RT8800

RT8800/B General Purpose 2/3-Phase PWM Controller for High-Density Power Supply General Description The RT8800/B are general purpose multi-phase synchronous buck controllers dedicating for high density power supply regulation. The parts implement 2, and 3 buck switching stages operating in interleaved phase set automatically. The output voltage is regulated and controlled following the input voltage of FB pin. With such a single analog control, the RT8800/B provide a simple, flexible, wide-range and extreme cost-effective highdensity voltage regulation solutions for various high-density power supply application. The RT8800/B multi-phase architecture provide high output current while maintaining low power dissipation on power devices and low stress on input and output capacitors. The high equivalent operating frequency also reduces the component dimension and the output voltage ripple in load transient. RT8800/B implement both voltage and current loops to achieve good regulation, response and power stage thermal balance. The RT8800/B apply the time sharing DCR current sensing technology newly as well; with such a topology, the RT8800/B extract the DCR of output inductor as sense component to deliver a more precise load line regulation and better thermal balance capability. Moreover, the parts monitor the output voltage for overcurrent and over-voltage protection; Soft-start and programmable under-voltage lockout are also provided to assure the safety of power system. Features 5V Power Supply Voltage 2/3-Phase Power Conversion with Automatic Phase Selection (RT8800 : 2/3-Phase, RT8800B : 2-Phase) Output Voltage Controlled by External Reference Voltage Precise Core Voltage Regulation Power Stage Thermal Balance by DCR Current Sensing Extreme Low-Cost, Lossless Time Sharing Current Sensing Internal Soft-start Hiccup Mode Over-Current Protection Over-Voltage Protection Adjustable Operating Frequency and Typical at 300kHz Per Phase Power Good indication Small 16-Lead VQFN Package (For RT8800 only) RoHS Compliant and 100% Lead (Pb)-Free Ordering Information RT8800/B Package Type QV : VQFN-16L 3x3 (V-Type) S : SOP-16 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) 2-Phase 2/3-Phase Applications Desktop CPU core power L ow Output Voltage, High power density DC-DC Converters Voltage Regulator Modules Note : RichTek Pb-free and Green products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. 100% matte tin (Sn) plating. Marking Information For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail. All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 1 RT8800/B Pin Configurations (TOP VIEW) PWM3 PWM2 PWM1 VDD 16 15 14 13 DACFB 1 DACQ 2 FB 3 DVD 4 5 12 ISP1 GND 11 ISP2 10 ISP3 9 PGOOD 6 7 8 COMP ICOMMON VDD DACFB DACQ FB DVD COMP PI RT 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 PWM2 PWM1 N/C ISP1 ISP2 PGOOD GND ICOMMON PI RT SOP-16 RT8800B VQFN-16L 3x3 RT8800 Functional Pin Description DACFB Negative input of internal buffer amplifier for reference voltage regulation. The pin voltage is locked at internal VREF = 0.8V by properly close the buffer amplifier feedback loop. DACQ The pin is defined as the output of internal buffer amplifier for reference voltage regulation. FB The pin is defined as the inverting input of internal error amplifier. DVD The pin is defined as a programmable power UVLO detection input. Trip threshold = 0.8V at VDVD rising. COMP The pin is defined as the output of the error amplifier and the input of all PWM comparators. PI The pin is defined as the positive input of the error amplifier. RT Switching frequency setting. Connect this pin to GND with a resistor to set the frequency. All brand name or trademark belong to their owner respectively www.richtek.com 2 DS8800/B-06 March 2007 ICOMMON Common negative input of current sense amplifiers for all three channels. PGOOD Output power-good indication. The signal is implemented as an output signal with open-drain type. ISP1 , ISP2 , ISP3 Current sense positive inputs for individual converter channel current sense. PWM1 , PWM2 , PWM3 PWM outputs for each phase