DEMO MANUAL DC185 NO-DESIGN SWITCHER DEMO MANUAL DC185 DESCRIPTIO LT1370 6A Switch 2.7V to 12V Input 5V or 12V Output U Demonstration board DC185 is a complete DC/DC stepdown regulator using the LT ®1370 constant frequency, high efficiency converter in a 7-pin DD package. High frequency switching allows the use of small inductors, making this all surface mount solution ideal for spaceconscious systems. , LTC and LT are registered trademarks of Linear Technology Corporation. W U WW PERFOR A CE SU ARY TA = 25°C, VIN = 5V, ILOAD = 1A, VOUT = 12V (jumper J1 removed), S/D pin open, unless otherwise specified. PARAMETER CONDITIONS MIN TYP MAX UNITS Output Voltage Jumper J1 Removed (Note 1) Jumper J1 Inserted 11.6 4.85 12.0 5.00 12.4 5.17 V V 6 8 (Note 2) 2.7 Maximum ISW Input Voltage Range Switching Frequency 440 Output Ripple Voltage 500 10 A 12 V 580 80 kHz mVP-P Line Regulation VIN = 2.7V to 11V, ILOAD = 0.5A 20 mV Load Regulation ILOAD = 10mA to 1.75A 18 mV S/D Shutdown Threshold 0.6 S/D Synchronization Range 600 Supply Current S/D = 0V, ILOAD = 0A (Note 3) Note 1: Output voltage variations include ±1% tolerance of feedback divider network. For tighter voltage range, use lower tolerance resistors. Note 2: With the boost topology, input voltage must always be lower than output voltage. See the LT1370 data sheet for maximum device ratings. 1.3 2 V 800 kHz µA 100 Note 3: The boost topology provides a path from input to output even with the LT1370 in shutdown. Applications are available that remove this direct path and reduce shutdown supply current to 12µA, independent of loading. W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO Maximum Load Current vs Input Voltage Output Efficiency 90 5.5 VIN = 5V VOUT = 12V 88 5.0 4.5 LOAD CURRENT (A) 86 EFFICIENCY (%) Component Side VIN = 3.3V VOUT = 5V 84 82 80 VOUT = 5V 4.0 3.5 3.0 VOUT = 12V 2.5 2.0 1.5 78 1.0 76 0.5 0 0.5 1.0 1.5 2.0 LOAD CURRENT (A) 2.5 3.0 DM185 G01 2 3 4 9 5 7 8 6 INPUT VOLTAGE (V) 10 11 DC185 BP DM185 G02 1 DEMO MANUAL DC185 W W U PACKAGE A D SCHE ATIC DIAGRA SM R4 C7 10Ω 1000pF 5% E1 VIN L1 6.8µH VIN 1 + C1 33µF 16V 6 7 NFB E2 S/D 1 S/D 3 S/S VIN VSW U1 LT1370CR FB GND E3 GND 1 E4 GND 1 D1 MBRD835L 5 2 C5 0.1µF + C2 100µF 16V + C3 100µF 16V E5 VOUT C6 4.7µF DM185 F01 R1 6.19k 1% 1 R4 470Ω 5% R3 28.7k 1% FRONT VIEW VC 4 R2 53.6k 1% J1 5V/12V LINK 7 6 5 4 3 2 1 C4 OPTIONAL VIN NFB VSW GND S/S FB VC R PACKAGE 7-LEAD PLASTIC DD Figure 1. 5V/12V Output Boost Converter LT1370CR PARTS LIST REFERENCE DESIGNATOR C1 C2, C3 C4 C5 C6 C7 D1 E1 to E5 R1 R2 R3 R4 R5 L1 J1 J1 U1 QUANTITY 1 2 1 1 1 1 1 5 1 1 1 1 1 1 1 1 1 PART NUMBER T495D336M016AS T495X107M016AS Optional 08055C104MAT3S 1206YG475MAT3S 08053A102KAT MBRD835L 2501-2 CR10-6191F-T CR10-5362F-T CR10-2872F-T CT10-471J-T CR10-100J-T 501-0726 2802S-02-G2 CCIJ2MM-138-G LT1370CR DESCRIPTION 33µF 16V Tantatum Capacitor, Case-D 100µF 16V Tantalum Capacitor, Case-D VENDOR Kemet Kemet TELEPHONE (714) 640-9320 (714) 640-9320 0.1µF 50V X7R Chip Capacitor, 0805 4.7µF 16V Y5V Chip Capacitor, 1206 1000pF, 25V NPO Chip Capacitor, 0805 SMT Diode, D-Pak Pad Turret, PAD.092 6.19k 1/8W 1% Chip Resistor, 0805 53.6k 1/8W 1% Chip Resistor, 0805 28.7k 1/8W 1% Chip Resistor, 0805 470Ω 1/8W 5% Chip Resistor, 0805 10Ω 1/8W 5% Chip Resistor, 0805 6.8µH 20% Inductor, Qtr-Pak 0.079" Center 2-Pin Header 0.079" Center 2-Pin Shunt 7-Lead DD IC AVX AVX AVX Motorola Mill-Max TAD TAD TAD TAD TAD BH-Elec Comm Con Comm Con LTC (803) 946-0362 (803) 946-0362 (803) 946-0362 (602) 244-3576 (516) 922-6000 (800) 508-1521 (800) 508-1521 (800) 508-1521 (800) 508-1521 (800) 508-1521 (612) 894-9590 (818) 301-4200 (818) 301-4200 (408) 432-1900 U OPERATIO DC185 Operation The DC185 demonstration board is intended for evaluating the LT1370 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 2 LT1370 data sheet for additional specifications and applications information. You may find Linear Technology’s SwitcherCADTM software helpful for creating your own designs. SwitcherCAD is a trademark of Linear Technology Corporation. DEMO MANUAL DC185 U OPERATIO Hook-Up Connect the input supply and measurement instruments to the VIN and GND terminals. The S/D pin (synchronization/shutdown) can be connected