February 2016 I N T H I S I S S U E low IQ, 60V monolithic boost/sepic/inverting converter in ThinSOT or 3mm x 2mm DFN 10 98% efficient buck-boost LED driver with internal PWM dimming and spread spectrum 14 matrix LED dimmer enables accurate color control in RGBW LEDs 24 monolithic 3mm × 3mm, 17V, 2A step-down regulator 29 Volume 26 Number 1 The Evolution of High Voltage Digital Power System Management Hellmuth Witte ® The LTC 3886 takes inputs up to 60V and produces two 0.5V-to13.8V outputs—enabling it to easily drop into industrial, server and automotive environments as an intermediate or point-of-load (POL) supply. Other controllers with similarly impressive input/ output ranges cannot match the LTC3886’s digital management capabilities. Its I2C-based PMBus-compliant serial interface allows power supply designers to configure, monitor, control and expand ® capabilities via PC-based, graphical LTpowerPlay and then store optimal production settings in the LTC3886’s onboard EEPROM. No board changes are required, since capabilities and optimization settings (including compensation) can be changed via software. This 2-channel PolyPhase® DC/DC synchronous step-down switching regulator controller employs a constant-frequency, current-mode architecture, with accurate input and output current sensing and programmable loop compensation, and is available in a 52-lead (7mm × 8mm) QFN package. Accurate voltage and current sensing, adjustable compensation and dedicated PGOOD pins make the LTC3886 ideal for industrial applications that demand versatile power system design, control, monitoring, programming and accuracy. FLEXIBLE FEATURE SET Figure 1 shows a generalized schematic of a LTC3886. The 100k Hz to 750k Hz PWM switching frequency range, and low RDS(ON) integrated N-channel MOSFET gate drivers support a plethora of external components and enable power capability and system cost optimization. The The LTC6811 ushers in Linear’s fourth generation of multicell battery stack monitors. See page 2 for more about this powerful device. w w w. li n ea r.com (continued on page 4) The LTC3886’s regulation and supervision accuracy reduces total system costs with fewer output capacitors, while still meeting the tight input voltage requirements of downstream ICs. (LTC3886, continued from page 1) LTC3886 can readily accommodate a wide variety of industrial, medical, and point-of-load applications due to a flexible programmable feature set that addresses the specific application at hand. ADAPTABILITY THROUGH PROGRAMMABILITY The following parameters of the LTC3886 are configurable and storable in the onboard EEPROM via the I2C/SMBus interface: •Fault response and fault propagation via the FAULT pins •Device address Switching frequency, device phasing and output voltage are also programmable with external configuration resistors. In addition, all 128 possible addresses are resistor selectable. POWER GOOD, SEQUENCING AND PROGRAMMABLE FAULT RESPONSE •Output voltage, overvoltage, undervoltage and overcurrent limit •Input ON/OFF voltage, input overvoltage and input overcurrent warning •Digital soft-start/stop, sequencing, margining •Control loop compensation • PWM switching frequency and phasing The dedicated PGOOD pin for each channel simplifies enabling event-based sequencing across multiple LTC3886s and other power system management ICs. The LTC3886 also supports time-based sequencing. After waiting the TON_DELAY amount of time following the RUN pin going high, a PMBus command to turn on, or the VIN pin voltage rising above a preprogrammed voltage, the outputs are enabled. Time-based power off sequencing is handled in a similar way. To assure proper time based sequencing, simply connect all SHARE_CLK pins together and connect together the RUN pins of all the power system management ICs. The LTC3886 FAULT pins are configurable to indicate a variety of faults including OV, UV, OC, OT, timing faults and peak current faults. In addition, the FAULT pins can be pulled low by external sources, indicating a fault in some other portion of the system. The fault responses of the LTC3886 are configurable and allow the following options: •Ignore •Shut Down Immediately—latchoff •Shut Down Immediately—retry indefinitely at the time interval specified in MFR_RETRY_DELAY Table 1. Summary of Linear’s power system management controllers and PSM µModule regulators µMODULE REGULATORS CONTROLLERS LTM4675 LTM4676A