LINEAR TECHNOLOGY JANUARY 2009 IN THIS ISSUE… COVER ARTICLE 2-Phase, Non-Synchronous Boost Controller Simplifies Design of High Voltage, High Current Supplies ............................................................1 Muthu Subramanian and Tick Houk Linear in the News…............................2 DESIGN FEATURES Reliable Precision Voltage Reference with 5ppm/°C Drift is Factory Trimmed and Tested at –40°C, 25°C and 125°C ............................................................7 Michael B. Anderson and Brendan Whelan Ultralow Noise 15mm ×15mm × 2.8mm µModule™ Step-Down Regulators Meet the Class B of CISPR 22 and Yield High Efficiency at up to 36VIN ...........10 Judy Sun, Jian Yin, Sam Young and Henry Zhang Dual Hot Swap™ Controller Brings Digital Monitoring to AdvancedTCA, µTCA and AMC Applications...............15 Josh Simonson ±32V Triple-Output Supply for LCDs, CCDs and LEDs Includes Fault Protection in a 3mm × 3mm QFN .......20 Eko T Lisuwandi PD Interface for PoE+ Includes 25.5W Classification and Protection Features in a Low Profile 4mm × 3mm DFN ..........................................................26 Kirk Su DESIGN IDEAS .....................................................30–42 (complete list on page 30) Design Tools.......................................43 Sales Offices......................................44 VOLUME XVIII NUMBER 4 2-Phase, Non-Synchronous Boost Controller Simplifies Design of High Voltage, High Current Supplies by Muthu Subramanian and Tick Houk Introduction Due to an increasing need for high power step-up power supplies in automotive and industrial applications, Linear Technology has recently introduced the LTC3862 family of 2-phase, single output non-synchronous boost DC/DC controllers. The LTC3862 provides a flexible, high performance step-up controller in three convenient package options: GN24, 5mm × 5mm 24-pin exposed pad QFN and 24-pin exposed pad TSSOP. The LTC3862 is optimized for power MOSFETs that require 5V gate drive, whereas the LTC3862-1 is designed for 10V gate drive MOSFETs. The LTC3862 utilizes a fixed frequency, peak current mode control topology to drive ground-referenced power MOSFETs, each with a current sense resistor in its source. The use of a precision transconductance (gm) error amplifier allows for easy loop compensation and facilitates the parallel connection of several ICs in multiphase applications. The operating frequency can be programmed from 75kHz to 500kHz using a single resistor, and a phase lock loop allows the switching frequency to be synchronized to an external clock over a 50kHz to 650kHz range. The LTC3862 is a versatile control IC optimized for a wide variety of step-up DC/DC converter applications. This makes it easy to optimize efficiency, size and weight of the power supply, while keeping component and manufacturing costs low. A 24V, 5A Car Audio Power Supply Today’s high end car audio systems require significant power to drive upwards of seven speakers inside the passenger compartment. High frequency speakers such as tweeters are generally very efficient, but low frequency drivers such as subwoofers require substantial power to achieve high volume. In addition to the need for high power, the car audio system should be itmmune to changes in the battery voltage. These requirements can be met through the use of a step-up converter for the power continued on page L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered trademarks of Linear Technology Corporation. Adaptive Power, Bat-Track, BodeCAD, C-Load, DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode Dimming, No Latency ΔΣ, No Latency Delta-Sigma, No RSENSE, Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, TimerBlox, True Color PWM, UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. DESIGN FEATURES L LTC3862, continued from page VIN 5V TO 24V L1 4.2µH CDEP145-4R2 1nF GATE1 SENSE1 SLOPE BLANK LTC3862 ITH FB 100pF 130k 22µF 25V 22µF 25V 22µF 25V VIN 100µF 10µF 50V 35V 4.7µF INTVCC 6.98k VOUT 84.5k 1µF SS 26.7k 