to VIN or left open. Connect the output load and measurement instruments to the VOUT and GND terminals. LT1370 Operation The LT1370 is a monolithic, high frequency, current mode switcher. The part can operate from an input supply range of 2.7V to 30V (DC185 maximum VIN = 12V) and draws only 4.5mA quiescent current. The on-chip current limited power switch is guaranteed to 6A minimum switch current with a 0.065Ω typical “on” resistance and a 35V minimum breakdown voltage. The switch, which operates at a fixed frequency of 500kHz, can also be easily synchronized to a higher frequency by driving the S/D pin with a logic-level source. Shutdown is activated by holding the S/D pin below 0.6V, which reduces device supply current to 40µA maximum. mode power supply applications. At these high frequencies, input and output ripple voltages are more a function of the ESR of the capacitor than of the capacitance value. For example, at 500kHz a 100µF capacitor has a capacitive reactance of only 0.003Ω, which is much lower than the limiting 0.1Ω 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. If trace connections to the load are a few inches or more in length, the parasitic inductance, combined with any local load bypass capacitor, will virtually eliminate the spikes at the load. Under normal operating conditions, a 1.245V reference voltage is developed at the Feedback pin. The output voltage is set by R1 and R2, where VOUT = VREF (1 + R2/R1). 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 – 2.48V reference voltage is developed at the NFB pin. Snubber The VC pin is the output of the error amplifier. During normal regulator operation, this pin sits at a voltage between 1V (low output current) and 1.9V (high output current). Loop frequency compensation is performed at the VC pin via an RC network to ground. Diodes COMPONENTS Inductor The inductor is a BH Electronics 501-0726, a 6.8µH toroidal ferrite unit. It was selected for its small size, low EMI, low DCR and 5A ISAT rating. Capacitors (and Input/Output Ripple Voltage) The capacitors on this board are low ESR (effective series resistance) tantalum units specifically designed for switch R4 and C7 form a snubber network across the catch diode, D1. This reduces the spikes seen on the output due to ringing of the catch diode on switching edges. The snubber reduces efficiency typically by 0.5%. Trace inductance and decoupling capacitors on the application board may remove the need for a snubber network. Use diodes designed for switching applications, with adequate current rating and fast turn-on times, such as Schottky or ultrafast 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-circuit conditions, peak diode current is limited to the switch current limit of 7.5A maximum. 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 DC185 U OPERATIO there are a few things to be aware of with high frequency converter layouts. Keep the traces connecting the Switch (Pin 5), output diode, output capacitor and ground return path (Pin 4 and Tab) 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 excessive die temperatures. Please consult the LT1370 data sheet or Linear Technology’s SwitcherCAD software for more information. PCB Layout In many cases, the circuit area traces of the demonstration board may be dropped directly into your PCB layout. If not, U W PCB LAYOUT A D FIL Silkscreen Top Component Side Solder Mask Top Solder Side Solder Mask Bottom Paste Mask Top U PC FAB DRAWI G SYMBOL DIAMETER # OF HOLES PLATED A 0.020 58 Yes B 0.037 2 Yes C 0.025 3 Yes D 0.072 2 No E 0.095 5 Yes TOTAL HOLES 2.000 NOTES: UNLESS OTHERWISE SPECIFIED D A E C B E A A 70 E A E D 4 1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ COPPER CLAD THICKNESS 0.062 ±0.006 TOTAL OF 2 LAYERS A Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 2.000 2. FINISH: ALL PLATED HOLES 0.001 MIN/0.0015 MAX COPPER PLATE ELECTRODEPOSITED TIN-LEAD COMPOSITION BEFORE REFLOW, SOLDER MASK OVER BARE COPPER (SMOBC) 3. SOLDER MASK: BOTH SIDES USING GREEN PC-401 OR EQUIVALENT C E 4. SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK 5. ALL DIMENSIONS ARE IN INCHES dc185f LT/TP 0398 500 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1998