ADP3194JRUZ-RL

www.DataSheet4U.com 6-Bit, Programmable 2-/3-/4-Phase, Synchronous Buck Controller ADP3194 FEATURES Selectable 2-, 3-, or 4-phase operation Up to 1 MHz per phase ±9.5 mV worst-case differential sensing error over temperature Logic-level PWM outputs for interface to external high power drivers PWM Flex-ModeTM architecture for excellent load transient performance Active current balancing between all output phases Built-in power good/crowbar blanking supports OTF VID code changes 6-bit digitally programmable 0.8375 V to 1.6 V output Programmable short circuit protection with programmable latch-off delay FUNCTIONAL BLOCK DIAGRAM VCC 28 SHUNT REGULATOR UVLO SHUTDOWN AND BIAS OSCILLATOR SET RESET EN 27 PWM1 RAMPADJ 14 RT 13 ADP3194 EN 11 GND 19 CMP DAC + 150mV CSREF CMP CURREN TBALANCING CIRCUIT RESET 2-/3-/4-PHASE DRIVER LOGIC RESET 26 PWM2 CMP 25 PWM3 DAC – 250mV CMP PWRGD 10 DELAY RESET CURRENT LIMIT 23 SW1 ILIMIT 15 EN 22 SW2 21 SW3 20 SW4 CURREN TLIMIT CIRCUIT SOFT START 17 CSSUM 16 CSREF 18 CSCOMP 24 PWM4 CROWBAR APPLICATIONS Desktop PC power supplies for Next-generation Intel® processors VRM modules Games consoles DELAY 12 COMP 9 8 FB PRECISION REFERENCE 7 FBRTN 1 2 3 VID DAC 4 5 6 06022-001 VID4 VID3 VID2 VID1 VID0 VID5 Figure 1. Functional Block Diagram GENERAL DESCRIPTION The ADP3194 1 is a highly efficient, multiphase, synchronous buck switching regulator controller optimized for converting a 5 V or 12 V main supply into the core supply voltage required by high performance Intel processors. It uses an internal 6-bit DAC to read a voltage identification (VID) code directly from the processor that is used to set the output voltage between 0.8375 V and 1.6 V. The device uses a multimode PWM architecture to drive the logic-level outputs at a programmable switching frequency that can be optimized for VR size and efficiency. The phase relationship of the output signals can be programmed to provide 2-, 3-, or 4-phase operation, allowing for the construction of up to four complementary buck switching stages. The ADP3194 also includes programmable, no-load offset, and slope functions to adjust the output voltage as a function of the load current, so it is always optimally positioned for a system transient. The ADP3194 also provides accurate and reliable short-circuit protection, adjustable current limiting, and a delayed power good output that accommodates on-thefly (OTF) output voltage changes requested by the CPU. The devices are specified over the commercial temperature range of 0°C to +85°C and are available in a 28-lead TSSOP. 1 Protected by U. S. Patent Number 6,683,441; other patents pending. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved. www.DataSheet4U.com ADP3194 TABLE OF CONTENTS Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Typical Performance Characteristic and Test Circuits ................ 7 Theory of Operation ........................................................................ 8 Startup Sequence .......................................................................... 8 Master Clock Frequency.............................................................. 8 Output Voltage Differential Sensing .......................................... 8 Output Current Sensing .............................................................. 8 Active Impedance Control Mode............................................... 9 Current-Control Mode and Thermal Balance.......................... 9 Voltage Control Mode.................................................................. 9 Soft Start ........................................................................................ 9 Current-Limit, Short-Circuit, and Latch-Off Protection...... 10 Dynamic VID.............................................................................. 10 Power Good Monitoring ........................................................... 12 Output Crowbar ......................................................................... 12 Output Enable and UVLO ........................................................ 12 Application Information................................................................ 13 Setting the Clock Frequency ..................................................... 13 Soft Start and Current-Limit Latch-Off Delay Times ........... 13 Inductor Selection ...................................................................... 13 Designing an Inductor............................................................... 14 Sense Resistor.............................................................................. 14 Sense Resistor Selection ............................................................ 14 Output Droop Resistance–Sense Resistor............................... 14 Output Offset .............................................................................. 15 Design Comparison Trade-Off Between DCR and Sense Resistor ........................................................................................ 15 COUT Selection ............................................................................. 16 Ramp Resistor Selection............................................................ 17 COMP Pin Ramp ....................................................................... 17 Current-Limit Setpoint.............................................................. 17 Feedback Loop Compensation Design.................................... 17 CIN Selection and Input Current di/dt Reduction.................. 19 Tuning the ADP3194 ................................................................. 20 RAMPADJ Filter......................................................................... 22 Shunt Resistor Design................................................................ 22 Design Example Using DCR Method.......................................... 23 Inductor Selection Using DCR................................................. 23 Designing an Inductor Using DCR.......................................... 23 Inductor DCR Temperature Correction ................................. 23 Output Droop Resistance–DCR Method................................ 24 Power MOSFETs......................................................................... 24 Layout and Component Placement.............................................. 26 General Recommendations....................................................... 26 Power Circuitry Recommendations ........................................ 26 Signal Circuitry Recommendations......................................... 26 Outline Dimensions ....................................................................... 29 Ordering Guide .......................................................................... 29 REVISION HISTORY 10/06—Revision 0: Initial Version Rev. 0 | Page 2 of 32 www.DataSheet4U.com ADP3194 SPECIFICATIONS VCC = 5 V, FBRTN = GND, TA = 0°C to +85°C, unless otherwise noted. 1 Table 1. Parameter ERROR AMPLIFIER Output Voltage Range Accuracy Accuracy Line Regulation Input Bias Current FBRTN Current Output Current Gain Bandwidth Product Slew Rate VID INPUTS Input Low Voltage Input High Voltage Input Current, Input Voltage Low Input Current, Input Voltage High Pull-Up Resistance Internal Pull-Up Voltage VID Transition Delay Time 2 No CPU Detection Turn-Off Delay Time2 OSCILLATOR Frequency Range2 Frequency Variation Symbol VCOMP VFB VFB ΔVFB IFB IFBRTN IO(ERR) GBW(ERR) Conditions Min 0 −8.0 −9.5 0.05 15.5 100 500 20 25 Typ Max VCC +8.0 +9.5 Unit V mV mV % μA μA μA MHz V/μs V V μA μA kΩ V ns ns MHz MHz MHz MHz V mV μA mV nA MHz V/μs V mV V μA mV kΩ μA % Relative to nominal DAC output, referenced to FBRTN, CSSUM = CSCOMP; VOUT < 1 V Relative to nominal DAC output, referenced to FBRTN, CSSUM = CSCOMP; VOUT > 1 V VCC = 4.75 V to 5.25 V 14 FB forced to VOUT – 3% COMP = FB CCOMP = 10 pF 17 140 VIL(VID) VIH(VID) IIL(VIDX) IIH(VIDX) RVID 0.4 0.8 VID(X) = 0 V VID(X) = 1.25 V 35 1.0 400 400 0.25 1.55 –25 5 60 1.2 –35 15 85 VID code change to FB change VID code change to 11111 to PWM going low fOSC fPHASE Output Voltage RAMPADJ Output Voltage RAMPADJ Input Current Range CURRENT SENSE AMPLIFIER Offset Voltage Input Bias Current Gain Bandwidth Product Slew Rate Input Common-Mode Range Positioning Accuracy Output Voltage Range Output Current CURRENT BALANCE CIRCUIT Common-Mode Range Input Resistance Input Current Input Current Matching 3 VRT VRAMPADJ IRAMPADJ VOS(CSA) IBIAS(CSSUM) GBW(CSA) TA = +25°C, RT = 247 kΩ, 4-phase TA = +25°C, RT = 138 kΩ, 4-phase TA = +25°C, RT = 84 kΩ, 4-phase RT = 100 kΩ to GND RAMPADJ – FB 1.8 –50 0 –1.5 –10 2 3 4 2.0 4.5 2.45 2.3 +50 100 +1.5 +10 CSSUM – CSREF CCSCOMP = 10 pF CSSUM and CSREF ΔVFB ICSCOMP VSW(X)CM RSW(X) ISW(X) ΔISW(X) 10 10 0 –77 0.05 –80 500 –600 12 5 –5 +200 28 17 +5 3 –83 VCC SW(X) = 0 V SW(X) = 0 V SW(X) = 0 V 20 11 Rev. 0 | Page 3 of 32 www.DataSheet4U.com ADP3194 Parameter CURRENT LIMIT COMPARATOR Output Voltage Normal Mode Shutdown Mode Output Current, Normal Mode Maximum Output Current2 Current Limit Threshold Voltage Current Limit Setting Ratio DELAY Normal Mode Voltage DELAY Overcurrent Threshold Latch-Off Delay Time SOFT START Output Current, Soft Start Mode Soft Start Delay Time ENABLE INPUT Input Low Voltage Input High Voltage Input Current POWER GOOD COMPARATOR Undervoltage Threshold Overvoltage Threshold Output Low Voltage Power Good Delay Time During Soft Start VID Code Changing VID Code Static Crowbar Trip Point Crowbar Reset Point Crowbar Delay Time VID Code Changing VID Code Static PWM OUTPUTS Output Low Voltage Output High Voltage SUPPLY—ADP3194 VCC DC Supply Current UVLO Threshold Voltage UVLO Hysteresis 1 2 3 Symbol Conditions Min Typ Max Unit VILIMIT(NM) VILIMIT(SD) IILIMIT(NM) VCL VDELAY(NM) VDELAY(OC) tDELAY IDELAY(SS) tDELAY(SS) VIL(EN) VIH(EN) IIL(EN) VPWRGD(UV) VPWRGD(OV) VOL(PWRGD) EN > 0.8 V, RILIMIT = 250 kΩ EN < 0.4 V, IILIMIT = –100 μA EN > 0.8 V, RILIMIT = 250 kΩ VCSREF – VCSCOMP, RILIMIT = 250 kΩ VCL/IILIMIT RDELAY = 250 kΩ RDELAY = 250 kΩ RDELAY = 250 kΩ, CDELAY = 12 nF During startup, DELAY < 2.8 V RDELAY = 250 kΩ, CDELAY = 12 nF, VID code = 011111 2.8 3 12 3.3 400 60 105 2.8 1.6 125 10.4 3 1.9 1.5 20 1 145 3.3 2.2 V mV μA μA mV mV/μA V V ms μA ms V V μA mV mV mV ms μs ns mV mV μs ns 15 25 0.4 0.8 –1 Relative to