High Performance Single Phase DC/DC Controller with Power System Management – Design Note 517 Yi Sun Introduction The LTC ®3883 is a single phase synchronous stepdown DC/DC controller featuring a PMBus interface for digital control and monitoring of key regulator parameters. It has integrated MOSFET gate drivers and can function either standalone or in a digitally managed system with other Linear Technology PMBus-enabled parts. The LTC3883 features: n4.5V to 24V input voltage range and 0.5V to 5.5V output voltage range n±0.5% output voltage accuracy over the full opera- tional temperature range of –40°C to 125°C n PMBus interface with programmable voltage, current limits, sequencing, margining, OV/UV thresholds, frequency synchronization and fault logging n Telemetry readback parameters including VIN, IIN, VOUT, IOUT, temperature and faults n External voltage dividers to set the chip address and default switching frequency and the output voltage n Input current sensing and inductor DCR autocalibration 1.8V/30A Single Phase Digital Power Supply with IIN 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 the DCR current sense, the L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and LTpowerPlay is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. 5mΩ VIN 7V TO 14V 10µF D1 INTVCC 100Ω 1µF 100Ω TG LTC3883 BOOST IIN_SNS VIN_SNS 10nF 3Ω VIN 10k PMBus INTERFACE 10k 10k 10k 10k 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 10k M1 SW 10nF 10µF 0.1µF 22µF 50V 1µF ISENSE+ ISENSE– VSENSE+ VSENSE– + TSNS GND 1.0µF D1: CENTRAL CMDSH-3TR L: COILCRAFT XAL7070-551ME ITH 2200pF 100pF COUT 1520µF MMBT3906 4.99k DN517 F01 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 08/13/517 VOUT 1.8V 30A LTC3883 senses inductor temperature and compensates for the temperature coefficient of the winding resistance. This method ensures the accuracy of the readback current and overcurrent limit. The LTC3883’s control loop uses peak current mode control to achieve fast transient response and cycleby-cycle current limit. Figure 2 shows the typical waveforms for a 10A load step transient, resulting in only a 60mV maximum deviation from nominal. VOUT 100mV/DIV AC-COUPLED The LTC3883 accurately measures the input current, IIN, the duty cycle (D) and the current sense voltage (VCS) and calibrates the real DCR value based on the relation: DCRCALIBRATED = VCS • D IIN With this auto-calibration method, the output current read back accuracy is within 3% regardless of inductor DCR tolerance. 120mV 30A IOUT 10A/DIV DC-COUPLED IL 10A/DIV DC-COUPLED proprietary inductor DCR auto-calibration function. Figure 3 shows the simplified diagram of this circuit. 20A DN517 F02 20µs/DIV Figure 2. Transient Performance for a 10A Load Step Input Current Sensing 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. In addition, an internal IC sense resistor senses the chip’s supply current at VIN, so it can provide both the chip and the power stage’s input current measurements. Inductor DCR Auto-Calibration The problem with 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 LTpowerPlay™ GUI All power system management functions can be controlled by LTpowerPlay, a PC-based graphical user interface compatible with all of Linear’s power system management products. With LTpowerPlay, designers can easily program and control the entire power system without writing a line of code. With this tool, it is easy to configure any chip on the bus, verify system status, read the telemetry, check fault status and control supply sequencing. LTpowerPlay can be downloaded at www.LTpowerPlay.com. Conclusion The LTC3883 combines a best in class analog DC/DC controller with complete power system 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 power systems. The powerful LTpowerPlay software simplifies the development of complex power systems. If dual outputs are needed, use the LTC3880 which shares common power system management features. IIN VIN + CIN VIN VIN_SNS IIN_SNS TG LTC3883 M1 SW BG ISENSE+ ISENSE– M2 IOUT DCR + COUT + – VCS + VOUT – DN517 F03 Figure 3. DCR Auto-Calibration Data Sheet Download www.linear.com/LTC3883 Linear Technology Corporation For applications help, call (408) 432-1900, Ext. 3780 dn517f LT/AP 0813 111K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2013