LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET KEY FEATURES DESCRIPTION The additional outputs are capable of supplying up to 5A (Linear Regulator Driver) and 15A (Switching Regulator) for I/O, memory, termination, and other supplies surrounding today’s microprocessor designs. Each PWM regulator output is programmed via a simple voltage-divider network. The LX1671, utilizing MOSFET RDS(ON) impedance, monitors current limit conditions, in each PWM phase, without the use of expensive current sense resistors. The LX1671 was designed to give design engineers maximum flexibility with respect to the MOSFET supply. Each phase can utilize different supply voltages for efficient use of available supply rails. Additionally, when two phases are configured in Bi-Phase output, the LoadSHARETM topology can be programmed via inductor ESR selection. There are three other methods that can also be used with LoadSHARETM. These other methods are presented in the theory of operation section of this data sheet. Up to Four Independently Regulated Outputs Outputs As Low As 0.8V Generated From An Internal 1% Reference Multiphase High Current Output Reduces Required Capacitance Integrated High Current MOSFET Drivers 300kHz High Frequency Operation Minimizes External Component Requirements Independent Phase Programmable Soft-Start and Power Sequencing Adjustable Linear Regulator Driver Output No current-sense resistors DDR Termination Compliant WWW . Microsemi .C OM The LX1671 is a highly integrated power supply controller IC featuring three PWM switching regulator stages with an additional onboard linear regulator driver. Two of the constant frequency voltage-mode PWM phases can be easily configured for a single Bi-Phase high current output or two independently regulated outputs. Each phase incorporates a fully programmable soft-start sequence. This versatility yields either three or four independently regulated outputs with full power sequencing capability giving system designers the ultimate flexibility in power supply design. In Bi-Phase operation, the high current (>30A) output can utilize different supply rails allowing Forced Current Sharing† from different sources. Power loss and noise, due to the ESR of the input capacitors, are minimized by operating each PWM output 180° out of phase. This architecture also minimizes capacitor requirements while maximizing regulator response. APPLICATIONS/BENEFITS Multi-Output Power Supplies Video Card Power Supplies PC Peripherals Portable PC Processor and I/O Supply IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com LoadSHARE is a Trademark of Microsemi Corporation Protected by US Patents: 6,285,571 & 6,292,378 PRODUCT HIGHLIGHT DDR Termination Refer to Typical Application for complete circuit. Memory Core .... 12V 5V Core LX1671 Graphics Controller Memory Bus DDR Memory LX1671 3.3V I/O TA (°C) 0 to 70 PW PACKAGE ORDER INFO Plastic TSSOP Plastic MLPQ LQ 38-Pin 38-Pin RoHS Compliant / Pb-free Transition DC: 0518 RoHS Compliant / Pb-free Transition DC: 0512 LX1671CPW LX1671CLQ Note: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1671CPW-TR) Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET PACKAGE PIN OUT x = Denotes Phase 1, 2, or 3 THERMAL DATA PW Plastic TSSOP 38-Pin 85°C/W 20 (Top View) HO2 VC2 LDGD LDFB LDDIS DGND AGND RSVD SS2 RF2 FB2 EO2 1 38 37 36 35 34 33 32 31 2 30 3 29 4 28 Connect Bottom to Power GND 5 6 7 8 27 26 25 24 9 23 10 22 11 12 LQ Plastic MLP 38-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 19 H01 VC1 VC3 HO3 LO3 PG3 VCCL VCC N/U VS3 CS3 N.C. N.C. EO3 FB3 SS3 VS1 CS1 EO1 21 13 14 15 16 17 18 19 20 LO3 PG3 VCCL VCC N.C. N.C. VS3 CS3 N.C. EO3 FB3 SS3 CS2 VS2 SS1 FB1 EO1 CS1 VS1 THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 38 PW PACKAGE Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal. The limitation on transient time is thermal and is due to zener diodes on the supply pins, application of maximum voltages will increase current into that pin and increase package power dissipation. 1 LO2 PG1 LO1 HO1 VC1 VC3 Note: LO1 PG1 LO2 HO2 VC2 LDGD LDFB LDDIS DGND AGND RSVD SS2 RF2 FB2 EO2 CS2 VS2 SS1 FB1 HO3 Supply Voltage (VCC) DC ................................................................-0.3V to 5.5V Supply Voltage (VCC) Transient ......................................................-0.3V to 6.0V Driver Supply Voltage (VCx, VCCL) DC ............................................-0.3V to 12V Driver Supply Voltage (VCx, VCCL) Transient ...................................-0.3V to 14V Linear Regulator Gate Drive, VLDGD ...................................................-0.3V to 9V Current Sense Inputs (VSX, CSX) ....................................................... -0.3V to 12V Error Amplifier Inputs (FBX, RF2, LDFB)........................................-0.3V to 5.5V Input Voltage (SS/Enable, LDDIS) ...................................................-0.3V to5.5V Output Drive Peak Current Source (HOx, LOx)....................................1A (500ns) Output Drive Peak Current Sink (HOx, LOx) .......................................1A (500ns) Operating Junction Temperature.................................................................. 150°C Storage Temperature Range...........................................................-65°C to 150°C RoHS Peak Package Solder Reflow Temperature (40 second maximum exposure) ..................................................... 260°C (+0, -5) 35°C/W Junction Temperature Calculation: TJ = TA + (PD x θJC). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. LQ PACKAGE (Top View) N.C. – No Internal Connection N/U – Not Used RSVD – Do Not Use Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 PACKAGE DATA RoHS / Pb-free 100% Matte Tin Lead Finish Copyright © 2000 Rev. 1.2b, 2006-02-13 WWW . Microsemi .C OM ABSOLUTE MAXIMUM RATINGS LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET NAME DESCRIPTION FB1 Bi-Phase Operation: Phase 1 and 2 Voltage Feedback Single Phase Operation: Phase 1 Voltage Feedback , connect to the output through a resistor network to set desired output voltage of Phase 1 EOX Error Amplifier Output – Sets external compensation for the corresponding phase denoted by “X”. FB3 Phase 3 Voltage . Feedback, connect to the output through a resistor network to set desired output voltage of Phase 3. FB2 Bi-Phase Operation: Load Sharing Voltage Sense Feedback – Connect filtered phase 2 switching output (preinductor) to FB2 to ensure proper current sharing between phase 1 and phase 2. Single Phase Operation: Phase 2 Voltage Feedback, connect to the output through a resistor network to set desired output voltage of Phase 2. RF2 B-Phase Operation: Load Sharing Voltage Sense Feedback Reference – Sets reference for current sharing control loop. Connecting filtered phase 1 switching output (pre-inductor) to REF2 forces average current in phase 2 to be equal to phase 1. Single Phase Operation: Phase 2 Voltage Reference – connected to SS2 pin as a reference. VCC IC supply voltage (nominal 5V). LDFB Low Dropout Regulator Voltage Feedback – Sets output voltage of external MOSFET via resistor network. CSX Over-Current Limit Set – Connecting a resistor between CS pin and the source of the high-side MOSFET sets the current-limit threshold for the corresponding phase denoted by “X”. Exceeding the current-limit threshold forces the corresponding phase into hiccup mode protection. A minimum of 1KΩ must be in series with this input. SSX Enable & Soft-start/Hiccup Capacitor Pin – During start-up, the voltage on this pin controls the output voltage of its respective regulator. An internal 20kΩ resistor and the external capacitor set the time constant for soft-start function. The Soft-start function does not initialize until the supply voltage exceeds the UVLO threshold. When an over-current condition occurs, this capacitor is used for the timing of hiccup mode protection. Pulling the SS pin below 0.3V disables the corresponding phase denoted by “X”. AGND Analog ground reference. DGND Digital ground reference. LDGD Low Dropout Regulator Gate Drive – Connects to gate of external N-Channel MOSFET for linear regulator function. Driver Power Ground. Connects to the source of the bottom N-channel MOSFETS of phase 1& 2 where X=1, and phase 3 where X=3. HOX High Side MOSFET Gate Driver – “X” denotes corresponding phase. LOX Low Side MOSFET Gate Driver – “X” denotes corresponding phase. VCX Phase High-Side MOSFET Gate Driver Supply – Connect to separate supply or boot strap supply to ensure proper high-side gate driver supply voltage. “X” denotes corresponding phase. If the phase is not used connect to VCC LDDIS Active High disables LDO output. VCCL Power Supply pin for all Low side drivers. VSX RSVD Voltage reference for Current sense. This pin is also the supply pin for the Current Sense Comparator. “X” denotes corresponding phase. This pin cannot be left floating, if a phase is not used connect to VCC. Do not make any connection to this pin Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 PACKAGE DATA PGX WWW . Microsemi .C OM FUNCTIONAL PIN DESCRIPTION LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET Parameter ` Symbol Test Conditions Min LX1671 Typ VCC 4.5 VCCL , VCX Operation Current ICC Reference Voltage VSS 12 V Static and Dynamic 12 mA 0.8 V 0°C ≤ TA ≤ 70°C 0.816 V Line Regulation (Note 2) -1 1 % Load Regulation (Note 2) -1 1 % 250 nS Load = 3000pF 85 % ERROR AMPLIFIERS Input Offset Voltage Vos Common Mode Input Voltage = 1V -6.0 DC Open Loop Gain Unity Gain Bandwidth UGBW High Output Voltage VOH I Source = 2 mA Low Output Voltage VOL I Sink = 10uA Input Offset Voltage < 20mV Input Common Mode Range Input Bias Current 3.8 6.0 mV 70 dB 16 MHz 5.0 V 0.1 100 mV 3.5 V IIN 0 and 3.5 V Common Mode Voltage 100 nA ISET VCSX = VVSX – 0.3V , VVSX = 5V 45 50 55 μA Reference to VSX , VVSX = 5V 260 300 340 mV CURRENT SENSE Current Sense Bias Current Trip Threshold VTRIP Current Sense Delay TCSD Current Sense Comparator ICSX Operating Current OUTPUT DRIVERS – N-CHANNEL MOSFETS 350 Current into VSX pins 2 nS 5 mA Low Side Driver Operating Current IVCCL Static 2.5 mA High Side Driver Operating Current IVCX Static 3 mA Drive Rise Time, Fall Time TRF CL = 3000pF 50 nS High Level Output Voltage VDH ISOURCE = 20mA, VCCL = 12V Low Level Output Voltage VDL ISINK = 20mA, VCCL = 12V 10 11 V 0.15 0.25 V 300 345 KHz OSCILLATOR PWM Switching Frequency Ramp Amplitude Copyright © 2000 Rev. 1.2b, 2006-02-13 255 FSW VRAMP 1.25 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 VPP Page 4 ELECTRICALS ` V 0.784 Maximum Duty Cycle ` 5.5 TA=25°C Minimum Pulse Width ` Units SWITCHING REGULATORS Input Voltage ` Max WWW . Microsemi .C OM ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 70°C except where otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VCX = 12V HOX = LOX = 3000pF Load LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET Min LX1671 Typ Max Start-Up Threshold (VCX VCCL ) 3.5 4.0 4.5 V Start-Up Threshold (VCC) 4.0 4.25 4.5 V Parameter ` Symbol (VCC) SS