nominal DAC output Relative to nominal DAC output IPWRGD(SINK) = 4 mA RDELAY = 250 kΩ, CDELAY = 12 nF, VID code = 011111 –180 90 –250 150 225 +1 –300 200 400 1 100 90 450 100 VCROWBAR tCROWBAR Relative to nominal DAC output Relative to FBRTN Overvoltage to PWM going low Blanking time 250 200 150 550 250 400 160 5 5 20 7 0.9 200 650 VOL(PWM) VOH(PWM) VCC VUVLO IPWM(SINK) = –400 μA IPWM(SOURCE) = +400 μA VSYSTEM = 12 V, RSHUNT = 300 Ω 500 4.0 4.75 mV V V mA V V VCC rising 6.3 30 8.0 All limits at temperature extremes are guaranteed via correlation using standard statistical quality control (SQC). Guaranteed by design, not production tested. Relative current matching from each phase to the average of all four phases. Rev. 0 | Page 4 of 32 www.DataSheet4U.com ADP3194 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter VCC VID4 to VID0, VID5 FBRTN SW1 to SW4 All Other Inputs and Outputs Storage Temperature Range Operating Ambient Temperature Range Operating Junction Temperature Thermal Impedance (θJA) Lead Temperature Soldering (10 sec) Vapor Phase (60 sec) Infrared (15 sec) Rating –0.3 V to +6 V –0.3 V to +6 V –0.3 V to +0.3 V −5 V to +25 V –0.3 V to VCC + 0.3 V –65°C to +150°C 0°C to +85°C 125°C 100°C/W 300°C 215°C 220°C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in combination. Unless otherwise specified, all other voltages are referenced to GND. ESD CAUTION Rev. 0 | Page 5 of 32 www.DataSheet4U.com ADP3194 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS VID4 1 VID3 2 VID2 3 VID1 4 VID0 5 28 VCC 27 PWM1 26 PWM2 25 PWM3 24 PWM4 VID5 6 FBRTN 7 FB 8 COMP 9 PWRGD 10 EN 11 DELAY 12 RT 13 RAMPADJ 14 ADP3194 TOP VIEW (Not to Scale) 23 SW1 22 SW2 21 SW3 20 SW4 19 GND 18 CSCOMP 17 CSSUM 16 CSREF 15 ILIMIT 06022-002 Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. 1 to 6 Mnemonic VID4 to VID0, VID5 Description Voltage Identification DAC Inputs. These six pins are pulled up to an internal reference, providing Logic 1 is left open. When in normal operation mode, the DAC output programs the FB regulation voltage from 0.8375 V to 1.6 V (see Table 2). Leaving all the VID pins open results in ADP3194 going into a No CPU mode, shutting off their PWM outputs and pulling the PWRGD output low. Feedback Return. VID DAC and error amplifier reference for remote sensing of the output voltage. Feedback Input. Error amplifier input for remote sensing of the output voltage. An external resistor between this pin and the output voltage sets the no-load offset point. Error Amplifier Output and Compensation Point. Power Good Output. Open drain output that signals when the output voltage is outside of the proper operating range. Power Supply Enable Input. Pulling this pin to GND disables the PWM outputs and pulls the PWRGD output low. Soft Start Delay and Current-Limit Latch-Off Delay Setting Input. An external resistor and capacitor connected between this pin and GND sets the soft start ramp-up time and the overcurrent latch-off delay time. Frequency Setting Resistor Input. An external resistor connected between this pin and GND sets the oscillator frequency of the device. PWM Ramp Current Input. An external resistor from the converter input voltage to this pin sets the internal PWM ramp. Current Limit Set Point/Enable Output. An external resistor from this pin to GND sets the current limit thresh old of the converter. This pin is actively pulled low when the ADP3194 EN input is low or when VCC is below its UVLO threshold to signal to the driver IC that the driver high-side and low-side outputs should go low. Current Sense Reference Voltage Input. The voltage on this pin is used as the reference for the current sense amplifier and the power good and crowbar functions. This pin should be connected to the common point of the output inductors. Current Sense Summing Node. External resistors from each switch node to this pin sum the average inductor currents together to measure the total output current. Current Sense Compensation Point. A resistor and capacitor from this pin to CSSUM determines the slope of the load line and the positioning loop response time. Ground. All internal biasing and the logic output signals of the device are referenced to this ground. Current Balance Inputs. Inputs for measuring the current level in each phase. Leave the SW pins of unused phases open. Logic Level PWM Outputs. Each output is connected to the input of an external MOSFET driver such as the ADP3120A. Connecting the PWM3 and/or PWM4 outputs to GND causes that phase to turn off, allowing the ADP3194 to operate as a 2-, 3-, or 4-phase controller. A 300 Ω resistor should be placed between the 12 V system supply and the VCC pin to ensure 5 V. Rev. 0 | Page 6 of 32 7 8 9 10 11 12 13 14 15 FBRTN FB COMP PWRGD EN DELAY RT RAMPADJ ILIMIT 16 CSREF 17 18 19 20 to 23 24 to 27 CSSUM CSCOMP GND SW4 to SW1 PWM4 to PMW1 VCC 28 www.DataSheet4U.com ADP3194 TYPICAL PERFORMANCE CHARACTERISTIC AND TEST CIRCUITS 7000 6000 5000 FREQUENCY (kHz) 12V 300Ω 28 ADP3194 VCC 4000 18 CSCOMP 39kΩ 100nF CSSUM 17 3000 2000 1kΩ CSREF 16 1000 0 1.0V 06022-003 0 100 200 300 400 500 RT (kΩ) 600 700 800 900 19 Figure 3. Master Clock Frequency vs. RT (kΩ) Figure 5. Current Sense Amplifier VOS 12V ADP3194 1 VID4 2 VID3 3 VID2 300Ω + 1µF 100nF VCC 28 PWM1 27 PWM2 26 PWM3 25 PWM4 24 SW1 23 SW2 22 SW3 21 SW4 20 GND 19 CSCOMP 18 6-BIT CODE 4 VID1 5 VID0 6 VID5 7 FBRTN 8 FB 12V 300Ω 28 ADP3194 VCC 1kΩ 9 COMP 10 PWRGD 200kΩ 200kΩ 100nF CSCOMP 18 1.25V 11 EN 12 DELAY CSSUM 17 20kΩ CSSUM 17 CSREF 16 ILIMIT 15 250kΩ 12nF 250kΩ 100nF ΔV CSREF 16 13 RT 14 RAMPADJ 1.0V 19 06022-004 GND 06022-006 ΔVFB = FBΔV = 80mV – FBΔV = 0mV Figure 4. Closed-Loop Output Voltage Accuracy Figure 6. Positioning Voltage Rev. 0 | Page 7 of 32 06022-005 GND VOS = CSCOMP – 1V 40 www.DataSheet4U.com ADP3194 THEORY OF OPERATION The ADP3194 combines a multimode, fixed frequency PWM control with multiphase logic outputs for use in 2-, 3-, and 4-phase synchronous buck CPU core supply power converters. The internal VID DAC is designed to interface with the Intel 6-bit VRD/VRM 10- and 10.1-compatible CPUs. Multiphase operation is important for producing the high currents and low voltages demanded by today’s microprocessors. Handling the high currents in a single-phase converter places high thermal demands on the components in the system, such as the inductors and MOSFETs. The multimode control of the ADP3194 ensures a stable, high performance topology for • • • • • • • • • Balancing currents and thermals between phases High speed response at the lowest possible switching frequency and output decoupling Minimizing thermal switching losses due to lower frequency operation Tight load line regulation and accuracy High current output for up to 4-phase operation Reduced output ripple due to multiphase cancellation PC board layout noise immunity Ease of use and design due to independent component selection Flexibility in operation for tailoring design to low cost or high performance After this time, if the PWM output is not grounded, the 5 kΩ resistance is removed and it switches between 0 V and 5 V. If the PWM output is grounded, it remains off. The PWM outputs are logic-level devices intended for driving external gate drivers, such as the ADP3120A. Because each phase is monitored independently, operation approaching 100% duty cycle is possible. Also, more than one output can be on at the same time for overlapping phases. MASTER CLOCK FREQUENCY The clock frequency of the ADP3194 is set with an external resistor connected from the RT pin to ground. The frequency follows the graph in Figure 3. To determine the frequency per phase, the clock is divided by the number of phases in use. If PWM4 is grounded, divide the master clock by 3 for the frequency of the remaining phases. If PWM3 and PWM4 are grounded, divide by 2. If all phases are in use, divide by 4. OUTPUT VOLTAGE DIFFERENTIAL SENSING The ADP3194 differential sense compares a high accuracy VID DAC and a precision reference to implement a low offset error amplifier. This maintains a worst-case specification of ±9.5 mV differential sensing error over their full operating output voltage and temperature range. The output voltage is sensed between the FB pin and the FBRTN pin. Connect FB through a resistor to the regulation point, usually the remote sense pin of the microprocessor. Connect FBRTN directly to the remote sense ground point. The internal VID DAC and precision reference are referenced to FBRTN, which has a minimal current of 100 μA to allow accurate remote sensing. The internal error amplifier compares the output of the DAC to the FB pin to regulate the output voltage. STARTUP SEQUENCE During startup, the number of operational phases and their phase relationship is determined by the internal circuitry that monitors the PWM outputs. Normally, the ADP3194 operate as a 4-phase PWM controller. Grounding the PWM4 pin programs 3-phase operation, and grounding the PWM3 pin and the PWM4 pin programs 2-phase operation. When the ADP3194 are enabled, the controller outputs a voltage on PWM3 and PWM4, which is approximately 675 mV. An internal comparator checks each pin’s voltage vs. a threshold of 300 mV. If the pin is grounded, it is below the threshold, and the phase is disabled. The output resistance of the PWM pins is approximately 5 kΩ during this detection time. Any external pull-down resistance connected to the PWM pins should not be less than 25 kΩ to ensure proper operation. PWM1 and PWM2 are disabled during the phase detection interval that occurs during the first two clock cycles of the internal oscillator. OUTPUT CURRENT SENSING The ADP3194 provide a dedicated current sense amplifier (CSA) to monitor the total output current for proper voltage positioning vs. load current and for current-limit detection. Sensing the load current at the output gives the total average current being delivered to the load, which is an inherently more accurate method than peak current detection or sampling the current across a sense element, such as the low-side MOSFET. This amplifier can be configured several ways, depending on the objectives of the system: Output inductor DCR sensing without a thermistor for lowest cost, Output inductor DCR sensing with a thermistor for