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| (R) SP6120HV High Voltage, Synchronous ,Buck Controller Ideal for 2A to 20A, High Performance, DC-DC Power Converters Optimized for Single Supply, 3V - 12V Applications N/C 1 16 BST High Efficiency: Greater Than 95% Possible 15 GH ENABLE 2 "AnyFETTM" Technology: Capable Of Switching Either 14 SWN ISP 3 SP6120HV PFET Or NFET High Side Switch 13 GND ISN 4 Selectable Discontinuous or Continuous Conduction 16 Pin TSSOP 12 PGND VFB 5 Mode 11 GL COMP 6 Fast Transient Response from Window Comparator 10 VCC SS 7 16-Pin TSSOP, Small Size 9 PROG ROSC 8 Accurate 1% Reference Over Line, Load and Temperature Accurate 10% Frequency Now Available in Lead Free Packaging Accurate, Rail to Rail, 43mV, Over-Current Sensing APPLICATIONS Resistor Programmable Frequency DSP Resistor Programmable Output Voltage Microprocessor Core Low Quiescent Current: 950A, 10A in Shutdown I/O & Logic Hiccup Over-Current Protection Industrial Control Capacitor Programmable Soft Start Distributed Power Guaranteed Boost Voltage to Enhance High Side NFET Low Voltage Power DESCRIPTION The SP6120HV is a fixed frequency, voltage mode, synchronous PWM controller designed to work from a single 12V, 5V or 3.3V input supply. Sipex's unique "AnyFETTM" Technology allows the SP6120HV to be used for resolving a multitude of price/performance trade-offs. It is separated from the PWM controller market by being the first controller to offer precision, speed, flexibility, protection and efficiency over a wide range of operating conditions. NMOS High Side Drive PROG = GND NC ENABLE ENABLE ISP ISN VFB COMP RZ 15k CP 100pF CZ 4.7nF CSS 0.33F SS ROSC ROSC 18.7k (R) MBR0530 CB 1F QT 3.3V VIN CIN 330F x 2 CS 39nF 1.9V 1A to 8A VOUT PMOS High Side Drive PROG = VCC NC ENABLE ENABLE ISP ISN (R) 3.3V VIN CIN 330F x 2 QT1 RS 22.1k L1 2.5H CS 39nF 1.9V 1A to 8A VOUT BST GH SWN GND CBST 1F BST GH SWN GND RS 22.1k L1 2.5H SP6120B SP6120B PGND GL VCC PROG CVCC 2.2F RI 10k VIN QB DS COUT 470F x 3 VFB COMP RZ 15k CP 100pF CZ 4.7nF CSS 0.33F SS ROSC ROSC 18.7k PGND GL VCC PROG CVCC 2.2F RI 10k VIN QB DS COUT 470F x 3 RF 5.23k RF 5.23k QT, QB = FAIRCHILD FDS6690A QT1 = FAIRCHILD FDS6375 (PMOS only) L1 = PANASONIC ETQP6F2R5SFA Date: 5/25/04 DS = STMICROELECTRONICS STPS2L25U CIN = SANYO 6TPB330M COUT = SANYO 4TPB470M (c) Copyright 2004 Sipex Corporation SP6120HV Low Voltage, Synchronous Buck Controller 1 ABSOLUTE MAXIMUM RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. VCC .......................................................................... 13.2V BST ........................................................................... 19V BST-SWN ............................................................... 13.2V SWN ............................................................. -1V to 13.2V GH ..................................................... -0.3V to BST +0.3V GH-SWN ................................................................ 13.2V All Other Pins ....................................... -0.3V to VCC +0.3V Peak Output Current < 10s GH, GL ........................................................................ 2A Operating Temperature Range SP6120C ................................................ 0C to +70C SP6120E .............................................. -40C to +85C Junction Temperature, TJ ...................................... +125C Storage Temperature Range .................. -65C to +150C Power Dissipation Lead Temperature (soldering 10 sec) ................... +300C ESD Rating ........................................................ 