Input Resistance SS Shutdown Threshold 0.1 V RSS 20 KΩ VSHDN 0.3 V CSS = 0.1μF 10 % VLDFB = 0.8V, COUT = 330µF 2 % 0.2 mA Hiccup Mode Duty Cycle LINEAR REGULATOR CONTROLLER Voltage Reference Tolerance ` Units UVLO AND SOFT-START (SS) Hysteresis ` Test Conditions WWW . Microsemi .C OM ELECTRICAL CHARACTERISTICS (CONTINUED) Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 70°C except where otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VCX = 12V , HOX = LOX = 3000pF Load. Source Current ILDGD VLDGD = 9V Sink Current ILDGD Vout = 0.4V 6 ma DISABLE INPUT LDO Disable LDDIS Threshold Pulldown Resistance 2 V 100 ΚΩ Note 1 – X = Phase 1, 2, 3 Note 2 – System Specification ELECTRICALS Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET RSET WWW . Microsemi .C OM BLOCK DIAGRAM ISET CSX +12V CS Comp IRESET PWM + VTRIP VSX VIN(5V) ISET R Q S Q VCX R2 CIN R1 HOX OUT 1 L1 ESR EOX LOX COUT PGX +5V Error Comp + FBX VCCL Hiccup - + Amplifier/ Compensation VREF 16V 20k Ramp Oscillator UVLO +5V 16V UVLO VCC F FAULT R SS1 SS2 SS3 S S S 5.5V TEMP SS/ENABLE CSS Figure 1 – Typical Block Diagram of Phase 1 and 3 +12V +V LDGD VC1 VREF BLOCK DIAGRAM + - VOUT4 LDFB +5V LDDIS Figure 2 – LDO Controller Block Diagram Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET RSET ISET +5V CS2 VIN(12V) CS Comp IRESET VS2 VTRIP PWM + R Q ISET S Q VC2 CIN HO2 L2 OUT 1 ESR EO2 LO2 LPF2 COUT WWW . Microsemi .C OM BLOCK DIAGRAM PG1 +5V Error Comp + FB2 VCCL Hiccup - + Amplifier/ Compensation VREF RF2 16V 20k LPF1 +5V 16V UVLO Ramp Oscillator UVLO VCC S F FAULT S R SS1 SS2 SS3 S TEMP 5.5V PHASE1 SS/ENABLE CSS Figure 3 – Block Diagram of Phase 2 Connected in LoadSHARE Mode BLOCK DIAGRAM Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET +5V L1 VOUT1 LO1 H01 PG1 VC1 LO2 VC3 H02 HO3 VC2 LO3 LDGD PG3 LDFB VCCL LDDIS VCC DGND N/U +12V WWW . Microsemi .C OM APPLICATION CIRCUIT L2 +5V +5V VOUT4 AGN D LX1671 CPW VS3 L3 RSVD CS3 SS2 N.C. RF2 N.C. FB2 EO3 EO2 FB3 CS2 SS3 VS2 VS1 SS1 CS1 FB1 EO1 VOUT3 Figure 4 – Bi-Phase Operation With Phase 1 and 2 LoadSHARing From 12V and 5V (Phase 2 high-side MOSFET driver bootstrapped to 17V) APPLICATION Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET WWW . Microsemi .C OM APPLICATION CIRCUIT +5V + L1 VOUT1 + LO1 H01 PG1 VC1 LO2 VC3 +5V + H02 HO3 VC2 LO3 LDGD PG3 LDFB VCCL LDDIS VCC L2 + DGND AGN D N/U LX1671 CPW + VOUT2 +5V VS3 L3 RSVD CS3 SS2 N.C. RF2 N.C. FB2 EO3 EO2 FB3 CS2 SS3 VS2 VS1 SS1 CS1 FB1 EO1 + VOUT3 APPLICATION Figure 5 – Single Phase Operation 5V Only (ALL PHASES BOOTSTRAPPED) (LDO NOT FUNCIONAL ) Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET +5V L1 VOUT1 LO1 H01 PG1 VC1 LO2 VC3 H02 HO3 VC2 LO3 LDGD PG3 LDFB VCCL LDDIS VCC DGND N/U +12V +3.3V WWW . Microsemi .C OM APPLICATION CIRCUIT L2 +3.3V +5V VOUT2 +5V AGN D LX1671 CPW VS3 L3 RSVD CS3 SS2 N.C. RF2 N.C. FB2 EO3 EO2 FB3 CS2 SS3 VS2 VS1 SS1 CS1 FB1 EO1 VOUT3 Figure 6 – Bi-Phase Operation With Phase 1 and 2 LoadSHARing From 3.3V and 5V APPLICATION Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET GENERAL DESCRIPTION The LX1671 is a voltage-mode pulse-width modulation controller integrated circuit. The internal ramp generator frequency is fixed to 300kHz. The device has external compensation, for more flexibility of output current magnitude. UNDER VOLTAGE LOCKOUT (UVLO) Hiccup is disabled during the soft-start interval, allowing start up with maximum current. If the rate of rise of the output voltage is too fast, the required charging current to the output capacitor may be higher than the limit-current. In this case, the peak MOSFET current is regulated to the limit-current by the currentsense comparator. If the MOSFET current still reaches its limit after the soft-start finishes, the hiccup is triggered again. When the output has a short circuit the hiccup circuit ensures that the average heat generation in both MOSFETs and the average current is much less than in normal operation. At power up, the LX1671 monitors the supply voltage for VCC, VCCL, and VCX (there is no requirement for sequencing the supplies). Before all supplies reach their under-voltage lockout (UVLO) thresholds, the soft-start (SS) pin is held low to prevent soft-start from beginning, the oscillator is disabled and all MOSFETs are held off. Over-current protection can also be implemented using a sense resistor, instead of using the RDS(ON) of the upper MOSFET, for greater set-point accuracy. SOFT-START OSCILLATOR FREQUENCY Once the supplies are above the UVLO threshold, the soft-start capacitor begins to be charged by the reference through a 20kΩ internal resistor. The capacitor voltage at the SS pin rises as a simple RC circuit. The SS pin is connected to the error amplifier’s non-inverting input that controls the output voltage. The output voltage will follow the SS pin voltage if sufficient charging current is provided to the output capacitor. The simple RC soft-start allows the output to rise faster at the beginning and slower at the end of the soft-start interval. Thus, the required charging current into the output capacitor is less at the end of the soft-start interval. A comparator monitors the SS pin voltage and indicates the end of soft-start when SS pin voltage reaches 95% of VREF. OVER-CURRENT PROTECTION (OCP) AND HICCUP The LX1671 uses the RDS(ON) of the upper MOSFET, together with a resistor (RSET) to set the actual current limit point. The current sense comparator senses the MOSFET current 350nS after the top MOSFET is switched on in order to reduce inaccuracies