LTM4677 LTC3880 LTC3882 LTC3883 LTC3884 LTC3886 LTC3887 V OUT range (V) 0.5–5.5 0.5–5.5 0.5–5.5 0.5–4.0, ch0 0.5–5.4, ch1 0.5–5.3 0.5–5.4 0.5–5.4 0.5–13.2 0.5–5.5 V IN range (V) 4.5–17 4.5–17 4.5–17 4.5–24 3.0–38 4.5–24 4.5–38 4.5–60 4.5–24 V OUT accuracy (%) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Input current sense calibrated calibrated calibrated inferred L L L inferred I OUT max (A) dual 9 or single 18 dual 13 or single 26 dual 18 or single 36 30/phase 1 40/phase 1 30/phase 1 30/phase 1 30/phase 1 30/phase 1 DCR sensing NA NA NA low ultralow low very low low low L L Digitally adjustable loop compensation 1Controller maximum I OUT depends on external components 4 | February 2016 : LT Journal of Analog Innovation design features Figure 1. The LTC3886 is versatile and flexible. It features wide input and output ranges and and it is highly customizable via PMBus. Accurate telemetry is also available over the digital bus. All features can be controlled via LTpowerPlay. ACCURACY AND PRECISION VIN 4.5V TO 60V LTC3886 HOST COMPUTER 3 UP TO SIX PHASES PMBus/ SMBus/ I2C VCHANNEL1 0.5V TO 13.8V ≤30A LOAD OR CURRENT SHARE ≤60A VSENSE1 VIN PROGRAMMABLE LOOP COMPENSATION VCHANNEL1 0.5V TO 13.8V ≤30A EEPROM DATA LOGGING LOAD VSENSE0+ VSENSE0– FAULT LOGGING AND TELEMETRY The LTC3886 supports fault logging, which stores telemetry and fault status data in a continuously updated RAM buffer. After a fault event occurs, the buffer is copied from RAM to EEPROM and becomes a persistent fault log, which can be read back at a later date to determine what caused the fault. EXTV CC PIN FOR MAXIMUM EFFICIENCY The EXTVCC pin is provided to minimize application power loss and supports voltages of 5V to 14V. It enables designs with optimal circuit efficiency and minimal die temperature, and enables the LTC3886 to efficiently supply its own bias power from the output voltage. Modern applications require supply voltage regulation and supervision with stringent tolerances. These requirements are met with a high speed analog control loop and an integrated 16-bit ADC and 12-bit DACs. The output voltage accuracy of the LTC3886 is guaranteed at ±0.5% over the full operating temperature. In addition, the output voltage overvoltage and undervoltage comparators have less than ±2% error over temperature. The LTC3886’s regulation and supervision accuracy reduces total system costs with fewer output capacitors, while still meeting the tight input voltage requirements of downstream ICs. The unique high side 60V input current sense amplifier measures the input current with less than ±1.2% error over temperature. The output current is guaranteed accurate to ±1.5% over temperature. The internal die temperature measurement of the LTC3886 is guaranteed accurate to 0.25°C, and the external temperature telemetry has less than ±1°C error. Figure 2. LTpowerPlay February 2016 : LT Journal of Analog Innovation | 5 Figure 3. High efficiency 425kHz 4-phase, 48V input to 5V output, 50A step-down converter using the LTC3870 phase expander with the LTC3886 10µF M5 4mΩ L3 2.6µH D3 0.1µF TG1 BOOST0 M7 D4 INTVCC VIN TG0 1µF M6 0.1µF L2 2.6µH BOOST1 SW0 SW1 BG0 BG1 ISENSE0+ ISENSE1+ ISENSE0– ISENSE1– ILIM SYNC FAULT0 30Ω INTVCC_LTC3870 PHASMD FREQ FAULT1 530µF 30Ω 1000pF 1000pF 30Ω 4mΩ M8 LTC3870 30Ω VIN 22µF RUN0 MODE0 RUN1 MODE1 100k TO LTC3886 VOUT EXTVCC + ITH0 100pF GND ITH1 530µF + VOUT PGOOD ITH RUN FAULT SYNC EXPANSION State of the art power management systems require increasing power and control, but must fit into dwindling board space. Parallel multiphase rails are the best solution for high power requirements because they enable high power density and efficient expandability. The LTC3886 supports accurate PolyPhase® current sharing for up to six phases between multiple LTC3886s. This allows system designers to add power stages as needed. In addition, the dualphase LTC3870 PolyPhase expander IC mates seamlessly with the LTC3886 to create 6-phase PolyPhase rails at a lower price point. Figure 3 shows a 4-phase 6 | February 2016 : LT Journal of Analog Innovation solution. Figure 4 shows the dynamic current sharing among the phases. The LTC3870 requires no additional I2C addresses, and it supports all programmable features as well as fault protection. When configuring a PolyPhase rail with multiple LTC3886/LTC3870s, the user simply shares the SYNC, ITH, SHARE_CLK, FAULTn, PGOODn and ALERT pins of all the