improved accuracy with tracking of inductor temperature, Sense resistors for highest accuracy measurements. Rev. 0 | Page 8 of 32 www.DataSheet4U.com ADP3194 The positive input of the CSA is connected to the CSREF pin, which is connected to the output voltage. The inputs to the amplifier are summed together through resistors from the sensing element (such as the switch node side of the output inductors) to the inverting input, CSSUM. The feedback resistor between CSCOMP and CSSUM sets the gain of the amplifier and a filter capacitor is placed in parallel with this resistor. The gain of the amplifier is programmable by adjusting the feedback resistor to set the load line required by the microprocessor. The current information is then given as the difference of CSREF − CSCOMP. This difference signal is used internally to offset the VID DAC for voltage positioning and as a differential input for the current-limit comparator. To provide the best accuracy for sensing current, the CSA is designed to have a low offset input voltage. Also, the sensing gain is determined by external resistors, so it can be made extremely accurate. External resistors can be placed in series with individual phases to create, if desired, an intentional current imbalance such as when one phase may have better cooling and can support higher currents. Resistor RSW1 through Resistor RSW4 (see the typical application circuit in Figure 19 and Figure 20) can be used for adjusting thermal balance. It is best to have the ability to add these resistors during the initial design, so make sure that placeholders are provided in the layout. To increase the current in any given phase, make RSW for this phase larger (make RSW = 0 for the hottest phase, and do not change during balancing). Increasing RSW to only 500 Ω makes a substantial increase in phase current. Increase each RSW value by small amounts to achieve balance, starting with the coolest phase first. VOLTAGE CONTROL MODE A high gain bandwidth voltage mode error amplifier is used for the voltage-mode control loop. The control input voltage to the positive input is set via the VID logic according to the voltages listed in Table 4. This voltage is also offset by the droop voltage for active positioning of the output voltage as a function of the current, commonly known as active voltage positioning. The output of the amplifier is the COMP pin, which sets the termination voltage for the internal PWM ramps. The negative input (FB) is tied to the output sense location with a resistor (RB) and is used for sensing and controlling the output voltage at this point. A current source from the FB pin flowing through RB is used for setting the no-load offset voltage from the VID voltage. The no-load voltage is negative with respect to the VID DAC. The main loop compensation is incorporated into the feedback network between FB and COMP. ACTIVE IMPEDANCE CONTROL MODE For controlling the dynamic output voltage droop as a function of output current, a signal proportional to the total output current at the CSCOMP pin can be scaled to equal the droop impedance of the regulator multiplied by the output current. This droop voltage is then used to set the input control voltage to the system. The droop voltage is subtracted from the DAC reference input voltage directly to tell the error amplifier where the output voltage should be. This differs from previous implementations and allows an enhanced feed-forward response. CURRENT-CONTROL MODE AND THERMAL BALANCE The ADP3194 has individual inputs for each phase, which are used for monitoring the current in each phase. This information is combined with an internal ramp to create a current balancing feedback system, which has been optimized for initial current balance accuracy and dynamic thermal balancing during operation. This current-balance information is independent of the average output current information used for positioning described previously. The magnitude of the internal ramp can be set to optimize the transient response of the system. It also monitors the supply voltage for feed-forward control for changes in the supply. A resistor connected from the power input voltage to the RAMPADJ pin determines the slope of the internal PWM ramp. Detailed information about programming the ramp is given in the Application Information section. SOFT START The power-on ramp-up time of the output voltage is set with a capacitor and resistor in parallel from the DELAY pin to ground. The RC time constant also determines the current-limit latch-off time. In UVLO, or when EN is logic low, the DELAY pin is held at ground. After the UVLO threshold is reached and EN is logic high, the DELAY capacitor is charged with an internal 20 μA current source. The output voltage follows the ramping voltage on the DELAY pin, limiting the inrush current. The soft start time depends on the value of the VID DAC and CDLY, with a secondary effect from RDLY. See the Application Information section for detailed information on setting CDLY. If EN is taken low or if VCC drops below UVLO, the DELAY capacitor is reset to ground to be ready for another soft start cycle. Figure 7 shows a typical soft start sequence for the ADP3194. Rev. 0 | Page 9 of 32 www.DataSheet4U.com ADP3194 This prevents the DELAY capacitor from discharging, so the 1.8 V threshold is never reached. The resistor has an impact on the soft start time because the current through it adds to the internal 20 μA current source. During startup, when the output voltage is below 200 mV, a secondary current limit is active. This is necessary because the voltage swing of CSCOMP cannot go below ground. This secondary current limit controls the internal COMP voltage to the PWM comparators to 2 V. This limits the voltage drop across the low-side MOSFETs through the current balance circuitry. An inherent per phase current limit protects individual phases, if one or more phases stops functioning because of a faulty component. This limit is based on the maximum normal mode COMP voltage. Figure 7. Typical Start-Up Waveforms Channel 1: PWRGD, Channel 2: CSREF, Channel 3: DELAY, Channel 4: COMP CURRENT-LIMIT, SHORT-CIRCUIT, AND LATCH-OFF PROTECTION The ADP3194 compares a programmable current-limit setpoint to the voltage from the output of the current sense amplifier. The level of current limit is set with the resistor from the ILIMIT pin to ground. During normal operation, the voltage on ILIMIT is 3 V. The current through the external resistor is internally scaled to give a current-limit threshold of 10.4 mV/μA. If the difference in voltage between CSREF and CSCOMP rises above the currentlimit threshold, the internal current-limit amplifier controls the internal COMP voltage to maintain the average output current at the limit. After the limit is reached, the 3 V pull-up on the DELAY pin is disconnected, and the external delay capacitor is discharged through the external resistor. A comparator monitors the DELAY voltage and shuts off the controller when the voltage drops below 1.8 V. The current-limit latch-off delay time is, therefore, set by the RC time constant discharging from 3 V to 1.8 V. The Application Information section discusses the selection of CDLY and RDLY. Because the controller continues to cycle the phases during the latch-off delay time, the controller returns to normal operation if the short is removed before the 1.8 V threshold is reached. The recovery characteristic depends on the state of PWRGD. If the output voltage is within the PWRGD window, the controller resumes normal operation. However, if a short circuit has caused the output voltage to drop below the PWRGD threshold, a soft start cycle is initiated. The latch-off function can be reset by either removing and reapplying VCC to the ADP3194 or by pulling the EN pin low for a short time. To disable the short-circuit latch-off function, the external resistor to ground should be left open, and a high value (>1 MΩ) resistor should be connected from DELAY to VCC. Figure 8. Overcurrent Latch-Off Waveforms Channel 1: CSREF, Channel 2: DELAY, Channel 3: COMP, Channel 4: Phase 1 Switch Node 06022-007 DYNAMIC VID The ADP3194 has the ability to dynamically change the VID input while the controller is running. This allows the output voltage to change while the supply is running and supplying current to the load. This is commonly referred to as VID OTF. A VID OTF can occur under either light or heavy load conditions. The processor signals the controller by changing the VID inputs in multiple steps from the start code to the finish code. This change can be positive or negative. When a VID input changes state, the ADP3194 detects the change and ignores the DAC inputs for a minimum of 400 ns. This time prevents a false code due to logic skew while the six VID inputs are changing. Additionally, the first VID change initiates the PWRGD and crowbar blanking functions for a minimum of 100 μs to prevent a false PWRGD or crowbar event. Each VID change resets the internal timer. Rev. 0 | Page 10 of 32 06022-008 www.DataSheet4U.com ADP3194 Table 4. VID Codes for the ADP3194 VID4 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 VID3 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 1 1 VID2 1 1 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 0 0 0 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 0 0 0 0 1 1 1 VID0 1 1 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 0 VID5 1 0 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 Output No CPU No CPU 0.8375 V 0.8500 V 0.8625 V 0.8750 V 0.8875 V 0.9000 V 0.9125 V 0.9250 V 0.9375 V 0.9500 V 0.9625 V 0.9750 V 0.9875 V 1.0000 V 1.0125 V 1.0250 V 1.0375 V 1.0500 V 1.0625 V 1.0750 V 1.0875 V 1.1000 V 1.1125 V 1.1250 V 1.1375 V 1.1500 V 1.1625 V 1.1750 V 1.1875 V 1.2000 V VID4 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 0 0 0 0 VID3 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 1 1 1 1 VID2 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 1 0 0 0 VID1 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 VID0 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 VID5 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 Output 1.2125 V 1.2250 V 1.2375 V 1.2500 V 1.2625 V 1.2750 V 1.2875 V 1.3000 V 1.3125 V 1.3250 