2kV HBM SPECIFICATIONS Unless otherwise specified: 3.0V < VCC <5.5V, 3.0V < BST < 13.2V, ROSC = 18.7k, CCOMP = 0.1F, CSS = 0.1F, ENABLE = 3V, CGH = CGL = 3.3nF, VFB = 1.25V, ISP = ISN = 1.25V, SWN = GND = PGND = 0V, -40C < TAMB <85C (Note 1) PARAMETER QUIESCENT CURRENT VCC Supply Current VCC Supply Current (Disabled) BST Supply Current ERROR AMPLIFIER Error Amplifier Transconductance COMP Sink Current COMP Source Current COMP Output Impedence VFB Input Bias Current REFERENCE Error Amplifier Reference VFB 3% Low Comparator VFB 3% High Comparator OSCILLATOR & DELAY PATH Oscillator Frequency Oscillator Frequency #2 Duty Ratio ROSC Voltage Minimum GH Pulse Width CONDITIONS MIN TYP MAX UNITS No Switching ENABLE = 0V No Switching, VBST = VCC No Switching, VCC = 5V, VBST = 10V - 0.95 5 1 100 1.8 20 20 150 mA A A A s 600 VFB = 1.35V, COMP = 0.5V, No Faults VFB = 1.15V, COMP = 1.6V 15 15 35 35 3 60 100 65 65 A A M nA Trimmed with Error Amp in Unity Gain 1.238 1.250 3 3 1.262 V %VREF %VREF 270 ROSC = 10.2k Loop In Control -100% DC possible Information Only - Moves with Oscillator Trim VCC > 4.5V, Ramp up COMP Voltage > 0.6V until GH starts Switching 450 300 500 95 0.65 120 330 550 kHz kHz % V 250 ns Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 2 SPECIFICATIONS: continued Unless otherwise specified: 3.0V < VCC <5.5V, 3.0V < BST < 13.2V, ROSC = 18.7k, CCOMP = 0.1F, CSS = 0.1F, ENABLE = 3V, CGH = CGL = 3.3nF, VFB = 1.25V, ISP = ISN = 1.25V, SWN = GND = PGND = 0V, -40C < TAMB <85C (Note 1) PARAMETER SOFTSTART SS Charge Current SS Discharge Current COMP Discharge Current COMP Clamp Voltage SS Ok Threshold SS Fault Reset SS Clamp Voltage CONDITIONS MIN TYP MAX UNITS VSS = 1.5V VSS = 1.5V VCOMP = 0.5V, Fault Initiated VFB < 1.0V, VSS = 2.5V 25 2 200 2.0 1.7 0.2 2.0 50 5 500 2.4 2.0 0.25 2.4 70 7 2.8 2.2 0.3 2.8 A A A V V V V OVER CURRENT & ZERO CURRENT COMPARATORS Over Current Comparator Threshold Voltage ISN, ISP Input Bias Current Zero Current Comparator Threshold UVLO VCC Start Threshold VCC Stop Threshold ENABLE Enable Threshold ON OFF Enable Pin Source Current GATE DRIVER GH Rise Time GH Fall Time GL Rise Time GL Fall Time GH to GL Non-Overlap Time GL to GH Non-Overlap Time VBST OK Threshold Forced GL ON VCC > 4.5V VCC > 4.5V VCC > 4.5V VCC > 4.5V VCC > 4.5V VCC > 4.5V VCC = 3.0V, FB=1.15V, Search GL High VCC = 5.5V, FB=1.15V, Search GL High VBST < VBST OK Threshold, FB =1.15V 0 0 4.0 7.3 200 40 40 40 40 60 60 4.8 7.8 350 110 110 110 110 140 140 5.0 8.3 650 ns ns ns ns ns ns V V ns 1.45 0.65 0.6 4 9 V A 2.75 2.65 2.85 2.75 2.95 2.9 V V VISP - VISN Rail to Rail Common Mode Input 32 43 60 2 54 250 mV nA mV Note 1: Specifications to -40C are guaranteed by design, characterization and correlation with statistical process control. Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 3 PIN DESCRIPTION NAME 1 2 3 4 5 FUNCTION N/C ENABLE ISP ISN VFB PIN NUMBER No Connection TTL compatible input with internal 4uA pullup. Floating or Venable> 1.5V will enable the part, Venable < 0.65V disables part. Current Sense Positive Input: Rail to Rail Input for Over-Current Detection, 43mV threshold with 10s (typ) response time. Current Sense Negative Input: Rail to Rail input for Over-Current Detection. Feedback Voltage Pin: Inverting input of the error amplifier and serves as the output voltage feedback point for the buck converter. The output voltage is sensed and can be adjusted through an external resistor divider. Error Amplifier Compensation Pin: A lead lag network is typically connected to this pin to compensate the feedback loop. This pin is clamped by the SS voltage and is limited to 2.8V maximum. Soft Start Programming Pin: This pin sources 50A on start-up. A 0.01F to 1F capacitor on this pin is typically enough capacitance to soft start a power supply. In addition, hiccup mode timing is controlled by this pin through the 5A discharge current. The SS voltage is clamped to 2.7V maximum. Frequency Programming Pin: A resistor to ground is used to program frequency. Typical values - 18,700, 300kHz; 10,200, 500kHz. Programming Pin: PROG = GND; MODE = NFET/CONTINOUS PROG = 68k to GND; MODE = NFET/DISCONTINOUS PROG = VCC; MODE = PFET/CONTINOUS PROG = 68k to VCC; MODE = PFET/DISCONTINOUS I.C. Supply Pin: ESD structures also hooked to this pin. Properly bypass this pin to PGND with a low ESL/ESR