due to ringing. A current source supplies a current (ISET), whose magnitude is 50µA. The set resistor RSET is selected to set the current limit for the application. RSET and VSX should be connected directly at the upper MOSFET drain and source to get an accurate measurement across the low resistance RDS(ON). If any phase is not used connect the VSX and VCX pins to VCC, do not leave them floating. Copyright © 2000 Rev. 1.2b, 2006-02-13 An internal oscillator sets the switching frequency at 300kHz. THEORY OF OPERATION CONFIGURATION FOR A BI-PHASE, LOADSHARE The basic principle used in LoadSHARE, in a multiple phase buck converter topology is that if multiple, identical, inductors have the same identical voltage impressed across their leads, they must then have the same identical current passing through them. The current that we would like to balance between inductors is mainly the DC component along with as much as possible the transient current. All inductors in a multiphase buck converter topology have their output side tied together at the output filter capacitors. Therefore this side of all the inductors have the same identical voltage. If the input side of the inductors can be forced to have the same equivalent DC potential on this lead, then they will have the same DC current flowing. To achieve this requirement, phase 1 will be the control phase that sets the output operating voltage, under normal PWM operation. To force the current of phase 2 to be equal to the current of phase 1, a second feedback loop is used. Phase 2 has a low pass filter connected from the input side of each inductor. This side of the inductors has a square wave signal that is proportional to its duty cycle. The output of each LPF is a DC (+ some AC) signal that is proportional to the magnitude and duty cycle of its respective inductor signal. The second feedback loop will use the output of the phase 1 LPF as a reference signal for an error amplifier that will compare this reference to the output of the phase 2 LPF. This error signal will be amplified and used to control the PWM circuit of phase 2. Therefore, the duty cycle of phase 2 will be set so that the equivalent voltage potential will be forced across the phase 2 inductor as compared to the phase 1 inductor. This will force the current in the phase 2 inductor to follow and be equal to the current in the phase 1 inductor. There are four methods that can be used to implement the LoadSHARE feature of the LX1671 in the Bi-Phase mode of operation. Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 11 APPLICATION When the sensed voltage across RDS(ON) plus the set resistor exceeds the 300mV, VTRIP threshold, the OCP comparator outputs a signal to reset the PWM latch and to start hiccup mode. The soft-start capacitor (CSS) is discharged slowly (10 times slower than when being charged up by RSS). When the voltage on the SS pin reaches a 0.2V threshold, hiccup finishes and the circuit softstarts again. During hiccup both MOSFETs for that phase are held off. WWW . Microsemi .C OM THEORY OF OPERATION LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET BI-PHASE, LOADSHARE (ESR METHOD) The first method is to change the ratio of the inductors equivalent series resistance, (ESR). As can be seen in the previous example, if the offset error is zero and the ESR of the two inductors are identical, then the two inductor currents will be identical. To change the ratio of current between the two inductors, the value of the inductor’s ESR can be changed to allow more current to flow through one inductor than the other. The inductor with the lower ESR value will have the larger current. The inductor currents are directly proportional to the ratio of the inductor’s ESR value. The following circuit description shows how to select the inductor ESR for each phase where a different amount of power is taken from two different input power supplies. A typical setup will have a +5V power supply connected to the phase 1 half bridge driver and a +3.3V power supply connected to the phase 2 half bridge driver. The combined power output for this core voltage is 18W (+1.5V @ 12A). For this example the +5V power supply will supply 7W and the +3.3V power supply will supply the other 11W. 7W @ 1.5V is a 4.67A current through the phase 1 inductor. 11W @ 1.5V is a 7.33A current through the phase 2 inductor. The ratio of inductor ESR is inversely proportional to ESR1 I2 the power level split. = ESR 2 I1 The higher current inductor will have the lower ESR value. If the ESR of the phase 1 inductor is selected as 10mΩ, then the ESR value of the phase 2 inductor is calculated as: ⎛ 4.67 A ⎞ ⎜ ⎟ × 10 mΩ = 6.4 mΩ ⎝ 7.33A ⎠ Depending on the required accuracy of this power sharing; inductors can be chosen from standard vendor tables with an ESR ratio close to the required values. Inductors can also be designed for a given application so that there is the least amount of compromise in the inductor’s performance. +5V @ 7W 10mΩ 6.4mΩ L2 Sometimes it is desirable to use the same inductor in both phases while having a much larger current in one phase versus the other. A simple resistor divider can be used on the input side of the Low Pass Filter that is taken off of the switching side of the inductors. If the Phase 2 current is to be larger than the current in Phase 1; the resistor divider is placed in the feedback path before the Low Pass Filter that is connected to the Phase 2 inductor. If the Phase 2 current needs to be less than the current in Phase 