Application Note 54 March 1993 Power Conversion from Milliamps to Amps at Ultra-High Efficiency (Up to 95%) Dimitry Goder Randy Flatness INTRODUCTION High efficiency is frequently the main goal for power supplies in portable computers and hand-held equipment. Efficient converters are necessary in these applications to minimize power drain on the input source (batteries, etc.) and heat buildup in the power components, allowing for smaller, lighter, and longer-lived systems. Power conversion efficiency must be in the 90% range in order to meet these goals. This application note features power supply circuits that satisfy these design requirements and attain high efficiency over a wide operating range. The recent development of the LTC®1142, LTC1143, LTC1147, LTC1148, and LTC1149 makes ultra-high efficiency conversion possible. In addition, the LTC1148, LTC1149, and LTC1142 are synchronous switching regulators, achieving high efficiency conversion at output currents in excess of 10A. These controllers feature a current mode architecture that has automatic Burst ModeTM operation at low currents. This technology makes 90% efficiencies possible at output currents as low as 10mA, maximizing battery life while a product is in sleep or standby mode. These ultra-high efficiency converters also implement constant off-time architecture, fully synchronous switching and low dropout regulation. All these features make this series of converters a really excellent choice for a vast variety of applications. Achieving high efficiency is one of the primary goals of switching regulator design. Every application circuit shown in this note includes detailed efficiency graphs. Almost all of the magnetic parts used in the circuits are standard products, available off-the-shelf from various manufacturers. and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. AN54-1 Application Note 54 TABLE OF CONTENTS Buck LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology ................................................................ Figure 1 LTC1148: (5V-14V to 5V/2A) Buck Converter .................................................................................................................. Figure 2 LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology...................................... Figure 3 LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ............................................................. Figure 4 LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology ............................................................. Figure 5 LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter ..................................................................................... Figure 6 LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter .................................................................................... Figure 7 LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter ........................................................................................... Figure 8 LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs ................ Figure 9 LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter ....................................................................................... Figure 10 LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter ........................................................................................ Figure 11 LTC1149: (16VRMS to 13.8/10A) Buck Converter ........................................................................................................... Figure 12 LTC1149: (32VRMS to 27.6V/5A) Buck Converter ........................................................................................................... Figure 13 LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology .............................................................. Figure 14 LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ........................................................... Figure 15 LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology .......................................................... Figure 16 LTC1148: (10V-14V to 5V/10A) High Current Buck Convert .......................................................................................... Figure 17 LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter ................................................................... Figure 18 LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter ................................................................. Figure 19 LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter ............................................................... Figure 20 LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter ................................................................................ Figure 26 LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter ................................................................................ Figure 27 LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage Buck Converter .............................................................................. Figure 28 LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter ............................................................................... Figure 29 LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter ...................................................... Figure 30 LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter ............................ Figure 31 Single LTC1149: Dual Output Buck Converter ............................................................................................................... Figure 35 LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter ................................................................................ Figure 36 LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter......................................................................... Figure 37 AN54-3 AN54-4 AN54-5 AN54-6 AN54-7 AN54-8 AN54-9 AN54-10 AN54-11 AN54-12 AN54-13 AN54-14 AN54-15 AN54-16 AN54-17 AN54-18 AN54-19 AN54-20 AN54-21 AN54-22 AN54-28 AN54-29 AN54-30 AN54-31 AN54-32 AN54-34 AN54-38 AN54-39 AN54-40 Buck-Boost and Inverting Topologies LTC1148: (4V-14V to 5V/1A) SEPIC Converter .............................................................................................................. Figure 21 LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter ................................................................................. Figure 22 LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter ...................................................................................... Figure 23 LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter .............................................................................................. Figure 24 AN54-23 AN54-24 AN54-25 AN54-26 Boost LTC1148: (2V-5V to 5V/1A) Boost Converter ................................................................................................................. Figure 25 AN54-27 Battery Charging Circuits LTC1148: High Efficiency Charger Circuit ...................................................................................................................... Figure 32 LTC1148: High Voltage Charger Circuit ......................................................................................................................... Figure 33 LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger ......................................... Figure 34 AN54-35 AN54-36 AN54-37 Appendix A Topics of Common Interest ........................................................................................................................................................... AN54-40 Appendix B Suggested Manufacturers ............................................................................................................................................................. AN54-42 AN54-2 Application Note 54 LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology A basic LTC1148 application is shown in Figure 1A. This is a conventional step-down converter that provides 5V output at 1A maximum output current. All the components used are surface mounted and no heat sink is required. During Q1 on-time, inductor L1's current is sensed by R2 and monitored by an internal current sensing comparator. To filter out noise from the current sense waveform, C6 is added to the circuit. When the current ramp reaches a preset value, Q1 is turned off, and a clamp diode D1 starts conducting for a short period of time, until the internal control logic senses that Q1 is completely off. Then NDRIVE output goes high turning Q2 on, which shorts out D1. This provides synchronous rectification and significantly reduces conduction losses during Q1’s off-time. This regulator has a constant off-time defined by the timing capacitor C5. To control the output, on-time is varied, changing the operating frequency and therefore, the duty cycle. If the input voltage is reduced, frequency decreases keeping output voltage at the same level. Q1’s on-time stretches to infinity with low input voltage, providing 100% duty cycle and very low dropout. Under dropout conditions, the output voltage follows the input, less any resistive losses in Q1, L1 and R2. Under conditions of light output currents, the regulator enters Burst Mode operation to ensure high efficiency. Continuous operation is interrupted by an internal voltage sensing comparator with built-in hysteresis. in this mode both Q1 and Q2 are turned off and the comparator monitors decreasing output voltage. When the output capacitor discharges below a fixed threshold, operation resumes for a short period of time bringing the output voltage back to normal. Then the regulator shuts down again conserving quiescent current. Under Burst Mode operation the output ripple is typically 50mV as set by the hysteresis in the comparator. + VIN 5V TO 14V C3 22µF × 2 25V 3 + C1 1µF C2 0.1µF VIN 10 PDRIVE 1 Q1 Si9430DY SHUTDOWN L1 1 4 LTC1148-5 6 SENSE – R1 1k 4 C4 3300pF X7R C5 390pF NPO CT NDRIVE SGND 11 C1 C3 C7 Q1 Q2 D1 3 R2 0.1Ω 5V 1A 100µH SENSE + ITH 2 8 7 C6 0.01µF + 14 PGND Q2 Si9410DY D1 MBRS140T3 C7 220µF 10V 12 (Ta) AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 40V R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ® CORE AN54 • F01A ALL OTHER CAPACITORS ARE CERAMIC QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 200mA Figure 1A. LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology Kool Mµ is a registered trademark of Magnetics, Inc. AN54-3 Application Note 54 Figure 1B shows efficiency versus output current for three different input voltages. Generally speaking, efficiency drops as a function of input voltage due to gate charge losses and LTC1148 DC bias current. The curves converge at maximum output current as these losses become less significant. 