DEMO MANUAL DC053A DEMONO-DESIGN MANUAL SWITCHER DC053A LT1372/LT1377 5V to 12V Step-Up Converters DESCRIPTIO U Demonstration board DC053A is a complete DC/DC stepup switching regulator using the LT ®1372 or the LT1377 constant frequency, high efficiency converter in an 8-pin SOIC package. High frequency switching allows the use of W U WW PERFOR A CE SU ARY very small inductors, making this all surface mount solution ideal for space conscious systems. , LTC and LT are registered trademarks of Linear Technology Corporation. TA = 25°C, VIN = 5V, S/S pin open, unless otherwise specified. PARAMETER CONDITIONS MIN TYP MAX UNITS Output Voltage R2 = R3 = 1% (Note 1) 11.60 12.04 12.50 Output Current VIN = 5V 250 Input Voltage Range (Note 2) 2.7 Switching Frequency LT1372 LT1377 500 1 kHz MHz Output Ripple Voltage ILOAD = 250mA ILOAD = 250mA (Note 3) VOUT2, ILOAD = 250mA 150 80 3 mVP-P mVP-P mVP-P V mA 11 V Supply Current ILOAD = 0A 4.5 mA Shutdown Supply Current ILOAD = 0A, VS/S = 0V (Note 4) 100 µA Note 1: The reference voltage tolerance of the LT1372/LT1377 is ±1.6% over temperature. Output voltage is a worst-case summation of R2, R3 and reference tolerances, plus feedback input current times R3. For a tighter output voltage range, use lower tolerance feedback resistors, or a fixed voltage version of the LT1372/LT1377 (consult Linear Technology Marketing). Note 2: Increase L1 to 10µH for VIN < 4.75V or to 15µH for VIN < 3.3V. Note 3: To reduce output ripple voltage, change C7 to a 2.2µF ceramic chip capacitor (Tokin 1E225ZY5U-C203). Note 4: Single inductor step-up converters have a direct path from the input supply to the output, and therefore draw some supply current even when the LT1372/LT1377 is in shutdown. Shutdown supply current will also increase with the addition of an output load. Applications are available which remove this direct path and reduce shutdown supply current to 30µA maximum, independent of loading. W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO 12V Output Efficiency Maximum Output Current vs Input Voltage* VIN = 5V VOUT = 12V 0.9 90 EFFICIENCY (%) Component Side 1.0 MAXIMUM OUTPUT CURRENT (A) 100 80 70 60 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 50 0.01 0.1 OUTPUT CURRENT (A) 1 DC053A G01 0 2 3 4 9 5 7 8 6 INPUT VOLTAGE (V) 10 11 DC053A BP DC053A G02 *INCREASE L1 TO 10µH FOR VIN < 4.75V OR TO 15µH FOR VIN < 3.3V 1 DEMO MANUAL DC053A W W U PACKAGE A D SCHE ATIC DIAGRA SM VIN 5V L1* 4.7µH E2 + OPTIONAL OUTPUT FILTER L2** 1µH C3 22µF 25V + E1 S/S 4 S/S NC 3 1 C1 0.047µF C2 0.0047µF 5 VIN 8 VSW NFB U1 LT1372/LT1377 FB VC GNDS GND 6 R1 2k 2 7 D1 MBRS130 C6 4.7µF 25V E4 VOUT 12V 0.25A R3 53.6k, 1% R2 6.19k 1% TOP VIEW E6 VOUT2 12V 0.25A + C4 22µF 25V + C5 OMIT VC 1 8 VSW FB 2 7 GND NFB 3 6 GNDS S/S 4 5 VIN S8 PACKAGE 8-LEAD PLASTIC SO LT1372CS8 LT1377CS8 C7 0.1µF (NOTE 4) E3 E5 GND GND *SUMIDA CD43-4R7KC **MILLER PM20-1R0K NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTOR VALUES OHMS, 1/8W, 5% 2. ALL CAPACITOR VALUES µF, 50V, 20% 3. ALL POLARIZED CAPACITOR AVX TPS SERIES OR EQUIVALENT 4. PLACE C7 AT THE LOAD DC053A F01 Figure 1. Switching Regulator 5V to 12V, 0.25A; 500kHz for the LT1372 and 1MHz for the LT1377 PARTS LIST REFERENCE DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE C1 1 AVX 12065C473MAT2A 0.047µF, 50V, 20%, X7R Capacitor AVX C2 1 AVX 12065C472MAT2A 0.0047µF, 50V, 20%, X7R Capacitor AVX (803) 946-0362 C3, C4 2 AVX TPSD226M025R0200 22µF, 25V, 20%, Tantalum Capacitor AVX (207) 282-5111 AVX 12065C104MAT2A 0.1µF, 50V, 20%, X7R Capacitor AVX (803) 946-0362 C5, C6 0 C7 1 (803) 946-0362 Capacitor, Optional (See Text) D1 1 MBRS130LT3 30V, 1A, Schottky Diode Motorola (602) 244-5768 E1 to E5 5 1502-2 2-Turret, 0.092 Terminal Keystone (718) 956-8900 E6 0 L1 1 CD43-4R7KC 4.7µH, SMT Inductor Sumida (708) 956-0666 2k, 5%, SMT1206 Resistor AVX (803) 946-0524 Terminal, Optional (See Text) L2 0 R1 1 AVX CR32-202J-T Inductor, Optional (See Text) R2 1 AVX CR32-6191F-T 6.19k, 1%, SMT 1206 Resistor AVX (803) 946-0524 R3 1 AVX CR32-5362F-T 53.6k, 1%, SMT-1206 Resistor AVX (803) 946-0524 U1* 1 LT1372CS8 SO-8, LT1372, Switching Regulator IC LTC® (408) 432-1900 U1* 1 LT1377CS8 SO-8, LT1377, Switching Regulator IC LTC (408) 432-1900 *The two demo board versions are: DC53A-A: U1 = LT1372CS8 DC53A-B: U1 = LT1377CS8 2 DEMO MANUAL DC053A U OPERATIO DC053A Operation This DC053A demonstration board is intended for evaluating the LT1372/LT1377 switching regulator in a typical step-up application. Solid turret terminals are provided for easy connection to test equipment. A device pinout and board schematic are shown in Figure 1. Please refer to the LT1372/LT1377 data sheet for additional specifications and applications information. Also useful is Linear Technology’s SwitcherCAD software when creating your own designs. tween 1V (low output current) and 1.9V (high output current). The VC pin is also where loop frequency compensation is performed with an RC network to ground. COMPONENTS Inductors Connect the input supply and measurement instruments to the VIN and GND terminals on the left side of the board. The S/S pin (synchronization/shutdown) can be connected to VIN or left open. Connect the output load and measurement instruments to the VOUT and GND terminals on the right side of the board. VOUT2 is for evaluating an optional output filter and can be left open. The inductor is a Sumida CD43-4R7KC, which is a 4.7µH unshielded ferrite unit. It was selected for low cost and small physical size. Similar units are available from other manufacturers. There are benefits to higher frequency switching (1MHz LT1377 versus 500kHz LT1372) and higher value inductors. Both higher frequency switching and higher value inductors allow more output current because they reduce peak current in the switch. Both also reduce input ripple voltage and output ripple voltage. An inductor with a closed magnetic path (i.e., E-core or toroid) may also be chosen to reduce the RFI/EMI of the circuit. LT1372/LT1377 Operation Capacitors (and Input/Output Ripple Voltage) The LT1372/LT1377 are monolithic high frequency current mode switchers. Each device can operate from an input supply range of 2.7V to 25V (DC053A maximum VIN = 11V), and draws only 4mA quiescent current. The onchip current limited power switch is guaranteed to 1.5A minimum switch current with a 0.5Ω typical “on” resistance and a 35V minimum breakdown voltage. Running at a fixed frequency of 500kHz (LT1372) or 1MHz (LT1377), switching can also be easily synchronized to a higher frequency by driving the S/S pin with a logic level source. Shutdown is activated by pulling the S/S pin below 0.6V, which reduces device supply current to 30µA maximum. The capacitors on this board are low ESR (Effective Series Resistance) tantalum units specifically designed for switchmode power supply applications. At these high frequencies, input and output ripple voltages are more a function of the ESR of the capacitor than the capacitance value. For example, at 500kHz a 22µF capacitor has a capacitive reactance of only 0.014Ω, which is much lower than the limiting 0.2Ω maximum ESR of the capacitors used. Therefore, if a reduction in input or output ripple voltage