High Efficiency Power Supply for Intel IMVP-6/IMVP-6+/IMVP-6.5 CPUs Jian Li and Gina Le The LTC3816 is a single-phase synchronous step-down DC/DC switching regulator controller that complies with Intel Mobile Voltage Positioning (IMVP)-6/6+/6.5 specifications. It uses a constant-frequency voltage mode architecture with a leading edge modulation topology, allowing extremely low output voltages and very fast load transient response. The LTC3816 satisfies all of the IMVP-6, IMVP-6+ and IMVP-6.5 requirements, including 7-bit VID code, start-up to a preset boot voltage, differential remote output voltage sensing with programmable active voltage positioning (AVP), IMON output current reporting, power optimization during sleep state and fast or slow slew rate sleep state exit. It is suitable for a wide range of input voltages from 4.5V to 36V and output voltages up to 1.5V. The LTC3816 is available in 38-pin thermally enhanced eTSSOP and 5mm × 7mm QFN packages. Figure 1. An IMVP-6.5 converter using temperature-compensated inductor DCR sensing 10k 14k 8.25k ISENN 15nF 15nF 5.1k 21k ITCFB IMAX ITC ISENP RPTC 1000pF VRON LFF PREIMON IMON IMON LTC3816 VRON 22pF 2.2nF 470pF 22pF VID0 VID1 VID2 VID3 VID4 VID5 VID6 COMP VIN EXTVCC SS INTVCC DPRSLPVR 20 | October 2011 : LT Journal of Analog Innovation BG VID0 BSOURCE MODE/SYNC RFREQ VID1 VID6 VID2 VID5 VID3 PWRGD 1.9k 1.1V 3.3V GND VID4 VIN 4.5V TO 24V + NTC 0.1µF BOOST VFB CSLEW CLKEN# 1.9k CLKEN# TG SERVO 10pF 56Ω 2.55k SW VCC(SEN) 12k 0.1µF VRTT# VRTT# PWRGD VSS(SEN) 10k 6.98k DB 5V QT 100Ω CVIN 100Ω L + QB PTC CBULK CCER 4.7µF CBULK: 3 × SANYO 2TPF330M6 (330µF) CCER: 20 × 10µF + 2 × 1µF CIN: 2 × SANYO OS-CON 35SVPD47M + 2 × 10µF DB: CMDSH-4E L: IHLP-5050CE-01 (0.33µH, DCR = 1.3mΩ) NTC: MURATA NCP18XH103 PTC: MURATA PRF18BC471QB1RB QB: 2 × RENESAS RJK0330DPB QT: RENESAS RJK0305DPB VCC(CORE) ILOAD(MAX) = 27A design features The LTC3816 meets all of Intel’s IMVP-6, IMVP-6+ and IMVP-6.5 specifications in a small 5mm × 7mm 38-pin QFN. With strong gate drivers and short dead-time, the LTC3816 offers high efficiency solutions over a wide input voltage range. Its leading edge modulation topology allows very small duty cycle operation and ultrafast transient response. 0.78 100 MEASURED RESULT VCC_CORE(DC MAX) VCC_CORE(DC MIN) 0.76 80 EFFICIENCY (%) VOUT (V) 0.74 0.72 0.7 INTEL’S SPEC 0.68 70 60 50 40 30 20 0.66 0.64 PULSE SKIPPING MODE fSW = 400kHz 90 VOUT = 0.9V VOUT = 1.2V VOUT = 1.5V 10 0 5 10 15 20 25 30 0 0 10 1 ILOAD (A) 100 ILOAD (A) Figure 2. Load regulation with -3mV/A slope Figure 3. Efficiency with 12V input AN IMVP-6.5 CONVERTER WITH 4.5V~24V INPUT AND 27A OUTPUT dead-time, the LTC3816 offers a highly efficienct solution, as shown in Figure 3. Figure 1 shows an IMVP-6.5 application using temperature-compensated inductor DCR sensing. The output voltage is programmed by a 7-bit VID code. With temperature-compensated inductor DCR sensing, the LTC3816 provides an accurate –3mV/A AVP slope over temperature as shown in Figure 2. With strong integrated FET drivers and short The LTC3816’s leading edge modulation topology allows ultrafast transient response to meet Intel’s stringent requirements. As shown in Figure 4, no undershoot other than AVP is observed during a load step-up test, easily meeting Intel’s specifications. Moreover, the LTC3816 incorporates a line feedforward function to compensate for changes in the line VOUT = 1V VOUT 50mV/DIV voltage and to simplify the loop compensation. The LTC3816 feedback loop is also capable of dynamically changing the regulator output to different VID DAC voltages as shown in Figure 5. Upon receiving a new VID code, the LTC3816 regulates to its new potential with a programmable slew rate selected to prevent the converter from generating audible noise. During start-up, the output voltage is charged to VBOOT first, according to Intel’s VRON 