design ideas High Performance Single Phase DC/DC Controller with Digital Power Management Yi Sun LTC3883 is a single phase synchronous step-down DC/DC controller featuring a PMBus interface for digital control and monitoring, and integrated MOSFET gate drivers. It can function either standalone or in a digitally managed system with other Linear Technology PMBus enabled parts. 5mΩ VIN 6V TO 24V 10µF 100Ω 1µF 100Ω 10nF 3Ω 10nF VIN 10k 10k PMBus INTERFACE 10k 10k 10k 10k •±0.5% output voltage accuracy over the operation temperature range of –40°C to 125°C. • PMBus, which provides programmable voltage, current limits, sequencing, margining, OV/UV thresholds, frequency synchronization and fault logging. •Telemetry read back including VIN, IIN, VOUT, IOUT, temperature and faults. •External voltage divider to set the chip address, switching frequency and the output voltage. •Input current sensing and inductor DCR auto calibration. 1.8V/30A SINGLE PHASE DIGITAL POWER SUPPLY WITH I IN SENSE Figure 1 shows a 7V to 14V input, 1.8V/30A output application that features inductor DCR current sensing. To improve the accuracy of DCR current sense, the LTC3883 senses inductor temperature and 10k 5k VDD33 PGOOD SDA M2 ALERT RUN 1.4k 1µF VDD25 20k 24.9k 10k 20k 12.7k 9.09k 23.2k 17.8k FREQ_CFG SCL VOUT_CFG 1.4k VTRIM_CFG 0.22µF SHARE_CLK ASEL GPIO SYNC WP VDD25 VDD33 1.0µF 0.56µH BG PGND 10µF M1 0.1µF SW VIN_SNS The LTC3883 features: •4.5V to 24V input voltage range and 0.5V to 5.5V output voltage range. TG LTC3883 BOOST IIN_SNS 22µF 50V 1µF D1 INTVCC ISENSE+ ISENSE– VSENSE+ VSENSE– + TSNS GND ITH 2200pF 1.0µF 100pF D1: CENTRAL CMDSH-3TR L: COILCRAFT XAL7070-551ME VOUT 1.8V 30A COUT 1520µF MMBT3906 4.99k M1: INFINEON BSC050N03LSG COUT: 4× 330µF SANYO 2R5TPE330M9, 2× 100µF AVX 12106D107KAT2A M2: INFINEON BSC011N03LSI Figure 1. 1.8V/30A single phase digital power supply with IIN sense compensates for the TC of the DCR. This method ensures the accuracy of the readback current and overcurrent limit. The LTC3883’s control loop uses peak current mode control, which offers fast transient response. Figure 2 shows the typical waveforms of a 10A load step transient. Figure 2. Transient performance of a 10A load step VOUT 100mV/DIV (AC-COUPLED) IOUT 10A/DIV (AC-COUPLED) 120mV 30A 20A IL 10A/DIV (AC-COUPLED) 20µs/DIV January 2013 : LT Journal of Analog Innovation | 37 The LTC3883 uses a proprietary inductor DCR autocalibration function, which enables output current read back accuracy within 3%, regardless of inductor DCR tolerance. LTPOWERPLAY DEVELOPMENT IIN VIN + CIN VIN VIN_SNS IIN_SNS TG LTC3883 Figure 3. DCR auto calibration INDUCTOR DCR AUTO CALIBRATION The problem with the conventional inductor DCR current sensing is that the tolerance of the DCR can be as large as ±10%, greatly limiting the current read back accuracy. To solve this problem, the LTC3883 uses a proprietary inductor DCR autocalibration function. Figure 3 shows the simplified diagram of this circuit. The LTC3883 accurately measures the input current, IIN, the duty cycle, D and calibrates the real DCR value based on the relation: LTpowerPlay LTpowerPlay™ software is available for free at www.llinear.com/ltpowerplay SW BG ISENSE+ ISENSE– The LTC3883 features input current sensing via a resistor in series with the input side of the buck converter—a 5mΩ sense resistor as shown in Figure 1. The sense voltage is translated into a power stage input current by the LTC3883’s 16-bit internal ADC. An internal sense resistor senses chip’s supply current at VIN, so it can provide both the chip and the power stage’s input current measurements. M1 M2 IOUT DCR + + – COUT VCS DCRCALIBRATED = VCS • + D IIN With this auto-calibration method, the output current read back accuracy can be within 3%, regardless of inductor DCR tolerance. 