1; the resistor divider is then placed in the feedback path before the Low Pass Filter that is connected to the Phase 1 inductor. As in Figure 7, the millivolts of DC offset created by the resistor divider network in the feedback path, appears as a voltage generator between the ESR of the two inductors. A divider in the feedback path from Phase 2 will cause the voltage generator to be positive at Phase 2. With a divider in the feedback path of Phase 1 the voltage generator becomes positive at Phase 1. The Phase with the positive side of the voltage generator will have the larger current. Systems that operate continuously above a 30% power level can use this method, a down side is that the current difference between the two inductors still flows during a no load condition. This produces a low efficiency condition during a no load or light load state, this method should not be used if a wide range of output power is required. The following description and Figure 8 show how to determine the value of the resistor divider network required to generate the offset voltage necessary to produce the different current ratio in the two output inductors. The power sharing ratio is the same as that of Figure 7. The Offset Voltage Generator is symbolic for the DC voltage offset between Phase 1 & 2. This voltage is generated by small changes in the duty cycle of Phase 2. The output of the LPF is a DC voltage proportional to the duty cycle on its input. A small amount of attenuation by a resistor divider before the LPF of Phase 2 will cause the duty cycle of Phase 2 to increase to produce the added offset at V2. The high DC gain of the error amplifier will force LPF2 to always be equal to LPF1. The following calculations determine the value of the resistor divider necessary to satisfy this example. 1.5V @ 12A 18W APPLICATION 1.5V + 46.7mV +3.3V @ 11W 4.67A L1 BI-PHASE, LOADSHARE (FEEDBACK DIVIDER METHOD) 7.33A Figure 7 –LoadSHARE Using Inductor ESR Copyright © 2000 Rev. 1.2b, 2006-02-13 WWW . Microsemi .C OM THEORY OF OPERATION (CONTINUED) Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 12 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET +5V @ 7W L1, Switch Side 100 62k Not Used Resistor Divider RF2 1.5V +46.7mV - Resistor Divider 62k LPF2 4.67A - Offset Voltage Generator Vou 1.5V @ 12A 18W + 62k V2 100 TBD ESR L1 10mΩ PWM Input 4700pF FB2 L2, Switch Side V1 Phase 1 + LPF1 Phase 2 Error Amp WWW . Microsemi .C OM THEORY OF OPERATION (CONTINUED) 1.5V +73.3mV 4700pF ESR L2 10mΩ Phase 2 7.33A +3.3V @ 11W Figure 8 – LoadSHARE Using Feedback Divider Offset Where V1 = 1.5467 ; V2 = 1.5733 and K = V1 V2 then TBD = K × 100 1− K = 5.814 K APPLICATION Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 13 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET Also a speed up capacitor can be used between the offset amplifier output and the negative input of the Phase 2 error amplifier. This will improve the transient response of the Phase 2 output current, so that it will share more equally with phase 1 current during a transient condition. BI-PHASE, LOADSHARE (PROPORTIONAL METHOD) The best topology for generating a current ratio at full load and proportional between full load and no load is shown in figure 9. The DC voltage difference between LPF1 and VOUT is a voltage that is proportional to the current flowing in the Phase 1 inductor. This voltage can be amplified and used to offset the voltage at LPF2 through a large impedance that will not significantly alter the characteristics of the low pass filter. At no load there will be no offset voltage and no offset current between the two phases. This will give the highest efficiency at no load. The use of a MOSFET input amplifier is required for the buffer to prevent loading the low pass filter. The gain of the offset amplifier, and the value of Ra and Rb, will determine the ratio of currents between the phases at full load. Two external amplifiers are required or this method. WWW . Microsemi .C OM THEORY OF OPERATION (CONTINUED) L1, Switch Side Offset Amp LPF1 + 62k + Rin - - Vos Rf 4700pF Phase 2 Error Amp 1.5V +46.7mV ESR L1 10mΩ V1 4.67A Phase 1 + PWM Input RF2 Offset Voltage Generator L2, Switch Side +5V @ 7W Vou 1.5V @ 12A 18W + FB2 62k LPF2 62k Ra 1.5V +73.3mV 4700pF 1M Rb V2 ESR L2 10mΩ Phase 2 7.33A +3.3V @ 11W Figure 9 – LoadSHARE Using Proportional Control APPLICATION Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 14 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET The circuit in Figure 9 sums a current through a 1MΩ resistor (Rb) offsetting the phase 2 error amplifier to create an imbalance in the L1 and L2 currents. Although there are many ways to calculate component values the approach taken here is to pick Ra, Rb, Rin, Vout, and inductor ESR. A value for the remaining resistor Rf can then be calculated. The first decision to be made is the current sharing ratio, follow the previous examples to understand the basics of LoadSHARE. The most common reason to imbalance the currents in the two phases is because of limitations on the available power from the input rails for each phase. Use the available input power and total required output power to determine the inductor currents for each phase. All references are to Figure 9 1) Calculate the voltages V1 and V2. V 1 = L 1 Current × L 1 ESR + Vout V 2 = L 2 Current × L 2 ESR + Vout BI-PHASE, LOADSHARE (SERIES RESISTOR METHOD) A fourth but less desirable way to produce the ratio current between the two phases is to add a resistor in