1V/DIV VOUT = IOUT • RDROOP VBOOT VOUT 1V/DIV VOUT 200mV/DIV VOUT = 0.5V IOUT 20A/DIV CLKEN 5V/DIV PWRGD 5V/DIV 20µs/DIV Figure 4. Transient response with 20A load step 200µs/DIV Figure 5. Output voltage transition from 0.5V to 1.0V in dynamic VID mode 2ms/DIV Figure 6. Start-up test with preset boot voltage 1.1V October 2011 : LT Journal of Analog Innovation | 21 The LTC3816 includes an onboard current limit circuit, so that the peak inductor current can be sensed via inductor DCR or a discrete sense resistor. The LTC3816 current limit architecture allows momentary overcurrent events for a predefined duration. The LTC3816 also provides input undervoltage lockout, output overvoltage protection and PWRGD and overtemperature flags. IMVP specification. As shown in Figure 6, VBOOT is 1.1V in IMVP-6.5 and 1.2V in IMVP-6. Once the output voltage reaches VBOOT, the CLKEN# output goes low and the output voltage transitions to the voltage programmed by the VID code. ISENN ITCFB IMAX ITC ISENP IMON INTVCC RPTC VRON LTC3816 VRON 22pF 6800pF 470pF 22pF COMP VIN EXTVCC SS INTVCC DPRSLPVR Figure 7. A dual-channel IMVP-6 converter with 44A output using RSENSE sensing configuration BG VID0 BSOURCE MODE/SYNC RFREQ VID1 VID6 VID2 VID5 VID3 P BOOST VFB CSLEW CONCLUSION CLKEN# TG SERVO 10pF C SW VCC(SEN) 12k V VRTT# PWRGD VSS(SEN) 10k 3k LFF PREIMON The LTC3816 includes an onboard current limit circuit, so that the peak inductor current can be sensed via inductor DCR or a discrete sense resistor. The LTC3816 current limit architecture allows momentary overcurrent events for a predefined duration. The LTC3816 also provides input undervoltage lockout, output overvoltage protection and PWRGD and overtemperature flags. 22 | October 2011 : LT Journal of Analog Innovation 2.43k 22pF Figure 7 demonstrates that for high current applications, multiple LTC3816s can be paralleled to provide more power. The current sharing performance is very good in both static and dynamic operation conditions, as shown in Figure 8. The LTC3816 meets all of Intel’s IMVP-6, IMVP-6+ and IMVP-6.5 specifications in a small 5mm × 7mm 38-pin QFN. With strong gate drivers and short dead-time, the LTC3816 offers high efficiency solutions over a wide input voltage range. Its leading edge modulation topology allows very small duty cycle operation and ultrafast transient response. The LTC3816 provides high efficiency, high power density, and high reliability solutions for embedded computing, mobile computers, Internet devices and navigation displays. n 10.2k 1000pF GND VID4 VID6 VID5 VID4 VID3 VID2 VID1 VID0 CBULK: 4 × SANYO 2TPF330M6 (330µF) CCER: 32 × 10µF + 2 × 1µF CIN: 3 × SANYO OS-CON 35SVPD47M + 2 × 10µF DB: CMDSH-4E L: IHLP-5050CE-01 (0.33µH, DCR = 1.3mΩ) PTC: MURATA PRF18BC471QB1RB QT: RENESAS RJK0305DPB QB: 2 × RENESAS RJK0330DPB RSENSE: PANASONIC ERJM1WTF1M0U (1mΩ) 5V design features The LTC3816 feedback loop is also capable of dynamically changing the regulator output to different VID DAC voltages. Upon receiving a new VID code, the LTC3816 regulates to its new potential with a programmable slew rate selected to prevent the converter from generating audible noise. VIN 4.5V TO 24V 100Ω 100Ω 2.43k 1000pF 1.1V 3.3V 511Ω 511Ω 56Ω 3k 1000pF VRTT# PWRGD DB PREIMON LTC3816 CLKEN# L CVIN + QB CBULK PTC – CCER L QT QB PTC + VCC_CORE ILOAD(MAX) = 54A 4.7µF DB VCC(SEN) TG 0.1µF SERVO BOOST 5V VFB VIN EXTVCC COMP INTVCC SS BG 4.7µF BSOURCE MODE/SYNC RFREQ DPRSLPVR VID6 400kHz SQUARE WAVE 10k 10pF 12k 6800pF 22pF 22pF 470pF CSLEW VID0 VID1 VID5 VID4 INTVCC VSS(SEN) SW RSENSE RSENSE IMON RPTC VRON PWRGD + 0.1µF ITC VRTT# QT 22pF LFF 3.3V 1000pF ITCFB IMAX ISENP 1.9k CLKEN# 1.9k ISENN 10.2k VID2 GND VID3 VOUT 200mV/DIV IL1 10A/DIV Figure 8. Current sharing performance for a dual-channel IMVP-6 converter IL2 10A/DIV 20µs/DIV October 2011 : LT Journal of Analog Innovation | 23