condition indefinitely without overstressing onboard power MOSFETS and inductor. Power consumption during output short-circuit and during Hiccup mode is less than 10% of 10A full current load. Features • • • • • • • • High efficiency switching 3.3V power supply Up to 92% efficiency for 12V to 3.3V application. Internally compensated 16Mhz bandwidth opamp provides fast transient response Lossless Hiccup RDS_ON sensing current limit protection Voltage mode opamp requires no external compensation Built in MOSFET drivers reduce overall cost. Short Circuit protection: Can sustain output short circuit without overstressing MOSFET and inductors on board, Differential Kelvin current sensing provides superior performance than LX1681/LX1682 in terms of ease of use, accuracy and noise immunity. Capacitor selection The LXE1684 are shipped from factory with aluminum electrolytic capacitors in order to minimize overall cost. The designer should choose long life, 105°C high temperature and high maximum ripple current electrolytic capacitors in order to meet the demand of high ripple currents inherent to DC/DC high current switching power supplies. Traditional aluminum electrolytic capacitors however are bulky in comparison to newer type of special polymer dielectric or organic dielectric capacitors. The LXE1684 PCB layout therefore is designed with both surface mount pads and through hole pads for its power components such as FETs, inductors and capacitors, can be easily reconfigured to use all surface mount components for high performance and low profile space constrained applications such as video cards, memory power supply and other PCI bus and AGP bus multimedia interface cards. Copyright © 2001 Rev. 0.1 6/2/06 Page 3 New Product Information LXE1684 USER GUIDE The major advantage of LX1684 over LX1681 is that with differential current sensing with both positive current sense and negative current sense, the topside power MOSFET can be far away from LX1684 and/or have different voltage and still provide superior performance in comparison with the LX1682. The LX1684 does not limit the power input option to 5V, if current sensing is used. With 5V readily available on desktop AT and ATX power supplies, the LXE1684 can provide a DC to DC power supply which can draw power from 12V, 5V or 3.3V to provide output voltages as low as 1.25V while providing lossless RDS_ON sensing for all power input options. Ripple voltage can be lower than 10mV if high performance Poly capacitors or OSCON capacitors are used. The LX1684 provides stable operation with total output capacitor ESR as low as 5mΩ when used in a DC to DC buck configuration. LXE1684 Evaluation Board Installation Guide Not Recommended For New Design MOSFET Selection The LXE1684 can accommodate Top and Bottom MOSFETs with both through hole and surface mount footprints such as TO-220, SMD220, TO-263,TO-252, SOT-223 such as the Vishay Logic MOSFET SUB45N05-20L. Please refer to LX1684 data sheet for MOSFET selections. For 12V application, care must be taken in selecting MOSFET to make sure that LX1684 junction temperature is within acceptable limits. Die temperature should be less than 125°C. For 12V to 3.3V application, the current flow through the bottom MOSFET is more than twice the current flow through the top MOSFET. The power supply designer therefore should choose a larger MOSFET and larger heat sink for the bottom MOSFET. Please refer to LX1684 data sheet for calculation of power dissipation on the top and bottom MOSFETs. WWW . Microsemi .C OM The top and bottom FETs MUST be Logic level MOSFETs. For a 12V power input application the total gate capacitance of each MOSFET should be less than 50nC. This is due to the fact that SOIC-14 package has a junction to ambient temperature coefficient of 165°C per Watt. Maximum VDS rating of MOSFETs for 12V operation should be at least 30V. LXE1684 Evaluation Board Schematic 12V 10% V IN Power* 5V 5% V IN Controller C5 1µF R1 162 O hm 1 14 FB VCC 2 V OU T = V R EF (1+R1/R2) NC NC SS CS CSP NC G ND VC1 4 Css 0.1µF 5 6 7 12 RSET 3.3K BDR NC TDR C4,C4A,C4B 5817SM T 11 10 PG ND 3x 820µF, 16V D1A0 13 3 R2 100 O hm C1 0.1µF 9 Q1 SUB45N 05-20L L1 is a powdered iron toroid 8 *V PW R can be reconfigured to any voltage between 3V and 13.2V. This change m ay require different a input/output capacitance and changes to the output voltage divider resistors, etc, see data sheet. Q2 SUB45N0520L L1 10µF VO UT 3.3V 10A 4x 1500µF 6.3V C3B,C,D,E LXE1684 USER GUIDE Copyright © 2001 Rev. 0.1 6/2/06 Page 4 New Product Information LXE1684 Evaluation Board Installation Guide Not Recommended For New Design LXE1684 COMPONENT LIST MISCELLANEOUS COMPONENTS Buck PWM Controller N-Channel MOSFET Schottky DIODE Inductor, 10uH Toroid Iron Powder Manufacturer & Part # Microsemi LX1684 Vishay SUB45N05-20L Microsemi 1N5817 Micrometal Reference Designators Qty U1 Q1, Q2 D1A0 L1 1 2 1 1 Reference Designators Qty WWW . Microsemi .C OM Part Description CAPACITORS Part Description Manufacturer & Part # Capacitor, 0.1µF, Ceramic 1206, 50V Any Capacitor, 1500µF, 6.3V, AL Elect. Panasonic EEU-FC0J152 Capacitor, 820µF, 16V, AL Elect. Capacitor, 1µF, Ceramic 1206 Panasonic EEU-FC1C821S Any C1,CSS C3B, C3C, C3D, C3E C4, C4B, C4C C5 1 4 3 1 RESISTORS Part Description Resistor, 162, 1%, 1206 Resistor, 100, 1%, 1206 Resistor, 3.3K, 5%, 1206 Manufacturer & Part # Any Any Any Reference Designators Qty R1 R2 RSET 1 1 1 Additional power and ground through hole pads for improved current conduction and ease of use. User can solder wires directly from power supply and to load without removing components. LXE1684 USER GUIDE Copyright © 2001 Rev. 0.1 6/2/06 Page 5 New Product Information LXE1684 Evaluation Board Installation Guide Not Recommended For New Design SILK SCREEN WWW . Microsemi .C OM Solder Side LXE1684 USER GUIDE Component Side Copyright © 2001 Rev. 0.1 6/2/06 Page 6 New Product Information