® RT8809 Dual-Phase PWM Controller for GPU Core Power Supply General Description Features The RT8809 is a dual-phase synchronous Buck PWM controller with integrated drivers which are optimized for high-performance graphic microprocessor and computer applications. The IC integrates a G-NAVP TM PWM z Dual-Phase PWM Controller z Two Embedded MOSFET Drivers and Embedded Switching Boot Diode Green-NAVP TM (Green Native Adaptive Voltage Positioning) Topology Dynamic Auto-Phase Control with Adjustable Threshold Cross-talk Jitter Suspend (CJSTM) Remote GND Detection for High Accuracy Automatic Diode Emulation Mode/or Ultrasonic Mode at Light Load Lossless RDS(ON) Current Sensing for Current Balance Lossless DCR Current Sensing for AVP & OCP Reference Voltage Output with 1% Accuracy External Reference Input with Soft-Start (RISS) Embedded One-Bit VID Control Adjustable OCP Threshold Adjustable Switching Frequency Reference-Tracking UVP/OVP Protection Shoot Through Protection and Short Pulse Free Technology RoHS Compliant and Halogen Free controller, two 12V MOSFET drivers with internal bootstrap diodes, as well as output current monitoring and protection functions into the WQFN-24L 4x4 package. The RT8809 adopts DCR and RDS(ON) current sensing. Load line voltage positioning (droop) and over-current protection are accomplished through continuous inductor DCR current sensing, while RDS(ON) current sensing is used for accurate channel-current balance. Using both methods of current sampling utilizes the best advantages of each technique. The RT8809 also features a one-bit VID control operation in which the feedback voltage is regulated and tracks external input reference voltage. Other features include output current indication, adjustable operating frequency, power good indication, external compensation, and enable/shutdown functions. z z z z z z z z z z z z z z z Simplified Application Circuit VIN VDD C8 VCC RT8809 BOOT1 R18 R22 R16 VIN EN/MODE R17 BOOT2 PS RMPSET LGATE2 TON C10 VIN Q3 UGATE2 L2 Q4 R11 C3 EN/MSEL PGND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 R10 C14 PHASE2 R20 Q2 LGATE1 OCP VOUT L1 PHASE1 VSET R21 C6 Q1 UGATE1 VREF VRTN C9 CSP CSN FB VRTN R14 R15 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8809 Applications z z z z Marking Information Middle to High End GPU Core Power High End Desktop PC Memory Core Power Low Voltage, High Current DC/DC Converter Voltage Regulator Modules Ordering Information RT8809 DQ=: Product Code DQ=YM DNN YMDNN : Date Code Pin Configurations (TOP VIEW) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` 24 23 22 21 20 19 VSET VREF EN/MSEL RMPSET COMP FB 1 18 2 17 3 15 25 5 14 13 6 7 Suitable for use in SnPb or Pb-free soldering processes. 16 PGND 4 8 VCC VDD LGATE1 PHASE1 UGATE1 BOOT1 9 10 11 12 VRTN TON OCP CSN CSP PS ` RSET VID BOOT2 UGATE2 PHASE2 LGATE2 Package Type QW : WQFN-24L 4x4 (W-Type) (Exposed Pad-Option 2) WQFN-24L 4x4 Functional Pin Description Pin No. Pin Name Pin Function Output Voltage Setting. Connect a voltage divider from VREF to VSET to set the output voltage. 1 VSET 2 VREF 3 EN/MSEL 4 RMPSET 5 COMP Compensation Node. This pin is the output node of the error amplifier. 6 FB Feedback Voltage Input. This pin is the negative input node of the error amplifier. 7 VRTN Remote Differential Feedback, Invert Input. This pin is the negative node of the differential remote voltage sensing. 8 TON 9 OCP 10 CSN On-Time (Switching Frequency) Setting. Connect a resistor (R TON) from TON to VIN to set the switching frequency. The value of RTON must be set equal to RRMP. OCP Level Setting. Connect a resistor from OCP to GND to set the current limit threshold. This pin is negative input of current sensing. 11 CSP This pin is positive input of current sensing. 12 PS Dynamic Phase Control Input. Connect a resistor from PS to GND to set the auto down phase threshold. Reference Voltage Output (2V). The RT8809 generates a 2V reference voltage from VREF to VRTN. Enable Control Input and Mode Selection. This pin is a tri-state input. Pull up this pin to exceed than 4V, controller operation into DEM mode. Pull up this pin to between 1.2V to 3V, controller operation into ASM mode. Pull down this pin to GND, controller will shutdown. Internal Ramp Slew-Rate Setting. Connect a resistor (RRMP) from RMPSET to GND to the ramp slew rate. The value of RRMP must be set equal to RTON. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Pin No. Pin Name Pin Function 13 BOOT1 Supply for High-Side Gate Driver of Phase 1. 14 UGATE1 High-Side Gate Driver of PHASE1. This pin provides the gate drive for the converter's high-side MOSFET. Connect this pin to the high-side MOSFET gate. 15 PHASE1 This pin is return node of the high-side driver of PHASE1. Connect this pin to high-side MOSFET Source together with the low-side MOSFET Drain and the inductor. 16 LGATE1 Low-Side Gate Driver of PHASE1. This pin provides the gate drive for the converter's low-side MOSFET. Connect this pin to the low-side MOSFET gate. 17 VDD Regulator Power for Internal Circuit. The regulated voltage provides power supply for all low-voltage circuits. 18 VCC Supply Voltage Input. Connect this pin to GND by a ceramic cap larger than 1μF. 19 LGATE2 Low-Side Gate Driver of PHASE2. This pin provides the gate drive for the converter's low-side MOSFET. Connect this pin to the low-side MOSFET gate. 20 PHASE2 This pin is return node of the high-side driver of PHASE2. Connect this pin to high-side MOSFET Source together with the low-side MOSFET Drain and the inductor. 21 UGATE2 High-Side Gate Driver of PHASE2. This pin provides the gate drive for the converter's high-side MOSFET. Connect this pin to the high-side MOSFET gate. 22 BOOT2 Bootstrap Supply for High-Side Gate Driver of Phase 2. This pin powers the high-side MOSFET driver. 23 VID Programming Output Voltage Control. When VID pin is logic high, internal N-MOSFET that connected to RSET pin is turn on. 24 RSET Output Voltage Setting. Connect a resistor from RSET pin to VSET pin, the output voltage can be switched two level by driving VID pin. 25 (Exposed Pad) PGND Power Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8809 Function Block Diagram VID VREF RSET VCC Reference Output Gen. PGOOD Up Trip Point Internal Regulator&BG + - PGOOD Down Trip Point VDD Power On Reset & Central Logic + VSET UV Trip Point + Control & Protection Logic - OV Trip Point + - Boot-Phase Detection 1 Ramp Gen RMPSET VRTN Soft Start & Slew Rate Control FB EN/MSEL + + ERROR AMP COMP EN/Mode Select Boot-Phase Detection 2 VSETA + + + + + LPF + + BOOT1 UGATE1 PHASE1 TON Gen 1 PWM CMP PWM1 - To Power on Reset To driver Logic ZCD To Power on Reset PHASE1 To driver Logic LGATE1 Driver Logic TON Gen 2 PWM2 LGATE2 PGND VIN Detection TON S/H GM + S/H GM + Current Balance PS CSP CSN OCP Phase shedding + - 5 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 BOOT2 UGATE2 PHASE2 Isum OCP 1/2 + To Protection Logic is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Operation The RT8809 integrates a PWM controller, two 12V MOSFET drivers with internal bootstrap diodes, as well as output current monitoring and protection functions. Power On Reset The Power On Reset (POR) circuit monitors the supply voltage of the controller (VCC). When VCC exceeds the POR rising threshold, the controller will be enabled. If VCC falls below the POR falling threshold during normal operation, all MOSFETs stop switching. There is a hysteresis between the POR rising threshold and falling threshold to prevent noise mis-trigger. Soft-Start Current Balance The RT8809 implements internal current balance mechanism in the current loop. The RT8809 senses each phase current signal and compares it with the average current. If the sensed current of any particular phase is higher than average current, the on-time of this phase will be adjusted to be shorter. OCP Once the sensed total current exceeds the current limit threshold, the driver will be forced to turn off the gate drivers for high side power MOSFETs. Until the OCP situation is removed. An internal soft-start function is used to prevent large inrush current while converter is powered-up. The FB voltage will track the internal soft-start voltage during softstart interval. During the soft-start period, the controller will operate in dual-phase mode to ensure enough charge for output loads. Over-Voltage Protection EN/Mode Select Under-Voltage Protection The RT8809 supports DEM (Diode Emulation Mode) and ASM (Audio Skipping Mode) operation which can be enabled by EN/MSEL