switching drive. VDD Chip power supply. Connect this pin to a 5V supply. GND Chip power ground. Exposed Pad (RT8800) Exposed pad should be soldered to PCB board and connected to GND. Typical Application Circuit DS8800/B-06 March 2007 D1 SS12/SM 12V C7 1uF R20 10 C9 1uF C12 1uF C11 2200uF Q1 5V L1 C13 1uH 1000uF 12V C1 33pF Optional for R&C 14 VDD PVCC UGATE1 PHASE1 Q2 R25 2.2 PHASE1 C14 3.3nF C4 C8 1uF 11 BOOT1 12 13 R22 0 Q3 PHB95N03LT PHB83N03LT R2 C3 R16 0 5 R21 0 R1 15k C2 10nF R3 3k 1 PWM1 RT9602 4 L2 0.5uH VCORE 6 1 FB 4 VDD 15 PWM1 COMP VID5 R4 110k R5 56k RDROOP PWM2 GND 10 3 GND PHASE2 LGATE2 7 PHB83N03LT 7 PWM2 UGATE2 8 9 R23 0 (Note : The inductor’ s DCR value must be large than 0.3mΩ VID0 PI 16 R17 0 LGATE1 2 R6 27k VID1 VID2 R7 13k R11 1.8k 3 DACQ RT8800B 12 6 PGND R18 PHASE2 R 2 DACFB ISP2 ISP1 C15 2200uF C16 1uF C18 to C29 1000uF x 12 Q4 PHASE2 L3 0.5uH C30 to C33 10uF x 4 VID3 R8 6.8k 11 ICOMMON VID4 R9 3.3k R12 10k PGOOD 3.3V DVD 5 RT 8 R10 5.1k 13 Optional C5 1uF Optional 430 RICOMMON1 C6 1uF VCORE R R19 PHASE1 D2 SS12/SM 9 Figure A. 2-phase with resistive DAC BOOT2 10 C10 1uF R24 0 PHB95N03LT 12V R15 16k Q5 Q6 R13 27k R14 3k R26 2.2 C17 3.3nF : X7R/R-type capacitor is required for all time constant setting capacitor of DCR sensing.) All brand name or trademark belong to their owner respectively Optional RICOMMON2 RT8800/B www.richtek.com 3 PVCC2 PHASE2 LGATE2 16 BOOT2 RT9605 PVCC3 GND PHASE3 15 11 12V PWM3 PWM2 PWM1 BOOT1 LGATE3 7 15 5 4 R16 PHASE3 R UGATE2 R1 15k C3 10nF R3 3k NC PHASE1 PVCC1 LGATE1 ICOMMON DVD 4 RT 7 Figure B. 3-phase with resistive DAC C15 R18 0 12V 1uF R20 0 5V C4 4.7uF C10 to C13 1500uF x 4 C14 1uF R10 5.1k 3.3V 12 R13 R15 16k Optional 430 Optional C7 1uF VCORE RICOMMON1 R R17 PHASE1 D2 Q4 12V VIN C6 1uF R C17 1uF R21 0 27k Optional R17 PHASE2 1 UGATE1 24 22 12V 23 C18 1uF 8 R23 10 R22 0 C19 1uF VDD www.richtek.com 4 PHASE2 L1 0.5uH 12V VIN Q3 Q1 D1 Q2 1uH C8 1000uF C9 1uF R19 2.2 C16 3.3uF C24 to C35 1000uF x 12 RT8800/B C1 33pF Optional C2 R2 17 19 21 20 3 Q7 PHASE3 C23 3.3nF Q8 C21 1uF R27 2.2 R26 0 L2 0.5uH R25 14 0 C36 to C39 10uF x 4 16 5 FB 3 VDD R4 110k 13 PWM1 COMP VID5 RDROOP VID0 R5 56k R6 27k 6 PI 2 DACQ RT8800 GND ISP3 2 ISP2 C5 1uF PWM3 PWM2 10 11 Optional 14 VCORE Q9 VID1 R7 13k R11 1.8k UGATE3 10 BOOT3 9 C22 1uF VID2 1 DACFB D3 VID3 R8 6.8k 9 ISP1 PGOOD VID4 R9 3.3k R12 10k 12V VIN 8 12V 5VSB PHASE1 L3 0.5uH Q5 R24 2.2 C20 3.3nF Q6 All brand name or trademark belong to their owner respectively R14 3k RICOMMON2 DS8800/B-06 March 2007 PHASE2 L1 0.5uH 12V VIN Q3 Q1 Q2 C17 C11 to C14 1500uF x 4 C15 1uF R13 0 12V 1uF R15 0 C25 to C36 1000uF x 12 D1 1uH C9 1000uF C10 1uF 5V C5 4.7uF R14 2.2 C16 3.3uF PVCC2 UGATE2 PHASE2 LGATE2 NC PHASE1 PVCC1 LGATE1 ICOMMON 3.3V DVD 4 RT 7 R7 27k R8 3k Optional 430 Optional C8 1uF VCORE RICOMMON1 R Q4 12V VIN R12 PHASE1 D2 R9 16k C7 1uF R C18 1uF R16 0 12V Optional R11 PHASE2 1 UGATE1 24 22 23 C19 1uF 8 R19 10 R18 0 C20 1uF VDD DS8800/B-06 March 2007 17 19 21 20 3 Q7 PHASE3 C24 3.3nF Q8 C22 1uF R22 2.2 R21 0 L2 0.5uH VCORE Q9 C1 33pF Optional C3 R2 R1 15k C2 10nF R3 3k 16 5 16 BOOT2 RT9605 PVCC3 GND PHASE3 UGATE3 10 BOOT3 9 C23 1uF 3 LGATE3 15 11 12V 14 FB 7 PWM3 PWM2 PWM1 BOOT1 15 5 4 R10 Optional PHASE3 R C6 1uF R20 0 C37 to C40 10uF x 4 VDD 13 PWM1 COMP RDROOP 6 RT8800 GND ISP3 2 ISP2 ISP1 11 10 PWM2 14 PWM3 C4 10nF PI 2 DACQ R4 5.1k 1 DACFB R5 5.1k 9 PGOOD R6 10k 12V VIN 12 8 12V 5VSB PHASE1 RT9401A/B Figure C. 3-phase with RT9401A/B DAC generator L3 0.5uH Q5 R17 2.2 C21 3.3nF Q6 All brand name or trademark belong to their owner respectively 1 VID2 VID3 8 2 VID1 VID4 7 RICOMMON2 3 VDA GND 6 RT8800/B 5V 4 VDD VID0 5 www.richtek.com 5 Oscillator & Ramp Generator PWM Logic & Driver PWM1 + + PWMCP INH PWM Logic & Driver PWM2 + + + + + + PWMCP EA + - OVP OCP Sample & Hold MAJ SUM/N & OCP Detection Sample & Hold Sample & Hold Mux Mux 500mV + Buffer Amplifier 0.8V VREF DACQ All brand name or trademark belong to their owner respectively Power On Reset Soft Start + + PWMCP INH PWM Logic & Driver PWM3 + + GND + GM ICOMMON ISP1 ISP2 ISP3 www.richtek.com 6 PGOOD VDD DVD