100 VIN = 6V EFFICIENCY (%) 90 VIN = 10V VIN = 14V 80 70 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) LTC1148: (5V-14V to 5V/2A) Buck Converter A step-down regulator with 2A output current capability is shown in Figure 2A. To provide higher output power levels the sense resistor value is decreased, thus increasing the current limit. This also increases maximum allowable ripple current in the inductor, so its value can be reduced. Note that timing capacitor C5 is changed to optimize performance for a standard inductor value. In this Figure C7 consists of two parallel capacitors ensuring minimum capacitance requirement for all conditions. A circuit board has been laid out for this circuit and has subsequently been thoroughly tested under full operating conditions and optimized for mass production requirements. A Gerber file for the board is available upon request. 1 AN54 • F01B Figure 1B. LTC1148: (5V-14V to 5V/1A) Buck Converter Measured Efficiency VIN 5V TO 14V + + C2 0.1µF C1 1µF 3 VIN 10 PDRIVE 1 Q1 Si9430DY SHUTDOWN C3 22µF × 3 25V L1 62µH R2 0.05Ω 5V 2A LTC1148-5 6 SENSE – R1 1k C4 3300pF X7R C1 C3 C7 Q1 Q2 D1 R2 L1 SENSE + ITH 4 C5 470pF NPO CT SGND 11 NDRIVE PGND 8 7 C6 0.01µF + 14 Q2 Si9410DY D1 MBRS140T3 12 (Ta) AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 40V KRL SL- 1-C1-0R050J Pd = 1W COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE (THROUGH HOLE) QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 400mA ALL OTHER CAPACITORS ARE CERAMIC AN54 • F02A Figure 2A. LTC1148: (5V-14V to 5V/2A) Buck Converter AN54-4 C7 220µF × 2 10V Application Note 54 100 LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology VIN = 6V EFFICIENCY (%) 90 VIN = 10V Figure 3A presents essentially the same circuit as Figure 2A, but implementing changes to operate at a higher frequency. Timing capacitor C5 is reduced to achieve higher switching rate. This approach allows the use of a smaller value inductor with surface mount technology, resulting in a more compact design. VIN = 14V 80 70 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 2 AN54 • F02B Figure 2B. LTC1148: (5V-14V to 5V/2A) Buck Converter Measured Efficiency VIN 5V TO 14V + + C2 0.1µF C1 1µF 3 VIN 10 C3 22µF × 3 25V PDRIVE 1 Q1 Si9430DY SHUTDOWN 1 4 6 C1 C3 C7 Q1 Q2 D1 R2 L1 LTC1148-5 SENSE + SENSE – R1 1k C4 3300pF X7R ITH 4 C5 220pF NPO CT SGND 11 NDRIVE PGND L1 33µH 2 3 R2 0.05Ω 5V 2A 8 7 C6 0.01µF + 14 Q2 Si9410DY D1 MBRS140T3 C7 220µF × 2 10V 12 (Ta) AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 40V KRL SL-1-C1-0R050J Pd = 1W COILTRONICS CTX33-4 DCR = 0.06Ω Kool Mµ CORE QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 400mA ALL OTHER CAPACITORS ARE CERAMIC AN54 • F03A Figure 3A. LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology AN54-5 Application Note 54 Let us compare efficiency graphs in Figures 2B and 3B. Gate charge losses are directly proportional to operating frequency, and as a result the efficiency of Figure 3A is 100 VIN = 6V EFFICIENCY (%) 90 VIN = 10V 80 decreased. However, the effect is most noticeable at high input voltages and low currents. At maximum load I2R losses dominate so that the regulator performance varies only slightly. These two circuits illustrate the fact that best overall efficiency is reached at moderate frequencies. They represent a nice example of compromising between regulator compactness and efficiency. LTC1148: (4V-14V to 3.3V) Buck Converters with Surface Mount Technology VIN = 14V 70 Figures 4A and 5A show application circuits for the LTC1148-3.3 which provides a fixed 3.3V output. The circuits deliver 1A and 2A output currents, and use exactly the same circuit configuration and component values as Figures 1A and 2A. Even though the LTC1148 can achieve low dropout, the minimum input voltage is limited to 4V to meet requirements for power MOSFET gate drive, and to ensure proper operation of the LTC1148 internal circuitry. 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 2 AN54 • F03B Figure 3B. LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter Measured Efficiency VIN 4V TO 14V + + C1 1µF C2 0.1µF 3 VIN 10 C3 22µF × 2 25V PDRIVE 1 Q1 Si9430DY SHUTDOWN 1 4 6 LTC1148-3.3 SENSE + SENSE – R1 1k 4 C4 3300pF X7R C1 C3 C7 Q1 Q2 D1 R2 L1 ITH C5 560pF NPO CT SGND 11 NDRIVE PGND L1 100µH 2 3 R2 0.1Ω 8 7 C6 0.01µF + 14 Q2 Si9410DY D1 MBRS140T3 C7 220µF 10V 12 (Ta) AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 40V KRL SP-1/2-A1-0R100J Pd = 0.75W COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 250mA ALL OTHER CAPACITORS ARE CERAMIC Figure 4A. LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology AN54-6 3.3V 1A AN54 • F04A Application Note 54 Low output voltage causes efficiency degradation at light loads when the chip’s DC supply current and gate charge current play major parts in total losses. Figures 4B and 5B illustrate this point as the efficiency falls off below 10mA output current. High input voltage compounds the problem. 100 100 VIN = 5V 90 VIN = 5V 90 EFFICIENCY (%) EFFICIENCY (%) VIN = 10V VIN = 10V 80 70 VIN = 14V 80 VIN = 14V 70 60 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) 50 0.001 1 0.01 0.1 OUTPUT CURRENT (A) Figure 4B. LTC1148: (4V-14V to 3.3V/1A) Buck Converter Measured Efficiency C1 1µF C2 0.1µF 3 VIN 10 6 PDRIVE 4 C4 3300pF X7R C5 470pF NPO 1 Q1 Si9430DY SHUTDOWN ITH LTC1148-3.3 SENSE + SENSE – R1 1k C1 C3 C7 Q1 Q2 D1 R2 L1 Figure 5B. LTC1148: (4V-14V to 3.3V/2A) Buck Converter Measured Efficiency + + CT NDRIVE SGND 11 2 AN54 • F05B AN54 • F04B VIN 4V TO 14V 1 C3 22µF × 3 25V L1 50µH R2 0.05Ω 3.3V 2A 8 7 C6 0.01µF + 14 PGND Q2 Si9410DY D1 MBRS140T3 C7 220µF × 2 10V 12 (Ta) AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 40V KRL SL-1-C1-0R050J Pd = 1W COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE (THROUGH HOLE) QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 450mA ALL OTHER CAPACITORS ARE CERAMIC AN54 • F05A Figure 5A. LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology AN54-7 Application Note 54 100 LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter EFFICIENCY (%) Many new microprocessor designs require 3.3V, yet they are used in systems where 5V is the primary source of power. A high efficiency 5V to 3.3V converter is drawn in Figure 6A. It supplies up to 5A load using only surface mount components. Two P-channel MOSFETs are connected in parallel to decrease their conduction losses. Efficiency at 5V input is 90%; this means only 1.6W is lost. The lost power is distributed between RSENSE, L1 and the power MOSFETs, thus no heat sinking is required. 90 80 70 0.001 0.01 0.1 1 OUTPUT CURRENT (A) 10 AN54 • F06B Figure 6B. LTC1148: (5V to 3.3V/5A) Buck Converter Measured Efficiency VIN 5V + C2 0.1µF C1 1µF 3 Q2 Si9433DY VIN PDRIVE 1 Q1 Si9433DY + L1 5µH 10 6 R1 470Ω 4 C4 3300pF C1 C3 C6 Q1, Q2 Q3 D1 R2 L1 C5 150pF NPO SHUTDOWN ITH SENSE + 8 SENSE – 7 CT NDRIVE SGND 11 C7 0.01µF 14 PGND Q3 Si9410DY D1 MBRS140T3 12 TANTALUM PANASONIC ECG-COJB330 AVX (Ta) TPSE227K01R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 12V DCRON = 0.075Ω Qg = 60nC SILICONIX NMOS BVDSS = 30V DCRON = 0.050Ω Qg = 30nC MOTOROLA SCHOTTKY VBR = 30V KRL MP-2A-C1-0R020J Pd = 3W COILTRONICS CTX02-12483-1 Figure 6A. LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter AN54-8 VOUT 3.3V 5A R2 0.02Ω LTC1148-3.3 0V = NORMAL >2V = SHUTDOWN C3 33µF 6.3V ×2 + C6 220µF 10V ×3 AN54 • F06A Application Note 54 100 LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter 95 90 EFFICIENCY (%) Some processors require 3.5V or other intermediate voltage derived from a 5V supply. A good solution for them is the circuit in Figure 7A. An adjustable version of the LTC1148 allows precise output voltage adjustment, while preserving efficiencies of 95%. The output voltage is set by resistors R3 and R4. 85 80 75 70 65 60 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 4 AN54 • F07B Figure 7B. LTC1148: (5V to 3.5V/3A) Measured Efficiency VIN 5V + + Q1 Si9433DY 1 C2 0.1µF 2 3 4 5 6 C5 180pF NPO C4 3300pF X7R 7 R1 510Ω NDRIVE PDRIVE NC VIN CT INT VCC ITH SENSE – NC LTC1148 PGND SGND SHUTDOWN ADJ SENSE + D1 MBRS130T3 14 C3 22µF 25V ×2 Q2 Si9410DY 13 L1 10µH 12 11 10 SHUTDOWN 100pF 9 R4 10k 1% + 8 C6, 0.01µF R2 0.033Ω R3 18.2k 1% C6 100µF 10V ×3 + VOUT C3 C6 Q1 Q2 D1 R2 L1 AVX (Ta) TPSD226M025R0200 ESR = 0.20Ω IRMS = 0.866A AVX (Ta) TPSD107M01R0100 ESR = 0.10Ω IRMS = 1.225A SILICONIX PMOS BVDSS = 12V DCRON = 0.110Ω Qg = 20nC SILICONIX NMOS BVDSS = 30V DCRON = 0.05Ω Qg = 30nC MOTOROLA SCHOTTKY VBR = 30V KRL SL-C1-1/2-0R033J Pd = 1/2W COILTRONICS CTX10-4 DCR = 0.038Ω Kool Mµ CORE 3.5V 3A VOUT = 1.25V (1 + R3/R4) AN54• F07A Figure 7A. LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter AN54-9 Application Note 54 Previous circuits can accept inputs up to 14V. If higher input voltage is required the LTC1149 can be used. This IC is designed for inputs of up to 48V. A basic step-down application circuit is shown in Figure 8A. It operates in the same fashion as the circuit in Figure 1A and provides 5V/2A output. However, different MOSFETs are used since they must withstand 48V between source and drain. High current efficiency exceeds 92% over wide range of input voltages. Since the control and drive circuitry are powered directly from the input line, DC bias current and gate charge current result in slightly lower efficiency at light and moderate loads due to high input voltage (relative to LTC1148). This characteristic is eliminated in the circuit of Figure 11A. A circuit board has been laid out for this circuit and has subsequently been thoroughly tested under full VIN 10V TO 48V C4 1µF C5 0.1µF 5 C6 0.068µF Z5U 16 10 15 7 6 R1 1k C7 3300pF X7R C2 C4 C10 Q1 Q2 D1 D2 R2 L1 100 90 VIN = 12V 80 VIN = 24V VIN = 36V 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) C8 680pF NPO 2 VCC PGATE VCC PDRIVE CAP SD1 LTC1149-5 SENSE + SD2 SENSE – Q1 IRFU9024 C3 0.047µF Z5U C2 330µF 63V L1 62µH R2 0.05Ω 5V 2A 9 8 C9 0.01µF + ITH CT SGND 11 PGND 12 NGATE RGND 13 Q2 IRFU024 D2 MBR160 C10 220µF × 2 10V 14 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A (Ta) SANYO (OS-CON) 10SA22OM ESR = 0.035Ω IRMS = 2.360A IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-1A-C1-0R050J Pd = 1W COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA ALL OTHER CAPACITORS ARE CERAMIC Figure 8A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter AN54-10 2 Figure 8B. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter Measured Efficiency 1 4 1 AN54 • F08B D1 1N4148 VIN VIN = 48V 70 + C1 0.1µF 3 + operating conditions and optimized for mass production requirements. A Gerber file for the board is available upon request. EFFICIENCY (%) LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter AN54 • F08A Application Note 54 LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs Remember, the “best” MOSFET selection depends on the particular application. 100 VIN 10V TO 48V C4 1µF C5 0.1µF 5 C6 0.068µF Z5U 16 10 15 7 6 R1 1k C7 3300pF X7R C2 C4 C10 Q1 Q2 D1 D2 R2 L1 VIN = 12V 80 VIN = 24V 70 VIN = 48V 60 VIN = 36V 50 0.001 0.01 0.1 OUTPUT CURRENT (A) C8 680pF NPO VCC PDRIVE VCC CAP PGATE SD1 LTC1149-5 SENSE + SD2 SENSE – 1 4 2 AN54 • F09B D1 1N4148 2 VIN 1 Figure 9B. LTC1149: (10V-48V to 5V/2A) Measured Efficiency with Large P-Channel and N-Channel MOSFETs + C1 0.1µF 3 + 90 EFFICIENCY (%) Figure 9A is similar to Figure 8A with much larger MOSFETs (TO220 package). These transistors have lower RDS(ON) which reduces their I2R losses by roughly a factor of 2. However, the efficiency improves (compared to Figure 8B) only at 2A output current with minimum input voltage. Under other conditions higher gate capacitance causes increased gate charge current leading to higher driver loss. Also for high input voltages (roughly greater than 24V), transition losses play a significant part. These losses are proportional to the reverse transfer capacitance CRSS, maximum output current, and the square of input voltage. Larger CRSS for the oversized P-channel MOSFET causes an efficiency drop (especially for higher input voltages). C3 0.047µF Z5U Q1 IRF9Z34 C2 330µF 63V L1 62µH R2 0.05Ω 5V 2A 9 8 C9 0.01µF + ITH CT SGND 11 PGND 12 NGATE RGND 13 Q2 IRFZ34 C10 220µF × 2 10V D2 MBR160 14 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A (Ta) SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-1A-C1-0R050J Pd = 1W QUIESCENT CURRENT = 1.5mA COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 560mA ALL OTHER CAPACITORS ARE CERAMIC AN54 • F09A Figure 9A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs AN54-11 Application Note 54 100 LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter 90 VIN = 12V EFFICIENCY (%) If 3.3V has to be generated efficiently from a high voltage input, use the circuit of Figure 10A. It copies the configuration presented in Figure 8A but uses the LTC1149-3.3 regulator to provide a precise 3.3V output. In spite of the high input and low output voltages, efficiency still reaches 92%. 80 VIN = 24V 70 60 VIN = 48V VIN = 36V 50 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 2 AN54 • F10B Figure 10B. LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter Measured Efficiency VIN 10V TO 48V + C1 0.1µF 3 + C4 1µF C5 0.1µF C6 0.068µF Z5U 5 16 10 15 7 6 R1 1k C7 3300pF X7R C2 C4 C10 Q1 Q2 D1 D2 R2 L1 C8 470pF NPO D1 1N4148 2 VIN VCC PGATE 1 PDRIVE 4 SD1 LTC1149-3.3 SENSE + 9 SD2 SENSE – VCC CAP 8 Q1 IRFU9024 C3 0.047µF Z5U C2 330µF 63V L1 50µH 3.3V 2A C9 0.01µF + ITH CT SGND 11 NGATE PGND 12 13 RGND Q2 IRFU024 D2 MBR160 C10 220µF 10V 14 UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A (Ta) SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-1A-C1-0R050J Pd = 1W COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA ALL OTHER CAPACITORS ARE CERAMIC Figure 10A. LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter AN54-12 R2 0.05Ω AN54 • F10A Application Note 54 observed that Q4 turns on when the output is less than 10V (the internal regulator output) and stays on or off under all conditions. LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter The LTC1149 contains an internal 10V low dropout linear regulator to provide power to the control circuitry. It actually means that the DC bias current as well as the gate charge current come directly from the input line, causing slight efficiency degradation, especially for high input voltages (additional power is dissipated by the internal regulator). A solution for this problem is presented in Figure 11A. When the output level reaches about 5V, Zener D3 starts conducting and saturates Q3, which in turn switches Q4 on. Now VCC pins 3 and 5 are powered directly from the output. Losses caused by DC current and gate charge current are significantly reduced allowing improved efficiency at high input voltage. 100 EFFICIENCY (%) 90 C1 0.1µF Q4 2N3906 3 + 33k C4 1µF C5 0.1µF 5 16 10k C6 0.068µF Z5U 33k D3 5.1V 7 Q3 2N3904 R1 1k 10k C2 C4 C10 Q1 Q2 D1 D2 R2 L1 15 C7 3300pF X7R 6 C8 200pF NPO VCC VCC PDRIVE D4 1N4148 CAP VFB SENSE + SENSE – SD2 ITH VIN = 48V 75 VIN = 36V 60 0.001 1 0.01 0.1 OUTPUT CURRENT (A) Figure 11B. LTC1149: (10V-48V to 5V/2A) Measured Efficiency with Large P-Channel and N-Channel MOSFETs 1 4 10 + Q1 IRF9Z34 C3 0.047µF Z5U 11 PGND 12 NGATE RGND C2 330µF 63V L1 62µH 9 8 VOUT 12V 2A + 13 Q2 IRFZ34 D2 MBR160 14 UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A (Ta) SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-1A-C1-0R050J Pd = 1W COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE R2 0.05Ω 432k 1% C9 0.01µF LTC1149 CT SGND 10 AN54 • F11B D1 1N4148 PGATE 80 65 2 VIN 85 70 The regulator output must be set up for an output voltage less than 14.5V to provide a margin for the LTC1149 pin 5 absolute maximum rating of 16V. It should also be VIN 10V TO 48V VIN = 15V 95 C10 220µF × 2 10V 49.9k 1% QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 560mA ALL OTHER CAPACITORS ARE CERAMIC AN54 • F11A Figure 11A. LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter AN54-13 Application Note 54 100 LTC1149: High Power Buck Converters 95 Figures 12A and 13A are examples of high power (more than 100W) converters that use the LT1149. The regulators are powered from the full wave rectified output of a 16VRMS to 32VRMS transformer. Input capacitance is very bulky, but it has to ensure that ripple valleys do not dip below the minimum regulator input requirement. The circuit in Figure 13A has additional gate driver circuits which are required to improve MOSFET switching times. Overall efficiency goes as high as 98%! Remember, at these output current levels layout becomes extremely important, and all the recommendations from the LTC1149 data sheet must be closely followed. 0.33µF EFFICIENCY (%) 90 85 80 75 70 65 0.01 0.1 1 OUTPUT CURRENT (A) AN54 • F12B Figure 12B. LTC1149: (16VRMS to 13.8V/10A) Buck Converter Measured Efficiency 0.22µF D1 1N4148 VIN 16VRMS RECTIFIED Q1 RFG60P06E 0.33µF + 1 2 3 4 5 6 7 CT 270pF 3300pF 8 CAP VIN SD2 VCC RGND PDRIVE NGATE VCC D2 MBR380 10µF PGATE LTC1149 CT PGND SGND ITH VFB SENSE – SENSE + + CIN 20000µF 35V SHUTDOWN (NORMALLY GND) 14 13 12 L 33µH 11 10 100pF R2 205k 9 470Ω 100Ω 1µF WIMA 1.5µF 63V WIMA Q2 IRFZ44 16 15 10 R1 20.5k 1% + COUT, 1500µF 25V, × 2 VOUT 13.8V 10A RS 0.0082Ω 1000pF 33k 100Ω COUT PANASONIC HFQ SERIES D2 MOTOROLA SCHOTTKY Q1 HARRIS PMOS BV DSS = 60V RDSON = 0.03Ω Figure 12A. LTC1149: (16VRMS to 13.8V/10A) Buck Converter AN54-14 OUTPUT GROUND CONNECTION AN54 • F12A Application Note 54 VIN 32VRMS RECTIFIED MPSW06 0.33µF D1 1N4148 0.22µF Q1 SMP40P06 D2 MBR380 0.33µF + MPSA56 10µF PDRIVE BUFFER 1 2 3 4 5 6 7 CT 150pF 3300pF 8 PGATE CAP VIN SD2 VCC RGND PDRIVE NGATE LTC1149 VCC CT PGND SGND ITH VFB SENSE – SENSE + CIN 5000µF 75V SHUTDOWN (NORMALLY GND) 14 1N4148 13 MPSA56 NDRIVE BUFFER 12 L 62µH 11 10 100pF R2 432k 9 470Ω 100Ω 1µF WIMA + Q2 IRFZ34 16 15 1.5µF 63V WIMA + R1 20.5k 1% COUT, 1000µF 35V VOUT 27.6V 5A RS 0.016Ω 1000pF 33k OUTPUT GROUND CONNECTION 100Ω COUT PANASONIC HFQ SERIES D2 MOTOROLA SCHOTTKY Q1 SILICONIX PMOS BV DSS = 60V RDSON = 0.045Ω AN54 • F13A Figure 13A. LTC1149: (32VRMS to 27.6V/5A) Buck Converter 100 95 EFFICIENCY (%) 90 85 80 75 70 65 0.01 0.1 1 OUTPUT CURRENT (A) 10 AN54 • F13B Figure 13B. LTC1149: (32VRMS to 27.6V/5A) Buck Converter Measured Efficiency AN54-15 Application Note 54 100 LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology VIN = 6V 90 VIN 5V TO 14V + EFFICIENCY (%) The LTC1147 (Figure 14A) is a great way to implement a high efficiency regulator using a minimum number of external components and occupying the least board space. This regulator provides many advantages of the LTC1148 including constant off-time configuration, low dropout regulation and Bust Mode operation, comes in a smaller package and does not require the N-channel MOSFET. The only sacrifice made is synchronous rectification which degrades the efficiency of this circuit up to three percentage points. Compare efficiency graphs in Figures 1B and 14B! Since the clamp diode D1 conducts all the time during the off-time, a larger diode (MBRD330) is used for this circuit. The LTC1147 is an excellent choice where the output current is less than 1A, and where the input voltage is less than twice the output voltage. VIN = 10V 80 VIN = 14V 70 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) AN54 • F14B Figure 14B. LTC1147: (5V-14V to 5V/1A) Buck Converter Measured Efficiency + C1 0.1µF 6 C2 22µF x 2 25V 1 VIN PDRIVE 8 Q1 Si9430DY 1 SHUTDOWN 4 3 LTC1147-5 SENSE + SENSE – R1 1k 2 C3 3300pF X7R C2 C5 Q1 D1 R2 L1 ITH L1 100µH 2 3 R2 0.1Ω 5V 1A 5 4 C5 0.001µF + C6 220µF 10V CT C4 390pF NPO GND D1 MBRD330 7 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC MOTOROLA SCHOTTKY VBR = 30V KRL SP-1/2-A1-0R100J Pd = 0.75W COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE QUIESCENT CURRENT = 190µA TRANSITION CURRENT (Burst Mode OPERATION/ CONTINUOUS OPERATION) = 170mA ALL OTHER CAPACITORS ARE CERAMIC