ceramic capacitor. Synchronous FET Driver: 1nF/20ns typical drive capability. Power Ground Pin: Used for Power Stage. Connect Directly to GND at I.C. pins for optimal performance. Ground Pin: Main ground pin for I.C. Switch Node Reference: High side MOSFET driver reference. Can also be tied to GND for low voltage applications. HIgh Side MOSFET Driver: Can be NFET or PFET depending on Program Mode. 1nF/20ns typical drive capability. Maximum voltage rating is referenced to SWN. High Side Driver Supply Pin. When VBST is less than VBST OK Threshold, GL is forced to turn on for at least 300ns. This is intended for enough time to charge the BST capacitor. 6 COMP 7 SS 8 9 ROSC PROG 10 11 12 13 14 15 VCC GL PGND GND SWN GH 16 BST Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 4 BLOCK DIAGRAM SS 2V + - VFB 3% Low ENABLE VFB 3% +- + + RESET Dominant Window Comparator Logic ON 100% Continuous/ Discontinuous NFET/PFET OFF 100% Program Logic 9 PROG ENABLE 2 Reference 1.25V 3% -+ VFB GND 13 SS VFB 5 16 BST GM Error Amplifier + - + PWM Latch R Q S QPWM Driver Logic 15 GH Synchronous Driver 14 SWN 11 GL COMP 6 VCC 10 0.65V 12 PGND 8 ROSC ICHARGE 2.85 VON 2.75 VOFF ISP 3 ISN 4 UVLO 1V RAMP F (kHz) = 5.7E6/ROSC () Set Dominant Fault Latch S + OVC + x 10 + 10s 430mV Q FAULT R - Soft Start & Hiccup Logic TOFF + + Zero crossing detect 250mV 7 SS APPLICATION SCHEMATIC NMOS High Side Drive PROG = GND NC ENABLE ENABLE ISP ISN VFB COMP RZ 15k CP 100pF CZ 4.7nF CSS 0.33F SS ROSC ROSC 18.7k (R) MBR0530 CB 1F QT 3.3V VIN CIN 330F x 2 CS 39nF 1.9V 1A to 8A VOUT BST GH SWN GND CBST 1F RS 22.1k L1 2.5H SP6120B PGND GL VCC PROG CVCC 2.2F RI 10k VIN QB DS COUT 470F x 3 RF 5.23k Figure 1. Schematic 3.3V to 1.9V Power Supply QT, QB = FAIRCHILD FDS6690A L1 = PANASONIC ETQP6F2R5SFA DS = STMICROELECTRONICS STPS2L25U Date: 5/25/04 CIN = SANYO 6TPB330M COUT = SANYO 4TPB470M SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 5 Typical Performance Characteristics Refer to circuit in Figure 1 with VIN = 3.3V; VOUT = 1.9V, ROSC = 18.7k, and TAMB = +25C unless otherwise noted. 100 1.925 1.920 90 1.915 1.910 Efficiency (%) VOUT (V) 80 1.905 1.900 1.895 1.890 70 60 1.885 1.880 50 0 2 4 6 8 10 Output Current (A) 1.875 0 1 2 3 4 5 Load Current (A) Figure 2. Efficiency vs. Output Current Figure 3. Load Regulation VOUT VOUT Gate High Gate High IOUT(1A/div) IOUT(5A/div) Figure 4. Load Step Response: 0.4A to 2A Figure 5. Load Step Response: 0.4A to 7A VOUT VOUT VIN VIN Soft Start Soft Start IIN (1A/div) IOUT (5A/div) Figure 6. Start-Up Response: 5A Load Figure 7. Overcurrent: 9A Load Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 6 Typical Performance Characteristics Unless otherwise specified: VCC = BST = ENABLE = 3.3V, ROSC = 18.7k, CCOMP = 0.1F, CSS = 0.1F, CGH = CGL = 3.3nF, VFB = 1.25V, ISP = ISN = 1.25V, SWN = GND = PGND = 0V, TAMB = 25C. 0.30 48 0.20 1.25VREF (%) 46 44 42 Overcurrent (mV) 0.10 0.00 40 38 -40 -15 10 35 Temperature (C) 60 85 -0.10 -0.20 -40 -15 10 35 Temperature (C) 60 85 Figure 8. Error Amplifier Reference vs. Temperature Figure 9. Overcurrent Comparator Threshold Voltage vs. Temperature -44 5.25 5.20 -45 SS Discharge (A) SS Charge (A) 5.15 5.10 -46 5.05 -47 -40 -15 10 35 Temperature (C) 60 85 5.00 -40 -15 10 35 Temperature (C) 60 85 Figure 10. SS Charge Current vs. Temperature with VSS = 1.5V Figure 11. SS Discharge Current vs. Temperature with VSS = 1.5V 3.6 -2.2 VFB High (% VREF) 3.4 VFB Low (% VREF) -2.4 3.2 -2.6 3.0 -2.8 2.8 -3.0 2.6 -40 -15 10 35 60 85 -3.2 -40 -15 10 35 60 85 Temperature (C) Temperature (C) Figure 12. VFB 3% High Comparator vs. Temperature Figure 13. VFB 3% Low Comparator vs. Temperature Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 7 Typical Performance Characteristics Unless otherwise specified: VCC = BST = ENABLE = 3.3V, ROSC = 18.7k, CCOMP = 0.1F, CSS = 0.1F, CGH = CGL = 3.3nF, VFB = 1.25V, ISP = ISN = 1.25V, SWN = GND = PGND = 0V, TAMB = 25C. 2.900 2.850 2.875 VCC Start (V) VCC Stop (V) 2.825 2.850 2.800 2.825 2.775 2.800 -40 -15 10 35 Temperature (C) 60 85 2.750 -40 -15 10 35 Temperature (C) 60 85 Figure 14. VCC Start Threshold vs. Temperature Figure 15. VCC Stop Threshold vs. Temperature 302 800 700 Frequency (kHz) Frequency (kHz) -40 -15 10 35 Temperature (C) 60 85 301 600 500 400 300 300 299 298 200 5 10 15 20 ROSC (k) 25 30 Figure 16. Oscillator Frequency vs. Temperature Figure 17. Oscillator Frequency vs. ROSC with VCC = 5V and CGH = CGL = Open. THEORY OF OPERATION General Overview The SP6120HV is a constant frequency, voltage mode PWM controller for low voltage, DC/DC step down converters. It has a main loop where an external resistor (ROSC) sets the frequency and the driver is controlled by the comparison of an error amp output (COMP) and a 1V ramp signal. The error amp has a transconductance of 600S, an output impedance of 3 M, an internal pole at 2 MHz and a 1.25V reference input. Although the main control loop is capable of 0% and 100% duty cycle, its response time is limited by the external component selection. Therefore, a secondary loop, including a window comparator positioned 3% above and below the reference, has been added to insure fast response to line and load transients. A unique "Ripple & Frequency Date: 5/25/04 Independent" algorithm, added to the secondary loop, insures that the window comparator does not interfere with the main loop during normal operation. In addition to receiving driver commands from the main and secondary loops, the Driver Logic is also controlled by the Programming Logic, Fault Logic and Zero Crossing Comparator. The Programming Logic tells the Driver Logic whether the controller is using a PFET or NFET high side driver as well as whether the controller is operating in continuous or discontinuous mode. The Fault Logic holds the high and low side drivers off if VCC dips below 2.75V, if an over current condition exists, or if the part is disabled through the ENABLE pin. The Zero Crossing Comparator turns the lower driver off (c) Copyright 2004 Sipex Corporation SP6120HV Low Voltage, Synchronous Buck Controller 8 General Overview: continued if the conduction current reaches zero and the Driver Logic has made an attempt to turn the lower driver on and the Programming Logic is set for discontinuous mode. Lastly, the 4 drivers have internal gate non-overlap circuitry and are designed to drive MOSFETs associated with converter designs in the 5A to 10A range. Typically the high side driver is referenced to the SWN pin; further improving the efficiency and performance of the converter. ENABLE on, the BST pin may not be high enough to fully enhance the switch. To prevent this operation, SP6120HV monitors the BST pin voltage in reference to the VCC voltage. When the BST pin voltage is less than VBST OK threshold, the controller forces the GL to turn on for MINIMUM GL ON at the end of the switching cycle. This provides enough time to recharge the CBST and ensures the proper operation of the bootstrap circuit. UVLO Low quiescent mode or "Sleep Mode" is initiated by pulling the ENABLE pin below 650mV. The ENABLE pin has an internal 4A pull-up current and does not require any external interface for normal operation. If the ENABLE pin is driven from a voltage source, the voltage must be above 1.45V in order to guarantee proper "awake" operation. Assuming that VCC is above 2.85V, the SP6120HV transitions from "Sleep Mode" to "Awake Mode" in about 20s to 30s and from "Awake Mode" to "Sleep Mode" in a few microseconds. SP6120HV quiescent current in sleep mode is 20A maximum. During Sleep Mode, the high side and low side MOSFETs are turned off and the COMP and SS pins are held low. Bootstrap Circuit Assuming that the ENABLE pin is either pulled high or floating, the voltage on the VCC pin then determines operation of the SP6120HV. As VCC rises, the UVLO block monitors VCC and keeps the high side and low side MOSFETs off and the COMP and SS pins low until VCC