RT INH RT8800/B Function Block Diagram COMP FB PI DACFB DS8800/B-06 March 2007 RT8800/B Table. Output Voltage Program VID5 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 VID4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 VID3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 VID2 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 VID1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 VID0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 Nominal Output Voltage (V) 1.0800 1.1000 1.1125 1.1250 1.1375 1.1500 1.1625 1.1750 1.1875 1.2000 1.2125 1.2250 1.2375 1.2500 1.2625 1.2750 1.2875 1.3000 1.3125 1.3250 1.3375 1.3500 1.3625 1.3750 1.3875 1.4000 1.4125 1.4250 1.4375 1.4500 1.4625 1.4750 1.4875 1.5000 1.5125 1.5250 1.5375 1.5500 To be continued All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 7 RT8800/B Table. Output Voltage Program VID5 0 1 0 1 1 1 1 1 1 1 1 1 1 1 Note: 1 : Open 0 : VSS or GND VID4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 VID3 1 1 1 1 1 1 0 0 0 0 0 0 0 0 VID2 1 0 0 0 0 0 1 1 1 1 0 0 0 0 VID1 0 1 1 1 0 0 1 1 0 0 1 1 0 0 VID0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 Nominal Output Voltage (V) 1.5625 1.5750 1.5875 1.6000 1.6250 1.6500 1.6750 1.7000 1.7250 1.7500 1.7750 1.8000 1.8250 1.8500 All brand name or trademark belong to their owner respectively www.richtek.com 8 DS8800/B-06 March 2007 RT8800/B Absolute Maximum Ratings (Note 1) Supply Voltage, VDD ------------------------------------------------------------------------------------------- 7V Input, Output or I/O Voltage ---------------------------------------------------------------------------------- GND − 0.3V to VDD + 0.3V Power Dissipation, PD @ TA = 25°C VQFN-16L 3X3 -------------------------------------------------------------------------------------------------SOP-16 ----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 4) VQFN-16L 3X3, θJA --------------------------------------------------------------------------------------------SOP-16, θJA ----------------------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------ESD Susceptibility (Note 2) HBM (Human Body Mode) ----------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------1.47W 1W 68°C/W 100°C/W 150°C 260°C −65°C to 150°C 2kV 200V Recommended Operating Conditions (Note 3) Supply Voltage, VDD ------------------------------------------------------------------------------------------- 5V ± 10% Ambient Temperature Range --------------------------------------------------------------------------------- 0°C to 70°C Junction Temperature Range --------------------------------------------------------------------------------- 0°C to 125°C Electrical Characteristics (VDD = 5V, TA = 25°C, unless otherwise specified) Parameter VDD Supply Current Nominal Supply Current Power-On Reset Rising VDD Threshold Hysteresis 4.0 0.2 0.75 -RRT = 16kΩ RRT = 16kΩ 4.2 0.5 0.8 65 4.5 -0.85 -V V V mV IDD PWM 1,2,3 Open -5 -mA Symbol Test Conditions Min Typ Max Units DVD Rising Threshold DVD Hysteresis Oscillator Free Running Frequency Frequency Adjustable Range Ramp Amplitude Ramp Valley Maximum On-Time of Each Channel Minimum On-Time of Each Channel RT Pin Voltage VRT RRT = 16kΩ fOSC fOSC_ADJ ΔVOSC VRV 170 50 --62 -0.77 200 -1.7 1.0 66 120 0.82 230 400 --75 -0.87 kHz kHz V V % ns V To be continued All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 9 RT8800/B Parameter Reference Voltage Reference Voltage DACFB Sourcing Capability Error Amplifier DC Gain Gain-Bandwidth Product Slew Rate Current Sense GM Amplifier Recommended Full Scale Source Current OCP trip level Protection Over-Voltage Trip (VFB - VDACQ) Power Good PGOOD Output Low Voltage PGOOD Delay VPGOOD IPGOOD = 4mA -4 --0.2 8 V ms -500 -mV IOCP -160 100 190 -220 μA μA GBW SR CL = 10pF CL = 10pF ---65 10 8 ---dB MHz V/μs VDACFB 0.79 -0.8 -0.81 10 V mA Symbol Test Conditions Min Typ Max Units TPGOOD_Delay 90% * VOUT to PGOOD_H Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. θJA is measured in the natural convection at T A = 25 °C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. All brand name or trademark