24.9k + RUN FREQ 10nF 1nF 0.007Ω 100µF 1W 35V 10nF PHASEMODE SENSE1– 45.3k Q1 Si7386DP 10Ω + + 3V8 DMAX D1 MBRD835L 10Ω PGND SGND CLKOUT SYNC PLLFLTR 0.007Ω 1W Q2 Si7386DP GATE2 SENSE2– 10nF L2 4.2µH CDEP145-4R2 SENSE2+ VOUT 24V 5A (MAX) 10µF 50V 10µF 50V 10µF 50V D2 MBRD835L Figure 1. A 120W 2-phase, 24V/5A output car audio power supply amplifiers. Figure 1 shows a 2-phase, 24V/5A output audio power supply that operates from a car battery, and Figure 2 shows the efficiency curve for this converter. A 2-phase design with an operating frequency of 300kHz allows the use of significantly smaller output capacitors and inductors than a single-phase design. To keep the output ripple voltage below 60mV peak-to-peak and satisfy the RMS ripple current demand, a combination of two 100µF, 35V aluminum electrolytic capacitors are connected in parallel with four 10µF, 50V ceramic capacitors. The 4.2µH, 10.6A inductor (CDEP145-4R2) from Sumida Inductors is chosen for its high 100 A 2-phase design with an operating frequency of 300kHz allows the use of significantly smaller output capacitors and inductors than a single-phase design. Also, the output current of this converter can easily be scaled by adding additional power stages and controllers, without modifying the basic design. 10000 VIN = 12V VOUT = 24V 95 EFFICIENCY (%) POWER LOSS 1000 85 80 75 100 POWER LOSS (mW) EFFICIENCY 90 ILOAD 5A/DIV IL1 5A/DIV IL2 5A/DIV VOUT 500mV/DIV 1000 LOAD CURRENT (mA) 100 10000 Figure 2. Efficiency and power loss vs load current for the 120W car audio power supply Linear Technology Magazine • January 2009 VIN = 12V VOUT = 24V ILOAD = 2A TO 5A 500µs/DIV Figure 3. Inductor current waveforms in load step show accurate current matching between load sharing channels saturation current rating and surface mount package design. The MOSFET is a Vishay Si7386DP, which has a maximum RDS(ON) of 7mΩ at VGS = 10V and 9.5mΩ at VGS = 4.5V. The 35V, 8A Schottky from On Semiconductor (MBRD835L) offers surface mount capability and small size. It should be noted that the output current of a converter such as this can easily be scaled by adding additional power stages and controllers, without modifying the basic design. Excellent Channel-to-Channel Current Matching Ensures a Balanced Thermal Design In order to provide the best channelto-channel inductor current matching, the LTC3862 is designed to make the transfer function from the output of the error amplifier (the ITH pin) to the current comparator inputs (SENSE+ and SENSE– pins) as accurate as possible. The specification for the maximum current sense threshold is 75mV, and the channel-to-channel (VSENSE1 – VSENSE2) mismatch specification is ±10mV, over the –40°C to 150°C temperature range. This excellent matching ensures balanced inductor currents and a thermally stable design, even with multiple regulators daisychained together. Figure 3 shows how L DESIGN FEATURES SW1 50V/DIV IL1 5A/DIV SW2 50V/DIV SW2 10V/DIV IL1 2A/DIV IL2 2A/DIV IL1 1A/DIV IL2 1A/DIV VIN = 12V VOUT = 48V ILOAD = 100mA VIN = 24V 2.5µs/DIV VOUT = 48V, 1.5A Figure 4. Inductor current and switch node voltage waveforms at heavy load, continuous conduction mode (CCM) well matched the inductor currents are for the car audio power supply during a load step. Constant Frequency Operation over a Wide Load Current Range Figure 5. Inductor and switch node voltage waveforms at light load, discontinuous conduction mode (DCM) VIN = 12V 2µs/DIV VOUT = 48V 1A PHASEMODE = SGND Figure 7. Synchronizing the LTC3862 to an external clock using the phase lock loop Strong Gate Drivers and a High Current Internal LDO as shown in Figure 6. This is a normal Complete the Package operating condition that doesn’t cause any problems in the system, as long as the peak inductor current is low. In general, the lower the load current at the onset of pulse-skipping, GATE1 150k LTC3862-1 45.3k FB 6.8µF 50V VIN ITH 100pF 10Ω SGND 324k CLKOUT 0.020Ω 1W VOUT 72V 2.2µF 100V s6 Q2 HAT2267H 10nF SENSE2+ L2 58µH PA2050-583 D2 B3100 Figure 