reaches 2.85V. If no faults are present, the SP6120HV will initiate a soft start when VCC exceeds 2.85V. Hysteresis (about 100mV) in the UVLO comparator provides noise immunity at start-up. Soft Start When SP6120HV is programmed to drive a high side N channel MOSFET, a bootstrap circuit is required to generate a voltage higher than VIN to fully enhance the top MOSFET. A typical bootstrap only requires a capacitor and diode shown as CBST and DBST in the application circuit on the front page. When the bottom MOSFET QB is turned on, DBST is forward biased and charges the CBST close to VIN. When the top MOSFET turn on, the switch node swings to the VIN voltage. Now the voltage at the BST pin is 2*VIN and DBST is reverse biased. The BST pin voltage powers the high side MOSFET driver, and thus the GH output goes up to 2*VIN to provide a VDS equal to VIN. Under certain conditions, the bottom MOSFET may not turn on long enough to replenish CBST voltage. Therefore, when the top MOSFET turns Date: 5/25/04 (see figures on next page) Soft start is required on step-down controllers to prevent excess inrush current through the power train during start-up. Typically this is managed by sourcing a controlled current into a programming capacitor (on the SS pin) and then using the voltage across this capacitor to slowly ramp up either the error amp reference or the error amp output (COMP). The control loop creates narrow width driver pulses while the output voltage is low and allows these pulses to increase to their steady-state duty cycle as the output voltage increases to its regulated value. As a result of controlling the inductor volt*second product during start-up, inrush current is also controlled. The presence of the output capacitor creates extra current draw during start-up. Simply stated, dVOUT/dt requires an average sustained current in the output capacitor and this current must be considered while calculating peak inrush current and over current thresholds. Since the SP6120HV ramps up the error amp reference voltage, an expression for the output capacitor current can be written as: ICOUT = (COUT/CSS) * (VOUT/1.25) * 50A SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 9 As the figure shows, the SS voltage controls a variety of signals. First, provided all the external fault conditions are removed, the fault latch is reset and the SS cap begins to charge. When the SS voltage reaches around 0.3V, the error amp reference begins to track the SS voltage while maintaining the 0.3V differential. As the SS voltage reaches 0.7V, the driver begins to switch the high side and low side MOSFETs with narrow pulses in an effort to keep the converter output regulated. As the error amp reference ramps upward, the driver pulses widen until a steady state value is reached. The "bump" in the inductor current transfer curve is indicative of excess charge current incurred due to the finite propagation delay of the controller. When the SS voltage reaches 2.0V, the secondary loop including the 3% window comparator is enabled. Lastly, the SS voltage is clamped at 2.4V, ending the soft start charge cycle. 2.4V 2.0V Hiccup Mode When the converter enters a fault mode, the driver holds the high side and low side MOSFETs off for a finite period of time. Provided the part is enabled, this time is set by the discharge of the SS capacitor. The discharge time is roughly 10 times the charge interval thereby giving the power supply plenty of time to cool during an over current fault. The driver off-time is predominantly determined by the discharge time. Restart will occur just like a normal soft start cycle. However, if a fault occurs during the soft start charge cycle, the FAULT latch is immediately set, turning off the high side and low side MOSFETs. The MOSFETs remain off during the remainder of the charge cycle and subsequent discharge cycle of the SS capacitor. Again, provided there are no external fault conditions, the FAULT latch will