DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER DESCRIPTIO LT1506 Monolithic 4A Switcher 5V to 15V Input 3.3V Output U Demonstration circuits DC237/DC238 are complete DC/DC step-down regulators using the LT(R)1506, constant frequency, high efficiency converter in 7-pin DD (DC238) and SO-8 (DC237) packages. These circuits are primarily used in personal computers, disk drives, portable handheld devices and, in larger systems, as local onboard regulators. High frequency switching allows the use of small inductors, making this all surface mount solution ideal for space conscious systems. , LTC and LT are registered trademarks of Linear Technology Corporation. WW U W PERFORmANCE SU ARY TA = 25C, VIN = 12V, ILOAD = 2A, VOUT = 3.3V, SHDN and SYNC pins open, unless otherwise specified. PARAMETER CONDITIONS MIN TYP MAX UNITS Output Voltage (Note 1) 3.23 3.3 3.42 V Maximum ILOAD (Note 2) 15 V 540 kHz 4 Input Voltage Range 4.5 Switching Frequency 460 Output Ripple Voltage A 500 70 mVP-P Line Regulation 5V to 15V 2 mV Load Regulation ILOAD = 10mA to 4A 14 mV SHDN Lockout Threshold 2.3 2.38 2.46 V SHDN Shutdown Threshold 0.15 0.37 0.6 V Synchronization Range DC237 Only Supply Current SHDN = 0V Note 1: Output voltage variations include 1% tolerance of feedback divider network. For tighter voltage range, use lower tolerance resistors or fixed 3.3V output device, LT1506-3.3. 580 1000 20 kHz A Note 2: For DC237, additional thermal restrictions apply. BOARD PHOTOS DC237 Component Side DC238 Component Side 1 DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER U W TYPICAL PERFOR A CE CHARACTERISTICS 3.3V Output Efficiency Temperature Rise vs Load Current 120 88 100 DIE TEMPERATURE RISE (C) 90 5VIN EFFICIENCY (%) 86 12VIN 84 82 80 78 76 VIN = 5V VOUT = 3.3V DC237 80 DC238 60 40 20 0 0 1 2 4 3 0 1 LOAD CURRENT (A) 2 4 3 LOAD CURRENT (A) DC237/38TA01 DC237/38TA02 W W U PACKAGE A D SCHE ATIC DIAGRA SM DC237 D2* MMBD914LT1 E1 VIN 5V TO 15V C4 1F 10V D3* OPTIONAL + C3 10F 25V 2 1 6 E2 SHDN L1 6.8H E3 GND BOOST VIN U1 SW LT1506CS8 SHDN SYNC GND FB VC 4 D1 MBRD835L 8 7 3 + C5 100F 10V E2 SHDN C3 10F 25V C4 1F 10V 5 2 E3 GND VIN SW U1 LT1506CR SHDN GND 4 *MOVE D2 TO POSITION D3 FOR OUTPUT CURRENTS > 3A FB VC TOP VIEW VIN 1 E4 GND 3 R1 OPTIONAL C2 OPTIONAL + C5 100F 10V + + C7 OPTIONAL R3 4.99k 1% 1 DC238 SCHEM C1 1500pF 50V 6 SHDN 5 VC DC238 R2 1.82k 1% 7 7 SYNC LT1506CS8 DC237 SCHEM C1 1500pF 50V D1 MBRD835L 8 VSW BOOST 2 FB OR 3 SENSE GND 4 S8 PACKAGE 8-LEAD PLASTIC SO L1 6.8H 6 BOOST E5 VOUT 3.3V/4A R3 4.99k 1% D2* MMBD914LT1 + C6 0.47F 10V R2 1.82k 1% E6 SYNC R1 OPTIONAL C2 OPTIONAL D3* OPTIONAL + C7 OPTIONAL 5 *MOVE D2 TO POSITION D3 FOR OUTPUT CURRENTS > 3A E1 VIN 5V TO 15V + C6 0.47F 10V E5 VOUT 3.3V/4A E4 GND FRONT VIEW TAB IS GND 7 6 5 4 3 2 1 R PACKAGE 7-LEAD PLASTIC DD PAK LT1506CR 2 FB OR SENSE BOOST VIN GND VSW SYNC OR SHDN VC DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER PARTS LISTS DC237 REFERENCE DESIGNATOR C1 QUANTITY 1 PART NUMBER DESCRIPTION VENDOR 08055C152MAT2S 1500pF 50V X7R Chip Capacitor AVX (843) 946-0362 TELEPHONE 10F 25V Y5V Chip Capacitor Murata (814) 237-1431 C2 0 C3 1 GRM235Y5V106Z Optional Capacitor C4 1 0805ZC105MAT2S 1F 10V X7R Chip Capacitor AVX (843) 946-0362 C5 1 TPSD107M010R0080 100F 10V TPS Tantalum Capacitor AVX (207) 282-5111 C6 1 0603ZG474MAT3S 0.47F 10V Y5V Chip Capacitor AVX (843) 946-0362 C7 1 D1 1 MBRD835L SMT Diode Motorola (800) 441-2447 D2 1 MMBD914LT1 1N914 Diode Motorola (800) 441-2447 2501-2 Pad Turret Mill-Max (516) 922-6000 Optional Capacitor D3 1 E1 to E6 6 Optional Diode R1 0 R2 1 