V 1.3375 V 1.3500 V 1.3625 V 1.3750 V 1.3875 V 1.4000 V 1.4125 V 1.4250 V 1.4375 V 1.4500 V 1.4625 V 1.4750 V 1.4875 V 1.5000 V 1.5125 V 1.5250 V 1.5375 V 1.5500 V 1.5625 V 1.5750 V 1.5875 V 1.6000 V Rev. 0 | Page 11 of 32 www.DataSheet4U.com ADP3194 POWER GOOD MONITORING The power good comparator monitors the output voltage via the CSREF pin. The PWRGD pin is an open-drain output whose high level (when connected to a pull-up resistor) indicates that the output voltage is within the nominal limits specified in Table 4. These limits are based on the VID voltage setting. PWRGD goes low if the output voltage is outside of this specified range, if all of the VID DAC inputs are high, or whenever the EN pin is pulled low. PWRGD is blanked during a VID OTF event for a period of 250 μs to prevent false signals during the time the output is changing. The PWRGD circuitry also incorporates an initial turn-on delay time based on the DELAY ramp. The PWRGD pin is held low until the DELAY pin reaches 2.6 V. The time between when the PWRGD undervoltage threshold is reached and when the DELAY pin reaches 2.6 V provides the turn-on delay time. This time is incorporated into the soft start ramp. To ensure a 1 ms delay time on PWRGD, the soft start ramp must also be >1 ms. See the Application Information section for detailed information on setting CDLY. Turning on the low-side MOSFETs pulls down the output as the reverse current builds up in the inductors. If the output overvoltage is due to a short in the high-side MOSFET, this action current-limits the input supply or blows its fuse, protecting the microprocessor from being destroyed. OUTPUT ENABLE AND UVLO For the ADP3194 to begin switching, the input supply (VCC) to the controller must be higher than the UVLO threshold, and the EN pin must be higher than its logic threshold. If UVLO is less than the threshold or the EN pin is logic low, the ADP3194 is disabled. This holds the PWM outputs at ground, shorts the DELAY capacitor to ground, and holds the ILIMIT pin at ground. In the application circuit, the ILIMIT pin should be connected to the OD pins of the ADP3120A drivers. Grounding ILIMIT disables the drivers so that both the DRVH and DRVL are also grounded. This feature is important in preventing the discharge of the output capacitors when the controller is shut off. If the driver outputs were not disabled, a negative voltage could be generated during output due to the high current discharge of the output capacitors through the inductors. OUTPUT CROWBAR As part of the protection for the load and output components of the supply, the PWM outputs are driven low (turning on the low-side MOSFETs) when the output voltage exceeds the upper crowbar threshold. This crowbar action stops once the output voltage falls below the release threshold of approximately 550 mV. Rev. 0 | Page 12 of 32 www.DataSheet4U.com ADP3194 APPLICATION INFORMATION The design parameters for a typical Intel VRD 10.1-compliant CPU application are as follows: • • • • • • Input voltage (VIN) = 12 V VID setting voltage (VVID) = 1.300 V Duty cycle (D) = 0.108 Nominal output voltage at no load (VONL) = 1.281 V Nominal output voltage at 101 A load (VOFL) = 1.159 V Static output voltage drop based on a 1.2 mΩ load line (RO) from no load to full load (VD) = VONL − VOFL = 1.281 V − 1.159 V = 121.2 mV Maximum output current (IO) = 120 A Maximum output current step (ΔIO) = 85 A Number of phases (n) = 4 Switching frequency per phase (fSW) = 1.125 MHz However, as long as RDLY is kept greater than 200 kΩ, this effect is minor. The value for CDLY can be approximated by ⎛ VVID C DLY = ⎜ 20 μA − ⎜ 2 × RDLY ⎝ ⎞ t SS ⎟× ⎟V VID ⎠ (2) where tSS is the desired soft start time. Assuming an RDLY of 390 kΩ and a desired soft start time of 3 ms, CDLY is 36 nF. The closest standard value for CDLY is 39 nF. Once CDLY is chosen, RDLY can be calculated for the current-limit latchoff time by RDLY = 1.96 × t DELAY C DLY (3) • • • • If the result for RDLY is less than 200 kΩ, a smaller soft start time should be considered by recalculating Equation 2, or a longer latchoff time should be used. RDLY should never be less than 200 kΩ. In this example, a delay time of 9 ms results in RDLY = 452 kΩ. The closest standard 5% value is 470 kΩ. SETTING THE CLOCK FREQUENCY The ADP3194 uses a fixed-frequency control architecture. The frequency is set by an external timing resistor (RT). The clock frequency and the number of phases determine the switching frequency per phase, which relates directly to switching losses and the sizes of the inductors and/or the input and output capacitors. With n = 4 for four phases, a clock frequency of 4 MHz sets the switching frequency (fSW) of each phase to 1 MHz, which represents a practical trade-off between the switching losses and the sizes of the output filter components. Figure 3 shows that to achieve 4 MHz oscillator frequency, the correct value for RT is 84 kΩ. 3 MHz oscillator frequency, the correct value for RT is 138 kΩ. 2 MHz oscillator frequency, the correct value for RT is 247 kΩ. Alternatively, the value for RT can be calculated using INDUCTOR SELECTION The choice of inductance for the inductor determines the ripple current in the inductor. Less inductance leads to more ripple current, which increases the output ripple voltage and conduction losses in the MOSFETs; but it allows using smaller inductors and, for a specified peak-to-peak transient deviation, less total output capacitance. Conversely, a higher inductance means lower ripple current and reduced conduction losses but requires larger inductors and more output capacitance for the same peak-to-peak transient deviation. In any multiphase converter, a practical value for the peak-to-peak inductor ripple current is less than 50% of the maximum dc current in the same inductor. Equation 4 shows the relationship between the inductance, oscillator frequency, and peak-to-peak ripple current in the inductor. IR = VVID × (1 − D ) f SW × L RT = 3 − 79 kΩ n × f SW × 4.6 pF (1) (4) where 4.6 pF and 79 kΩ are internal IC component values. For good initial accuracy and frequency stability, a 1% resistor is recommended. Equation 5 can be used to determine the minimum inductance based on a given output ripple voltage. L≥ VVID × RO × (1 − (n × D )) f SW × VRIPPLE SOFT START AND CURRENT-LIMIT LATCH-OFF DELAY TIMES Because the soft start and current-limit latch-off delay functions share the DELAY pin, these two parameters must be considered together. The first step is to set CDLY for the soft start ramp. This ramp is generated with a 20 μA internal current source. The value of RDLY has a second-order impact on the soft start time because it sinks part of the current source to ground. (5) Solving Equation 5 for a 10 mV p-p output ripple voltage yields L≥ 1.3 V × 1.2 mΩ × (1 − 0.108) 1.125 M Hz × 4.4 mV = 280 nH If the resulting ripple voltage is less than it was designed for, make the inductor smaller until the ripple value is met. This allows optimal transient response and minimum output decoupling. Rev. 0 | Page 13 of 32 www.DataSheet4U.com ADP3194 The smallest possible inductor should be used to minimize the number of output capacitors. For this example, choosing a 280 nH inductor is a good starting point and gives a calculated ripple current of 3.68 A. The inductor should not saturate at the peak current of 31.84 A and should be able to handle the sum of the power dissipation caused by the average current of 30 A in the winding and core loss. SENSE RESISTOR SELECTION The resistance value of the sense resistor must be chosen to minimize the conduction loss, but be large enough for accurate current measurement. The lower the resistance, the lower the signal to noise ratio that appears at the ADP3194 input. This directly affects the current sense accuracy. A sense resistor of 1 mΩ is chosen. The power loss in the resistor is calculated as: PRS = I 2 × R SENSE DESIGNING AN INDUCTOR Once the inductance is known, the next step is either to design an inductor or to find a standard inductor that comes as close as possible to meeting the overall design goals. The first decision in designing the inductor is to choose the core material. Several possibilities for providing low core loss at high frequencies include the powder cores (for example, Kool-Mμ® from Magnetics, Inc. or from Micrometals) and the gapped soft ferrite cores (for example, 3F3 or 3F4 from Philips). Avoid low frequency powdered iron cores due to their high core loss, especially when the inductor value is relatively low and the ripple current is high. The best choice for a core geometry is a closed-loop type such as a potentiometer core, PQ, U, or E core or toroid. A good compromise between price and performance is a core with a toroidal shape. Many useful magnetics design references are available for quickly designing a power inductor, such as Magnetic Designer Software™ by Intusoft and Designing Magnetic Components for High-Frequency DC-DC Converters, by William T. McLyman, KG Magnetics, Inc., ISBN 1883107008. (6) If the design has 30 A per phase, then: PRS = 30 A × 30 A × 1 mΩ = 900 mW This results in a 900mW conduction loss through the sense resistor in a 30 A per phase design. Therefore, a 1 mΩ, 1 W sense resistor is chosen. There is a parasitic inductance (LP) associated with the sense resistor. This value can be found on the data sheet of the sense resistor. A typical value is of the order of 2.2 nH. OUTPUT DROOP RESISTANCE–SENSE RESISTOR The design requires the regulator output voltage measured at the CPU pins to drop when the output current increases. The specified voltage drop corresponds to a dc output resistance (RO). The output current is measured by summing the voltage across each inductor and passing the signal through a low-pass filter. This summer filter is the CS amplifier configured with resistors RPH(X) (summers), and RCS and CCS (filter). The output resistance of the regulator is set by the following equations: RO = RCS × RSENSE RPH ( X ) (7) (8) Selecting a Standard Inductor Power inductor manufacturers can provide design consultation and deliver power inductors optimized for high power applications upon request. Such manufacturers include Coilcraft, Coiltronics, Sumida Electric Company, and Vishay Intertechnology. CCS = LP RSENSE × RCS where RSENSE is the resistance of the sense resistor. The user has the flexibility of choosing either RCS or RPH(X). It is best to select RCS equal to 100 kΩ, and then solve for RPH(X) by rearranging Equation 6. RPH ( X ) = RSENSE × RCS RO SENSE RESISTOR A dedicated sense resistor can be used for current sensing. An advantage to this is the fact that there is much less temperature variation than using the DCR method. Therefore, a thermistor is not required. The trade-off is that a sense resistor is required for each phase. So, one thermistor is saved, but four sense resistors are needed in a four phase design. Also, there is extra power dissipation due to the sense resistor in series with the power delivery. (9) RPH ( X ) = 1.0 mΩ 1.2 mΩ × 100 kΩ = 82.5 kΩ Next, use Equation 8 to solve for CCS. CCS = 2.2 nH 1.0 mΩ × 100 kΩ = 220 pF Therefore, set RCS equal to 100 kΩ, CCS equal to 220 pF, and RPH equal to 82.5 kΩ. Rev. 0 | Page 14 of 32 www.DataSheet4U.com ADP3194 L2 280nH SENSE 1mΩ 1W 560µF/4V × n SANYO SEPC SERIES + + VCC (CORE) VCC (CORE) RTN VCC 28 ADP3194 CSCOMP 18 RPH1 RCB1 CCB1 CCB2 KEEP THIS PATH AS SHORT AS POSSIBLE AND WELL AWAY FROM SWITCH NODE LINES. 