belong to their owner respectively www.richtek.com 10 DS8800/B-06 March 2007 RT8800/B Typical Operating Characteristics Load Line 1.4 1.38 Efficiency vs. Output Current 100 90 80 RLL = 1.5mΩ, RICOMMON2 = 10kΩ, RDROOP = 100Ω VIN = 12V VIN = 12V, VOUT = 1.4V Output Voltage (V) 1.36 1.34 1.32 1.3 1.28 1.26 1.24 0 10 20 30 40 50 60 70 80 90 100 Efficiency (%) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Driver RT9605 Output Current (A) Output Current (A) Frequency vs. RRT 1000 900 800 GM 90 80 70 60 RICOMMON1 = 430Ω Frequency (kHz) 700 I ADJ (uA) 600 500 400 300 200 100 0 0 5 10 15 20 25 30 35 40 45 50 55 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 GM3 GM2 GM1 90 100 110 RRT (k Ω) (k ) VC (mV) VREF v s. Temperature 0.815 0.81 0.805 OCP Trip Point vs. Temperature 240 210 180 150 V REF (V) Ix (uA) -25 -10 5 20 35 50 65 80 95 110 125 0.8 0.795 0.79 0.785 0.78 120 90 60 30 0 -25 -10 5 20 35 50 65 80 95 Temperature (°C) All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 Temperature (°C) www.richtek.com 11 RT8800/B Frequency vs. Temperature 350 300 Load Transient Response V CORE (200mV/Div) Frequency (kHz) 250 200 150 100 50 UGATE1 (20V/Div) UGATE2 (20V/Div) UGATE3 (20V/Div) phase 1, IOUT = 5A to 85A @SR = 93A/us) RRT = 16kΩ 0 -25 -10 5 20 35 50 65 80 95 110 125 Temperature (°C) Time (2.5μs/Div) Load Transient Response V CORE (200mV/Div) V CORE (200mV/Div) Load Transient Response UGATE1 (20V/Div) UGATE2 (20V/Div) UGATE3 (20V/Div) phase2, IOUT = 5A to 85A @SR = 93A/us) UGATE1 (20V/Div) UGATE2 (20V/Div) UGATE3 (20V/Div) phase 3, IOUT = 5A to 85A @SR = 93A/us) Time (2.5μs/Div) Time (2.5μs/Div) Over Current Protection Short While Turn_On Over Current Protection Short After Turn_On IL1+IL2 (50A/Div) IL1+IL2 (50A/Div) V CORE (1V/Div) PWM1 (10V/Div) VCOMP (2V/Div) Time (10ms/Div) V CORE (1V/Div) PWM1 (10V/Div) VCOMP (2V/Div) Time (10ms/Div) All brand name or trademark belong to their owner respectively www.richtek.com 12 DS8800/B-06 March 2007 RT8800/B VID On the Fly Falling IOUT = 5A VID On the Fly Falling V CORE (50mV/Div) PWM (5V/Div) VFB (200mV/Div) IOUT = 90A PWM (5V/Div) V CORE (100mV/Div) VFB (200mV/Div) VID0 (2V/Div) Time (25μs/Div) VID0 (2V/Div) Time (25μs/Div) VID On the Fly Rising IOUT = 5A VID On the Fly Rising IOUT = 90A PWM (5V/Div) PWM (5V/Div) V CORE (200mV/Div) VFB (200mV/Div) VID0 (2V/Div) Time (10μs/Div) V CORE (200mV/Div) VFB (200mV/Div) VID0 (2V/Div) Time (10μs/Div) All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 13 RT8800/B Application Information RT8800/B are multiphase DC/DC controllers for extreme low cost applications that precisely regulate CPU core voltage and balance the current of different power channels using time sharing current sensing method. The converter consisting of RT8800/B and its companion MOSFET driver RT96xx series provide high quality CPU power and all protection functions to meet the requirement of modern VRM. Phase Setting and Converter Start Up RT8800/B interface with companion MOSFET drivers (like RT9602, RT9603, and RT9605) for correct converter initialization. RT8800/B will sense the voltage on PWM pins at the instant of POR rising. If the voltage is smaller than (VDD − 1.2V) the related channel is activated. Tie the PWM to VDD and the corresponding current sense pins to GND or left float if the channel is unused. For example, for 2-Channel application, tie PWM3 to VDD and ISP3 to GND (or let ISP3 open). PGOOD Function and Soft Start To indicate the condition of multiphase converter, RT8800/B provide PGOOD signal through an open drain connection. The output becomes high impedance after internal SS ramp > 3.5V. duty width according to its magnitude above the ramp signal. The output follows the ramp signal, SS. However while VOUT increases, the difference between VOUT and SSE(SS − V GS) is reduced and COMP leaves the saturation and declines. The takeover of SS lasts until it meets the COMP. During this interval, since the feedback path is broken, the converter is operated in the open loop. 3) Mode3 ( Cross-over< SS < VGS + VREF) When the Comp takes over the non-inverting input for PWM Amplifier and when SSE (SS − VGS) < VREF, the output of the converter follows the ramp input, SSE (SS − VGS). Before the crossover, the output follows SS signal. And when Comp takes over SS, the output is expected to follow SSE (SS − VGS). Therefore the deviation of VGS is represented as the falling of VOUT for a short while. The COMP is observed to keep its decline when it passes the cross-over, which shortens the duty width and hence the falling of VOUT happens. Since there is a feedback loop for the error amplifier, the output’ s response to the ramp input, SSE (SS − VGS) is lower than that in Mode 2. 