pin. When the EN/MSEL pin is pulled up above 4.2V, the controller will operate in DEM and reduce the switching frequency at light load conditions for saving power loss. If the EN/MSEL voltage is between 1.2V and 3V, the controller will operate in ASM. In ASM operation, the minimum switching frequency is limited to 30kHz to avoid acoustic noises. If the pin is pulled to GND, the RT8809 will be shut down. The voltage on CSN pin is also monitored for Under-Voltage Protection (UVP). If the output voltage is lower than the UVP threshold, the controller will turn off both high side and low side MOSFETs. When the UVP is triggered, the RT8809 will enter hiccup mode and continuously try to restart until the UVP situation is removed. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 The RT8809 monitors the output voltage via the CSN pin for Over-Voltage Protection (OVP). Once the output voltage exceeds the OVP threshold, the controller will turn off high side MOSFETs and turn on low side MOSFETs to protect the load until the OVP situation is removed. is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8809 Absolute Maximum Ratings z z z z z z z z z z z z z (Note 1) VDD, VSEN, COMP, VSET, VREF, EN/MSEL, PS, OCP, CSN, CSP, RSET, VID, RMPSET to PGND ---------------------------------------------------------VCC, TON to PGND ------------------------------------------------------------------------------VRTN to PGND -------------------------------------------------------------------------------------BOOTx to PHASEx -------------------------------------------------------------------------------PHASE to PGND DC -----------------------------------------------------------------------------------------------------<20ns ------------------------------------------------------------------------------------------------LGATEx to PGND DC -----------------------------------------------------------------------------------------------------<20ns ------------------------------------------------------------------------------------------------UGATEx to PHASEx DC -----------------------------------------------------------------------------------------------------<20ns ------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-24L 4x4 ------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-24L 4x4, θJA -------------------------------------------------------------------------------WQFN-24L 4x4, θJC ------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 6V −0.3V to 15V −0.3V to 0.3V −0.3V to 15V −3V to 15V −5V to 30V −0.3V to PVCC+ 0.3V −5V to (VCC + 5V) −0.3V to BOOTx − PHASEx −5V to (BOOTx − PHASEx + 5V) 3.57W 28°C/W 7.1°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Voltage, VCC ------------------------------------------------------------------------------- 4.5V to 13.2V Junction Temperature Range --------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC = 12V, No Load, TA = 25°C, unless otherwise specified) Parameter Symbol Conditions Min Typ Max Unit 4.5 12 13.2 V Supply Input Supply Voltage VCC Supply Current IVCC + IPVCC EN = 3.3V, Not Switching -- 4 -- mA Shutdown Current ICC + IPVCC EN = 0V -- -- 500 μA (No Load, Active Mode ) -- 2 -- Accuracy −1% -- 1% VSET pin (this max. voltage will affect VCOMP max.) 0.5 -- 2 Reference Reference Output VREF Reference Input Range VSET Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 V V is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Parameter Symbol Conditions Min Typ Max Unit -- 2 -- ms -- 300 -- μs -- 0.5 -- mV/μs −8 -- 8 mV RL = 47kΩ -- 80 -- dB CLOAD = 5pF CLOAD = 10pF (Gain = −4, Rf = 47k, VOUT = 0.5V to 3V) RL = 47kΩ (max. depend on VSET max.) VCOMP = 2V -- 10 -- MHz -- 5 -- V/μs 0.5 -- 3 V -- 250 -- μA Start Up Delay Initial Soft-Start time Reference Change Delay Time Internal VID Change Slew Rate Error Amplifier Input Offset Voltage tb Initially, VOUT = 0.1V to 1.2V tc td VOUT = 1.2V to Set Voltage VOSEA DC Gain Gain-Bandwidth Product GBW Slew Rate SR Output Voltage Range VCOMP MAX Source Current IOUTEA Current Sense Amplifier (for Droop and OCP and Phase Shedding) Input Offset Voltage VOSCS −1 -- 1 mV Impedance at Neg. Input RISEN_N 1 -- -- MΩ Impedance at Pos Input RISEN 1 -- -- MΩ -- 5 -- V/V −50 -- 100 mV DC Gain Input range VISEN_in TON Setting TON Pin