be reset when the SS voltage reaches 250 mV. Over Current Protection SS Voltage 0.7V 0.25V 0V dVSS/dt = 50A/CSS Error Amplifier Reference 1.25V Voltage VOUT = V(Eamp REF)* (1+RF/RI) 0V ILOAD Inductor Current The SP6120HV over current protection scheme is designed to take advantage of three popular detection schemes: Sense Resistor, Trace Resistor or Inductor Sense. Because the detection threshold is only 43mV, both trace resistor and inductor sense become attractive protection schemes. The inductor sense scheme adds no additional dc loss to the converter and is an excellent alternative to Rdson based schemes; 43mV 0V V(VCC) V(ISP) - V(ISN) FAULT Reset Voltage 0V 0V 2.4V 2.0V V(VCC) SS Voltage 250mV 0V SWN Voltage 0V V(VCC) V(VCC) FAULT Voltage 3% Low Enable Voltage 0V 0V TIME Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 10 Over Current Protection: continued providing continuous current sensing and flexible MOSFET selection. An internal, 10s filter conditions the over current signal from transients generated during load steps. In addition, because the over current inputs, ISP and ISN, are capable of rail to rail operation, the SP6120HV provides excellent over current protection during conditions where VIN approaches VOUT. Zero Crossing Detection Continuous Load Current 0A GH, GL Voltage 0V In some applications, it may be undesirable to have negative conduction current in the inductor. This situation happens when the ripple current in the inductor is higher than the load current. Therefore, the SP6120HV provides an option for "discontinuous" operation. If the Program Logic (see next section) is set for discontinuous mode, then the Driver Logic looks at the Zero Crossing Comparator and the state of the lower gate driver. If the low side MOSFET was "on" and V(ISP)-V(ISN) < 0 then the low side MOSFET is immediately turned off and held off until the high side MOSFET is turned "on". When the high side MOSFET turns "on" , the Driver Logic is reset. The following figures show continuous and discontinuous operation for a converter with an NFET high side MOSFET. Discontinuous vs. Continuous Mode 0V Discontinuous Load Current 0A GH, GL Voltage 0V 0V TIME The discontinuous mode is used when better light load efficiency is desired, for example in portable applications. Additionally, for power supply sequencing in some applications the DCDC converter output is pre-charged to a voltage through a switch at start-up, and discontinuous operation would be required to prevent reverse inductor current from discharging the pre-charge voltage. The continuous mode is preferable for lower noise and EMI applications since the discontinuous mode can cause ringing of the switch node voltage when it turns both switches off. Another example where continuous mode could be required is one where the inductor has an extra winding used for an over-winding regulator and thus continuous conduction is necessary to produce this second output voltage. Program Logic The Program pin (PROG) of the SP6120HV adds a new level of flexibility to the design of DC/DC converters. A 10A current flows either into or out of the Program pin depending on the initial potential presented to the pin. If no resistor is present, the Program Logic simply looks at the potential on the pin, sets the mode to "continuous" and programs NFET or PFET high side drive accordingly. If the 68k resistor is present, the voltage drop across the resistor signals the SP6120HV to put the Driver Logic in "discontinuous" mode. With one pin and a 68k resistor, the SP6120HV can be configured for a variety of operating modes: Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 11 Program Logic: continued PROGRAM LOGIC TRUTH TABLE PROGRAM PIN Short to GND 68 k to GND Short to VCC 68 k to VCC NFET OR PFET NFET NFET PFET PFET MODE Continuous Discontinuous Continuous Discontinous The NFET/PFET programmability is for the high side MOSFET. When designing DC/DC converters, it is not