4) Mode 4 (SS > VGS + VREF) When SS > VGS + VREF, the output of the converter follows the desired VREF signal and the soft start is completed now. Voltage Control COMP VRAMP_Valley Cross-over SS_Internal V CORE SSE_Internal 1) Mode 1 (SS< Vramp_valley) Initially the COMP stays in the positive saturation. When SS< VRAMP_Valley, there is no non-inverting input available to produce duty width. So there is no PWM signal and VOUT is zero. 2) Mode 2 (VRAMP_Valley< SS< Cross-over) When SS>VRAMP_Valley, SS takes over the non-inverting input and produce the PWM signal and the increasing The voltage control loop consists of error amplifier, multiphase pulse width modulator, driver and power components. As conventional voltage mode PWM controller, the output voltage is locked at the positive input of error amplifier and the error signal is used as the control signal of pulse width modulator. The PWM signals of different channels are generated by comparison of EA output and split-phase sawtooth wave. Power stage transforms VIN to output by PWM signal on-time ratio. Output Voltage Program The output voltage of a RT8800/B converter is programmed to discrete levels between 1.08V and 1.85V. The voltage identification (VID) pins program an external voltage reference (DACQ) with a 6-bit digital-to-analog converter (DAC). The level of DACQ also sets the OVP threshold. The output voltage should not be adjusted while the converter is delivering power. Remove input power before DS8800/B-06 March 2007 All brand name or trademark belong to their owner respectively www.richtek.com 14 RT8800/B changing the output voltage. Adjusting the output voltage during operation may trigger the over-voltage protection. The DAC function is a precision non-inverting summation amplifier shown in Figure 1. The resistor values shown are only approximations of the actual precision values used. Grounding any combination of the VID pins increases the DACQ voltage. The “ open” circuit voltage on the VID pins is the band gap reference voltage (VREF = 0.8V). VCORE v s. Temperature 1.38 1.375 1.37 CPU : P4-2.8G VCORE = 1.35V R = 1/3 V CORE (V) 1.365 1.36 1.355 1.35 1.345 R = 1/9 VID0 VID1 VID2 VID3 VID4 VID5 R R R R R R VREF (0.8V) VDACFB 1.34 The Original R + OP RF VDACQ 1.335 30 35 40 45 50 55 60 65 70 Temperature (°C) Figure 3 RG VCORE v s. Temperature 1.66 1.64 1.62 Figure 1. The Structure of Discrete DAC Generator DAC Design Guideline In high temperature environment, V CORE b ecomes unstable for the leakage current in VID pins is increasing. The leakage will increase current consumption of CPU, and then raise RT8800's VDACQ reference output, so does VCORE voltage. Below are four comparison charts for different CPUs. Note: In Below Figure 2 to Figure 5, The Original R means the resister values shown in typical application circuit. R=1/3 and R=1/9 mean that The Original R is divided by 3 or 9. CPU : Celeron 2.0G VCORE = 1.55V The Original R V CORE (V) 1.6 R = 1/3 1.58 1.56 1.54 1.52 30 35 40 45 50 55 60 65 70 R = 1/9 Temperature (°C) Figure 4 VCORE v s. Temperature 1.68 1.66 1.64 VCORE v s. Temperature 1.64 1.63 1.62 CPU : P4-3.06G VCORE = 1.55V The Original R CPU : P4-3.2G VCORE = 1.55V The Original R 1.61 V CORE (V) V CORE (V) 1.62 1.6 1.58 1.6 1.59 1.58 1.57 R = 1/3 R = 1/3 R = 1/9 1.56 1.56 1.55 R = 1/9 1.54 30 35 40 45 50 55 60 65 70 1.54 30 35 40 45 50 55 60 65 70 Temperature (°C) Temperature (°C) Figure 2 DS8800/B-06 March 2007 Figure 5 www.richtek.com 15 All brand name or trademark