8. An 8.5V–28V input, 72V/1.5A output low emissions diesel fuel injector actuator supply In high output voltage systems, switching losses in the power MOSFETs can sometimes exceed the conduction losses. In order to reduce switching losses as much as possible, the LTC3862 incorporates strong gate drivers. The PMOS pull-up transistor has a typical RDS(ON) of 2.1Ω, and the NMOS pull-down transistor has a typical RDS(ON) of 0.7Ω. In addition to reducing switching losses, these strong gate drivers allow two power MOSFETs to be connected in paral- VOUT 20V/DIV PGND GATE2 SENSE2– SYNC PLLFLTR 47µF 100V 4.7µF INTVCC 5.62k VOUT 6.8µF 50V 6.8µF 50V 1µF SS 47µF 100V 24.9k 0.1µF 1.5nF 0.020Ω 1W + RUN FREQ D1 B3100 Q1 HAT2267H 10nF PHASEMODE SENSE1– 45.3k L1 58µH PA2050-583 10Ω SENSE1+ BLANK the better, since constant frequency operation is maintained down to this threshold. In Figure 6 the onset of pulse-skipping occurs at a relatively low 0.2% of the maximum load current. For systems where synchronization to an external clock is required, the LTC3862 contains a phase lock loop (PLL). Figure 7 illustrates the switching waveforms with an external sync signal applied to the SYNC pin. CLKOUT 10V/DIV 1nF SLOPE Figure 6. Inductor and switch node voltage waveforms at light load (pulse-skipping) SYNC 10V/DIV VIN 8.5V TO 28V 3V8 VIN = 17V 1µs/DIV VOUT = 24V LIGHT LOAD (10mA) GATE1 10V/DIV GATE2 10V/DIV Constant frequency operation eases the task of input and output filter design, and prevents a power supply from becoming audible at light load. At heavy load, the inductor currents are generally continuous (CCM), as shown in Figure 4. At light load, the inductor current will go discontinuous (DCM), as shown in Figure 5. When the load current drops below what can be supported by the minimum on-time of the converter (approximately 180ns), the controller will begin to skip cycles in order to maintain output regulation, DMAX 1µs/DIV + SW2 50V/DIV IL2 5A/DIV VOUT 100mV/DIV AC COUPLED SW1 10V/DIV SW1 50V/DIV IL 5A/DIV VIN = 24V VOUT = 72V 500µs/DIV Figure 9. Load step waveforms for diesel fuel injector actuator supply Linear Technology Magazine • January 2009 DESIGN FEATURES L protecting the power MOSFETs from switching at low VGS. The LTC3862 is capable of operation over a 4V to 36V input voltage range, making it suitable for a wide variety of boost applications. Lower Emissions Diesel Fuel Injection: A 8.5V–28V Input, 72V, 1.5A Output Boost Tomorrow’s low emissions diesel fuel injection systems require more precise and faster actuation of the fuel injectors than do their gasoline counterparts. Stepping up the voltage VIN 4.5V TO 5.5V 1nF 3V8 DMAX GATE1 BLANK 10nF RUN SS LTC3862 ITH FB 330pF 33µF 10V 33µF 10V 33µF 10V VIN INTVCC 10Ω PGND SGND 15µF 25V 10nF SENSE2+ 3V8 GATE1 BLANK SENSE1– + RUN FREQ 1µF SS LTC3862 ITH FB SGND 33µF 10V 33µF 10V 33µF 10V VIN 10nF 10k 220µF 15µF 25V 16V 4.7µF INTVCC 10Ω PGND 0.005Ω 1W Q3 HAT2165H GATE2 CLKOUT SYNC PLLFLTR D1 MBRB2515LT41 0.005Ω 220µF 1W 16V 10nF PHASEMODE D2 MBRB2515LT41 Q1 HAT2165H 10Ω SENSE1+ SLOPE 330pF L2 2.7µH CDEP145-2R7 L1 2.7µH CDEP145-2R7 1nF DMAX 15µF 25V SENSE2– CLKOUT SYNC PLLFLTR 15µF 25V 15µF 25V 15µF 25V SENSE2– 10nF SENSE2+ VOUT 12V 15A 15µF 25V 0.005Ω 1W Q3 HAT2165H GATE2 45.3k 220µF 15µF 25V 16V 4.7µF 18.7k 165k 1µF + 3.83k VOUT 0.005Ω 220µF 1W 16V + FREQ 10nF 10nF ON/OFF CONTROL PHASEMODE SENSE1– 45.3k D1 MBRB2515LT41 Q1 HAT2165H 10Ω SENSE1+ SLOPE L1 2.7µH CDEP145-2R7 of the system is an easy way to achieve fast actuation by increasing di/dt in the actuator, since the energy stored on a capacitor is CV2/2. Boosting the car battery voltage from 13V to 72V significantly increases the di/dt, enabling faster actuation. The actuation of the injector typically discharges the supply capacitor by 10V–20V, after which the boost converter recharges the output cap to 72V. Figure 8 illustrates this 8.5V to 28V input, 72V/1.5A output 2-phase boost converter. Figure 9 illustrates the load step for a simulated injector. + lel for each channel