06022-009 CSSUM 17 CSREF 16 Figure 9. Using a Sense Resistor OUTPUT OFFSET The Intel specification requires that at no load should 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 set by a constant current source flowing out of the FB pin (IFB) and flowing through RB. The value of RB can be found using Equation 10: RB = VVID − VONL I FB Table 5. Input Parameters Design Inputs Sense Resistor Method Value 4 1.00 mΩ 1.00 mΩ 120.0 A 90.0 A 0% 5% 1% 70°C 0.0 % 19.0 mV 8.0 mV 6.0 A 12 DCR Method Value 4 1.00 mΩ 1.00 mΩ 120.0 A 90.0 A 20% 5% 5% 70°C 26.6% 19.0 mV 8.0 mV 6.0 A 12 (10) RB = 1.3 V − 1.281 V 15.5 μA = 1.22 kΩ The closest standard 1% resistor value is 1.21 kΩ. DESIGN COMPARISON TRADE-OFF BETWEEN DCR AND SENSE RESISTOR Cost The inductor DCR method requires a thermistor, which costs about $0.03. The RSENSE method requires an extra sense resistors for each phase. This costs about 4 × $0.07 = $0.28. If it can also meet the Intel accuracy specification of 25mV across the full load range, then it is the preferred method in VR applications. Parameter N DCR Loadline Imax Istep L error C error RSENSE error Temp Rise RSENSE vs. Temp No-load Offset Total Output Vripple Inductor Iripple Gain Factor for TC 30 28 26 ERROR FROM LOADLINE (± AMOUNT SHOWN) THIS CHART IS ACTIVE. Accuracy Table 5 shows the accuracy results for a 4-phase VR10.1 application, using DCR method and sense resistor method. As can be seen, the sense resistor method improves the accuracy slightly. However, since the DCR method meets the Intel specification, it is the preferred solution, for cost reasons. ERROR (mV) VRD10.1 SPEC 24 22 20 18 16 14 SENSE RESISTOR METHOD 0 20 40 60 80 100 120 06022-010 DCR METHOD OUTPUT CURRENT (A) Figure 10. Accuracy Comparison of DCR and Sense Resistor Methods Rev. 0 | Page 15 of 32 www.DataSheet4U.com ADP3194 COUT SELECTION The required output decoupling for the regulator is typically recommended by Intel for various processors and platforms. Also, to determine what is required, use some simple design guidelines that are based on having both bulk and ceramic capacitors in the system. The first thing is to select the total amount of ceramic capacitance. This is based on the number and type of capacitor to be used. The best location for ceramic capacitors is inside the socket, with 12 to 18 of Size 1206 being the physical limit. Additional ceramic capacitors can be placed along the outer edge of the socket as well. Combined ceramic values of 200 μF to 400 μF are recommended, usually made up of multiple 10 μF or 22 μF capacitors. Select the number of ceramic capacitors, and find the total ceramic capacitance (CZ). Next, there is an upper limit imposed on the total amount of bulk capacitance (CX) when considering the VID OTF voltage stepping of the output (Voltage Step VV in Time tV with error of VERR). A lower limit is based on meeting the capacitance for load release for a given maximum load step, ∆IO, and a maximum allowable overshoot. The total amount of load release voltage is given as ΔVO = ΔIO × RO + ΔVrl where ΔVrl is the maximum allowable overshoot voltage. ⎛ ⎞ ⎜ ⎟ ⎜ ⎟ L × Δ IO C X ( MIN ) ≥ ⎜ − CZ ⎟ ⎛ ⎞ ΔVrl ⎜ ⎟ ⎜ ⎟ ⎜ n × ⎜ RO + ΔI ⎟ × VVID ⎟ O⎠ ⎝ ⎝ ⎠ larger than CX(MAX), the system cannot meet the VID OTF specification and may require the use of a smaller inductor or more phases (and may need the switching frequency to increase to keep the out-put ripple the same). This example uses 18, 22 μF 1206 MLC capacitors (CZ = 396 μF). The VID on-the-fly step change is 450 mV in 230 μs with a settling error of 2.5 mV. The maximum allowable load release overshoot for this example is 50 mV, so solving for the bulk capacitance yields ⎞ ⎛ ⎟ ⎜ ⎟ ⎜ 280 nH × 85 A C X ( MIN ) ≤ ⎜ − 396 μF ⎟ = 2.16 mF ⎛ ⎟ ⎜ 50 mV ⎞ ⎟ × 1. 3 V ⎟ ⎜ 4 × ⎜ 1.2 mΩ + ⎜ ⎟ ⎜ 85 A ⎟ ⎝ ⎠ ⎠ ⎝ C X ( MAX ) ≤ 4 × 4.62 × (1.2 mΩ ) 2 × 1.3 V 280 nH × 450 mV × 2 ⎛ ⎞ ⎛ 250 μs × 1.3 V × 4 × 4.6 × 1.2 mΩ ⎞ ⎜ ⎟ ⎜ ⎟ − 1⎟ − 396 μF = 40.5 mF ⎜ 1+ ⎜ ⎟ 450 mV × 280 nH ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ where K = 4.6. Using four 560 μF Al-Poly capacitors with a typical ESR of 5 mΩ each yields CX = 2.24 mF with an RX = 1.25 mΩ. One last check should be made to ensure that the ESL of the bulk capacitors (LX) is low enough to limit the high frequency ringing during a load change. This is tested using L X ≤ C Z × RO 2 × Q 2 L X ≤ 396 μF × (1.2 mΩ )2 × 2 = 1.14 nH (13) (11) where Q is limited to the square root of 2 to ensure a critically damped system. In this example, LX is approximately 175 pH for the four A1-Polys capacitors, which satisfies this limitation. If the LX of the chosen bulk capacitor bank is too large, the number of ceramic capacitors may need to be increased if there is excessive ringing. For this multimode control technique, all ceramic designs can be used as long as the conditions of Equation 11, Equation 12, and Equation 13 are satisfied. ⎛ ⎛V ⎜ nKRO V L × V × ⎜ 1 + ⎜ tV VID × C X ( MAX ) = 2 ⎜V nK 2 RO VVID ⎜ L V ⎝ ⎝ 2 ⎞ ⎞ ⎟ ⎟ − 1⎟ − C Z ⎟ ⎟ ⎠ ⎠ (12) ⎛V ⎞ where K = 1n ⎜ ERR ⎟ ⎜V ⎟ ⎝ V⎠ To meet the conditions of these equations and transient response, the ESR of the bulk capacitor bank (RX) should be less than two times the droop resistance (RO). If the CX(MIN) is Rev. 0 | Page 16 of 32 www.DataSheet4U.com ADP3194 RAMP RESISTOR SELECTION The ramp resistor (RR) is used for setting the size of the internal PWM ramp. The value of this resistor is chosen to provide the best combination of thermal balance, stability, and transient response. The following equation is used for determining the optimum value: CURRENT-LIMIT SETPOINT To select the current-limit setpoint, first find the resistor value for RLIM. The current-limit threshold for the ADP3194 is set with a 3 V source (VLIM) across RLIM with a gain of 10.4 mV/μA (ALIM). RLIM can be found using RLIM = ALIM × VLIM I LIM × RO RR = AR × L 3 × AD × RDS × CR (14) 0.2 × 280 nH 3 × 5 × 6.33 mΩ × 5 pF = 118 kΩ (17) RR = where: For values of RLIM greater than 500 kΩ, the current limit can be lower than expected, so some adjustment of RLIM may be needed. Here, ILIM is the average current limit for the output of the supply. In this example, choosing a peak current limit of 185 A for ILIM results in RLIM = 140 kΩ. The limit of the per-phase current-limit described earlier is determined by I PHLIM ≅ VCOMP ( MAX ) − VR − V BIAS A D × R DS ( MAX ) + IR 2 AR is the internal ramp amplifier gain AD is the current balancing amplifier gain RDS is the total low-side MOSFET on resistance CR is the internal ramp capacitor value. (18) The internal ramp voltage magnitude can be calculated by using VR = AR × (1 − D ) × VVID RR × CR × f SW (15) VR = 0.2 × (1 − 0.108 ) × 1.3 V 118 kΩ × 5 pF × 1.125 MHz = 35 0 m V For the ADP3194, the maximum COMP voltage (VCOMP(MAX)) is 3.3 V, the COMP pin bias voltage (VBIAS) is 1.2 V, and the currentbalancing amplifier gain (AD) is 5. Using VR of 0.35 V and RDS(MAX) of 7 mΩ, the per-phase peak current limit is calculated to be 51.8 A. Although this number may seem high, this current level can be reached only with an absolute short at the output, and the current-limit latch-off function shuts down the regulator before overheating can occur. This limit can be adjusted by changing the ramp voltage (VR), but make sure not to set the per-phase limit lower than the average per-phase current (ILIM/n). The per-phase initial duty cycle limit is determined by D MAX = D × VCOMP ( MAX ) − VBIAS VRT The size of the internal ramp can be made larger or smaller. If it is made larger, stability and transient response improve, but thermal balance degrades. Likewise, if the ramp is made smaller, thermal balance improves at the sacrifice of transient response and stability. The factor of 3 in the denominator of Equation 14 sets a ramp size that gives an optimal balance for good stability, transient response, and thermal balance. (19) COMP PIN RAMP A ramp signal on the COMP pin is due to the droop voltage and output voltage ramps. This ramp amplitude adds to the internal ramp to produce the following overall ramp signal at the PWM input: VRT = VR ⎛ 2 × (1 − n × D ) ⎜1 − ⎜ n× f ×C × R X SW O ⎝ ⎞ ⎟ ⎟ ⎠ In this example, the maximum duty cycle is 0.46. FEEDBACK LOOP COMPENSATION DESIGN Optimized compensation of the ADP3194 allows the best possible response of the regulator’s output to a load change. The basis for determining the optimum compensation is to make the regulator and output decoupling appear as an output impedance that is entirely resistive over the widest possible frequency range, including dc, and equal to the droop resistance (RO). With the resistive output impedance, the output voltage droops in proportion to the load current at any load current slew rate. This ensures optimal positioning and allows minimization of the output decoupling. (16) In this example, the overall ramp signal is 390 mV. Rev. 0 | Page 17 of 32 www.DataSheet4U.com ADP3194 With the multimode feedback structure of the ADP3194, the feedback compensation must be set to make the converter’s output impedance, working