Output Voltage V TON IRTON = 62μA -- VSET -- V ON-Time Setting T ON IRTON = 62μA -- 350 -- ns TON Input Current Range IRTON 25 -- 280 μA -- 3.8 -- V 2.1 -- -- V Protection Under Voltage Lockout Threshold VUVLO Falling edge Absolute Over-Voltage Protection Threshold VOVABS Respect to V OUT Over-Voltage Protection Threshold VREL_OV Respect to V OUT(MAX) -- 135% -- V Under-Voltage Protection Threshold VUV Measured at VSENS with respect to unloaded output voltage (UOV) -- 50% -- mV Negative-Voltage Protection VNV Threshold −50 -- -- mV Current Source by OCP Pin IOCP 7.2 8 8.8 μA -- -- 0.5 V ASM Mode 1.2 -- 3 DEM Mode 4 -- -- −1 -- +5 Logic Inputs EN Input Voltage EN Pin Mode Select Voltage VIL Low Level (SD) (Hysteresis) Leakage Current of EN Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 V μA is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8809 Parameter Symbol Conditions Min Typ Max Unit -- 8 -- μA -- 500 -- ns Auto Phase Control Current Source by PSI IPS Maximum Duty Cycle UGATE Min. Off-Time Gate Driver -- 1.2 -- A -- 2 -- Ω ILGATEsr VBOOTx − VPHASEx = 6V VUGATEx − V PHASEx = 0.1V, IUGATEx = 50mA VCC − VLGATEx = 6V -- 1.2 -- A RLGATEsk VLGATEx = 0.1V, ILGATEx = 50mA -- 1 -- Ω RBOOT PVCC to BOOTx -- 20 -- Ω Upper Driver Source IUGATEsr Upper Driver Sink RUGATEsk Lower Driver Source Lower Driver Sink Internal Boost Charging Switch On-Resistance Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and 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 may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Typical Application Circuit VIN 12V RT8809 17 VDD C8 10µF C4 Optional C5 Optional R18 11k VRTN R19 15k BOOT1 13 UGATE1 14 1 PHASE1 15 VSET R4 Optional R22 56k VIN 2 VREF 24 RSET R21 43k 9 OCP 12 PS R16 160k 4 RMPSET R20 160k 8 TON R17 100 EN/MODE VCC 18 3 EN/MSEL VID 23 BOOT2 22 UGATE2 21 PHASE2 20 PGND FB 6 VRTN 7 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 C9 0.1µF Q1 L1 R5 0 Q2 GPIO R9 0 C14 0.1µF Q3 R7 NC C12 NC VIN C13 10µF /16V x 5 R8 0 Q4 LGATE2 19 CSP 11 CSN 10 C6 10µF/16V x 5 R6 0 LGATE1 16 COMP 5 25 (Exposed pad) R3 1 C7 10µF R12 NC C15 NC 0.36µH /0.8m R10 9.1k VOUT 1.1V C10 820µF /2.5V x 4 C11 10µF /6.3V x 10 L2 0.36µH/0.8m R11 9.1k R13 NC C3 0.1µF C2 1.5nF C1 2.2nF R2 R1 3.9k 2k R14 100 R15 100 VCC_SNS VSS_SNS is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8809 Typical Operating Characteristics Efficiency vs. Load Current Efficiency vs. Load Current 100 100 90 90 80 80 Phase 2 Active Efficiency (%) Efficiency (%) 70 60 50 40 30 20 70 60 50 40 30 20 10 10 VIN = VCC = 12V, VOUT = 1.1V 0 0 5 10 15 20 25 30 35 40 VIN = VCC = 12V, VOUT = 1.1V 0 0.01 45 50 55 60 0.1 Load Current (A) TON vs. Temperature 10 VREF vs. Temperature 360 2.04 355 2.03 350 2.02 VREF (V) 345 TON (ns) 1 Load Current (A) 340 335 330 2.01 2.00 1.99 1.98 325 1.97 320 VIN = VCC = 12V, No Load 315 VIN = VCC = 12V, No Load 1.96 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 Temperature (°C) Temperature (°C) Inductor Current vs. Output Current Power On from EN 100 125 35 VIN = VCC = 12V, IOUT = 50A Inductor Current (A) 30 VEN (10V/Div) 25 Phase 1 Phase 2 20 VOUT (1V/Div) 15 10 UGATE1 (50V/Div) 5 UGATE2 (50V/Div) VIN = VCC = 12V 0 20 25 30 35 40 45 50 55 60 Time (1ms/Div) Output Current (A) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Power On from VCC Power Off from EN VIN = VCC = 12V, IOUT = 50A VEN (10V/Div) VIN = VCC = 12V, IOUT = 50A V CC (10V/Div) VOUT (1V/Div) VOUT (1V/Div) UGATE1 (50V/Div) UGATE1 (50V/Div) UGATE2 (50V/Div) UGATE2 (50V/Div) Time (1ms/Div) Time (1ms/Div) Power Off from VCC Dynamic Output Voltage Control VIN = VCC = 12V, IOUT = 50A V CC (10V/Div) VSET (1V/Div) VOUT (1V/Div) VOUT (500mV/Div) UGATE1 (50V/Div) UGATE1 (50V/Div) UGATE2 (50V/Div) UGATE2 (50V/Div) VIN = VCC = 12V, VSET = 0.8V to 1.1V, IOUT = 25A Time (1ms/Div) Time (400μs/Div) Dynamic Output Voltage Control Load Transient Response VIN = VCC = 12V, RLL = 1.5mΩ VSET (1V/Div) VOUT (500mV/Div) UGATE1 (50V/Div) UGATE2 (50V/Div) VOUT (500mV/Div) IOUT (50A/Div) UGATE1 (50V/Div) VIN = VCC = 12V, VSET = 1.1V to 0.8V, IOUT = 25A Time (400μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 UGATE2 (50V/Div) Time (10μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8809 OVP Load Transient Response VIN = VCC = 12V, IOUT = 25A VIN = VCC = 12V, RLL = 1.5mΩ VOUT (500mV/Div) VOUT (1V/Div) IOUT (50A/Div) UGATE1 (20V/Div) UGATE1 (50V/Div) UGATE2 (50V/Div) LGATE1 (10V/Div) Time (10μs/Div) Time (20μs/Div) UVP Short Circuit VIN = VCC = 12V VIN = VCC = 12V, IOUT = 50A VOUT (1V/Div) VOUT (1V/Div) UGATE1 (20V/Div) IL1 (20A/Div) LGATE1 (10V/Div) IL2 (20A/Div) Time (10μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Application Information The RT8809 is a dual-phase synchronous Buck PWM controller with integrated drivers which is optimized for high-performance graphic microprocessor and computer applications. A COT (Constant-On-Time) PWM controller and two 12V MOSFET drivers with internal bootstrap diodes are integrated so that the external circuit can be easily designed and the component count can be reduced. The RT8809 adopts G-NAVPTM (Green-Native Adaptive Voltage Positioning), which is Richtek's proprietary topology derived from finite DC gain compensator with current mode control. The load line can be easily programmed by setting the DC gain of the error amplifier. The IC also adopts lossless DCR and RDS(ON) current sensing. Voltage positioning, dynamic phase control and current limit are accomplished through continuous inductor DCR current sensing, while RDS(ON) current sensing is used for accurate channel-current balance. Dynamic mode transition function with various operating states, which include dual-phase, single phase, diode emulation and audio skipping modes is supported. These different operating states make the system efficiency as high as possible. A one-bit VID control operation in which the feedback voltage is regulated and tracks external input reference voltage is provided. The RT8809 also features complete fault protection functions including over-voltage, undervoltage and current limit. DEM/ASM Mode Selection DEM (Diode Emulation Mode) and ASM (Audio Skipping Mode) operation can be enabled by driving the tri-state EN/MSEL pin to a logic high level. The RT8809 can switch operation into DEM when EN/MSEL pin is pulled up to above 4V. In DEM operation, the RT8809 automatically reduces the operation frequency at light-load conditions for saving power loss. If EN/MSEL is pulled between 1.2V to 3V, the controller will switch operation into ASM. In ASM operation, the minimum switching frequency is limited to 30kHz to avoid the acoustic noise. Finally, if the pin is pulled to GND, the RT8809 will shutdown. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 Power On Reset The POR (power on reset) circuit monitors the supply voltage of the controller (VCC). When VCC exceeds the POR rising threshold, the controller will be enabled. After the soft-start, the output voltage will first boot to around 1V, and then change to the set level. If VCC falls below the POR falling threshold during normal operation, all MOSFETs stop switching and the controller resets. The POR rising and falling threshold has a hysteresis to prevent noise mis-trigger. Soft-Start The RT8809 provides soft-start function. The soft-start function is used to prevent large inrush current while converter is being powered-up. An internal current source charges the is internal soft-start capacitor such that the internal soft-start voltage ramps up in a monotone to a VBOOT voltage (1V). The FB voltage will track the internal soft-start voltage during soft-start interval. Therefore, the duty cycle of the UGATE signal at power up as well as the input current limited. During the soft-start period, the controller will be in dual-phase operation by default to ensure enough charge during start-up. One-Bit VID and Dynamic Output Voltage Control The output voltage is determined by the applied voltage on the VSET pin. The RT8809 generates a 2V reference voltage from VREF to VRTN. As shown in Figure 1, connecting a resistor divider from the VREF pin to the VSET pin can set the output voltage according to the equation below : VOUT = 2V × ⎛⎜ R2 ⎞⎟ ⎝ R1 + R2 ⎠ The RT8809 also features a one-bit VID control through an internal N-MOSFET also shown in Figure 1. By connect a resistor (R3) from RSET pin to VSET pin, the output voltage can be switched between two levels by controlling the VID pin. When the VID pin is logic high, the internal NMOSFET turns on to set the output