belong to their owner respectively RT8800/B In order to maintain the VDACQ within 1% tolerance in the worst case, the total driver current of the DAC regulator should support up to 40mA. As the design of RT8800/B, the maximum driving current of the internal OP is 10mA. As shown in Figure 6, we suggest to add an external transistor 2N3904 for higher current for VDAC regulation. VCC for switching, period = TS VIN - VO ⎡ ⎤ VO - ( ) x TS ⎥ ⎢ DCR VIN IX(S/H) = ⎢IL(AVG) ⎥x 2L ⎢ ⎥ RICOMMON1 ⎢ ⎥ ⎣ ⎦ Falling Slope = Vo/L IL IL(AVG) VID0 VID1 VID2 VID3 VID4 VID5 1.34k 645 310 162 81 2.63k VREF (0.8V) VDACFB + OP 43 VDACQ Q1 2N3904 PI Inductor Current IL(S/H) 121 PWM Signal & High Side MOSFET Gate Signal Figure 6. Immune circuit against CPU Leakage Current Current Sensing Setting RT8800/B senses the current flowing through inductor via its DCR for channel current balance and droop tuning. The differential sensing GM amplifier converts the voltage on the sense component (can be a sense resistor or the DCR of the inductor) to current signal into internal circuit (see Figure 7). Low Side MOSFET Gate Signal Figure 8. Inductor current and PWM signal Figure 9 is the test circuit for GM. We apply test signal at GM inputs and observe its signal process output by PI pin sinking current. Figure 10 shows the variation of signal processing of all channels. We observe zero offsets and good linearity between phases. L VC = R × C VC = DCR × IL I X = DCR RICOMMON1 L IL R + - DCR C +V C L DCR C ESR +V C VISPX +V ICOMMON RICOMMON1 GMx 1k Ix GMx Ix RICOMMON Figure 7. Current Sense Circuit The sensing circuit gets feedback. IX = IL x DCR RICOMMON1 by local Figure 9. The Test Circuit of GM IX is sampled and held just before low side MOSFET turns off (Figure 8). IX(S/H) = IL(S/H) x DCR VO TOFF ; IL(S/H) = IL(AVG) x RICOMMON1 L 2 VIN - VO TOFF = ( ) x TS VIN All brand name or trademark belong to their owner respectively www.richtek.com 16 DS8800/B-06 March 2007 RT8800/B GM 70 60 50 GM3 I ADJ (uA) GM2 40 30 20 10 0 0 20 40 60 80 100 For some case with preferable current ratio instead of current balance, the corresponding technique is provided. Due to different physical environment of each channel, it is necessary to slightly adjust current loading between channels. Figure 12. shows the application circuit of GM for current ratio requirement. Applying KVL along L+DCR branch and R1+C//R2 branch: L dIL dVC ⎞ ⎛ VC + DCR x IL = R1 ⎜ +C ⎟ + VC dt dt ⎠ ⎝ R2 GM1 dVC R1 + R2 VC + dt R2 R2 For VC = DCR x IL R1 + R2 = R1 x C VC (mV) Look for its corresponding conditions: L dIL dIL + DCR x IL = (R1//R2) x C x DCR x + DCR x IL dt dt L Let = (R1//R2) x C DCR Thus if L = (R1//R2) x C DCR R2 Then VC = x DCR x IL R1 + R2 Figure 10. The Linearity of GMx Figure 11 shows the time sharing technique of GM amplifier. We apply test signal at phase 3 and observe the waveforms at both pins of GM amplifier. The waveforms show time sharing mechanism and the perfomance of GM to hold both input pins equal when the shared time is on. Time Sharing of GM CH1:(2V/Div) CH2:(50mV/Div) CH3:(50mV/Div) With internal current balance function, this phase would share (R 1+R 2)/R 2 t imes current than other phases. Figure 13 &14 show different settings for the power stages. IL PWM3 VISP3 1.5uH 1m VISP3 and VICOMMON VICOMMON 3k 1uF 3k Time (1μs/Div) Figure 13. GM3 Setting for current ratio function Figure 11 Current Ratio Setting IL L DCR C R1 +V C R2 1.5k 1uF IL 1.5uH 1m Figure 14. GM1,2 Setting for current ratio function Figure 12. Application circuit for current ratio setting All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 17 RT8800/B L DCR C ESR 1.3 Load Line without dead zone at light loads 1.31 V CORE (V) GMx Ix V ISPX + V ICOMMON RICOMMON1 RICOMMON2 +V C 1.29 1.28 1.27 1.26 RICOMMOM2 open RICOMMON2 = 82k 1.25 Figure 15. Application circuit of GM For load line design, with application circuit in Figure 15, it can eliminate the dead zone of load line at light loads. VISPX = VOUT +IL x DCR if GM holds input voltages equal, then VISPX = VICOMMON IX = VICOMMON I × DCR +L RICOMMON2 RICOMMON1 1.24 1.23 0 5 10 15 20 25 