in parallel with the output decoupling, to meet this goal. Several poles and zeros created by the output inductor and decoupling capacitors (output filter) need to be compensated for. A type-three compensator on the voltage feedback is adequate for proper compensation of the output filter. Equation 20 to Equation 28 yield an optimal starting point for the design; some adjustments may be necessary to account for PCB and component parasitic effects (see the Layout and Component Placement section). The first step is to compute the time constants for all of the poles and zeros in the system: RSENSE × VRT VVID TD = where: C X × (RO − R' ) + C Z × RO 2 C X × C Z × RO (24) R' is the PCB resistance from the bulk capacitors to the ceramics RDS is the total low-side MOSFET on resistance per phase. In this example, AD is 5, VRT equals 0.39 V, R' is approximately 0.5 mΩ (assuming a 4-layer, 1 ounce motherboard), and LX is 175 pH for the four Al-Poly capacitors. The compensation values can then be solved using the following equations: CA = n × R O × TA RE × RB (25) (26) (27) (28) RA = + RE = n × RO + AD × RDS + 2 × L × (1 − n × D ) × VRT n × C X × RO × VVID TC CA TB RB TD RA (20) CB = C FB = R − R′ L TA = C X × (RO − R′) + X × O RO RX (21) (22) TB = (RX + R′ − RO ) × C X ⎛ A × R DS VRT × ⎜ L − D ⎜ 2 × f SW ⎝ TC = VVID × R E ⎞ ⎟ ⎟ ⎠ These are the starting values, prior to tuning the design, to account for layout and other parasitic effects (see the Layout and Component Placement section). The final values selected after tuning are CA = 3.3 nF, RA = 7.32 kΩ, CB = 1 nF, CFB = 33 pF. (23) Rev. 0 | Page 18 of 32 www.DataSheet4U.com ADP3194 Figure 11 and Figure 12 show the typical transient response using these compensation values. CIN SELECTION AND INPUT CURRENT di/dt REDUCTION In continuous inductor current mode, the source current of the high-side MOSFET is approximately a square wave with a duty ratio equal to n × VOUT/VIN and an amplitude of one-nth the maximum output current. To prevent large voltage transients, a low ESR input capacitor, sized for the maximum rms current, must be used. The maximum rms capacitor current is given by I CRMS = D × I O × 1 −1 N×D (29) 06022-011 I CRMS = 0.108 × 119 A × 1 − 1 = 14.7 A 4 × 0.108 Figure 11. Typical Transient Response for Design Example Load Step The capacitor manufacturer’s ripple current ratings are often based on only 2000 hours of life. This makes it advisable to further derate the capacitor or to choose a capacitor rated at a higher temperature than required. Several capacitors can be placed in parallel to meet size or height requirements in the design. In this example, the input capacitor bank is formed by two 2700 μF, 16 V aluminum electrolytic capacitors and eight 4.7 μF ceramic capacitors. To reduce the input current di/dt to a level below the recommended maximum of 0.1 A/μs, an additional small inductor (L > 370 nH at 18 A) should be inserted between the converter and the supply bus. This inductor also acts as a filter between the converter and the primary power source. 06022-012 Figure 12. Typical Transient Response for Design Example Load Release Figure 13. Efficiency of the Circuit of Figure 10 vs. Output Current Rev. 0 | Page 19 of 32 06022-012 www.DataSheet4U.com ADP3194 TUNING THE ADP3194 1. 2. Build a circuit based on the compensation values computed from the equations used in the example. Hook up the dc load to circuit, turn it on, and verify its operation. Also, check for jitter at no load and full load. Measure the output voltage at no load (VNL). Verify it is within tolerance. Measure the output voltage at full load cold (VFLCOLD). Let the board sit for ~10 minutes at full load, and then measure the output (VFLHOT). If there is a change of more than a few millivolts, adjust RCS1 and RCS2, using Equation 30 and Equation 31. RCS2 ( NEW ) = RCS2 (OLD ) × VNL − VFLCOLD VNL − VFLHOT 5. 6. Repeat Step 4 until the cold and hot voltage measurements remain the same. Measure the output voltage from no load to full load, using 5 Amps steps. Compute the load line slope for each change, and then average to get the overall load line slope (ROMEAS). If ROMEAS is off from RO by more than 0.05 mΩ, use the following to adjust the RPH values: RPH ( NEW ) = RPH (OLD ) × ROMEAS RO DC Load Line Setting 3. 4. 7. (31) 8. 9. Repeat Step 6 and Step 7 to check the load line, and repeat adjustments if necessary. Once the dc load line adjustment is complete, do not change RPH, RCS1, RCS2, or RTH for the remainder of the procedure. (30) 10. Measure the output ripple at no load and full load with a scope, and make sure it is within specifications. RCS1( NEW ) = ×R RCS1(OLD ) × RTH (25°C ) + R CS1 (OLD ) − RCS2 ( NEW ) CS1 (OLD ) − RTH (25° C ) ( 1 RCS1(OLD ) + RTH (25°C ) )( ) − 1 RTH (25° C ) (32) Rev. 0 | Page 20 of 32 www.DataSheet4U.com ADP3194 AC Load Line Setting 11. Remove the dc load from the circuit and hook up the dynamic load. 12. Hook up the scope to the output voltage and set it to dc coupling, with the time scale at 100 μs/div. 13. Set the dynamic load for a transient step of about 40 A at 1 kHz with a 50% duty cycle. 14. Measure the output waveform (if not visible, use dc offset on scope to view). Try to use a vertical scale of 100 mV/div or finer. This waveform should look similar to Figure 14. VDROOP Initial Transient Setting 18. With the dynamic load still set at the maximum step size, expand the scope time scale to see 2 μs/div to 5 μs/div. The waveform may have two overshoots and one minor undershoot (see Figure 15). Here, VDROOP is the final desired value. VTRAN1 VACDRP VDCDRP VTRAN2 06022-015 Figure 15. Transient Setting Waveform 19. If both overshoots are larger than desired, try making the following adjustments: 06022-014 Make the ramp resistor larger by 25% (RRAMP). For VTRAN1, increase CB, or increase the switching frequency. For VTRAN2, increase RA, and decrease CA by 25%. If these adjustments do not change the response, the output decoupling is the limiting factor. Check the output response every time a change is made, or nodes are switched, to make sure the response remains stable. 20. For load release (see Figure 16), if VTRANREL is larger than VTRAN1 (see Figure 15), there is not enough output capacitance. Either more capacitance is needed or the inductor values need to be smaller. If inductors are changed, start the design again using the spreadsheet and this tuning procedure. Figure 14. AC Load Line Waveform 15. Use the horizontal cursors to measure VACDRP and VDCDRP, as shown in Figure 14. Do not measure the undershoot or overshoot that happens immediately after this step. If VACDRP and VDCDRP are different by more than a few millivolts, use Equation 38 to adjust CCS. It may be necessary to parallel different values to get the correct one, because there are limited standard capacitor values available. It is a good idea to have locations for two capacitors in the layout for this. C CS ( NEW ) = C CS(OLD ) × V ACDRP V DCDRP (38) 16. Repeat Step 11 to Step 13, and repeat the adjustments, if necessary. Once complete, do not change CCS for the remainder of the procedure. 17. Set the dynamic load step to maximum step size. Do not use a step size larger than needed, and verify that the output waveform is square, which means that VACDRP and VDCDRP are equal. VTRANREL VDROOP Figure 16. Transient Setting Waveform Rev. 0 | Page 21 of 32 06022-016 www.DataSheet4U.com ADP3194 Because the ADP3194 turns off all of the phases (switches inductors to ground), there is no ripple voltage present during load release. Thus, headroom does not need to be added for ripple, allowing load release (VTRANREL) to be larger than VTRAN1 by the amount of ripple and still meet specifications. If VTRAN1 and VTRANREL are less than the desired final droop, this implies that capacitors can be removed. When removing capacitors, also check the output ripple voltage to make sure it is still within specifications. The CECC standard specification for power rating in surface mount resistors is 0603 = 0.1 W, 0805 = 0.125 W, 1206 = 0.25 W. For example, UVLO voltage specification = 8 V. From Figure 17, a shunt resistor value of 420 Ω is recommended. From Figure 17, the power dissipation is 140 mW. The user can choose any of the following: Two 840 Ω, 0603 resistors in parallel Two 840 Ω, 0805 resistors in parallel One 420 Ω, 1206 resistor. 9.5 RSHUNT 9.0 0.35 0.40 RAMPADJ FILTER It is recommended that a filter be placed on the RAMPADJ line. On the ADP3194, the VCC is 5 V, but the RAMPADJ still needs to be connected to the 12 V input supply. Therefore, the filter is needed to remove noise from the 12 V input supply. A 1 kΩ resistor and 1 μF cap are recommended for this filter. 8.5 0.30 SHUNT RESISTOR DESIGN When replacing an existing ADP3181 design with the ADP3194, the shunt resistor value needs to be determined. A trade-off can be made between the power dissipated in the shunt resistor and the UVLO threshold. Figure 17 shows the typical resistor value needed to realize certain UVLO voltages. It also gives the maximum power dissipated in the shunt resistor for these UVLO voltages. The maximum power dissipated is calculated using Equation 33. 