voltage to a lower level. The output voltage can be calculated as below : ⎡ (R2//R3) ⎤ VOUT = 2V × ⎢ ⎥ ⎣ R1 + (R2//R3) ⎦ is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8809 VREF REF Generator (2V) TON CCRCOT On-Time Computer R1 VSET R2 RTON VIN C1 RMPSET R3 RRMP RSET GPIO R1 On-Time VID Figure 2. On-Time Setting with RC Filter Frequency vs. RTON 700 Figure 1. Output Voltage Setting with One Bit VID Control 650 Switching Frequency Setting Switching frequency is a trade-off between efficiency and converter size. Higher operation frequency allows the use of smaller components. This is common in ultra-portable devices where the load currents are lower and the controller is powered from a lower voltage supply. On the other hand, lower frequency operation offers higher overall efficiency at the expense of component size and board space. Figure 2 shows the On-Time Setting Circuit. Connect a resistor (RTON) from TON to VIN and a resistor (R RMP) from RMPSET to GND to set the switching frequency according to the formula below : RTON VIN − VSET × = fS × C × VREF VSET + IL × (RDS(ON)_L-MOS + RDC − RLL ) VIN + IL × (RDS(ON)_L-MOS − RDS(ON)_H-MOS ) where fS : Switching frequency RTON : TON setting resistor C : Capacitance for on time compute VREF : Reference voltage for on time compute IL : Inductor current RDS(ON)_L-MOS : RDS(ON) of Low-Side MOSFET RDS(ON)_H-MOS : RDS(ON) of High-Side MOSFET Frequency (kHz)1 600 550 500 450 400 350 300 250 200 150 0 50 100 150 200 250 300 RTON (k Ω ) Figure 3. Frequency vs. RTON Current Sense Setting (with Temperature Compensation) The RT8809 uses continuous inductor current sensing to make the controller less noise sensitive. Low offset amplifiers are used for loop control and over current detection. The CSP and CSN denote the positive and negative input of the current sense amplifier of any phase. Since the DCR of the inductor is temperature dependent, it affects the down-phase threshold, OCP threshold and output voltage accuracy, especially at heavy load. Temperature compensation is recommended for the lossless inductor DCR current-sense method. Figure 4 shows a simple but effective way to compensate the unwanted temperature variations of the inductor DCR by using an NTC thermistor. RDC : DCR of inductor RLL : Load line resistance The value of RTON can be selected using Figure 3 and the value of RRMP must be set equal to RTON. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 To calculate DCR value at different temperatures, can use the equation below : VOUT L1 PHASE1 RS L2 DCR DCR PHASE2 DCRT°C = DCR25°C x [1 + 0.00393 x( T-25)] where the 0.00393 is the temperature coefficient of copper. RNTC RP RS CX can be obtained by below formula, RX CSP CSN ⎛ ⎞ RS L ×⎜2 + ⎟ ⎜ REQU_25°C ⎟⎠ ⎝ CX = RS × DCR25°C CX + VX - (4) COUT (5) Loop Control LGATE1 CCRCOT PWM Driver Logic VIN COUT RX UGATE2 PHASE2 L2 DCR LGATE2 CMP RX VCS + GM - CSP CX CSN C3 C2 C1 R2 R1 VSEN (2) 1 α − REQU_TH REQU_TL 1 ⎞ −⎛ 1 ⎞ ⎤ ⎫ ⎟ ⎜ ⎟ ⎨ ⎢ ⎥⎬ RNTC, T°C = R25°C × e⎩ ⎣⎝ T + 273 ⎠ ⎝ 278 ⎠ ⎦ ⎭ (3) where R25°C is the thermistor's nominal resistance at room temperature, β (beta) is the thermistor's material constant in Kelvins, and T is the thermistor's actual temperature in Celsius. Copyright © 2013 Richtek Technology Corporation. All rights reserved. FB VRTN VRTN VREF The standard formula for the resistance of the NTC thermistor as a function of temperature is given by : ⎧ ⎡⎛ β ⎜ COMP + GM - where α is equal to DCRTH/DCRTL DS8809-00 May 2013 L1 DCR PHASE1 + - RS = 2(α -1) VOUT UGATE1 - where R EQU_TH is equal to R P + R NTC // R X at high temperature and REQU_TL is equal to RP + RNTC // RX at low temperature. Usually, RX is set to equal RNTC (25°C). RP and RX are selected to linearize the NTC's temperature characteristic. For a given NTC and RP, the design is to first obtain RS and then CX. Usually, set RX = RNTC. To solve (1), RS must first be obtained as below : VIN + The RT8809 observes the voltage VX, across the CSP and CSN pins for inductor current information. To design VX without regard to the temperature coefficient, refer to the formula below : RS 2+ R DCRTH EQU_TH (1) = RS DCRTL 2+ REQU_TL The RT8809 adopts Richtek's proprietary G-NAVPTM topology. G-NAVPTM is based on the finite-gain peak current mode