series with one of the inductors. This will reduce the current in the inductor that has the resistor and increase the current in the inductor of the opposite phase. The example of Figure 7 can be used to determine the current ratio by adding the value of the series resistor to the ESR value of the inductor. The added resistance will lower the overall efficiency LoadSHARE ERROR SOURCES With the high DC feedback gain of this second loop, all phase timing errors, RDS(On) mismatch, and voltage differences across the half bridge drivers are removed from the current sharing accuracy. The errors in the current sharing accuracy are derived from the tolerance on the inductor’s ESR and the input offset voltage specification of the error amplifier. The equivalent circuit is shown next for an absolute worst case difference of phase currents between the two inductors. 2) Select values for Ra and Rb (Ra is typically 62KΩ ; Rb is typically 1MΩ) ESR L1 V1 Offset Error 5mV + 3) Calculate the offset voltage Vos at the output of the offset amplifier ⎛ V 2 − V1⎞ Vos = V 2 − ⎜ ⎟ × (Ra + Rb ) ⎝ Ra ⎠ VOUT Phase 1 ESR L2 V2 Phase 2 Figure 10 – Error Amplitude 4) Calculate the value for Rf Nominal ESR of 6mΩ. ESR ±5% (select a value for Rin typically 5KΩ) Max offset Error = 6mV ⎛ Vos − Vout ⎞ ⎟ ⎝ Vout − V 1 ⎠ +5% ESR L1 = 6.3 mΩ Rf = Rin ⎜ -5% ESR L2 = 5.7 mΩ Due to the high impedances in this circuit layout can affect the actual current ratio by allowing some of the switching waveforms to couple into the current summing path. It may be necessary to make some adjustment in Rf after the final layout is evaluated. Also the equation for Rf requires very accurate numbers for the voltages to insure an accurate result. If phase 1 current = 12 A = V 1 − VOUT = 12 × 6.3 × 10 −3 V 1 - VOUT ESRL 1 = 75.6 mV V 2 = V1 + 6 mV = 81.6 mV V 2 - VOUT 81.6 x 10−3 = = 14.32 A ESR L 2 5.7 x 10−3 APPLICATION Phase 2 current = Phase 2 current is 2.32A greater than Phase 1. Input bias current also contributes to imbalance. Copyright © 2000 Rev. 1.2b, 2006-02-13 WWW . Microsemi .C OM THEORY OF OPERATION (CONTINUED) Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 15 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET OUTPUT INDUCTOR OUTPUT CAPACITOR The output inductor should be selected to meet the requirements of the output voltage ripple in steady-state operation and the inductor current slew-rate during transient. The peak-topeak output voltage ripple is: D The output capacitor is sized to meet ripple and transient performance specifications. Effective Series Resistance (ESR) is a critical parameter. When a step load current occurs, the output voltage will have a step that equals the product of the ESR and the current step, ΔI. In an advanced microprocessor power supply, the output capacitor is usually selected for ESR instead of capacitance or RMS current capability. A capacitor that satisfies the ESR requirements usually has a larger capacitance and current capability than strictly needed. The allowed ESR can be found by: fs ESR × I RIPPLE + ΔI < VEX VRIPPLE = ESR × I RIPPLE where ΔI = VIN − VOUT L × ( ) ΔI is the inductor ripple current, L is the output inductor value and ESR is the Effective Series Resistance of the output capacitor. Where IRIPPLE is the inductor ripple current, ΔI is the maximum load current step change, and VEX is the allowed output voltage excursion in the transient. ΔI should typically be in the range of 20% to 40% of the maximum output current. Higher inductance results in lower output voltage ripple, allowing slightly higher ESR to satisfy the transient specification. Higher inductance also slows the inductor current slew rate in response to the load-current step change, ΔI, resulting in more output-capacitor voltage droop. When using electrolytic capacitors, the capacitor voltage droop is usually negligible, due to the large capacitance Electrolytic capacitors can be used for the output capacitor, but are less stable with age than tantalum capacitors. As they age, their ESR degrades, reducing the system performance and increasing the risk of failure. It is recommended that multiple parallel capacitors be used, so that, as ESR increase with age, overall performance will still meet the processor’s requirements. The inductor-current rise and fall times are: TRISE = L× (V ΔI IN − VOUT ) and TFALL = L× ΔI VOUT .The inductance value can be calculated by L= VIN − VOUT ΔI × WWW . Microsemi .C OM APPLICATION NOTE There is frequently strong pressure to use the least expensive components possible, however, this could lead to degraded longterm reliability, especially in the case of filter capacitors. Microsemi’s demonstration boards use the CDE Polymer AL-EL (ESRE) filter capacitors, which are aluminum electrolytic, and have demonstrated reliability. The OS-CON series from Sanyo generally provides the very best performance in terms of long term ESR stability and general reliability, but at a substantial cost penalty. The CDE Polymer AL-EL (ESRE) filter series provides excellent ESR performance at a reasonable cost. Beware of offbrand, very low-cost filter capacitors, which have been shown to degrade in both ESR and general electrolytic characteristics over time. D fs APPLICATION Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 16 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET INPUT CAPACITOR The input capacitor and the input inductor, if used, are to filter the pulsating current generated by the buck converter to reduce interference to other circuits