I OUT (A) Figure 16 Current Balance RT8800/B senses the inductor current via inductor’ s DCR for channel current balance and droop tuning. The differential sensing GM amplifier converts the voltage on the sense component (can be a sense resistor or the DCR of the inductor) to current signal into internal balance circuit. The current balance circuit sums and averages the current signals and then produces the balancing signals injected to pulse width modulator. If the current of some power channel is larger than average, the balancing signal reduces that channels pulse width to keep current balance. The use of single GM amplifier via time sharing technique to sense all inductor currents can reduce the offset errors and linearity variation between GMs. Thus it can greatly improve signal processing especially when dealing with such small signal as voltage drop across DCR. Voltage Reference for Converter Output & Load Droop The positive input of error amplifier is PI pin that sinks current proportional to the sum of converter output current. VDRP = 2ISINK x RDRP. The load droop proportional to load current can be set by the resistor between PI pin & external VDACQ produced by either buffer amplifier or other voltage source. The PI pin voltage should be larger than 0.8V for good droop circuit performance. = VOUT + IL × DCR I × DCR +L RICOMMON2 RICOMMON1 VOUT RICOMMON2 + IL × DCR RICOMMON2 I × DCR +L RICOMMON1 = For the lack of sinking capability of GM, RICOMMON2 should be small enough to compensate the negative inductor valley current especially at light loads. VICOMMON I × DCR ≥L RICOMMON2 RICOMMON1 Assume the negative inductor valley current is −5A at no load, then for RICOMMON1 = 330Ω, RADJ = 160Ω, VOUT = 1.300 - 5A × 1m Ω 1.3V ≥ RICOMMON2 330 Ω RICOMMON2 ≤ 85.8kΩ Choose RICOMMON2 = 82kΩ All brand name or trademark belong to their owner respectively www.richtek.com 18 DS8800/B-06 March 2007 RT8800/B Over Current Protection FB VDACQ PI + VDRP EA + ISINK 2xIX1 2xIX2 2xIX3 CH1:(5V/Div) CH2:(5V/Div) PWM Figure 17. Load Droop Circuit DAC Offset Voltage Tuning The Intel specification requires that at no load the nominal output voltage of the regulator be offset to a value lower than the nominal voltage corresponding to the VID code. The offset is tuning from RG in the DAC generator as Figure 18. VID0 VID1 VID2 VID3 VID4 VID5 R R R R R R RG VREF (0.8V) VDACFB IL Time (25ms/Div) Figure 19. The Over Current Protection in the interval + OP RF VDACQ Over Current Protection CH1:(5V/Div) CH2:(5V/Div) PWM Figure 18. The Structure of Discrete DAC Generator If VID0~6 is set at VSS (Ground), and to suppose that shunt resistance is Rs. From below equation, we can tune the value of RG to increase or decrease the base voltage of VDACQ. VDACQ = (1 + RF RF ) x VREF + x VREF RG RS VSS Time (25ms/Div) Figure 20. Over Current Protection at steady state Over Current Protection OCP comparator co\mpares each inductor current sensed & sample/hold by current sense circuit with this reference current(150uA). RT8800/B uses hiccup mode to eliminate fault detection of OCP or reduce output current when output is shorted to ground. Fault Detection The “ hiccup mode” operation of over current protection is adopted to reduce the short circuit current. The in-rush current at the start up is suppressed by the soft start circuit through clamping the pulse width and output voltage by an internal slow rising ramp. All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 19 RT8800/B Design Procedure Suggestion a.Output filter pole and zero (Inductor, output capacitor value & ESR). b.Error amplifier compensation & sawtooth wave amplitude (compensation network). Current Loop Setting a.GM amplifier S/H current (current sense component DCR, ICOMMON pin external resistor value). b.Over-current protection trip point (RICOMMON1 resistor). VRM Load Line Setting a.Droop amplitude (PI pin resistor). b.No load offset (RICOMMON2) Power Sequence & SS DVD pin external resistor and SS pin capacitor. 