1.2V/60A 3-PHASE DIGITAL POWER SUPPLY VOUT – All digital power management functions can be controlled by LTpowerPlay, PC-based software compatible with all of Lintear Technology’s digital power products. With LTpowerPlay, designers can easily program and control the entire power system without writing a line of code. It is easy to configure any chip on the bus, verify the system’s status, read the telemetry, check fault status, control supply sequencing. CONCLUSION The LTC3883 combines a best-in-class analog DC/DC controller with complete digital power management functions and precision data converters for unprecedented performance and control. Multiple LTC3883s can be used with other Linear Technology PMBus products to optimize multirail digital power systems. Powerful LTpowerPlay software simplifies the development of complex power systems. The LTC3883 can be used for telecom, computing, data storage, and other applications. n The LTC3883 has an analog current control loop, which makes it ideal for PolyPhase® operation. Figure 4 shows an example of a 3-phase single output circuit, with one LTC3883 and one LTC3880 for a 7V to 14V input, 1.2V/60A output application. The LTC3880 is a 2-phase synchronous buck controller with digital Figure 5. Transient performance of a 30A load power system management. The interstep for 3-phase power supply connection between these two chips is straightforward and easy. Note how VOUT 50mV/DIV the input current sense resistor of (AC-COUPLED) the LTC3883 is used to sense the total input current for all three phases. Figure 5 shows the dynamic current sharing for a load step transient. All the three phases can share the current evenly. IL0 10A/DIV IL0 10A/DIV IL0 10A/DIV 20µs/DIV 38 | January 2013 : LT Journal of Analog Innovation 60mV design ideas 5mΩ VIN 6V TO 14V 10µF INTVCC 100Ω 1µF TG LTC3883 BOOST IIN_SNS 100Ω Figure 4. 1.0V/60A 3-phase digital power supply with IIN sense VIN_SNS 10nF 22µF 50V 1µF D1 M1A 0.1µF M1 L0 0.56µH SW 10nF M1B BG PGND 3Ω 10k 10µF 1k PGOOD 10k PMBus INTERFACE VDD25 VIN 10k 10k SDA VOUT_CFG SCL VTRIM_CFG ALERT 10k GPIO 5k SYNC WP ASEL 0.22µF ISENSE– VSENSE+ TSNS ITH GND D2 VIN TG0 TG1 LTC3880 22µF 1µF M2A 0.1µF M2 L2 0.56µH SW1 BG0 M2B BG1 PGND VDD33 1µF COUT1 530µF 10nF BOOST1 SW0 M3B VOUT 1V 60A MMBT3906 2200pF D3 INTVCC BOOST0 1µF + VSENSE 4.99k 0.1µF 1k 1k ISENSE+ 1.0µF M3A 17.8k – VDD25 VDD33 1.0µF M3 L1 0.56µH 11.3k SHARE_CLK 10k 10µF 20k FREQ_CFG RUN 10k 1µF 24.9k 1k SYNC 1µF SDA SCL VDD25 ALERT VOUT1_CFG GPIO1 SHARE_CLK VTRIM0_CFG RUN0 RUN1 VTRIM1_CFG 0.22µF TSNS0 ISENSE0+ TSNS1 ISENSE1+ ISENSE0– ISENSE1– ITH0 MMBT3906 11.3k 15.8k 17.8k 0.22µF 1k ITH1 GND 100pF 10µF D1-D3: CENTRAL CMDSH-3TR L0-L2: COILCRAFT XAL7070-301ME 1µF VSENSE1 VSENSE0– COUT2 530µF 20k FREQ_CFG VSENSE0+ + 10k ASEL WP 1k 24.9k VOUT0_CFG GPIO0 MMBT3906 10nF + COUT3 530µF M1, M2, M3: FAIRCHILD FDMS3620S COUT1, COUT2, COUT3: 330μH SANYO 4TPF330ML, 2× 100µF AVX 12106D107KAT2A January 2013 : LT Journal of Analog Innovation | 39