CR10-1821F-T 1.82k 1/8W 1% Chip Resistor Tad (714) 255-9123 R3 1 CR10-4991F-T 4.99k 1/8W 1% Chip Resistor Tad (800) 508-1521 L1 1 DO3316P-682 6.8H 20% Inductor Coilcraft (847) 639-6400 U1 1 LT1506CS8 SO-8 Linear IC LTC (408) 432-1900 1 DC237 PCB 1 DC237 Stencil Stencil QUANTITY PART NUMBER DESCRIPTION VENDOR 1500pF 50V X7R Chip Capacitor AVX (843) 946-0362 Optional Resistor DC238 REFERENCE DESIGNATOR 08055C152MAT2S TELEPHONE C1 1 C2 0 C3 1 GRM235Y5V106Z 10F 25V Y5V Chip Capacitor Murata (814) 237-1431 C4 1 0805ZC105MAT2S 1F 10V X7R Chip Capacitor AVX (843) 946-0362 C5 1 TPSD107M010R0080 100F 10V TPS Tantalum Capacitor AVX (207) 282-5111 C6 1 0603ZG474MAT3S 0.47F 10V Y5V Chip Capacitor AVX (843) 946-0362 C7 1 D1 1 MBRD835L SMT Diode Motorola (800) 441-2447 D2 1 MMBD914LT1 1N914 Diode Motorola (800) 441-2447 2501-2 Pad Turret Mill-Max (516) 922-6000 Optional Capacitor Optional Capacitor D3 1 E1 to E6 6 Optional Diode R1 0 R2 1 CR10-1821F-T 1.82k 1/8W 1% Chip Resistor Tad (714) 255-9123 R3 1 CR10-4991F-T 4.99k 1/8W 1% Chip Resistor Tad (800) 508-1521 L1 1 DO3316P-682 6.8H 20% Inductor Coilcraft (847) 639-6400 U1 1 LT1506CR 7-Pin DD Pak Linear IC LTC (408) 432-1900 1 DC238 PCB 1 DC238 Stencil Stencil Optional Resistor 3 DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER U OPERATIO DC237 vs DC238 (Temperature vs Package Size) The DC237 and DC238 demonstration boards are intended for evaluation of the LT1506 switching regulator in the SO-8 and 7-pin DD packages respectively. The 7-pin DD package used in DC238 has no SYNC pin, but a version (LT1506CR-SYNC) replaces the SHDN function at Pin 2 with the SYNC function. The primary reason for choosing the SO-8 over the DD package is board space. The DC238 (DD package) occupies an active board area of approximately 0.75 square inches. Optimizing the DC237 board, using a Sumida coil and removing the layout options, a total active area of 0.4 square inches is possible. The DD package is more suitable for higher power or higher ambient temperature applications. Although both boards will supply 4A of output current, DC237 must be thermally derated to 3A continuous at 22C ambient to prevent excessive die temperatures. DC238 can run at 60C ambient at 4A output current. However, the SO-8 package can be used for dynamic loads up to the full rated switch current. shutdown. When the pin is taken below the lockout threshold, switching is disabled. This is typically used for input undervoltage lockout. Grounding the SHDN pin places the LT1506 in shutdown mode. This reduces total board supply current to 20A. Synchronization Synchronization is Available on DC237 Only (SYNC is an Optional Replacement for SHDN on the DD Package).For normal demo board operation, the SYNC pin can be left floating. If unused in the application, it is advisable to tie this pin to ground. To synchronize switching to an external clock, apply a logic-level signal to the SYNC pin. The amplitude must be from a logical low to greater than 2.2V, with a duty cycle from 10% to 90%. The synchronization frequency must be greater than the freerunning oscillator frequency and less than 1MHz. Additional circuitry may be required to prevent subharmonic oscillation. Refer to the LT1506 data sheet for more details. LT1506 Operation The LT1506 data sheet gives a complete description of the part, operation and applications information. The data sheet should be read in conjunction with this demo manual. Hook-Up Solid turret terminals are provided for easy connection to supplies and test equipment. Connect a 0V to 15V, 4.5A power supply across the VIN and