Figure 14A. LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology AN54-16 1 AN54 • F14A Application Note 54 100 LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology VIN = 5V 90 EFFICIENCY (%) Figure 15A shows another compact circuit with the LTC1147 series. It generates 3.3V/1A output using the same configuration as in the previous example. Despite the lack of synchronous rectification, efficiency approaches 95% with 5V input. VIN = 10V 80 VIN = 14V 70 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 AN54 • F15B Figure 15B. LTC1147: (4V-14V to 3.3V/1A) Buck Converter Measured Efficiency VIN 4V TO 14V + + C1 0.1µF 1 VIN 6 C2 22µF × 2 25V PDRIVE Q1 Si9430DY 8 1 SHUTDOWN 4 3 LTC1147-3.3 SENSE + SENSE – R1 1k 2 C3 3300pF X7R C2 C6 Q1 D1 R2 L1 ITH C4 560pF NPO L1 100µH 2 3 R2 0.1Ω 5 4 C5 0.001µF + CT GND 3.3V 1A C6 220µF 10V D1 MBRD330 7 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A SILICONIX BVDSS = 20V DCRON = 0.100Ω CRSS = 400pF Qg = 50nC MOTOROLA KRL SP-1/2-A1-0R100 Pd = 0.75W COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE QUIESCENT CURRENT = 170µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 170mA AN54 • F15A Figure 15A. LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology AN54-17 Application Note 54 100 LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology LTC1147-3.3 SUMIDA CDR74B VIN = 5V 95 90 EFFICIENCY (%) One more application circuit with LTC1147 is presented in Figure 16A. It is optimized for 5V to 3.3V conversion with input voltages of 4V to 8V (limited by the P-channel MOSFET). A circuit board has been laid out for this circuit and has subsequently been thoroughly tested under full operating conditions and optimized for mass production requirements. A Gerber file for the board is available upon request. LTC1147-3.3 SUMIDA CD54 VIN = 5V 85 80 75 70 65 60 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 2 AN54 • F16B Figure 16B. LTC1147: (4V-8V to 3.3/1.5A) Buck Converter Measured Efficiency VIN 4V TO 8V + C2 0.1µF Q1 P-CH Si9433DY 1 VIN 6 0V = NORMAL ≥ 2V = SHUTDOWN 3 R1 1k C3 3300pF PDRIVE LTC1147-3.3 SENSE + SENSE – 2 8 L1 10µH SHUTDOWN ITH GND R2 0.068Ω VOUT 3.3V 1.5A 5 C5 0.01µF 4 + CT C4 120pF C1 47µF 16V C6 100µF 10V D1 MBRS130LT3 7 AN54 • F16A C1 AVX TPSD476M016R0150 TANTALUM 47µF 16V C6 AVX TPSD107M010R0100 TANTALUM 100µF 10V D1 MOTOROLA MBRS130LT3 BVR = 30V L1 SUMIDA CDR74B-100LC 10 µH Q1 SILICONIX PMOS Si9433 R2 IRC LRC-LR2010-01-R068-F ALL OTHER CAPACITORS CERAMIC Figure 16A. LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology AN54-18 Application Note 54 LTC1148: (10V-14V to 5V/10A) High Current Buck Converter only inexpensive, readily available small-signal transistors, yet allows the use of all N-channel MOSFETs. Efficiency reaches 96% (see Figure 17B). Due to differences in physical structure between N- and Pchannel MOSFETs, the former are usually more cost effective, more available, and provide better internal parameters for the same size. This is especially important when high output currents are required. With 5A to 10A output currents the use of N-channel MOSFETs in place of P-channel is the most preferable solution. An implementation of this idea is presented in Figure 17A. 100 90 EFFICIENCY (%) VIN = 10V A special Q4 gate drive circuit that uses a bootstrapping technique is added to provide required gate drive. When pin 1 goes high it turns Q3 on, providing a path for fast Q4 gate capacitance discharge. With Q3 off, Q1 and Q2 saturate each other feeding positive voltage to Q4’s gate. As a result Q4 turns on, and the positive pulse at its source is AC coupled through C6 supplying bootstrapped VCC for the gate drive “SCR.” The external driver circuit contains VIN = 14V 70 60 50 1 OUTPUT CURRENT (A) 0.1 + C1 1µF R1 20k C2 0.1µF Figure 17B. LTC1148: (10V-14V to 5V/10A) High Current Buck Converter Measured Efficiency + C6 0.47µF R2 220 Q2 2N2222 VIN 6 R4 1k C3 3300pF X7R PDRIVE SHUTDOWN ITH LTC1148-5 SENSE + SENSE – 4 C4 820pF NPO CT 1 Q3 VN2222LL D2 1N4148 SGND 11 PGND L1 33µH R8 0.01Ω 5V 10A C5 0.001µF R6 100 14 NDRIVE Q4 IRFZ44 R5 100 8 7 C7 2700µF × 2 35V R3 220 Q1 2N3906 3 10 10 AN54 • F17B D1 1N4148 VIN 10V TO 14V C1 C7 C8 Q4, Q5 D1, D2 D3 80 R7 22k + Q5 IRFZ44 D3 1N5818 C8 2200µF × 3 16V 12 (Ta) UNITED CHEMI-CON (Al) LXF35VB272M16 X 40 ESR = 0.018Ω IRMS = 2.900A NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A IR NMOS BVDSS = 60V DCRON = 0.028Ω CRSS = 310pF Qg = 69nC MOTOROLA SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 30V R8 L1 KRL NP-2A-C1-0R010J Pd = 3W COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE ALL OTHER CAPACITORS ARE CERAMIC QUIESCENT CURRENT = 22mA AN54 • F17A Figure 17A. LTC1148: (10V-14V to 5V/10A) High Current Buck Converter AN54-19 Application Note 54 Two resistors are placed in series with the current sense pins. This significantly improves circuit noise immunity which is of great importance when switching high current. R7, connected between pin 7 and ground, disables Burst Mode operation so that the regulator operates continuously. an output referenced to ground is required. PGATE pin 1 provides the same drive signal referenced to VCC. 100 90 EFFICIENCY (%) LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter Figure 18A shows a high current, high voltage buck converter. The LTC1149 is used to accommodate the input voltage requirement. As in Figure 17A the top N-channel MOSFET is driven by an external circuit which inverts the chip’s P-drive output and uses bootstrapping to provide positive gate-source voltage. The peak-to-peak gate voltage is defined by the DC portion of the gate driver VCC. Therefore, not to exceed maximum gate voltage for the MOSFET, D1’s anode is connected to internal 10V regulator output. In this application PDRIVE pin 4 is used because D1 1N4148 VIN 12V TO 36V C1 0.1µF + C2 1µF C3 0.1µF 5 16 10 15 7 C4 3300pF X7R C2 C8 C9 Q1 Q2 Q3 Q4 R1 1k 6 C5 820pF NPO VIN PGATE VCC CAP PDRIVE LTC1149-5 SD1 SENSE + SD2 SENSE – 4 VIN = 36V 1 OUTPUT CURRENT (A) Figure 18B. LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter Measured Efficiency + R4 220Ω C7 0.22µF Q3 VN2222LL Q2 2N2222 9 11 12 NGATE RGND 13 5V 5A Q5 IRFZ34 D3 MBR160 + C9 220µF × 2 10V 14 (Ta) NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A PNP BV CEO = 30V NPN BVCEO = 40V SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω MOTOROLA NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 40nC Q5 D1, D2 D3 R7 L1 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-2A-C1-0R020J Pd = 3W COILTRONICS CTX50-5-52 DCR = 0.021Ω #52 IRON POWDER CORE ALL OTHER CAPACITORS ARE CERAMIC Figure 18A. LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter AN54-20 R7 0.02Ω C6 0.001µF R6 100Ω PGND L1 50µH R5 100Ω ITH CT SGND C8 1000µF 63V Q4 MTP30N06EL 8 5 AN54 • F18B D2 1N4148 1 70 0.1 R3 220Ω VCC VIN = 24V 50 2 3 80 60 Q1 2N3906 R2 10k VIN = 12V AN54 • F18A Application Note 54 100 LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter VIN = 12V 90 EFFICIENCY (%) The circuit in Figure 19A uses the same configuration but is designed to provide up to 10A output current. Besides the usual external component changes, the circuit uses higher current MOSFETs to improve efficiency at maximum power levels. Efficiency at 5A output is several percentage points better than in the previous example (compare Figures 18B and 19B). R7 keeps the regulator in continuous mode causing the rapid efficiency decrease at lighter loads. VIN = 24V VIN = 48V 80 70 VIN = 36V 60 50 1 OUTPUT CURRENT (A) 0.1 10 AN54 • F19B Figure 19B. LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter Measured Efficiency D1 1N4148 VIN 12V TO 48V + R2 20k C1 0.1µF + C2 1µF C3 0.1µF 5 16 10 15 7 C4 3300pF X7R C2 C8 C9 Q1 Q2 Q3 Q4 Q5 R1 1k 6 C5 820pF NPO VIN VCC PGATE VCC PDRIVE CAP SD1 LTC1149-5 SENSE + SD2 SENSE – 1 4 D2 1N4148 Q2 2N2222 Q4 IRFZ34 Q3 VN2222LL R6 100Ω 11 PGND 12 NGATE RGND 13 R7 22k 14 (Ta) NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A PNP BVCEO = 30V NPN BVCEO = 40V SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC R8 0.01Ω 5V 10A C6 0.001µF ITH CT SGND L1 33µH R5 100Ω 9 8 C8 1000µF × 2 63V C7 0.22µF R3 220Ω 2 3 + R4 220Ω Q1 2N3906 D1, D2 D3 R8 L1 Q5 IRFZ44 + D3 MBR160 C9 220µF × 3 16V SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-2A-C1-0R010J Pd = 3W COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE ALL OTHER CAPACITORS ARE CERAMIC QUIESCENT CURRENT = 26mA AN54 • F19A Figure 19A. LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter AN54-21 Application Note 54 100 LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter EFFICIENCY (%) If an output voltage other than 5V or 3.3V is required, an adjustable version of the regulator must be used. A 24V/ 10A example is shown in Figure 20A. The output voltage is set by resistors R8 and R9. The LTC1149 monitors VFB (pin 10) keeping it at 1.25V. Similar to the previous two circuits, an external gate driver is added to switch the N-channel MOSFET Q2. To ensure consistent start-up of the bootstrapping circuitry, the driver is initially powered by R2 and D2. (The main requirement at start-up is to supply the driver with VCC that exceeds output target voltage.) After the switching starts, D1 an D3 power the external gate drive circuit. 