with CCRCOT (Constant Current Ripple Constant On Time; CCRCOT) topology. The output voltage will decrease with increasing output load current. The control loop consists of PWM modulators with power stages, current sense amplifiers and an error amplifier as shown in Figure 5. COMP2 Figure 4. Inductor DCR Sensing Figure 5. Simplified Schematic for Droop and Remote Sense in CCM Similar to the peak current mode control with finite compensator gain, the HS_FET on-time is determined by the CCRCOT ON-Time generator. When the load current increases, VCS increases, the steady state COMP voltage also increases and VOUT decreases, achieving active voltage positioning (AVP). RT8809 internally cancels the inherent output offset of the finite gain peak current mode controller. is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8809 Droop Setting Due to the native droop characteristics, the active voltage positioning (AVP) can be conveniently achieved by properly setting the error amplifier gain. The target is to have VOUT = VREF − ILOAD x RLL (6) Then solving the switching condition VCOMP2 = VCS in Figure 5 yields the desired error amplifier gain as 5 × DCR R2 AV = = 2 R1 RLL (7) where C is the capacitance of the output capacitor, and RC is the ESR of output capacitor. C2 can be calculated as follows : C2 = RC × C R2 The zero of compensator has to be placed at half of the switching frequency to filter the switching-related noise, such that, 1 (10) C1 = R1× π × fS Dynamic Phase Number Control where RLL is the equivalent load line resistance as well as the desired static output impedance. For a given R1, the design is to get R2 according to (7). VOUT AV2 > AV1 The RT8809 controls the operation phase number according to the total current. Figure 7 shows the dynamic phase number control circuit. By connecting a resistor (RPS) from the PS pin to GND, the phase transition threshold can be set. The formula is : RPS = AV2 AV1 0 (9) Load Current Figure 6. Error Amplifier Gain (AV) Influence on VOUT Accuracy Loop Compensation Optimized compensation of the RT8809 allows for best possible load step response of the regulator's output. A type-I compensator with a single pole and single zero is adequate for a proper compensation. Figure 5 shows the compensation circuit. Prior design procedure shows how to determine the resistive feedback components of the error amplifier gain, C1 and C2 must be calculated for the compensation. The target is to achieve the constant resistive output impedance over the widest possible frequency range. The pole frequency, fP, of the compensator must be set to compensate the output capacitor ESR zero : 1 fP = (8) 2π × RC × C DCR × ISUM × 5 1μ where ISUM is the sum of the inductor valley current. For example, if DCR is 0.74mΩ, and the desired up-phase threshold is 15A, the value of RPS will be −3 RPS = 0.74 × 10 × 15 × 5 = 55.5kΩ 1× 10−6 Once the total inductor valley current is higher than the threshold, the controller will transit to dual-phase operation. when the total current becomes lower than the setting threshold minus around 5A hysteresis, the active phase number will return to single-phase. If the PS pin is set floating, the controller will force to dual-phase operation. PS L1 L2 DCR VPS + CMP - RPS Active Phase Number DCR RX RX CX COUT CSN CSP gm + VCX Figure 7. Dynamic Phase Number Control Circuit Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Current Balance Under-Voltage Protection The RT8809 implements internal current balance mechanism in the current loop. The RT8809 senses perphase current signal and compares it with the average current. If the sensed current of any particular phase is higher than average current, the on-time of this phase will be adjusted to be shorter. The voltage on CSN pin is also monitored for under-voltage protection. If the output voltage is lower than the UVP threshold, UVP will be triggered. The RT8809 will then turn off both high-side and low-side MOSFETs. When UVP is triggered, the RT8809 will enter hiccup mode and continuously try to restart until the UVP situation is cleared. Current Limit Setting The RT8809 includes a built-in current limit protection function. Figure 8 shows the protection circuit. The current limit threshold is adjusted by an external