channels connected to the rail. The relative phasing of all the channels should be set to be equally spaced. This phase interleaving results in the lowest peak input current and lowest output voltage ripple, and reduces input and output capacitor requirements. System architects often fragment the power system to meet functional and board space requirements: the LTC3886/ LTC3870 PolyPhase rail simplifies fragmentation by breaking up the power and control components, allowing them to be easily placed in available spaces. Fragmentation also spreads the heat of the power supply system over the PCB, simplifying overall thermal extraction and reducing hot zones. design features 10µF 5mΩ VIN 10µF M1 4mΩ D1 INTV V I + I – CC IN IN IN TG0 0.1µF L0 2.6µH BG0 5k SYNC L1 2.6µH 4mΩ LTC3886 M4 BG1 VDD25 SDA 10k SCL 10k ALERT 20k 20k 10k 10k 20k 17.8k 17.8k 23.2k 23.2k 15k VOUT0_CFG FAULT0 FAULT1 10k RUN0 VOUT1_CFG ASEL0 ASEL1 FREQ_CFG RUN1 WP PHAS_CFG SHARE_CLK 10k TSNS0 ISENSE0+ 30Ω 30Ω M2 0.1µF SW1 PGOOD1 10k TO LTC3870 1µF VIN 48V PGOOD0 10k VDD33 22µF BOOST1 SW0 10k TSNS1 ISENSE1+ 30Ω 1000pF 1000pF 30Ω ISENSE0– ISENSE1– VSENSE1 VSENSE0+ – VSENSE0 EXTVCC ITH0 ITH1 ITHR0 ITHR1 VDD33 GND VDD25 VOUT 530µF TG1 BOOST0 M3 D2 2Ω + 10nF 2200pF 220pF 1µF + 10nF VOUT 5V 50A 530µF 1µF VOUT PGOOD ITH RUN FAULT SYNC PROGRESSION Figure 2 shows a screen from LTpowerPlay, a powerful Windowsbased software development tool with graphical user interface (GUI) that fully supports the LTC3886. LTpowerPlay enhances evaluation when connected to demo boards and directly to application hardware. LTpowerPlay provides unparalleled development, diagnostic and debug features. Telemetry, system fault status and PMBus command values are all readily accessible through the GUI. The LTC3886 and other power system management ICs can be uniquely configured with ease using LTpowerPlay. Complete information is available at: http://www.linear.com/ltpowerplay. L0, L1, L2, L3: WÜRTH 7443556260 2.6µH M1, M2, M5, M6: RENESAS RJK0651DPB M3, M4, M7, M8: RENESAS RJK0653DPB Figure 4. Dynamic current sharing for the 4-phase circuit shown in Figure 3; load step (a) rising and (b) falling. (a) (b) ILx 5A/DIV ILx 5A/DIV 10µs/DIV 10µs/DIV February 2016 : LT Journal of Analog Innovation | 7 The LTC3886 offers programmable loop compensation to assure loop stability and optimize the transient response of the controller without any external component changes. Gone are the days of painstakingly soldering and unsoldering multitudes of components to achieve the ideal compensation. A few clicks of a mouse using LTpowerPlay, and the LTC3886 can have optimal compensation. ADJUSTABLE COMPENSATION The LTC3886 offers programmable loop compensation to assure loop stability and optimize the transient response of the controller without any external component changes. Gone are the days of painstakingly soldering and unsoldering multitudes of components to achieve the ideal compensation. A few clicks of a mouse using LTpowerPlay, and the LTC3886 can have optimal compensation. The control loop is fine-tunable quickly and painlessly, regardless of last minute component substitutions or variations. This empowers designers to squeeze the maximum performance out their systems by removing unnecessary output capacitors while saving board space and cost. The process of programming loop compensation is summarized in Figures 5, 6 and 7. The error amplifier gm (Figure 5) is programmable from 1.0mmho to 5.73mmho using bits[7:5] of the MFR_PWM_COMP command, and the compensation resistor RTH , inside the LTC3886 is programmable from 0kΩ to 62kΩ using bits[4:0] of the Figure 5. Programmable loop compensation MFR_PWM_COMP command. Only two external compensation capacitors, CTH and CTHP, are required in the design and the typical ratio between CTH and CTHP is set to a typical value of 10. By adjusting the gm and RTH only, the LTC3886 provides a programmable type II compensation network for optimizing the loop over a wide range of output capacitors, and compensation component tolerances. Adjusting the gm of the error amplifier proportionately changes the gain of the compensation loop over the entire frequency range without moving the pole and zero location, as shown in Figure 6. Adjusting the RTH resistor changes the pole and zero location, as shown in Figure 7. Once the voltage and current ranges of the LTC3886 are determined, changes to the output voltage or current