10 Figure 20B. LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter Measured Efficiency C2 1µF C3 0.1µF 5 16 VCC VCC PDRIVE CAP LTC1149 VFB 15 7 C4 3300pF X7R C2 C9 C10 Q4, Q5 Q1 Q2 D1, D2, D3, D4 D5 R10 L1 R1 1k 6 C5 270pF NPO R11 39k SD2 SENSE + SENSE – ITH CT SGND 11 PGND 12 C7 0.22µF NGATE RGND Q2 MPS651 1 4 Q3 VN2222LL Q4 IRFZ44 D4 1N4148 R6 100Ω 9 C7 0.001µF 8 C6 100pF Q5 IRFZ44 24V 10A + C10 1000µF × 3 35V R10 0.01Ω VOUT = 1.25V (1 + R8/R9) QUIESCENT CURRENT = 26mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 1.5A ALL OTHER CAPACITORS ARE CERAMIC Figure 20A. LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter AN54-22 R8 220k 1% R9 12k 1% R7 100Ω 13 (Ta) NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A NICHICON (Al) UPL1V102MRH ESR = 0.029Ω IRMS = 1.980A IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC PNP BVCEO = 50V NPN BVCEO = 60V SILICON VBR = 75V MOTOROLA SCHOTTKY VBR = 60V KRL NP-2A-C1-0R010J Pd = 3W COILTRONICS CTX50-10-KM DCR = 0.010Ω Kool Mµ CORE L1 50µH D5 MBR160 10 14 C8 1000µF × 2 63V R5 220Ω R4 220Ω PGATE + D3 1N4148 R3 20k 2 + 10A AN54 • F20B Q1 2N5087 VIN 100 1A OUTPUT CURRENT (mA) R2 5.1k VIN 32V TO 48V 3 70 50 D2 1N4148 C1 0.1µF VIN = 45V 80 60 D1 IN4148 + VIN = 32V 90 AN54 • F20A Application Note 54 Figure 21A provides the function of a step-up and stepdown converter without using a transformer. This topology is called a SEPIC converter. The P-channel transistor and L1 are arranged similarly to a buck-boost topology providing the boost part of the regulator. Pulses at Q2’s drain (actually two paralleled devices) are coupled via C8 to the buck portion that includes Q3 and L2. This circuit accepts 4V to 14V input and provides a solid 5V output. Even though the schematic shows two inductors, they carry the same current and can be wound on a single core. Such dual coils are readily available (see circuit parts list). This topology is acceptable for moderate loads only, as the coupling capacitor C8 carries the full load current and must be sized accordingly. When the sense resistor is placed at ground potential, such as the case in this circuit, the off-time increases approximately 40%. current sense resistor is placed at ground. This allows to provide different output voltages. D2 is included for foldback short-circuit protection. When VOUT equals zero (output is shorted) D2 clamps pin 6 and limits the output current. 100 VIN = 5V + VIN = 5V PDRIVE INT VCC VFB 0.01 0.1 OUTPUT CURRENT (A) 1 AN54 • F21B Figure 21B. LTC1148: (4V-14V to 5V/1A) Buck-Boost Converter Measured Efficiency + C8 220µF 10V 3 VIN 5 70 + C2 0.1µF VIN = 4V VIN = 14V 50 0.001 Q2 Si9430DY x 2 C1 1µF VIN = 4V 80 60 An adjustable version of the regulator is required when the VIN 4V TO 14V VIN = 10V 90 EFFICIENCY (%) LT1148: (4V-14V to 5V/1A) SEPIC Converter 1 C7 100µF 20V L2 50µH VOUT 5V 1A R3 75k 1% L1 50µH 9 LTC1148 10 D2 MBR0520L 6 TO VOUT R1 1k C4 3300pF X7R C1 C7 C8, C10 Q2 Q3 D1 R2 L1 4 C5 390pF NPO SHUTDOWN ITH SENSE + SENSE – CT SGND 11 NDRIVE PGND 8 7 + C6 0.1µF R2 0.082Ω D1 1N5818 14 12 (Ta) SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 30V KRL NP-1A-C1-0R082J Pd = 1W COILTRONICS CTX50-4P, CTX50-5P R4 25k 1% C10 220µF 10V Q3 Si9410DY C9 100pF VOUT = 1.25V (1 + R3/R4) QUIESCENT CURRENT = 200µA TRANSITION CURRENT (Burst Mode OPERATION/ CONTINUOUS OPERATION) = 250mA/VIN = 5V ALL OTHER CAPACITORS ARE CERAMIC AN54 • F21A Figure 21A. LTC1148: (4V-14V to 5V/1A) SEPIC Converter AN54-23 Application Note 54 100 LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter VIN = 5V VIN = 10V 90 EFFICIENCY (%) Applications requiring a split supply can use the circuit presented in Figure 22A. It contains the converter from Figure 21A and adds a synchronous charge pump Q4 to provide a –5V output. Q4 source is referenced to the –5V line, and its gate drive is AC coupled via C11 and clamped by D3. The outputs exhibit excellent tracking with line and load changes. This is a great way to build a dual output converter without any transformer. 80 VIN = 4V VIN = 14V 70 60 50 0.001 0.01 0.1 OUTPUT CURRENT (A) 0.5 AN54 • F22B Figure 22B. LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter Measured Efficiency VIN 4V TO 14V Q2 Si9430DY + C2 0.1µF 3 VIN PDRIVE 5 INT VCC SENSE + 1 D4 MBR0520L 6 VOUT R1 1k C5 390pF NPO C4 3300pF X7R C1 C8 C9, C10, C12 Q2 Q3, Q4 D1, D2 R2 L1 4 SHUTDOWN 7 VFB SGND 11 L2 50µH L1 50µH R3 75k 1% C7 0.1µF R2 0.05Ω NDRIVE PGND 12 + C10 220µF 10V + C12 220µF 10V 9 Q3 Si9410DY 14 D1 1N5818 C6 100pF C11 0.22µF (Ta) SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q4 Si9410DY SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 30V KRL NP-1A-C1-0R082J Pd = 1W COILTRONICS CTX50-4 VOUT = 1.25V (1 + R3/R4) D2 1N5818 QUIESCENT CURRENT = 250µA TRANSITION CURRENT (DIS/CONT) = 130mA/VIN = 5V R5 51k Figure 22A. LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter AN54-24 +VOUT 5V 0.5A SENSE – ITH CT C8 100µF 20V 8 LTC1148 10 + + C1 1µF C9 220µF 10V D3 1N4148 R4 25k 1% –VOUT –5V 0.5A AN54 • F22A Application Note 54 100 LTC1148: (4V-10V to –5V/1A) Positive-to-Negative Converter 95 VIN 4V TO 10V EFFICIENCY (%) 85 80 10V TO –5V/1A 75 70 65 60 0.001 + C1 1µF C2 0.1µF Q1 TP0610L Figure 23B. LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter Measured Efficiency 6 4 R1 1M R2 1k C3 6800pF X7R + C7 150µF × 2 16V INT VCC SENSE + SHUTDOWN SENSE – ITH VFB CT C4 560pF NPO NDRIVE SGND 11 L1 50µH 1 8 LTC1148 10 10 3 PDRIVE 5 1 0.01 0.1 OUTPUT CURRENT (A) AN54 • F23B Q2 Si9430DY VIN SHUTDOWN 4V TO –5V/1A 90 Figure 23A shows a buck-boost converter using the LTC1148. This is an inverting topology, and it can inherently buck or boost the input voltage. Ground pins of the chip are referenced to the output line; no additional level shifting circuit is required to drive the N-channel FET Q3 (its source is referenced to – 5V as well). Now even with minimum input level, the circuit provides a solid 9V peakto-peak MOSFET drive signal. However, so as not to exceed absolute maximum voltage at pin 3, the input line is limited to 10V. If the circuit is required to accept a higher input voltage, the LTC1148HV can be used instead. Q1 is added to provide a logic level shutdown feature. If shutdown is not needed omit Q1 and R1, and short pin 10 to pin 11. 7 C5 0.01µF R2 0.05Ω R3 75k 1% 9 14 PGND 12 C6 200pF Q3 Si9410DY + D1 1N5818 R4 25k 1% C8 220µF × 2 10V – 5V 1A C1 C7 C8 Q2 Q3 D1 R2 L1 (Ta) SANYO (OS-CON) 16SA150M ESR = 0.035Ω IRMS = 2.280A SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 30V KRL NP-1A-C1-0R050J COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE ALL OTHER CAPACITORS ARE CERAMIC VOUT = 1.25V (1 + R3/R4) AN54 • F23A Figure 23A. LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter AN54-25 Application Note 54 95 LTC1148: (5V-12V to – 15V/0.5A) Buck-Boost Converter 90 EFFICIENCY (%) Figure 24A presents an inverting regulator designed to accommodate higher output voltages. The LTC1148 cannot accept feedback directly from a negative output. To regulate negative outputs, the feedback must be inverted and compared against 1.25V. This function is provided by a DC level shifting amplifier consisting of Q1 and associated components. Resistor R4 provides amplifier negative feedback, effectively cancelling variations in VCC, and Q2 provides temperature compensation. The output voltage is set by resistors R4 and R5. As usual, with the sense resistor at ground potential, the off-time increases roughly by 40%. 85 80 12V TO –15V/0.5A 75 5V TO –15V/0.5A 70 65 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 AN54 • F24B Figure 24B. LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter Measured Efficiency VIN 5V TO 12V + C2 0.1µF U1 3 10 > 1.5V = SHUTDOWN 6 R6 1k C5 6800pF 4 C6 200pF 11 + Q3 Si9435DY ×2 C3 1µF C7 220µF 10V R3 56k 1 PDRIVE VIN SHUTDOWN LTC1148 ITH CT SGND SENSE + SENSE – VFB PGND L1 50µH 8 7 Q2 2N5210 C8 0.01µF R7 0.033Ω Q1 2N5210 9 12 R7 DALE LVR-3 0.033W L1 COILTRONICS CTX50-5-52 C7 SANYO OS-CON 105A220K C9, C10 SANYO OS-CON 255C47K C11 200pF D3 MBR735 + R4 49.9k 1% C9 47µF 25V + C10 47µF 25V R5 634k 1% VOUT –15V 0.5A AN54 • F24A Figure 24A. LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter AN54-26 Application Note 54 LTC1148: (2V-5V to 5V/1A) Boost Converter 100 95 Even though the LTC1148 is mainly used in step-down converters, it can also show excellent performance in the boost configuration. A boost implementation is shown in Figure 25A. This is a two-cell to 5V converter that uses the LT1109 to provide 12V to power the main regulator chip (unfortunately, MOSFETs do not operate with only 2V at the gate). The LT1109 is a small micropower IC that requires only three external components and provides great efficiency. An N-channel transistor is used as the switch, and general purpose MOSFETs Q1 and Q2 are used to form an inverting gate driver. When Q3 turns off, the voltage at its drain rises above VIN, and a Schottky diode D2 starts conducting. In a short period of time Q4 shorts it out providing a synchronous rectification feature and increasing efficiency. If 12V is already available, the LT1109 can be omitted and the 12V line connected directly to pin 3. 4V TO 5V/1A EFFICIENCY (%) 90 VIN 2V TO 5V 1 + VR1 VIN SW 7 SHUTDOWN S/D LT1109 SENSE D1 1N5818 70 65 0.001 1 AN54 • F25B Figure 25B. LTC1148: (2V-5V to 5V/1A) Boost Converter Measured Efficiency D2 1N5818 L2 25µH 5V 1A C1 100µF 10V Q4 Si9410 12V 8 C2 0.1µF 4 + C3 1µF 3 PDRIVE SENSE + 10 6 4 C5 390pF NPO SHUTDOWN SENSE – LTC1148 VFB ITH CT NDRIVE PGND SGND 11 R3 75k 1% Q1 TP0610L VIN C4 6800pF X7R 0.01 0.1 OUTPUT CURRENT (A) 3 GND R2 1k 2V TO 5V/1A 80 75 R1 0.05Ω L1 33µH 85 1 8 7 + Q3 Si9410 C8 220µF × 2 10V Q2 VN2222LL C6 0.001µF 9 14 12 C1 SANYO (OS-CON) 10SA100M ESR = 0.045Ω IRMS = 1.870A C3 (Ta) C8 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q3, Q4 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1, D2 MOTOROLA SCHOTTKY VBR = 30V C7 100pF R2 L1 L2 R4 25k 1% KRL SL-1-C1-0R050J Pd = 1W COILTRONICS CTX33-1 DCR = 0.220Ω Kool Mµ CORE COILTRONICS CTX25-4 VOUT = 1.25V (1 + R3/R4) AN54 • F25A Figure 25A. LTC1148: (2V-5V to 5V/1A) Boost Converter AN54-27 Application Note 54 LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter 95 A circuit that provides dual 3.3V/5V output is shown in Figure 26A. It uses a dual LTC1143 regulator that combines two LTC1147, non-synchronous switching regulators. The efficiency was measured with only one output loaded which provided worse results for low output current due to the presence of the second half’s quiescent current. This circuit provides very simple means to power dual voltage logic. It occupies small amount of board space and is very efficient! 85 EFFICIENCY (%) 90 8V TO 5V 8V TO 3.3V 80 14V TO 5V 14V TO 3.3V 75 70 65 60 0.001 0.01 0.1 1 OUTPUT CURRENT (A) 10 AN54 • F26B Figure 26B. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter Measured Efficiency VIN 5.2V TO 14V CIN3 22µF 25V ×2 VOUT3 3.3V/2A RSENSE3 0.05Ω + L1 20µH + 0.22µF Q1 P-CH Si9430DY 13 4 1 VIN3 0V = NORMAL >1.5V = SHUTDOWN 10 2 SHUTDOWN 3 16 COUT3 220µF 10V ×2 D1 MBRD330 VIN5 PDRIVE5 PDRIVE3 SENSE + 3 SENSE + 5 12 3 ITH5 CT5 GND5 15 7 6 11 RC3 1k RC5 1k ITH3 14 CT3 390pF CC3 3300pF L2 20µH VOUT5 5V/2A CC5 3300pF 8 CT5 200pF Figure 26A. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter AN54-28 RSENSE5 0.05Ω 0.01µF SENSE – 5 CT3 CIN5 22µF 25V ×2 9 LTC1143 SENSE – 3 GND3 KRL SL-1R050J RSENSE: L1, L2: COILTRONICS CTX20-4 AVX (Ta) TPSD226K025R0200 CIN3, CIN5: COUT3, COUT5: AVX (Ta) TPSE227K010R0080 Q1, Q2: SILICONIX PMOS Si9430DY Q2 P-CH Si9430DY 5 SHUTDOWN 5 0.01µF + 0.22µF D2 MBRD330 + COUT5 220µF 10V ×2 AN54 • F26A Application Note 54 100 LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter 7V TO 5V 95 90 12V TO 5V EFFICIENCY (%) The standard LTC1148 input voltage is limited to 16V absolute maximum level, which is not sufficient in some applications. Figure 27A shows a step-down regulator using the high voltage LTC1148HV. It contains the same internal functions but accepts up to 20V input (remember, MOSFET’s gates are usually rated at 20V maximum). As a building block it can be used in the same manner as LTC1148. Input tantalum capacitors now have to be rated at 35V to ensure reliable operation under maximum input voltage. 85 80 75 18V TO 5V 70 65 60 55 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 AN54 • F27B Figure 27B. LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter Measured Efficiency VIN 5.2V TO 18V Q1 Si9430DY + D1 MBRS140T3 CIN 10µF 35V ×2 Q2, Si9410DY 1 1µF + 2 3 4 CT 220pF 5 6 CC 3300pF 7 PDRIVE NDRIVE NC NC LTC1148HV-5 VIN PGND CT SGND INT VCC SHUTDOWN ITH SENSE – NC SENSE + 14 13 L1 50µH 12 11 10 SHUTDOWN 9 + 8 RC 1k 1000pF COUT 220µF 10V AVX R1 0.1Ω VOUT 5V/1A CIN COUT L1 R1 Q1 Q2 AVX (Ta) TPSD106K035R0300 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX50-4 KRL SP-1/2-A1-0R100 SILICONIX PMOS Si9430DY SILICONIX NMOS Si9410DY AN54 • F27A Figure 27A. LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter AN54-29 Application Note 54 100 LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage Buck Converter 4V to 3.3V 95 90 EFFICIENCY (%) Figure 28A: Here is a high voltage version of the circuit shown in Figure 4A with input voltage increased to 18V. 85 12V to 3.3V 80 75 18V to 3.3V 70 65 60 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 AN54 • F28B Figure 28B. LTC1148HV-3.3: (4V-18V TO 3.3V/1A) High Voltage Buck Converter Measured Efficiency VIN 4V TO 18V Q1 Si9430DY + D1 MBRS140T3 CIN 22µF 35V ×2 Q2, Si9410DY 1 1µF + 2 3 4 CT 270pF 5 6 CC 3300pF 7 RC 1k PDRIVE NDRIVE NC NC LTC1148HV-3.3 VIN PGND CT SGND INT VCC SHUTDOWN ITH SENSE – NC SENSE + 14 13 L1 50µH 12 11 10 SHUTDOWN 9 + 8 1000pF COUT 220µF 10V 0.1Ω VOUT 3.3V/1A CIN COUT L1 R1 Q1 Q2 AVX (Ta) TPSE226K035R0300 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX50-4 Kool Mµ CORE IRC LR2010-01-R100-G SILICONIX PMOS Si9430DY SILICONIX NMOS Si9410DY Figure 28A. LTC1148HV-3.3: (4V-18V to 3.3V/1A) High Voltage Buck Converter AN54-30 AN54 • F28A Application Note 54 100 LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter 95 90 EFFICIENCY (%) Figure 29A is another application of the LTC1148HV which is configured as a step-down converter to provide 12V/2A output. With this low dropout regulator, the input can go as low as 12.5V and still produce a regulated output. Resistors R2 and R3 set the output voltage level. 85 80 75 70 65 60 0.001 1 0.01 0.1 OUTPUT CURRENT (A) 10 AN54 • F29B Figure 29B. LTC1148HV: (16V to 12V/2A) High Voltage Buck Converter Measured Efficiency VIN 12.5V TO 18V + + C1 1µF C2 0.1µF 3 VIN 10 PDRIVE R1 1k C4 3300pF X7R C1 C7 Q1 Q2 D1 R2 L1 4 C5 150pF NPO Q1 Si9430DY SHUTDOWN SENSE – ITH VFB CT NDRIVE SGND 11 R2 0.05Ω 47µH LTC1148HV SENSE + 6 1 C3 22µF x 2 35V 12V 2A 8 7 C6 0.01µF 432k 1% 9 14 Q2 Si9410DY PGND 12 D1 MBRS140T3 49.9k 1% + C7 150µF × 3 16V 100pF (Ta) SANYO (OS-CON) 16SA150M SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC MOTOROLA SCHOTTKY VBR = 40V KRL SL-1-C1-0R050J Pd = 1W COILTRONICS CTX47-5P AN54 • F29A Figure 29A. LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter AN54-31 AN54-32 C2, C3, C6, C7, C9 C11, C12 C20, C21 L1 0V = 12V OFF >3V = 12V ON (6V MAX) DO NOT FLOAT 12V ENABLE –VIN C16 390pF 50V SHUTDOWN (TTL INPUT) SHUTDOWN (TTL INPUT) +VIN 6.5V TO 14V C17 200pF 50V R8 510Ω C4 3300pF C15 1µF 50V 24 17 3 2 1 Q1 VN7002 R5 18k C19 1000pF 7 6 4 5 NC7 NC6 NC4 8 VIN GND 3 ADJ VOUT LT1121CS8 SHDN R1 100Ω 4 Q2 Si9430DY R2 100Ω Q3 Si9410DY C18 2200pF 2 1 + 7 4 C10 20pF C20 220µF 10V R10 0.040Ω 8 3 9 2 D2 MBRS140 + 10 T1 1 R4 294k 1% + 5 C9 22µF 25V + + – 12V/150mA C8 22µF 35V + 2 1 + C11 100µF 10V + C12 100µF 10V C3 22µF 25V – 5V/2A + L1 33µH 2A CTX33-4 R9 0.050Ω 3 4 D1 MBRS140 C2 22µF 25V SHUTDOWN PINS 2 AND 16 MUST ACTIVELY BE DRIVEN EITHER HIGH OR LOW AND NOT ALLOWED TO FLOAT. + C21 220µF 10V C5 0.1µF 6 30µH, 2A LPE-6562-A026 1.8T R6 22 C7 22µF 25V D3 MBRS140 C13 1000pF C6 22µF 25V R3 649k 1% + Q5 Si9410DY Q4 Si9430DY Figure 30A. LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter R9 IRC LR2512-R050 R10 IRC LR2512-R040 T1 DALE, LPE-6562-AO26 3 VIN3 23 PDRIVE3 7 NC 6 NDRIVE3 1 SENSE+3 28 SENSE –3 9 PDRIVE5 21 LTC1142 NC 20 NDRIVE5 16 15 + SHUTDOWN5 SENSE 5 11 CT5 13 14 ITH5 SENSE – 5 12 INTV CC5 5 8 NC NC 4 18 PGND3 PGND5 22 19 NC NC SGND3 SGND5 AVX (Ta) TPSD226M025R0200 AVX (Ta) TPSD107K010R0100 AVX (Ta) TPSE227M010R0100 COILTRONICS CTX33-4 R7 510Ω C1 3300pF 10 VIN5 2 SHUTDOWN3 25 CT3 27 ITH3 26 INT VCC3 C14 1µF 50V – 3.3V/2A + AN54 • F30A + Application Note 54 Application Note 54 100 LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter LTC1142-5 VIN = 8V 90 EFFICIENCY (%) LTC1142 is a dual output synchronous switching regulator controller. Two independent controller blocks (LTC1148-based) simultaneously provide 3.3V and 5V outputs. The circuit in Figure 30A shows an application of this IC; it generates triple output voltages with 12V for flash memory programming in addition to the usual logic power levels. The 3.3V section is a regular buck converter circuit, the 5V section contains an off-the-shelf transformer T1 in place of the inductor. The secondary winding is used to boost the output level which is rectified and regulated by an LT1121 to provide a clean and stable 12V output. A turns ratio of 1:1.8 is used to ensure that the input voltage to the LT1121 is high enough to keep the regulator out of dropout. With LTC1142 synchronous switching, the auxiliary 12V output may be loaded without regard to the 5V primary output load as long as the loop remains in continuous operation mode. Continuous operation is ensured by R5 which inhibits Burst Mode whenever the 12V output is enabled (enable line goes high). Make sure that the enable lines are not floating and are driven by TTL level signals. A circuit board has been laid out for this circuit and has subsequently been thoroughly tested under full operating conditions and optimized for mass production requirements. A Gerber file for the board is available upon request. 95 85 LTC1142-3.3 VIN = 8V 80 75 70 65 60 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 2.5 AN54 • F30B Figure 30B. LTC1142:(6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter Measured Efficiency AN54-33 Application Note 54 LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter 100 Figure 31A shows the same configuration as Figure 30A using the high voltage LTC1142HV. Circuit operation is identical, but now it can accept up to 18V at the input. 90 LTC1142-5 VIN = 8V EFFICIENCY (%) 95 LTC1142-3.3 VIN = 8V 85 80 75 70 65 60 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 2.5 AN54 • F30B Figure 31B. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) Measured Efficiency VIN 6.5V TO 18V C1 22µF 25V ×2 + + VOUT3 3.3V/2A 23 L1 33µH RSENSE3 0.05Ω 1 C3 100µF 10V ×2 10 VIN5 SHUTDOWN 5 PDRIVE5 PDRIVE3 SENSE + 3 SENSE + 5 Q2 Si9430DY 6 Q5 Si9410DY SENSE – 4 1.8T 30µH RSENSE5 0.04Ω R2 100Ω 1000pF 3 SENSE 5 R1 100Ω NDRIVE5 SGND3 CT3 3 25 ITH3 ITH5 27 CT5 13 510Ω SGND5 PGND5 17 18 11 VOUT5 5V/2A 15 – NDRIVE3 PGND3 T1 9 LTC1142HV 28 + 16 SHUTDOWN 3 2000pF D1 MBRS140 1µF 2 24 VIN3 Q4 Si9430DY C2 22µF 25V ×2 + + 0V = NORMAL >1.5V = SHUTDOWN 1µF 14 D2 MBRS140 20 Q3 Si9410DY Q1 VN7002 510Ω R5 18k C4 220µF 10V ×2 + CT3 3300pF 3300pF CT5 390pF 200pF 12V ENABLE 0V = 12V OFF >3V = 12V ON (6V MAX) + 12V/150mA C1, C2 C3, C4 L1 RSENSE3 RSENSE5 T1 AVX (Ta) TPS226K035R0300 AVX (Ta) TPSD227K010R0100 COILTRONICS CTX33-4 KRL SL-C1-1/2-0R050J KRL SL-C1-1/2-0R040J DALE LPE-6562-A026 PRIMARY: SECONDARY = 1:1.8 22µF 25V + 20pF R3 660k VOUT SHUTDOWN ADJ R4 300k D3 MBRS140 1000pF LT1121 VIN GND Figure 31A. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter AN54-34 22µF 35V 22Ω AN54•F31A Application Note 54 LTC1148: High Efficiency Charger Circuit The LTC1148 regulator can be used as a highly efficient battery charging device. Figure 32 shows a circuit that is programmable for 1.3A fast charge or 100mA trickle charge mode. During the fast charge interval, the resistor divider network (R4 and R5) forces the LTC1148 feedback pin below 1.25V causing the regulator to operate at the maximum output current. Sense resistor R3 controls the current at approximately 1.3A. When the batteries are disconnected, the error amplifier sets the output voltage to be 8.1V (for proper operation this voltage should exceed VIN 8V TO 15V + C1 1µF 0V = NORMAL > 1.5A = SHUTDOWN C2 0.1µF 10 6 Q3 VN2222LL R2 1k C4 3300pF X7R 4 C5 200pF NPO C3 22µF × 2 35V 3 PDRIVE 1 SENSE – VFB CT NDRIVE SGND 11 L1 50µH 4 LTC1148 ITH 1 Q1 Si9430DY SHUTDOWN SENSE + “1” TRICKLE CHARGE Dual rate charging is controlled by Q3 which selects between fast and trickle charge. When the transistor turns on, R1 limits error amplifier output so that the current limiter starts operating at 100mA. If the trickle charge current needs to be altered, adjust R1. With 1.3A output current, this charger is capable of efficiency in excess of 90% which minimizes power dissipated in surface mount components. + VIN R1 51Ω maximum possible voltage across the battery pack). Diode D2 prevents the batteries from discharging through the divider network when the charger is shut down. PGND 12 2 3 D2 R3 MBRS340T3 0.1Ω VOUT 8 7 C6 0.01µF VBAT 4 CELLS R4 274k 1% 9 14 Q2 Si9410DY D1 MBRS140T3 R5 49.9k 1% + C8 220µF 10V C7 100pF C1 (Ta) C3 AVX (Ta) TPSD226K025R0100 ESR = 0.100 I RMS = 0.775A C8 AVX (Ta) TPSE227M010R0100 ESR = 0.100I RMS = 1.149A Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W D1, D2 MOTOROLA SCHOTTKY VBR = 40V R3 KRL SP-1/2-A1-0R100J Pd = 0.75V L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE VOUT = 1.25V • (1 + R4/R5) = 