resistor, ROC, at the OCP pin. The value of ROC can be set according to the following formula : DCR × ISUM × 6 ROC = 8μ where ISUM is the desired current limit threshold. Once the sensed total current exceeds the current limit threshold, the driver will be forced to turn off UGATE until the OCP situation is removed. Inductor Selection The switching frequency and ripple current determine the inductor value as follows : V − VOUT L(MIN) = IN × TON IRIPPLE(MAX) where TON is the UGATE turn on period. Higher inductance results in lower ripple current and higher efficiency but brings a slower load transient response. Thus, more output capacitors may be required. The lower DC resistance can reduce power loss. The core must be large enough and not to be saturated at the peak inductor current. Output Capacitor Selection OCP L1 L2 DCR VOC - CMP OCP + ROC DCR RX RX CX COUT CSN CSP gm + VCX Figure 8. Over Current Protection Circuit Over-Voltage Protection The RT8809 monitors the output voltage via the CSN pin for over-voltage protection (OVP). Once the output voltage exceeds the OVP threshold, OVP is triggered. The RT8809 will turn on low-side MOSFETs and turn off high-side MOSFETs to protect the load until the OVP situation is removed. A 4μs delay is used in the OVP detection circuit to prevent false trigger. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8809-00 May 2013 Output capacitors are used to maintain high performance for the output beyond the bandwidth of the converter itself. Two different kinds of output capacitors can be found, bulk capacitors closely located to the inductors and ceramic output capacitors close to the load. The latter ones are for mid-frequency decoupling with especially small ESR and ESL values while the bulk capacitors have to provide enough stored energy to overcome the low-frequency bandwidth gap between the regulator and the GPU. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT8809 where TJ(MAX) is the maximum junction temperature, TA is Layout Consideration the ambient temperature, and θJA is the junction to ambient thermal resistance. Careful PC board layout is critical to achieving low switching losses and clean, stable operation. The switching power stage requires particular attention. If possible, mount all of the power components on the top side of the board with their ground terminals flushed against one another. Follow these guidelines for optimum PC board layout : For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-24L 4x4 package, the thermal resistance, θJA, is 35°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : P D(MAX) = (125°C − 25°C) / (28°C/W) = 3.57W for WQFN-24L 4x4 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 8 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. ` Keep the high-current paths short, especially at the ground terminals. ` Keep the power traces and load connections short. This is essential for high efficiency. ` When trade-offs in trace lengths must be made, it’s preferable to allow the inductor charging path to be made longer than the discharging path. ` Place the current sense components close to the controller. CSP and CSN connections for current limit and voltage positioning must be made using Kelvin sense connections to guarantee the current sense accuracy. The PCB trace from the sense nodes should be paralleled back to the controller. ` Route high-speed switching nodes away from sensitive analog areas (COMP, FB, CSP, CSN, etc...) Maximum Power Dissipation (W)1 4.0 Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 8. Derating Curve of Maximum Power Dissipation Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 18 is a registered trademark of Richtek Technology Corporation. DS8809-00 May 2013 RT8809 Outline Dimension D2 D SEE DETAIL A L 1 E E2 e b A3 Symbol D2 E2 1 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A A1 1 2 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 3.950 4.050 0.156 0.159 Option 1 2.400 2.500 0.094 0.098 Option 2 2.650 2.750 0.104 0.108 E 3.950 4.050 0.156 0.159 Option 1 2.400 2.500 0.094 0.098 Option 2 2.650 2.750 0.104 0.108 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 24L QFN 4x4 Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS8809-00 May 2013 www.richtek.com 19