in high current applications. In order to simplify operation in single-supply systems, the LTC3862 includes a 5V low dropout regulator (LDO) that can support output currents up to 50mA. The use of a PMOS output transistor ensures that the full supply voltage is available for driving the power MOSFETs under low supply conditions, such as during automotive cold cranking. An undervoltage lockout circuit detects when the LDO output voltage falls below 3.3V and shuts off the gate drivers, thereby L2 2.7µH CDEP145-2R7 D2 MBRB2515LT41 Figure 10. A 4-phase, 12V/15A industrial power supply that operates from a 5V input Linear Technology Magazine • January 2009 L DESIGN FEATURES IL1 MASTER 5A/DIV IL2 MASTER 5A/DIV IL1 SLAVE 5A/DIV IL2 SLAVE 5A/DIV ILOAD 2.5A-5A 5A DIV IL1 MASTER 5A/DIV IL2 MASTER 5A/DIV IL1 SLAVE 5A/DIV IL2 SLAVE 5A/DIV VOUT 10V/DIV VOUT 200mV/DIV VIN 5V/DIV VIN = 5V VOUT = 12V RLOAD = 10Ω 1ms/DIV VIN = 5V VOUT = 12V Figure 11. Power supply start-up waveforms for 4-phase, 12V/15A industrial power supply This power supply operates at a switching frequency of 300kHz in order to reduce switching losses and uses a 57.8µH, 5A inductor (PA2050-583). An 80V Renesas HAT2267H MOSFET was chosen for this application, in order to provide sufficient guardband above the 72V output. The MOSFET has a maximum RDS(ON) of 13mΩ at VGS = 10V. The Diodes Inc surface mount diode (B3100) was chosen for the 3A output current level. A combination of a two 47µF, 100V electrolytic and six 2.2µF, 100V low ESR ceramic capacitors are used to reduce the output ripple to below 100mV peak-to-peak and satisfy the RMS ripple current requirement. A 4-Phase, 5V Input, 12V/15A Output, Industrial Power Supply Figure 10 illustrates an industrial power supply that converts a 5V input to a 12V output at up to 15A of load current. The use of four phases greatly eases the task of choosing the power components, and reduces output ripple significantly. Figure 11 250µs/DIV Figure 12. Load step waveforms for 4-phase, 12V/15A industrial power supply In high output voltage systems, switching losses in the power MOSFETs can sometimes exceed the conduction losses. In order to reduce switching losses as much as possible, the LTC3862 incorporates strong gate drivers. The PMOS pull-up transistor has a typical RDS(ON) of 2.1Ω, and the NMOS pull-down transistor has a typical RDS(ON) of 0.7Ω. In addition to reducing switching losses, these strong gate drivers allow two power MOSFETs to be connected in parallel for high current applications. shows the start-up waveforms for this converter. Figure 12 shows the load step waveforms. Multiphase operation is made possible using the PHASEMODE, SYNC and CLKOUT pins. The PHASEMODE pin controls the phase relationship between GATE 1 and GATE 2, as well as between GATE 1 and CLKOUT. The CLKOUT pin of a master controller is connected to the SYNC pin of a slave, where the phase lock loop ensures proper synchronization. The PHASEMODE pin can be used to program 2-, 3-, 4-, 6- and 12-phase operation. 48V/5A Demo Circuit The DC1286A demonstration circuit board is designed for high power applications, providing a 48V/5A output using the GN24 package option of the LTC3862 or LTC3862-1. The 6-layer PCB design ensures proper routing of the SENSE lines, and exhibits minimal jitter even at 50% duty cycle. Jumpers are provided to easily change the BLANK time, PHASE, maximum duty, and SLOPE compensation. There is an optional onboard 12V VIN supply to power the IC, and the component footprint provides flexibility to use various inductors, MOSFET’s and diodes. Conclusion Figure 13. 48V/5A output, high power demonstration circuit The LTC3862 is a versatile control IC optimized for a wide variety of stepup DC/DC converter applications. Its flexible, high performance operation and three convenient package options make it possible to optimize efficiency, size and weight of the power supply, while keeping the total component and manufacturing costs low. L Linear Technology Magazine • January 2009