connected to the same 5V rail. In addition, the input capacitor provides local de-coupling for the buck converter. The capacitor should be rated to handle the RMS current requirements. The RMS current is: I RMS = I L Values of Css equal to .1uf or greater are unlikely to result in saturation of the output inductor unless very large output capacitors are used. OVER-CURRENT PROTECTION Current limiting occurs at current level ICL when the voltage detected by the current sense comparator is greater than the current sense comparator threshold, VTRIP (300mV). d(1 − d) I CL × R DS(ON) + I SET × R SET = VTRIP Where IL is the inductor current and d is the duty cycle. The maximum value occurs when d = 50% then IRMS =0.5IL. For 5V input and output in the range of 2 to 3V, the required RMS current is very close to 0.5IL. So, R SET = VTRIP − I CL × R DS(ON) SOFT-START CAPACITOR The value of the soft-start capacitor determines how fast the output voltage rises and how large the inductor current is required to charge the output capacitor. The output voltage will follow the voltage at the SS pin if the required inductor current does not exceed the maximum allowable current for the inductor. The SS pin voltage can be expressed as: ( VSS = V ref 1 − e − t/R SSCSS ) Where RSS and CSS are the soft-start resistor and capacitor. The current required to charge the output capacitor during the soft start interval is. Iout = Cout dVss dt Taking the derivative with respect to time results in Iout = VrefCout − t/R SS C SS e RssCss 300 mV − I CL × R DS(ON) 50 µA Example: For 10A current limit, using FDS6670A MOSFET (10mΩ RDS(ON)): R SET = 0.3 − 10 × 0.010 50 × 10 −6 = 4.02 kΩ 1% Note: Maximum RSET is 6KΩ. Any resistor 6KΩ or greater will not allow startup since ICL will equal zero (50uA x 6KΩ=300mV). At low duty cycles where the upper gate drive is less than 350nS wide the 350nS delay for current limit enable may result in current pulses exceeding the desired current limit set point. If the upper MOSFET on time is less than 350nS and a short circuit condition occurs the duty cycle will increase, since Vout will be low. The current limit circuit will be enabled when the upper gate drive exceeds 350nS although the actual peak current limit value will be higher than calculated with the above equation. Short circuit protection still exists due to the narrow pulse width even though the magnitude of the current pulses will be higher than the calculated value. and at t=0 Im ax = I SET = VrefCout RssCss If OCP is not desired connect both VSX and VCX to VCC. Do not leave them floating. Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 APPLICATION The required inductor current for the output capacitor to follow the soft start voltage equals the required capacitor current plus the load current. The soft-start capacitor should be selected to provide the desired power on sequencing and insure that the overall inductor current does not exceed its maximum allowable rating. Copyright © 2000 Rev. 1.2b, 2006-02-13 WWW . Microsemi .C OM APPLICATION NOTE (CONTINUED) Page 17 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET OUTPUT ENABLE The LX1671 MOSFET driver outputs are shut off by pulling the soft-start pin below 0.3V. The LDO voltage regulator has its own Enable/Disable pin (LDDIS) for control of this output voltage. PROGRAMMING THE OUTPUT VOLTAGE The output Voltage is sensed by the feedback pin (FBX) which is compared to a 0.8V reference. The output voltage can be set to any voltage above 0.8V (and lower than the input voltage) by means of a resistor divider R1-R2 (see Figure 1). VOUT = VREF (1 + R 1 /R 2 ) Note: This equation is simplified and does not account for error amplifier input current. Keep R1 and R2 close to 1kΩ (order of magnitude). AN 18 For more information see Microsemi Application Note 18 LX1671 Product design Guide DDR VTT TERMINATION VOLTAGE Double Data Rate (DDR) SDRAM requires a termination voltage (VTT) in addition to the line driver supply voltage (VDDQ) and receiver supply voltage (VDD). Although it is not a requirement VDD is generally equal to VDDQ so that only VTT and VDDQ are required. The LX1671 can supply both voltages by using two of the three PWM phases. Since the currents for VTT and (VDD plus VDDQ) are quite often several amps, (2A to 6A is common) a switching regulator is a logical choice VTT for DDR memory can be generated with the LX1671 by using the positive input of the phase 2 error amplifier RF2 as a reference input from an external reference voltage VREF which is defined as one half of VDDQ. Using VREF as the reference input will insure that all voltages are correct and track each other as specified in the JEDEC (EIA/JESD8-9A) specification. The phase 2 output will then be equal to VREF and track the VDDQ supply as required. When an external reference is used the Soft Start will not be functional for that phase WWW . Microsemi .C OM APPLICATION NOTE (CONTINUED) See Microsemi Application Note 17 for more details. APPLICATION Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 18 LX1671 TM ® Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET 1. The power N-MOSFET transistor’s total gate charge spec, (Qg) should not exceed 40Nc when VCx = +12V. This condition will guarantee operation over the specified ambient temperature range. The Qg value of the N-MOSFET is directly related to the amount of power dissipation inside the IC package, from the three sets of MOSFET drivers. The equation relating Qg to the power dissipation of