is required, use two or more capacitors in parallel instead of a larger value capacitor. If very low output ripple voltage is needed, adding an output LC filter may be a cheaper solution. The output contains very narrow voltage spikes because of the parasitic inductance of the output capacitor. Due to their high frequency nature, the amplitude of the spikes is determined by the ESL (Effective Series Inductance) of the output capacitor. But this also makes them easy to filter. Small 0.1µF ceramic chip capacitors work well in reducing the spikes, and if the traces connecting to the load are a few inches or more, the parasitic inductance of the traces combined with any local load bypass capacitor will virtually eliminate the spikes at the load. Hook-Up Under normal operating conditions, a 1.245V reference voltage is developed at the Feedback pin. The output voltage is set by R2 and R3, where VOUT = VREF (1 + R3/R2). Although not used in this application, the part also has a Negative Feedback pin (NFB) which can be used to set the output voltage of positive-to-negative converters. When in use, a – 2.49V reference voltage is developed at the NFB pin. The VC pin is the output of the error amplifier. During normal regulator operation this pin sits at a voltage be- Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 3 DEMO MANUAL DC053A U OPERATIO Diodes sive die temperatures. Please consult the LT1372/LT1377 data sheet or Linear Technology’s SwitcherCAD software for more information. Use diodes designed for switching applications with adequate current rating and fast turn on times, such as Schottky or ultra-fast diodes. In selecting a diode, the basic parameters of interest are forward voltage, maximum reverse voltage, average operating current and peak current. Lower forward voltage yields higher circuit efficiency and lower power dissipation in the diode. The worst-case reverse voltage is equal to the output voltage. The average diode current will be equal to the output current, but the peak diode current can be many times higher than the output current. Except for output short conditions, peak diode current is limited to the switch current limit of 2.4A maximum. PCB Layout In many cases, the circuit area traces of the demonstration board may be dropped directly into your PCB layout. If not, there are a few things to be aware of with high frequency converter layouts. Keep the traces connecting the Switch (Pin 8), output diode, output capacitor and Ground pin (Pin 7) as short as possible. This will reduce RFI and limit the voltage spikes caused by parasitic inductance. Keep the more sensitive components, mainly the feedback resistors and VC pin network, away from the high current switching components. Thermal Considerations Care should be taken to ensure that the worst-case input voltage and load current conditions do not cause exces- U W PCB LAYOUT A D FIL Component Side Silkscreen Component Side Solder Side Component Mask U PC FAB DRAWI G 2.000 B A A NOTES: 1. FINISHED MATERIAL IS FR4, 0.062 THICK, 2-OZ COPPER 2. PCB WILL BE DOUBLE-SIDED WITH PLATED THROUGH-HOLES 3. PTH SIZES AFTER PLATING, 0.001 MIN WALL THICKNESS 4. SOLDER MASK BOTH SIDES USING PC401 OR EQUIVALENT 5. SILKSCREEN COMPONENT SIDE USING WHITE NONCONDUCTIVE INK 6. ALL DIMENSIONS IN INCHES, ±0.005 7. ALL HOLE SIZES AFTER PLATING, – 0 TO 0.003 MAX 2.000 HOLE CHART SYMBOL DIAMETER QTY PLT A A A 0.200 B Solder Mask 4 Linear Technology Corporation A NONE 0.020 3 YES A 0.094 6 YES 0.062 2 B NO TOTAL HOLES 11 0.400 DC053A FAB LT/GP 0895 500 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1995