2. Over-Current Protection Setting PCB Layout a.Sense for current sense GM amplifier input. b.Refer to layout guide for other items. Voltage Loop Setting Design Example Given: Apply for four phase converter VIN = 12V VCORE = 1.5V ILOAD(MAX) = 100A VDROOP = 100mV at full load (1mΩ Load Line) OCP trip point set at 35A for each channel (S/H) DCR = 1mΩ of inductor at 25°C L = 1.5μH COUT = 8000μF with 5mΩ equivalent ESR. 1. Compensation Setting a. Modulator Gain, Pole and Zero: From the following formula: Modulator Gain =VIN/VRAMP =12/2.4=5 (i.e 14dB) where VRAMP : ramp amplitude of saw-tooth wave All brand name or trademark belong to their owner respectively www.richtek.com 20 DS8800/B-06 March 2007 RB1 4.7k LC Filter Pole = 1.45kHz and ESR Zero =3.98kHz b. EA Compensation Network: Select R1 = 4.7k, R2 = 15k, C1 = 12nF, C2 = 68pF and use the Type 2 compensation scheme shown in Figure 21. By calculation, the F Z = 0 .88kHz, FP = 322kHz and Middle Band Gain is 3.19 (i.e 10.07dB). C2 68pF RB2 C1 15k 12nF EA + Figure 21. Type 2 compensation network of EA Consider the temperature coefficient of copper 3900ppm/°C, IL × DCR = 150 μA RICOMMON1 IL × 1.39m Ω = 150 μA 330Ω IL = 35.6A RT8800/B Layout Guide Place the high-power switching components first, and separate them from sensitive nodes. 1. Most critical path: The current sense circuit is the most sensitive part of the converter. The current sense resistors tied to ISP1,2,3 and ICOMMON should be located not more than 0.5 inch from the IC and away from the noise switching nodes. The PCB trace of sense nodes should be parallel and as short as possible. R&C filter of choke should place close to PWM and the R & C connect directly to the pin of each output choke, use 10 mil differencial pair, and 20 mil gap to other phase pair. Less via as possible. 2. Switching ripple current path: a. Input capacitor to high side MOSFET. b. Low side MOSFET to output capacitor. c. The return path of input and output capacitor. d. Separate the power and signal GND. e. The switching nodes (the connection node of high/low side MOSFET and inductor) is the most noisy points.Keep them away from sensitive small-signal node. f . Reduce parasitic R, L by minimum length, enough copper thickness and avoiding of via. 3. MOSFET driver should be closed to MOSFET. SW1 L1 VIN RIN CIN VOUT COUT RL V L2 SW2 Figure 22. Power Stage Ripple Current Path All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 21 RT8800/B Next to IC +12V 0.1uF VCC BST DRVH IN SW CBOOT LO1 CIN +12V or +5V PWM RT GND RICOM ICOMMON FB RFB Locate near MOSFETs CSPx GND PI RDRD COMP CC RC Locate next to FB Pin VCC CBP Next to IC +5VIN VCORE COUT RT8800/B RT9603 DRVL GND Figure 23. Layout Consideration Figure 24 All brand name or trademark belong to their owner respectively www.richtek.com 22 DS8800/B-06 March 2007 RT8800/B Figure 25 Figure 26 All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 23 RT8800/B Figure 27 All brand name or trademark belong to their owner respectively www.richtek.com 24 DS8800/B-06 March 2007 RT8800/B Outline Dimension D D2 SEE DETAIL A L 1 E E2 1 1 2 e A A1 A3 b 2 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol A A1 A3 b D D2 E E2 e L Dimensions In Millimeters Min 0.800 0.000 0.175 0.180 2.950 1.300 2.950 1.300 0.500 0.350 0.450 Max 1.000 0.050 0.250 0.300 3.050 1.750 3.050 1.750 Dimensions In Inches Min 0.031 0.000 0.007 0.007 0.116 0.051 0.116 0.051 0.020 0.014 0.018 Max 0.039 0.002 0.010 0.012 0.120 0.069 0.120 0.069 V-Type 16L QFN 3x3 Package All brand name or trademark belong to their owner respectively DS8800/B-06 March 2007 www.richtek.com 25 RT8800/B A H M J B F C I D Symbol A B C D F H I J M Dimensions In Millimeters Min 9.804 3.810 1.346 0.330 1.194 0.178 0.102 5.791 0.406 Max 10.008 3.988 1.753 0.508 1.346 0.254 0.254 6.198 1.270 Dimensions In Inches Min 0.386 0.150 0.053 0.013 0.047 0.007 0.004 0.228 0.016 Max 0.394 0.157 0.069 0.020 0.053 0.010 0.010 0.244 0.050 16– Lead SOP Plastic Package Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Richtek Technology Corporation Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com All brand name or trademark belong to their owner respectively www.richtek.com 26 DS8800/B-06 March 2007