limit do not affect the loop gain. When the output voltage is modified by either changing voltage command, or by margining, the transient response of the circuit remains constant. gm RTH ITH_R ITH CTH CTHP + VREF – FB 8 | February 2016 : LT Journal of Analog Innovation The LTC3886 has a wide input voltage range of 4.5V to 60V, and an output voltage range of 0.5V to 13.8V. This makes the LTC3886 an excellent choice for efficiently regulating a high voltage input supply voltage down to an intermediate bus voltage. The intermediate bus voltage powers downstream point-of-load converters (POL). When used as an intermediate bus converter to power downstream power system management POLs, the LTC3886 enables the user to optimize the intermediate bus voltage for maximum efficiency. Since voltage and current telemetry provided by the LTC3886 and power system management ICs is so accurate, it is possible to produce accurate system efficiency measurements in real time. This, in turn, makes it possible to create an optimization program, in which a microcontroller determines the optimal intermediate bus voltage for various conditions. Figure 7. RTH adjust Figure 6. Error amp gm adjust GAIN ACCURATE TELEMETRY FOR OPTIMIZING SYSTEM EFFICIENCY WITH AN INTERMEDIATE BUS TYPE II COMPENSATION GAIN TYPE II COMPENSATION INCREASE gm INCREASE RTH FREQUENCY FREQUENCY design features See the video: www.linear.com/solutions/5761 The LTC3886 expands Linear’s portfolio of power system management controllers into the high voltage arena. A wide output voltage range of 0.5V to 13.8V, along with accurate voltage and current sensing, adjustable compensation, and dedicated PGOOD pins, gives LTC3886 users maximum design flexibility and performance. The LTC3886 is ideal for industrial applications that demand versatile power system design, control, monitoring, programming and accuracy. n Figure 8. The LTC3886 set up as an intermediate bus to drive a power management IC POL converter. Telemetry from the LTC3886 intermediate supply and the POL ICs is used by a Linduino One demonstration circuit to optimize system efficiency by adjusting the intermediate bus voltage as load current changes. INTERMEDIATE SUPPLY VIN 48V LTC3886 9V–13V INTERMEDIATE BUS PMBus POINT-OF-LOAD CONVERTER (8-PHASE) LTM4676 (2-PHASE) VIN = 48V IIN = 6.6A VOUT = 9V–13V IOUT = 25A VOUT 0.6V TO 5V UP TO 100A LTM4676 (2-PHASE) LTM4676 (2-PHASE) LINDUINO ONE = 80 POUT VOUT I OUT = PIN VINIIN LTM4676 (2-PHASE) 95 VIN = 48V 75 70 65 ILOAD = 10A ILOAD = 20A ILOAD = 40A ILOAD = 80A ILOAD = 100A 60 55 50 VIN = 48V 90 EFFICIENCY (%) The efficiency of the LTC3886 vs the intermediate bus voltage is shown in Figure 9. The total system efficiency vs the intermediate bus voltage is shown in Figure 10. The curves represent point-ofload currents of 10A, 20A, 40A, 80A and 100A, with the peak efficiency shifting respective of load current. Higher load currents require a higher intermediate bus voltage to operate at peak efficiency. Setting the intermediate bus voltage at a fixed voltage that is too high lowers the total efficiency of the system at low load currents. Compared to a using a standard fixed 12V intermediate bus voltage, optimizing the intermediate bus voltage with the LTC3886 improves efficiency by 6.2% at 10A of load current, 3.5% at 20A, and 1% at 40A. This technique enables efficiency optimization over the full workload of a system. SUMMARY EFFICIENCY (%) To demonstrate this, a 9V-to-13V LTC3886 output intermediate supply was used to power the input of an LTM®4676 8-phase demonstration circuit configured as a point-of-load converter, as shown in Figure 8. A Linear Technology Linduino® One demonstration board (www.linear.com/solutions/linduino) measured and calculated the total efficiency of the system by reading the accurate voltage and current telemetry from the LTC3886 and LTM4676 via the PMBus. The Linduino application measured the total system efficiency at multiple intermediate bus voltages and modified the intermediate bus voltage for the lowest input power, achieving highest system efficiency, without user intervention. 6 11 12 9 10 8 INTERMEDIATE BUS VOLTAGE (V) 85 80 ILOAD = 10A ILOAD = 20A ILOAD = 40A ILOAD = 80A ILOAD = 100A 75 13 Figure 9. LTC3886 efficiency vs output voltage at various load currents 70 6 11 12 9 10 8 INTERMEDIATE BUS VOLTAGE (V) 13 Figure 10. System efficiency February 2016 : LT Journal of Analog Innovation | 9