8.0 0.25 7.5 0.20 7.0 PSHUNT 200 300 400 RSHUNT (Ω) 500 600 0.15 PMAX = where: (V IN ( MAX ) − VCC ( MIN ) ) 2 Figure 17. Typical Shunt Resistor Value and Power Dissipation for Different UVLO Voltages RSHUNT (33) VIN(MAX) is the maximum voltage from the 12 V input supply. (If the 12 V input supply is 12 V ±5%, then VIN(MAX) = 12.6 V. If the 12 V input supply is 12 V ±10%, then VIN(MAX) = 13.2 V.) Figure 17 shows the power when VIN(MAX) = 12.6 V. VCC(MIN) is the minimum VCC voltage of the ADP3194. It is specified as 4.75 V. RSHUNT is the shunt resistor value. Rev. 0 | Page 22 of 32 06022-017 6.5 100 0.10 700 POWER (mW) UVLO (V) www.DataSheet4U.com ADP3194 DESIGN EXAMPLE USING DCR METHOD The following are guidelines for designs that use an inductor DCR method instead of sense resistor method. The following procedure and equations yield values to use for RCS1, RCS2, and RTH (the thermistor value at 25°C) for a given RCS value. Select an NTC based on type and value. Because there is not a value yet, start with a thermistor with a value close to RCS. The NTC should also have an initial tolerance of better than 5%. Based on the type of NTC, find its relative resistance value at two temperatures. The temperatures that work well are 50°C and 90°C. These resistance values are called A (RTH(50°C)/RTH(25°C)) and B (RTH(90°C)/RTH(25°C)). The NTC’s relative value is always 1 at 25°C. Find the relative values of RCS required for each of these temperatures. This is based on the percentage change needed, which in this example is initially 0.39%/°C. These are called r1 (1/(1 + TC × (T1 − 25))) and r2 (1/(1 + TC × (T2 − 25))), where TC = 0.0039 for copper. T1 = 50°C and T2 = 90°C are chosen. From this, calculate that r1 = 0.9112 and r2 = 0.7978. Compute the relative values for RCS2, RCS1, and RTH using INDUCTOR SELECTION USING DCR Use the method and equations described in the Inductor Selection section to calculate the inductor. An important factor in the inductor design is the DCR, which is used for measuring the phase currents. A large DCR can cause excessive power losses, while too small a value can lead to increased measurement error. A good rule is to have the DCR be about 1 to 1½ times the droop resistance (RO). For this design, an inductor with a DCR of 1.4 mΩ is used. DESIGNING AN INDUCTOR USING DCR Once the inductance and DCR are known, the next step is either to design an inductor or to find a standard inductor that comes as close as possible to meeting the overall design goals. It is also important to have the inductance and DCR tolerance specified to control the accuracy of the system. 15% inductance and 8% DCR (at room temperature) are reasonable tolerances most manufacturers can meet. RCS2 = ( A − B ) × r1 × r2 − A × (1 − B ) × r2 + B × (1 − A ) × r1 A × (1 − B ) × r1 − B × (1 − A ) × r2 − ( A − B ) (1 − A ) 1 A − 1 − RCS2 r1 − RCS2 1 1 1 − 1 − RCS2 RCS1 (34) INDUCTOR DCR TEMPERATURE CORRECTION With the inductors DCR being used as the sense element and copper wire being the source of the DCR, compensation is needed for temperature changes of the inductor’s winding. Fortunately, copper has a well-known temperature coefficient (TC) of 0.39%/°C. If RCS is designed to have an opposite and equal percentage change in resistance to that of the wire, it cancels the temperature variation of the inductor’s DCR. Due to the nonlinear nature of NTC thermistors, Resistor RCS1 and Resistor RCS2 are needed. See Figure 18 to linearize the NTC and produce the desired temperature tracking. PLACE AS CLOSE AS POSSIBLE TO NEAREST INDUCTOR OR LOW-SIDE MOSFET RTH TO SWITCH NODES TO VOUT SENSE RCS1 = (35) RTH = (36) Calculate RTH = RTH × RCS, then select the closest value of thermistor available. Also, compute a scaling factor k based on the ratio of the actual thermistor value used relative to the computed one: k= RTH ( ACTUAL ) RTH (CALCULATED ) (37) ADP3194 RPH1 Calculate values for RCS1 and RCS2 using Equation 38 and Equation 39: RCS2 = RCS × ((1 − k ) + (k × RCS2 )) RCS1 = RCS × k × RCS1 (38) (39) RPH2 RPH3 CSCOMP 18 RCS1 CCS1 CCS2 RCS2 KEEP THIS PATH AS SHORT AS POSSIBLE AND WELL AWAY FROM SWITCH NODE LINES CSSUM 17 CSREF Figure 18. Temperature Compensation Circuit Values Rev. 0 | Page 23 of 32 06022-018 16 For this example, RCS has been calculated to be 110 kΩ. Start with a thermistor value of 100 kΩ. Next, look through the available 0603-size thermistors, and find a Vishay NTHS0603N01N1003JR NTC thermistor with A = 0.3602 and B = 0.09174. From these, compute RCS1 = 0.3795, RCS2 = 0.7195, and RTH = 1.075. Solve for RTH, which yields 118.28 kΩ. Then, choose 100 kΩ, which makes k = 0.8455. Finally, RCS1 and RCS2 are 35.3 kΩ and 83.9 kΩ. Choose the closest 1% resistor values, which yield a choice of 35.7 kΩ or 84.5 kΩ. www.DataSheet4U.com ADP3194 OUTPUT DROOP RESISTANCE–DCR METHOD The design requires the regulator output voltage measured at the CPU pins to drop when the output current increases. The specified voltage drop corresponds to a dc output resistance (RO). The output current is measured by summing the voltage across each inductor and passing the signal through a low-pass filter. This summer filter is the CS amplifier configured with RPH(X) (summers), RCS, and CCS (filter). The output resistance of the regulator is set by the following equations: RO = CCS = being dominant, the following equation shows the total power being dissipated in each synchronous MOSFET in terms of the ripple current per phase (IR) and average total output current (IO): ⎡⎛ I PSF = (1 − D ) × ⎢⎜ O ⎢⎜ nSF ⎣⎝ ⎞ 1 ⎛nI ⎟ + ×⎜ R ⎟ 12 ⎜ n ⎝ SF ⎠ 2 ⎞ ⎟ ⎟ ⎠ 2 ⎤ ⎥ × RDS (SF ) ⎥ ⎦ (43) RCS × RL RPH ( X ) L RL × RCS (40) (41) where RL is the DCR of the output inductors. The user has the flexibility of choosing either RCS or RPH(X). It is best to select RCS (equal to 100 kΩ) and then solve for RPH(X) by rearranging Equation 6. RPH ( X ) = RPH ( X ) = Knowing the maximum output current being designed for and the maximum allowed power dissipation, it is possible to find the required RDS(ON) for the MOSFET. For D-PAK MOSFETs up to an ambient temperature of 50°C, a safe limit for PSF is 1 W to 1.5 W at 120°C junction temperature. Thus, for this example (119 A maximum), RDS(SF) (per MOSFET) < 7.5 mΩ. This RDS(SF) is also at a junction temperature of about 120°C, so be certain to account for this temperature when making this selection. This example uses two lower-side MOSFETs at 4.8 mΩ each at 120°C. Another important factor for the synchronous MOSFET is the input capacitance and feedback capacitance. The ratio of the feedback to input needs to be small (less than 10% is recommended) to prevent accidental turn-on of the synchronous MOSFETs when the switch node goes high. Also, the time to switch the synchronous MOSFETs off should not exceed the nonoverlap dead time of the MOSFET driver (40 ns typical for the ADP3120A). The output impedance of the driver is approximately 2 Ω,and the typical MOSFET input gate resistances are about 1 Ωto 2 Ω, so a total gate capacitance of less than 6000 pF should be adhered to. Because there are two MOSFETs in parallel, the input capacitance for each synchronous MOSFET should be limited to 3000 pF. The high-side (main) MOSFET has to be able to handle two main power dissipation components: conduction and switching losses. The switching loss is related to the amount of time it takes for the main MOSFET to turn on and off and to the current and the voltage that are being switched. Basing the switching speed on the rise and fall time of the gate driver impedance and MOSFET input capacitance, the following equation provides an approximate value for the switching loss per main MOSFET: PS ( MF ) = 2 × f SW × VCC × I O n MF RL × RCS RO 1.0 mΩ 1.2 mΩ (42) × 100 kΩ = 82.5 kΩ Next, use Equation 41 to solve for CCS. CCS = 280 nH 1.0 mΩ × 100 kΩ = 2.8 nF It is best to have a dual location for CCS in the layout, so that standard values can be used in parallel to get as close as possible to the value desired. For accuracy, CCS should be a 5% or 10% NPO capacitor. This example uses a 5% combination for CCS of 2.2 nF and 560 pF in parallel. POWER MOSFETS This section is only applicable if power MOSFETs need to be selected. For this example, the N-channel power MOSFETs have been selected for one high-side switch and two low-side switches per phase. The main selection parameters for the power MOSFETs are VGS(TH), QG, CISS, CRSS, and RDS(ON). The minimum gate drive voltage (the supply voltage to the ADP3120A) dictates whether standard threshold or logic-level threshold MOSFETs must be used. With VGATE ~10 V, logic-level threshold MOSFETs (VGS(TH)°< 2.5 V) are recommended. The maximum output current (IO) determine1s the RDS(ON) requirement for the low-side (synchronous) MOSFETs. With the ADP3194, currents are balanced between phases, thus the current in each low-side MOSFET is the output current divided by the total number of MOSFETs (nSF). With conduction losses × RG × nMF × C ISS n (44) where: nMF is the total number of main MOSFETs, RG is the total gate resistance (2 Ω for the ADP3120A and about 1 Ω for typical high speed switching MOSFETs, making RG = 3 Ω), CISS is the input capacitance of the main MOSFET. Adding more main MOSFETs (nMF) does not really help the switching loss per MOSFET because the additional gate capacitance slows switching. The best way to reduce switching loss is to use lower gate capacitance devices. Rev. 0 | Page 24 of 32 www.DataSheet4U.com ADP3194 The conduction loss of the main MOSFET is given by the following equation: ⎡⎛ I PC ( MF ) = D × ⎢⎜ O ⎢⎜ n MF ⎣⎝ ⎞ 1 ⎛ n × IR ⎟+ ×⎜ ⎟ 12 ⎜ n MF ⎝ ⎠ 2 These numbers comply with the guideline to limit the power dissipation to 1 W per MOSFET. (45) One last thing to consider is the power dissipation in the driver for each phase. This is best described in terms of the QG for the MOSFETs and is given by the following equation: ⎡f ⎤ PDRV = ⎢ SW × (nMF × QGMF + nSF × QGSF ) + I CC ⎥ × VCC ⎢2×n ⎥ ⎣ ⎦ ⎞ ⎟ ⎟ ⎠ 2⎤ ⎥ × R DS ( MF ) ⎥ ⎦ where RDS(MF) is the on resistance of the MOSFET. Typically, for main MOSFETs, the highest speed (low CISS) device is preferred, but these usually have higher on resistance. Select a device that meets the total power dissipation (about 1.5 W for a single D-PAK) when combining the switching and conduction losses. For this example, an NTD40N03L was selected as the main MOSFET (eight total; nMF = 8), with a CISS = 584 pF (maximum) and RDS(MF) = 19 mΩ (maximum at TJ = 120°C). An NTD110N02L was selected as the synchronous MOSFET (eight total; nSF = 8), with CISS = 2710 pF (maximum) and RDS(SF) = 4.8 mΩ (maximum at TJ = 120°C). The synchronous MOSFET CISS is less than 3000 pF, satisfying that requirement. Solving for the power dissipation per MOSFET at IO = 119 A and IR = 11 A yields 958 mW for each synchronous MOSFET and 872 mW for each main MOSFET. (45) where: QGMF is the total gate charge for each main MOSFET QGSF is the total gate charge for each synchronous MOSFET The standby dissipation factor for the driver is ICC × VCC. For the ADP3120A, the maximum dissipation should be less than 400 mW. In this example (with ICC = 7 mA, QGMF = 5.8 nC, and QGSF = 48 nC) 297 mW is found in each driver, which is below the 400 mW dissipation limit. See the ADP3120A data sheet for more details. Rev. 0 | Page 25 of 32 www.DataSheet4U.com