a MOSFET driver is: Pd = f * Qg * Vd . f = 300KHs and Vd is the supply voltage for the MOSFET driver. The three bottom MOSFET drivers are powered by the VCCL pin that is connected to +5V. The upper MOSFET drivers can be connected to the +12V supply or to a bootstrap supply generated by its output bridge. The bootstrap supply will be at +17V. Depending on the thermal environment of the application circuit, the Qg value of the N-MOSFETs will have to be less than the 40nC value. A typical configuration of the input voltage rails to generate the output voltages required is having the 5volt supply on phase 1, the 3.3volt supply on phase 2, and the 12volt supply on phase 3. At the max Qg value, the three bottom MOSFET drivers will dissipate 60mw each. The upper MOSFET drivers for phases 1 and 2 will operate off of +12volts. Their dissipation is 144mw each. Phase 3 will have the bootstrap supply so its dissipation is 204mw. The total power dissipation for gate drive is 672mw. Icc x Vcc =15ma x 5 V= 75mW. Total package power dissipation = 747mW. Using the thermal equation of: Tj = Ta + Pd * Oja, the Junction temperature for this IC package is = 23 + .747 * 85 which = 86 deg C. This means that the ambient temperature rise has to be less than 64 deg C. 5. The maximum output voltage when using LoadSHARE is limited by the input common mode voltage of the error amplifier and cannot exceed the input common mode voltage. 6. The minimum RSET resistor value is 1k ohm for the current limit sensing. If this resistor becomes shorted, it will do permanent damage to the IC. 7. A resistor has been put in series with the gate of the LDO pass transistor to reduce the output noise level. The resistor value can be changed to optimize the output transient response versus output noise. 8. The LDO controller inside the IC uses the voltage at VC1 as the drive voltage. Due to noise considerations ideally the voltage on the VC1 pin would be a fixed +12volt supply. When VC1 is connected to a bootstrap supply the LDO output will reflect significant switching noise without filtering. When VC1 is generated with a bootstrap supply the LDO should not be used. 9. To delay the turn on of the LDO controller output, a capacitor should be connected between the LDDIS pin and the +5volts. The LDDIS input has a 100K pull down resistor, which keeps the LDO active until this pin is pulled high. During the power up sequence the capacitor connected to the LDDIS pin will keep the LDO off until this capacitor, being charge by the 100K pull down resistor, goes through the low input threshold level. APPLICATION 2. The Soft-Start reference input has a 300mv threshold, above which the PWM starts to operate. The internal operating reference level is set at 800mv. This means that the output voltage is 37.5% low when the PWM becomes active. This starts each phase up in the current limit mode without Hiccup operation. If more than one phase is using the 5volt rail for conversion, then their soft-start capacitor values should be changed so that the two phases do not start up together. This will help reduce the amount of 5volt input capacitance required. Also the VCC pin and the VCCL pin should be kept separated and should be decoupled separately. This will prevent the VCC pin from drooping back below the UVLO set point during start up. 4. When phases 1 and 2 are used in the Bi-phase mode to current share into the same output load, the phase 2 current is forced to follow the phase 1 current. It is important to use a larger softstart capacitor on phase 2 than phase 1 so that the phase 1 current becomes active before phase 2 becomes active. This will minimize any start up transient. It is also important to disable phase 1 and 2 at the same time. Disabling phase 1 without disabling phase 2, in the Bi-phase mode, lets phase 2 turn on and off randomly because it has lost its reference. 3. If a phase is not used connect the VSX and VCX pins to VCC. Do not leave them floating. A floating VSX pin will result in operation resembling a hiccup condition. Copyright © 2000 Rev. 1.2b, 2006-02-13 WWW . Microsemi .C OM APPLICATION NOTE CONSIDERATIONS Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 19 LX1671 ® TM Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET PW 38-Pin Thin Small Shrink Outline (TSSOP) Dim 38 20 P 19 1 F E D M A H B G LQ L C A B C D E F G H L M P *LC MILLIMETERS MIN MAX 0.85 0.95 0.19 0.25 0.09 0.20 9.60 9.80 4.30 4.50 0.50 BSC 0.05 0.15 – 1.10 0.50 0.75 0° 8° 6.25 6.50 – 0.10 INCHES MIN MAX 0.033 0.037 0.19 0.009 0.003 0.008 0.378 0.390 0.169 0.176 0.0196 BSC 0.002 0.005 – 0.043 0.020 0.030 0° 8° 0.246 0.256 – 0.004 MILLIMETERS MIN MAX 0.80 1.00 0 0.05 0.20 REF 0.18 0.30 5.00 BSC 3.00 3.25 7.00 BSC 5.00 5.25 0.50 BSC 0.30 0.50 INCHES MIN MAX 0.031 0.039 0 0.002 0.008 REF 0.007 0.011 0.196 BSC 0.118 0.127 0.275 BSC 0.196 0.206 0.019 BSC 0.012 0.020 WWW . Microsemi .C OM PACKAGE DIMENSIONS 38-Pin Plastic MLPQ (5x7mm EP) D L Dim E E2 3 2 1 e A A1 Note: b A3 Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(0.006”) on any side. Lead dimension shall not include solder coverage. Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 20 MECHANICALS A A1 A3 b D D2 E E2 e L D2 LX1671 TM ® Multiple Output LoadSHARE™ PWM P RODUCTION D ATA S HEET WWW . Microsemi .C OM NOTES NOTES PRODUCTION DATA – Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time. Copyright © 2000 Rev. 1.2b, 2006-02-13 Microsemi Integrated Products, Power Management 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 21