8.1V FAST CHARGE = 130mV/R3 = 1.3A TRICKLE CHARGE = 100mA EFFICIENCY > 90% AN54 • F32 ALL OTHER CAPACITORS ARE CERAMIC Figure 32. LTC1148: High Efficiency Charger Circuit AN54-35 Application Note 54 LTC1148: High Voltage Charger Circuit Figure 33 is a variation of Figure 32. It is designed to charge 6 cells and uses the LTC1148HV for higher input voltages. R4 value has been changed to provide 12.3V output when the battery is not connected. VIN 12V TO 18V + + C1 1µF C2 0.1µF 3 VIN 0V = NORMAL > 1.5A = SHUTDOWN 10 PDRIVE R1 51Ω “1” TRICKLE CHARGE Q3 VN2222LL R2 1k C4 3300pF X7R 4 C5 200pF NPO 1 SENSE – VFB CT NDRIVE SGND 11 PGND 12 2 3 D2 R3 MBRS340T3 0.1Ω VOUT 8 7 C6 0.01µF VBAT 6 CELLS R4 442k 1% 9 14 Q2 Si9410DY D1 MBRS140T3 + R5 49.9k 1% C8 100µF 16V ×2 C7 100pF C1 (Ta) C3 AVX (Ta) TPSD226K035R0200 ESR = 0.200 I RMS = 0.663A C8 AVX (Ta) TPSE107M016R0100 ESR = 0.100I RMS = 1.149A Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W D1, D2 MOTOROLA SCHOTTKY VBR = 40V R3 KRL SP-1/2-A1-0R100J Pd = 0.75V L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE VOUT = 1.25V • (1 + R4/R5) = 12.3V FAST CHARGE = 120mV/R3 = 1.3A TRICKLE CHARGE = 100mA EFFICIENCY > 90% ALL OTHER CAPACITORS ARE CERAMIC Figure 33. LTC1148: High Voltage Charger Circuit AN54-36 L1 50µH 4 LTC1148HV ITH 1 Q1 Si9430DY SHUTDOWN SENSE + 6 C3 22µF × 2 35V AN54 • F33 Application Note 54 3.3V/2A in a regular buck configuration. The other section is configured in the same way as the battery charger from Figure 32. It is powered from a wall adapter and provides the battery with fast or trickle charging rate. When the adapter is not connected, D3 prevents the battery from discharging through the R2/R1 divider network. LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger Figure 34 implements a high efficiency step-down converter with a built-in battery charger using a single IC. One section of the dual LTC1142A is used to convert 4-cells to VIN 8V TO 18V FROM WALL ADAPTER + D3 MBRS340T3 RSENSE1 0.1Ω 0V = CHARGE ON >1.5V = CHARGE OFF + CIN1 22µF 35V ×2 0.22µF P-CH Si9430DY 23 L1 50µH 24 VIN1 17 3 SHUTDOWN 1 PDRIVE2 PDRIVE1 SENSE + 2 SENSE + 1 R2 274k 1% R1 49.9k 1% 2 6 N-CH Si9410DY LTC1142A SENSE – 1 VFB2 NDRIVE1 NDRIVE2 PGND1 SGND1 CT1 5 4 25 100pF COILTRONICS CTX50-4 COILTRONICS CTX25-4 KRL SL-C1-1/2-1R100J KRL SL-C1-1/2-1R050J SENSE – 2 VFB1 ITH1 27 CT1 200pF “1” FOR TRICKLE CHARGE ITH2 13 CT2 SGND2 PGND2 11 RC1 1k RC2 1k CC1 3300pF CT2 CC2 3300pF 330pF VN2222LL L1 L2 RSENSE1 RSENSE2 L2 25µH 9 RSENSE2 0.05Ω VOUT2 3.3V/2A 15 1000pF 28 D1 MBRS140T3 VBATT 4 CELLS NiCAD P-CH Si9433DY 10 VIN2 SHUTDOWN 2 1000pF + CIN2 22µF 25V ×2 0.22µF 1 COUT1 220µF 10V 0V = OUTPUT ON >1.5V = 3.3V OUTPUT OFF RX 51Ω 18 19 14 16 + 20 N-CH Si9410DY D2 MBRS140T3 R4 84.5k 1% COUT2 220µF 10V ×2 R3 51k 1% 100pF FAST CHARGE = 130mV/RSENSE1 = 1.3A TRICKLE CHARGE = 130mV/RSENSE1 = 100mA AN54 • F34 Figure 34. LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger AN54-37 Application Note 54 LTC1149: Dual Output Buck Converter at the 3.3V output. The transformer used in this example is a standard product (see the parts list). A circuit board has been laid out for this circuit and has subsequently been thoroughly tested under full operating conditions and optimized for mass production requirements. A Gerber file for the board is available upon request. The circuit shown in Figure 35A implements the most elegant approach for dual output regulators that provide 3.3V and 5V outputs. It uses a single LTC1149. The synchronous rectification feature of this chip is used to provide excellent efficiency, as well as good cross regulation between the two outputs. Maximum output power of the converter is 17W, which may be drawn in any combination between 3.3V and 5V outputs. 100 98 96 VIN 6V TO 24V VIN = 6V 94 EFFICIENCY (%) A regular buck regulator is used for producing 3.3V output with T1’s primary in place of the buck inductor. The secondary of T1 forms a boost winding for 5V output. The transformer is wound with a simple trifilar winding to ensure that the primary is closely coupled to the secondary. Superior cross regulation is achieved by the close primary-to-secondary coupling and by splitting voltage feedback paths (resistors R1 and R2 provide feedback signals from both 3.3V and 5V outputs). Diodes D1, D2 and capacitor C7 comprise a soft-start circuit that causes the output voltage to increase slowly when the power is first applied to the circuit. This circuit prevents overshoot 92 VIN = 12V 90 88 VIN = 20V 86 84 82 80 0 2 4 6 8 10 12 14 TOTAL POWER OUTPUT 16 18 AN54 • F35B Figure 35B. LTC1149: Dual Output Buck Converter Measured Efficiency BOLD LINES INDICATE HIGH CURRENT PATHS (SHORT LEADS) + C5 + C6 22µF + C17 22µF + C18 22µF 22µF C19 0.1µF D3 BAS16 QP1 Si9435DY 4 QP2 Si9435DY 2 10 15 6 PDRIVE CT R5 24.9k 1% R4 1k 1 TP1 4 C12 56pF 12 14 4 3 220µF + C4 D5 MBRS140 4 R3 0.02Ω 220µF QN2 Si9410DY 3.3V OUT R8 33k QN1 Si9410DY + C15 + C1 D6 BAS16 D1 BAS16 C7 10µF + C3 • 6 C20 1µF 11 11 T •2 11 T R6 100Ω C14 R7 1000pF 100Ω 5V OUT 5 • 11 T C9 0.047µF S/D2 C8 0.068µF C13 2.2µF C11 1000pF PGATE 13 ITH LTC1149 NGATE 9 3 VO(REG) SENSE + 8 5 VI(REG) SENSE – 16 CAP PGND RGND SGND 7 C10 2200pF 1 VIN S/D1/VFB T1 HL-8700 220µF D4 MBRS140 + C2 220µF 220µF + C16 220µF R1 102k 1% D2 BAS16 R2 124k 1% + – VOUT –VIN AN54 • F35A C3, C4, C15, C16 C5, C6, C8, C17 R3 T1 AVX (Ta) TPSE227M010R 49BCPA AVX (Ta) TPSE226M035R 49BCPA IRC LR512-01-R020F HURRICANE, HL-8700 Figure 35A. Single LTC1149: Dual Output Buck Converter AN54-38 Application Note 54 100 LTC1148: Constant Frequency Buck Converters 95 Finally, Figures 36A and 37A show circuits that completely satisfy the demand in ultra-high efficiency converters operating synchronously with an external clock. The rising edge of the clock saturates Q3 pulling pin 4 below the internal comparator threshold. The internal logic assumes the end of the off-time, and turns Q1 on. Now the LTC1148 operates as a conventional constant frequency current mode controller and therefore requires slope compensation. Q2 generates an artificial ramp signal that is superimposed on the inductor current waveform sensed by the shunt R7. This is a standard technique to eliminate subharmonic oscillation, a phenomenon that occurs under simultaneous conditions of fixed frequency and fixed amplitude of inductor current when the duty cycle exceeds 50%. Subharmonic oscillations are not related to the closed-loop transfer function. VIN = 8V EFFICIENCY (%) 90 85 VIN = 15V 80 75 70 65 1 OUTPUT CURRENT (A) 0.1 10 AN54 • F36B Figure 36B. LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter Measured Efficiency VIN 8V TO 15V + C2 0.1µF C3 1µF + U1 R10 510k 3 10 > 1.5V = SHUTDOWN 6 R6 1k 4 C6 200pF C5 6800pF 11 PDRIVE VIN SHUTDOWN LTC1148-5 SENSE + ITH SENSE – CT NDRIVE SGND PGND 1 Q1 Si9430DY 8 7 C8 1000pF C4 51pF OSC IN 200kHz R4 100Ω R5 750Ω Q3 2N2222 Q4 Si9410DY AVX (Ta) TPSD226K025R0200 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX15-4 KRL SL-1-C1-0R040J PD = 1W L1 15µH R7 0.04Ω D3 MBR130T3 R9 100Ω + VOUT 5V 2A C9 220µF 10V 12 OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL. FOR APPLICATIONS WITH VIN > 2VOUT SLOPE COMPENSATION CAN BE DELETED. C7 C9 L1 R7 R8 100Ω 14 D2 1N4148 R3 220Ω C7 22µF 25V ×2 D4 1N4148 Q2 2N2222 D1 1N4148 R2 5.1k R1 30k C1 100pF SLOPE COMPENSATION AN54 • F36A Figure 36A. LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter AN54-39 Application Note 54 100 If the input voltage always exceeds twice the output (duty cycle in this case would be less than 50%) the circuit inside the dashed box can be omitted. Resistor R11 is added to the circuit of disable Burst Mode operation ensuring true in-sync operation over the full range of output current. The circuitry is designed to be synchronized by a 200kHz clock to accommodate other external frequencies; nothing more than component value changes is required. If the input voltage goes beyond specified range, the controller will lose synchronization (it will still regulate, however). R10 increases input voltage pull-in range and can be omitted if it is not required. Values above 430k ensure proper start-up. 4.5V TO 3.3V/2A 95 EFFICIENCY (%) 90 85 6.5V TO 3.3V/2A 80 75 70 65 1 OUTPUT CURRENT (A) 0.1 10 AN54 • F37B Figure 37B. LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter Measured Efficiency VIN 4.5V TO 6.5V + C2 0.1µF C3 1µF + U1 R10 470k 3 10 > 1.5V = SHUTDOWN 6 R6 100Ω 4 C6 150pF C5 3300pF 11 PDRIVE VIN SHUTDOWN SENSE + ITH LTC1148-3.3 SENSE – CT NDRIVE SGND PGND 1 Q1 Si9430DY 8 7 OSC IN 200kHz R4 100Ω R5 750Ω Q3 2N2222 R7 0.04Ω 14 Q4 Si9410DY D3 MBR130T3 R9 100Ω C9 220µF 10V D4 1N4148 OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL. C7 AVX (Ta) TPSD226K025R0200 C9 AVX (Ta) TPSE227K010R0080 L1 COILTRONICS CTX15-4 R7 KRL SL-1-C1-R040J PD = 1W Q2 2N2222 R11 18k R1 20k D1 1N4148 R2 2.2k C1 100pF SLOPE COMPENSATION Figure 37A. LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter AN54-40 + VOUT 3.3V 2A 12 D2 1N4148 C4 50pF R8 100Ω L1 15µH C8 1000pF C7 22µF 25V ×2 AN54 • F37A Application Note 54 APPENDIX A TOPICS OF COMMON INTEREST Defeating Bust Mode Operation Sometimes applications require Burst Mode operation to be defeated. It might be useful in a high output current circuit which never operates at light loads. Ensuring continuous operation in this case usually improves the circuit noise immunity and helps to eliminate audible noise from certain types of inductors when they are lighter loaded. The Burst Mode operation should be disabled if an overwinding is used to provide boosted voltage, additional to the main output (for example, see Figure 30A). This allows to draw power from the secondary with improved cross-regulation, even if the primary output is not loaded. Defeating of Burst Mode operation should also be considered when the fixed frequency circuits from Figures 36A and 37A are used. With continuous operation these circuits always operate fully synchronized to the external clock. Whatever the reason, Burst Mode operation can be suppressed with a simple external network which cancels the 25mV minimum current comparator threshold. An external offset is put in series with the SENSE – pin to subtract from the built-in 25mV offset. An example of this technique is shown in Figure A1. L 33µH