ADP3194 LAYOUT AND COMPONENT PLACEMENT The following guidelines are recommended for optimal performance of a switching regulator in a PC system. POWER CIRCUITRY RECOMMENDATIONS The switching power path should be routed on the PCB to encompass the shortest possible length in order to minimize radiated switching noise energy (that is, EMI) and conduction losses in the board. Failure to take proper precautions often results in EMI problems for the entire PC system as well as noise-related operational problems in the power converter control circuitry. The switching power path is the loop formed by the current path through the input capacitors and the power MOSFETs, including all interconnecting PCB traces and planes. Using short and wide interconnection traces is especially critical in this path for two reasons: it minimizes the inductance in the switching loop, which can cause high energy ringing; and it accommodates the high current demand with minimal voltage loss. Whenever a power dissipating component, (for example, a power MOSFET), is soldered to a PCB, the liberal use of vias, both directly on the mounting pad and immediately surrounding it, is recommended. This improves current rating through the vias and also improves thermal performance from vias extended to the opposite side of the PCB, where a plane can more readily transfer the heat to the air. Make a mirror image of any pad being used to heat-sink the MOSFETs on the opposite side of the PCB to achieve the best thermal dissipation to the air around the board. To further improve thermal performance, use the largest possible pad area. The output power path should also be routed to encompass a short distance. The output power path is formed by the current path through the inductor, the output capacitors, and the load. For best EMI containment, a solid power ground plane should be used as one of the inner layers extending fully under all the power components. GENERAL RECOMMENDATIONS For good results, a PCB with at least four layers is recommended. This allows the needed versatility for control circuitry interconnections with optimal placement; power planes for ground, input, and output power; and wide interconnection traces in the remainder of the power delivery current paths. Each square unit of 1 ounce copper trace has a resistance of ~0.53 mΩ at room temperature. Whenever high currents must be routed between PCB layers, vias should be used liberally to create several parallel current paths. Then, the resistance and inductance introduced by these current paths is minimized, and the via current rating is not exceeded. If critical signal lines, including the output voltage sense lines of the ADP3194, must cross through power circuitry, it is best if a signal ground plane can be interposed between those signal lines and the traces of the power circuitry. This serves as a shield to minimize noise injection into the signals at the expense of making the signal ground noisier. Use an analog ground plane around and under the ADP3194 as a reference for the components associated with the controller. This plane should be tied to the nearest output decoupling capacitor ground and not tied to any other power circuitry. This prevents power currents from flowing in the ground plane. Locate the components around the ADP3194 close to the controller with short traces. The most important traces to keep short, and away from other traces, are the FB pin and the CSSUM pin. Connect the output capacitors as close as possible to the load (or connector), for example, a microprocessor core that receives the power. If the load is distributed, the capacitors should also be distributed and generally be in proportion to where the load tends to be more dynamic. Avoid crossing any signal lines over the switching power path loop, as described in the Power Circuitry Recommendations section. SIGNAL CIRCUITRY RECOMMENDATIONS The output voltage is sensed and regulated between the FB pin and the FBRTN pin, which connect to the signal ground at the load. To avoid differential-mode noise pickup in the sensed signal, the loop area should be small. Thus, the FB and FBRTN traces should be routed adjacent to each other on top of the power ground plane back to the controller. The feedback traces from the switch nodes should be connected as close as possible to the inductor. The CSREF signal should be Kelvin connected through a 10 Ω resistor to the center point of the copper bar, which is the VCORE common node for the inductors of all the phases (see Figure 19 and Figure 20). Rev. 0 | Page 26 of 32 www.DataSheet4U.com ADP3194 +1 2V 14 13 12 11 10 5 +1 2V 1 2 3 4 5 6 1K 1K 1K 1K 1K 1K R40 14 RN1A 13 RN1B 12 RN1C 11 RN1D 10 RN1E 9 RN1F DL1 DL2 DL3 DL4 DL5 DL6 RED RED RED RED RED RED 3 NFET 2 Q6 3 NFET 2 Q5 NFET 2 3 Q4 3 NFET 2 Q3 NFET 2 3 Q2 3 NFET 2 Q1 1 1 1 1 1 1 2 3 4 6 1 2 3 4 5 6 RN3A 3.9 K RN3B 3.9 K RN3C 3.9 K RN3D 3.9 K RN3E 3.9 K RN3F 3.9 K 9 1.5K 1.5K 1.5K 1.5K 1.5K 1.5K 1 PHASE_1_RDY 374 Ohm DL 7 GRN 14 RN2A 13 RN2B 12 RN2C 11 RN2D 10 RN2E 9 RN2F PHASE_2_RDY R41 374 Ohm DL8 J2 GRN 1 3 5 7 9 11 2 4 6 8 10 12 CPU_VID0 CPU_VID1 CPU_VID2 CPU_VID3 CPU_VID4 CPU_VID5 CPU_VID0 CPU_VID1 CPU_VID2 CPU_VID3 CPU_VID4 CPU_VID5 PHASE_3_RDY R42 374 Ohm DL9 GRN R43 PHASE_4_RDY VCCP 1 R30 10 1 R31 10 2 2 R1 1 0 0 R2 R3 1 0 1 0 R4 1 2 VSSSocket VSSSocket 1 VCC1 C44 100 0p 1 C23 1uF/16V X7R(0805 ) + 2 VCCSocket VCCSocket 2 2 NI VCCSense NI VSSSense VCCSense VSSSense GND TP 2 VCCP +1 2V 7 1K 8 DL1 1 RN1G GRN 3 NFET 2 VID0 VID1 VID2 VID3 VID4 VID5 374 Ohm DL1 0 GRN HEADER_6x2 1 1 TP 1 VSSP TP13 VCC R10 10 1 2 D1 MM SD414 8 SOD-123 2 112VR CE13 100uF/16V 5x11mm 1 2 1 8 1 7 R32 470K VTT_Pwrg d TP 4 PWRGD 1 1 2 3.9K 1.5K 7 RN3G 8 RN2G RB 1.21K 1% TP20 1 FB 1 Q23 1 1 1 D6 BZX84C5V1FSCT R SHUNT 221 2 CB 1.5 nF 2 2 U1 VID4 VID3 VID2 VID1 VID0 VID5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 RR 118K 1% 2 VID4 VID3 VID2 VID1 VID0 VID5 FBRTN FB COMP PWRGD EN DELAY RT RAMPADJ ADP3194 1 1 VCC PWM1 PWM2 PWM3 PWM4 SW1 SW2 SW3 SW4 GND CSCOMP CSSUM CSREF ILIMIT 28 27 26 25 24 23 22 21 20 19 18 17 16 15 2 R34 1 0 2 RA 7.32K 1% 2 CA 1 nF X7 R 2 C FB 15 pF 1 2 PW M1 PW M2 PW M3 PW M4 R13 R14 R15 R16 1 1 1 1 2 2 2 2 715 Ohm 105 Ohm 619 Ohm 0 PHASE1 PHASE2 PHASE3 PHASE4 2 PW M1 1 1 1 TP 9 PW M1 TP10 PW M2 TP11 PW M3 TP12 PW M4 PW M2 1 PW M3 R44 R R45 R R46 R R47 R 1 1 TP6 DELAY SW1 2 TP 5 EN 2 C DLY 39n 2 R DLY 470K TP 3 COMP 2 2 1 R33 220K C43 39n X7 R 1 1 1 RT 154K 1% 1 Gr ound PW 4 f or M 3- Phase PW M4 oper at i on R PH1 15 K 1 1 1 1 1 1% 2 CS_PH1 1% 2 CS_PH2 1% 2 CS_PH3 1% 2 CS_PH4 R21 0 1 OD# 2 R LIM 140K 1% 2 C SC1 150 pF NPO 5% C SC2 DNI NPO 5% 2 2 R CS1 0 1% 1 R SC2 18.2K 1% 2 1 1 R PH2 15 K 1 R PH3 15 K 1 R PH4 15 K 1 2 1 2 4 TP18 AGND 1 JP1 SHORTPIN 1 2 C45 1uF JP3 TP 7 OD# 1 2 TP19 GND GND 1 2 12VR C46 10nF VCC1 1 1 R35 1K 1 3 2 1 2 1 C24 10 0p NPO 2 TP23 CSREF 1 1 21 R TH 100KOhm THERMISTOR 5% TP 8 R11 10 CSCOMP Not e: Ther m st or ( RTH) used onl y i f or DCR m hod. Do not i nser t et f or RSENSE m hod. et 2 VCCP CE1 560uF/4V 5mOhm 1 1 + + VCCP CE3 560uF/4V 5mOhm 1 1 + + CSREF C1 22uF/6.3V X5 R C3 22uF/6.3V X5 R 1 1 C5 22uF/6.3V X5 R 1 1 C7 22uF/6.3V X5 R 1 1 C9 22uF/6.3V X5 R 1 1 C11 22uF/6.3V X5 R 1 1 C13 22uF/6.3V X5 R 1 1 C15 22uF/6.3V X5 R 1 1 C17 22uF/6.3V X5 R 1 1 2 CE5 560uF/4V 5mOhm 1 1 + + CE7 560uF/4V 5mOhm 1 1 + + CE9 560uF/4V 5mOhm 1 1 + + 1 2 2 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 GND CE2 560uF/4V 5mOhm CE4 N/L 5mOhm CE6 N/L 5mOhm CE8 560uF/4V 5mOhm CE10 560uF/4V 5mOhm C2 22uF/6.3V X5 R GND C4 22uF/6.3V X5 R C6 22uF/6.3V X5 R C8 22uF/6.3V X5 R C10 22uF/6.3V X5 R C12 22uF/6.3V X5 R C14 22uF/6.3V X5 R C16 22uF/6.3V X5 R C18 22uF/6.3V X5 R Figure 19. Typical Applications Schematic Part 1 Rev. 0 | Page 27 of 32 06022-019 www.DataSheet4U.com ADP3194 TP32 RS5 TP33 RS5 TP24 1 1 TP21 12VR +12V Rsense5 1 2 3 4 10 mOhm 1% JP4 2X2 HDR CE11 2700uF/16V 12.5x30mm 1 L1 0.37u H 18A 1 VSWS_1 1 TP22 GND 1 GND 2 1 + 12VR 1 + 1 1 Vsws2 2 2 2 2 VDD Vsws1 GND CE12 2700uF/16V 12.5x30mm 9 U2 R28 0 Ohm 1 Vin 8 C50 4.7uF/16V C30 4.7uF/16V X5R(1206) 10 Q24 2 NTD100N02 SW2 OD# PWM1 GND PHASE_1_RDY 2 3 Enable PWM PGND Vsw 6 1 3 1 2 1 R36 10K 1 VCCP TP34 +5V 4 PRDY iP2003A TP25 PGND 5 L2 280nH 30A/0.8mohm 1 3 PHASE1 1 CS_PH1 TP14 SW1 2 Rsense1 TP35 -5V 7 2 PHASE_1_RDY 2 C29 1uF/16V X5R(0805) 1 1m Ohm 1% 1 R_PH1 10 1 JP2 HEADER 2 1 2 Vcc2 C51 VSWS_2 4.7uF/16V 1 1 2 1 1 9 2 2 TP26 C38 4.7uF/16V X5R(1206) 10 U3 R27 1 Vsws2 CE15 47uF/16V 5x11mm 2 + VDD Vsws1 0 Ohm VCCP Vin 8 L4 280nH 30A/0.8mohm 1 3 2 Rsense2 1m Ohm 1% 1 OD# PWM2 PHASE_2_RDY 1 2 3 Enable PWM PGND Vsw 6 4 GND PRDY iP2003A PGND 5 PHASE2 1 2 CS_PH2 R_PH2 10 PT1 VOUT VCCP 1 2 4 3 C37 1uF/16V X5R(0805) 1 TP27 TP15 SW2 1 2 PHASE_2_RDY CSREF 1 C52 4.7uF/16V 1 TP28 VSWS_3 10 1 7 C34 4.7uF/16V X5R(1206) PT2 GND OUT GND 1 2 4 3 2 U4 R26 0 Ohm 1 VDD 9 Vsws2 Vsws1 Vin 8 L3 280nH 30A/0.8mohm 1 3 2 Rsense 3 1m Ohm 1% 2 VCCP OD# PWM3 PHASE_3_RDY 1 2 3 Enable PWM PGND Vsw 6 CS_PH3 2 4 PRDY iP2003A TP29 PGND 5 PHASE3 1 TP16 SW3 R_PH3 10 1 C33 1uF/16V X5R(0805) 1 2 PHASE_3_RDY 1 1 2 7 C53 4.7uF/16V TP30 VSWS_4 2 C42 4.7uF/16V X5R(1206) Remove R29 for 3-Phase ope ration U7 1 OD# PWM4 1 1 VCCP R29 0 Ohm L5 280nH 30A/0.8mohm Vin 8 1 3 PHASE4 1 TP17 SW4 1 10 9 Vsws2 VDD Vsws1 Rsense 4 1m Ohm 1% 2 CS_PH4 2 2 3 Enable PWM PGND Vsw 6 R_PH4 10 C41 1uF/16V X5R(0805) PHASE_4_RDY 4 PRDY iP2003A TP31 PGND 5 2 1 06022-020 PHASE_4_RDY Figure 20. Typical Applications Schematic Part 2 Rev. 0 | Page 28 of 32 7 www.DataSheet4U.com ADP3194 OUTLINE DIMENSIONS 9.80 9.70 9.60 28 15 4.50 4.40 4.30 1 14 6.40 BSC PIN 1 0.65 BSC 0.15 0.05 COPLANARITY 0.10 0.30 0.19 1.20 MAX 8° 0° 0.75 0.60 0.45 SEATING PLANE 0.20 0.09 COMPLIANT TO JEDEC STANDARDS MO-153-AE Figure 21. 28-Lead Thin Shrink Small Outline Package [TSSOP] (RU-28) Dimensions shown in millimeters ORDERING GUIDE Model ADP3194JRUZ-RL 1 1 Temperature Range 0°C to +85°C Package Description 28-Lead TSSOP 13” Reel Package Option RU-28 Ordering Quantity 2500 Z = Pb-free part. Rev. 0 | Page 29 of 32 www.DataSheet4U.com ADP3194 NOTES Rev. 0 | Page 30 of 32 www.DataSheet4U.com ADP3194 NOTES Rev. 0 | Page 31 of 32 www.DataSheet4U.com ADP3194 NOTES ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06022-0-10/06(0) Rev. 0 | Page 32 of 32