GND terminals and the load across the VOUT and GND terminals. When measuring load/line regulation, remember to Kelvin connect to the turrets. Also, when measuring output ripple voltage with an oscilloscope probe, the wire from the probe to the ground clip will act as an antenna, picking up excessive noise. For improved results, the test hook should be removed from the tip of the probe. The tip should be touched against the output turret, with the bare ground shield pressed against the ground turret. This reduces the noise seen on the waveform. Shutdown For normal operation, the SHDN pin can be left floating. SHDN has two output-disable modes: lockout and 4 COMPONENTS Inductor L1 The inductor is a Coilcraft DO3316P-682, a 6.8H unshielded ferrite unit. It was selected for its low cost, small size and 4.6A ISAT rating. The equivalent Coiltronics UP2-6R8 unit can be substituted. If board space is at a premium and higher ripple current is acceptable, solder pads are available for the Sumida CD43-1R8 inductor. This 1.8H unit has a 2.9A ISAT rating. Ripple at 5VIN is 1.1A. This gives a maximum output current of (4.5A - 1.1A) = 3.4A. Input/Output Capacitors C3, C5, C6 and C7 The input capacitor C3 is a Tokin ceramic capacitor. It was selected for its small size, high voltage rating and low ESR (effective series resistance). The input ripple current for a buck converter is high, typically IOUT/2. Tantalum capacitors become resistive at higher frequencies, requiring careful ripple-rating selection to prevent excessive heating. Ceramic capacitors' ESL (effective series inductance) tends to dominate their ESR, making them less susceptible to ripple-induced heating. DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER U OPERATIO The output capacitor C5 is an AVX tantalum capacitor. A ceramic is not recommended as the main output capacitor since loop stability relies on a resistive characteristic at higher frequencies to form a zero. The AVX TPS series was specifically designed for switch-mode power supplies to have very low ESR. At switching frequencies, ripple voltage is more a function of ESR than of absolute capacitance value. If lower output ripple voltage is required, use the optional capacitor C7 to reduce ESR rather than increasing the capacitance of C5. For very low ripple, an additional LC filter in the output may be a less expensive solution. The output contains very narrow voltage spikes because of the parasitic inductance of C5. A small ceramic capacitor, C6, removes these spikes on the demo board. In application, trace inductance and local bypass capacitors will perform this function, negating the need for C6. Catch Diode D1 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 lowers power dissipation in the diode. The MBRD835L has a maximum forward drop of 0.4V at 3A. The reverse voltage rating must be greater than the input voltage. Average diode current is always less than output current, but under a shorted output condition, diode current can equal switch current limit. If the application must withstand this condition, the diode must be rated for maximum switch current. Compensation: C1, C2 and R1 A detailed discussion of frequency compensation can be found in the LT1506 data sheet. C1, a 1500pF capacitor from VC to ground, gives a stable loop response over a wide range of input and output conditions. Options R1 and C2 are included for optimization of the dynamic response to a specific application. Boost Voltage: D2, D3 and C4 A boost voltage of at least 2.8V is required throughout the on-time of the switch to guarantee that