LTC1148 FAMILY SENSE + RSENSE 0.05Ω VOUT 5V 2A R2 100Ω 100pF SENSE – R1 R3 100Ω 20k AN54 • FA01 Figure A1. Defeating Burst Mode Two 100Ω resistors are inserted in series with the leads from the sense resistor. With the addition of R3, a current is generated through R1 causing an offset of: R1 VOFFSET = VOUT × R1 + R3 If VOFFSET exceeds 25mV the minimum threshold will be cancelled and Burst Mode operation is prevented from occurring. Since the offset voltage is constant, the maximum load current is also decreased. Thus to get back to the same output current, the sense resistor must be lower: RSENSE = 75mV IMAX Soft-Start Circuits Right after the power-on, the regulator operates in a shortcircuit condition while charging output capacitors. With earlier voltage mode converters, this led to enormous current transient at start-up. Soft-start circuits were usually added to fix this problem. The LTC1148 series implements current mode technique which inherently provides current limiting and does not require any special soft-start circuits. Start-up current is limited to the shortcircuit current value of 150mV/RSENSE. Some applications might, however, require softer start. It helps to avoid output overshoot when the power is first applied to the circuit, and it also prevents the input supply’s overcurrent protection from latching, when the input voltage increases slowly. Figures A2 and A3 provide possible solutions for soft-start. Capacitor C1 in Figure A2 holds down ITH pin limiting the output current. C1 is charged via R1, when the voltage across its terminals exceeds DC level of ITH pin, D2 becomes reverse-biased and the capacitor no longer has an effect on the circuit operation. D1 provides discharge path for C1 when the input voltage is removed. The soft-start time constant is defined by R1 and C1. In Figure A3, capacitor C1 holds down the SENSE – pin providing additional offset to the current comparator. C1 charges through D1 and R2, slowly increasing maximum operating current. When C1 is fully charged D1 is reversebiased and the capacitor no longer affects the operation. AN54-41 Application Note 54 D2 provides a discharge path for C1 when the output voltage disappears. The soft-start time constant is defined by R2 and C1. VIN VIN D1 1N4148 R1 22k LTC1148 FAMILY D2 MBR0520L ITH C1 4.7µF 16V + R2 1k C2 3300pF AN54 • FA02 Figure A2. Soft-Start Circuit with ITH Pin Clamping L 33µH LTC1148 FAMILY SENSE + SENSE – RSENSE 0.05Ω R1 100Ω + C2 1000pF R2 100Ω D1 1N4148 D2 1N4148 C1 10µF 10V The simplest approach uses load step transient by switching in an additional load resistor and simultaneously monitoring the output. Switching regulators take several cycles to respond to a step in resistive load current. When a load step occurs, output voltage shifts by an amount equal to ∆ILOAD × ESR, where ESR is the output capacitor effective series resistance. Load current change also begins to charge or discharge output capacitor until the regulator loop adapts to the current change and returns VOUT to its steady state value. If during this recovery time VOUT has ringing, it indicates a stability problem, and the capacitor at ITH pin should be increased. A simple dynamic load circuit is shown in Figure A4 where the MOSFET Q1, driven by an external generator, switches a load resistor R2 in and out. The generator should provide 10V gate drive (not a TTL level). The drive signal frequency is not critical. A good starting point is 500Hz and the load change from 50% to the full load. VOUT 5V 2A LTC1148 FAMILY AN54 • FA03 + COUT R1 GENERATOR IN (10VP-P) R2 Q1 IRFZ44 100k (HEAD SINK MAY BE REQUIRED) Figure A3. Soft-Start Circuit with Sense Pin Clamping AN54 • FA04 Figure A4. Simple Dynamic Load Frequency Compensation The LTC1148 family of regulators contains both voltage and current loops, which, together with external capacitors and inductors, require a pretty complex mathematical approach to frequency compensation. Operating point changes with input voltage and output current variations add complications and suggest a more practical empirical method. AN54-42 The LTC1148 series regulators provide a very stable operation. The compensation values used in the circuits in this note have been tested over the wide range of operating conditions and proved to provide an adequate compensation for most applications. Usually no stability testing, as described above, is required. Application Note 54 APPENDIX B SUGGESTED MANUFACTURERS Linear Technology provides this list of manufacturers to get you started in your component selection process. We make no claims about any of these companies except that they provide components necessary in switching power supplies. There are many more companies to choose from; for a more complete list refer to the PCIM Buyer’s Philips Components 1440 W. Indian Town Rd. Jupiter, FL 33458 (407) 744-4200 Cer., Chip Capacitors Batteries Duracell OEM Sales & Marketing Berkshire Industrial Park Bethel, CT 06801 (800) 431-2656 Murata Erie North America 1900 W. College Ave. State College, PA 16801 (814) 237-1431 Eveready Battery Co. Checkerboard Square St. Louis, MO 63164 (314) 982-2000 Nichicon (America) Corporation 927 East State Parkway Schaumburg, IL 60173 (708) 843-7500 Aluminum Electrolytic Bipolar Transistors Motorola Inc. 3102 North 56th St. MS 56-126 Phoenix, AZ 85018 (800) 521-6274 Full Line Zetex 87 Modular Ave. Commack, NY 11725 (516) 543-7100 High Gain Bipolar Switching Transistors including Surface Mount Devices Capacitors AVX Corporation P.O. Box 867 Myrtle Beach, SC 29578 (803) 946-0690 Tant., Cer., Surface Mount Elpac 1567 Reynolds Ave. Irvine, CA 92714 Film Capacitors (714) 476-6070 Film Capacitors Intertechnical Group 2269 Saw Mill River Rd., Bldg. 4C P.O. Box 217 Elmsford, NY 10523 (914) 347-2474 Polycarbonate Film Guide. PCIM (Power Conversion & Intelligent Motion) is published by Intertec International Inc., 2472 Eastman Ave., Bldg. 33-34, Ventura, California 93003-5774, (805) 650-7070. PCIM is free to qualified applicants. Back issues, such as the Buyer’s Guide can be purchased. Sanyo Video Components (USA) Corp. 2001 Sanyo Ave. San Diego, CA 92173 (619) 661-6835 Low ESR Filter Capacitors-Solid Aluminum Electrolytic Capacitors (OS-CON) Sprague 678 Main St. P.O. Box 231 Sanford, ME 04073 (207) 324-4140 Tantalum Capacitors Current Sense Resistors Dale Electronics 1122 23rd St. P.O.Box 609 Columbus, NE 68602 (402) 564-3131 Resistors, Inductors, Xformers Diodes Fuji/Collmer 14368 Proton Rd. Dallas, TX 75244 (214) 233-1589 Low Current Schottkys General Instruments 10 Melville Park Rd. Melville, NY 11747 (516) 847-3222 Motorola Inc. 5005 E. McDowell Rd. P.O. Box 2953 Phoenix, AZ 85062 (602) 244-5768 Diodes Philips Components Disc. Prod. Div. 100 Providence Pike Slatersville, RI 02876 (401) 762-3800 Discrete Semi Group Ferrite Beads Fair-Rite Products Corp. 1 Commerial Row P.O. Box J Wallkill, NY 12589 (914) 895-2055 Toshiba America Elec. Components 9775 Toledo Way Irvine, CA 92718 (714) 455-2000 IRC 4222 South Staples St. Corpus Christi, TX 78411 (512) 992-7900 Heat Sinks Aavid Engineering, Inc. One Kool Path Box 400 Laconia, NH 03247 (603) 528-3400 KRL 160 Bouchard St. Manchester, NH 03103 (603) 668-3210 Int’l Electronic Research Group 135 W. Magnolia Blvd. Burbank, CA 91502 (213) 849-2481 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. AN54-43 Application Note 54 Thermalloy 2021 W. Valley View Lane Dallas, TX 75234 (214) 243-4321 Toko America Incorporated 1250 Feehanville Dr. Mount Propsect, IL 60056 (708) 635-3200 Inductors and Transformers Beckman Industrial Corp. 4200 Bonita Place Fullerton, CA 92635 (714) 447-2345 Inductors, Xformers including SMT Magnetic Materials Fair-Rite Products Corp. 1 Commercial Row P. O. Box J Wallkill, NY 12589 (914) 895-2055 Ferrite Caddell-Burns 258 East Second St. Mineola, NY 11501 (516) 746-2310 Micrometals, Inc. 1190 N. Hawk Circle Anaheim, CA 92807 (800) 356-5977 Powdered Iron Coilcraft 1102 Silver Lake Rd. Cary, IL 60013 (800) 322-2645 Coiltronics 6000 Park of Commerce Blvd. Boca Raton, FL 33487 (407) 241-7876 Full Line including Surface Mount Inductors Dale Electronics E. Highway 50 P. O. Box 180 Yankton, SD 57078 (605) 665-9301 Inductors, Xformers including SMT Gowanda Electronics Corp. 1 Industrial Place Gowanda, NY 14070 (716) 532-2234 Hurricane Electronics Lab P.O. Box 1280 Hurricane, UT 84737 (801) 635-2003 Murata Erie North America 2200 Lake Park Drive Smyrna, GA 30080 (404) 436-1300 Renco 60 E. Jefryn Blvd. Deerpark, NY 11729 (516) 586-5566 Sumida Electronic 5999 New Wilke Rd., Ste. 110 Rolling Meadows, IL 60008 (708) 956-0666 TDK Corp. of America 1600 Feehanville Dr. Mount Prospect, IL 60056 (708) 803-6100 AN54-44 Magnetics Div. Spang & Co P.O. Box 391 Butler, PA 16003-0391 (412) 282-8282 Molypermalloy, Kool Mµ, Ferrite Philips Components Disc. Prod. Div. Materials Group 1033 King Highway Saugerties, NY 12477 (914) 246-2811 Ferrite Pyroferric International, Inc. 200 Madison St. Toledo, IL 62468 (217) 849-3300 Powdered Iron Siemens Components, Inc. 186 Wood Ave. South Iselin, NJ 08830 (908) 906-4300 Ferrite TDK Corp. of America 1600 Feehanville Dr. Mount Prospect, IL 60056 (708) 803-6100 Ferrite Mounting Hardware Bergquist 5300 Edina Industrial Blvd. Minneapolis, MN 55439 (612) 835-2322 Thermally Conductive Insulators Thermalloy 2021 W. Valley View Lane Dallas, TX 75234 (214) 243-4321 Power Sockets, Thermal Compounds, and Adhesives Thermally Conductive Insulators, Mounting Kits Power MOSFETs International Rectifier Corp. 233 Kansas St. El Segundo, CA 90245 (310) 322-3331 Motorola Inc. 5005 E. McDowell Rd. Phoenix, AZ 85008 (602) 244-3576 Siliconix 2201 Laurelwood Rd. Santa Clara, CA 96056 (800) 554-5565 Resistors Micro-Ohm Corp. 1088 Hamilton Rd. Duarte, CA 91010 (818) 357-5377 Thermo Disc 1981 Port City Blvd. Muskegon, MI 49443 (616) 777-2602 RCD Components, Inc. 520 East Industrial Park Dr. Manchester, NH 03109 (603) 669-0054 Caddock Electronics 1717 Chicago Ave. Riverside, CA 92507-2364 (909) 788-1700 Wire Belden Wire & Cable P.O. BOX 1980 Richmond, IN 47375 (317) 983-5200 Stockwell Rubber 4749 Tolbut St. Philadelphia, PA 19136 (800) 523-0123 Thermally Conductive Insulators Linear Technology Corporation LT/GP 1094 5K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1993