it remains saturated. At output currents greater than 3A and higher ambient temperatures, diode D2 must be moved to position D3 to prevent boost from falling below this minimum. For output voltages above 3.3V, diode D2 provides sufficient boost voltage to C4. PCB LAYOUT In many cases, the layout of the demonstration board may be dropped directly into the application with minimal changes. If not, there are several precautions that must be taken when laying out high frequency converter circuits. The high frequency switching path runs from ground, through C3, to the VIN pin of the LT1506, out of the SW pin, through D1 and back to ground. This loop acts as an antenna and will radiate noise if not kept as short as possible. Also, at higher switching currents, the associated trace inductance can cause excessive voltage spikes across the switch. The use of a ground plane will reduce many noise problems. The ground pin of the LT1506 contains some high frequency signal currents, but more importantly, it is the 0V reference for the output voltage. Connect the ground pin directly to the ground plane. The FB and VC components should be kept away from the power components as much as possible. The ground for these components should be separated from power grounds. Run a Kelvin sense to VOUT as required but keep the divider network close to the LT1506 to prevent noise pickup on the FB node. Noise pickup on the VC pin appears as various problems, including poor load regulation, subharmonic oscillation and instability. Thermal management must also be considered. The SO-8 package has a fused ground pin. Soldering this pin to a large copper area will significantly reduce its thermal resistance. Solder-filled feedthroughs close to the ground pin provide a good thermal path to the ground plane. For the DD package, the grounded tab should be treated in the same manner. For more information or advice, contact the LTC Applications department. 5 DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER U W PCB LAYOUT A D FIL 6 (DC237) Component Side Silkscreen Component Side Component Side Solder Mask Component Side Paste Mask Solder Side Solder Side Solder Mask DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER U W PCB LAYOUT A D FIL (DC238) Component Side Silkscreen Component Side Component Side Solder Mask Component Side Paste Mask Solder Side Solder Side Solder Mask 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. 7 DEMO MANUAL DC237/DC238 NO-DESIGN SWITCHER U PC FAB DRAWI GS DC237 2.000" C A D D A B 2.000" D D B NOTES: UNLESS OTHERWISE SPECIFIED 1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ COPPER CLAD, THICKNESS 0.062 0.006 TOTAL OF 2 LAYERS 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 SR1020 OR EQUIVALENT 4. SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK 5. ALL DIMENSIONS IN INCHES 6. SCORING 0.017 B C SYMBOL DIAMETER NUMBER OF HOLES A 0.020 38 B 0.025 7 C 0.072 2 D 0.095 6 TOTAL HOLES 53 DC237 FD DC238 2.000" B A C C A C 2.000" NOTES: UNLESS OTHERWISE SPECIFIED 1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ COPPER CLAD, THICKNESS 0.062 0.006 TOTAL OF 2 LAYERS 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 SR1020 OR EQUIVALENT 4. SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK 5. ALL DIMENSIONS IN INCHES 6. SCORING 0.017 B SYMBOL DIAMETER NUMBER OF HOLES A 0.020 30 B 0.072 2 C 0.095 5 TOTAL HOLES 37 DC238 FD 8 Linear Technology Corporation dc2378f LT/TP 0299 500 * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 FAX: (408) 434-0507 www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1999