always obvious when to use an NFET with a charge pump or a simple PFET for the high side MOSFET. Often, the controller has to be changed, making performance evaluations difficult. This difficulty is worsened by the limited availability of true low voltage controllers. In addition, by also programming the mode, continuous or discontinuous, switch mode power designs that are successful in bus applications can now find homes in portable applications. Secondary Loop (3% Window Comparator) tor detects whether the output voltage is above or below the regulated value by 3%. Then, a proprietary "Ripple & Frequency Independent" algorithm synchronizes the output of the window comparator with the peak and valley of the inductor current waveform. 3% low detection is synchronized with inductor current peak; 3% high detection is synchronized with the inductor current valley. However, in order to eliminate any additional loops, the current peak and valley are determined by the edges associated with the on-time in the main loop. The set pulse corresponding to the start of an on-time indicates a MAX DC Load Current MIN 0A Output Voltage VOUT DSP, microcontroller and microprocessor applications have very strict supply voltage requirements. In addition, the current requirements to these devices can change drastically. Linear regulators, typically the workhorse for DC/DC step-down, do a great job managing accuracy and transient response at the expense of efficiency. On the other hand, PWM switching regulators typically do a great job managing efficiency at the expense of output ripple and line/load step response. The trick in PWM controller design is to emulate the transient response of the linear regulator. Of course improving transient response should be transparent to the power supply designer. Very often this is not the case. Usually the very circuitry that improves the controllers transient response adversely interferes with the main PWM loop or complicates the board level design of the power converter. The SP6120HV handles line/load transient response in a new way. First, a window comparaDate: 5/25/04 3% High Sync. 3% Low Sync. . Reset Main Loop Set V(VCC) 3% High Latch On 0V V(VCC) 3% Low Latch On 0V TIME SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 12 1.25V Cross. 3% High 3% Low Secondary Loop (3% Window Comparator): continued Output Drivers current valley and the reset pulse corresponding to the end of an on-time indicates a current peak. In effect, the main loop determines the status of the secondary loop. Notice that the output voltage appears to coast toward the regulated value during periods where the main loop would be telling the drivers to switch. It is during this interval that the 3% window comparator has taken control away from the main loop. The main loop regains control only if the output voltage crosses through its regulated value. Also notice where the 3% comparator takes over. The output voltage is considered "high" only if the trough of the ripple is above 3%. The output voltage is considered "low" only if the peak of the ripple is below 3%. By managing the secondary loop in this fashion, the SP6120HV can improve the transient response of high performance power converters without causing strange disturbances in low to moderate performance systems. Driver Logic The driver stage consists of one high side, 4 driver, GH and one low side, 4, NFET driver, GL. As previously stated, the high side driver can be configured to drive a PFET or an NFET high side switch. The high side driver can also be configured as a switch node referenced driver. Due to voltage constraints, this mode is mandatory for 5V, single supply, high side NFET applications. The following figure shows typical driver waveforms for the 5V, high side NFET design. As with all synchronous designs, care must be taken to ensure that the MOSFETs are properly chosen for non-overlap time, peak current capability and efficiency. GATE DRIVER TEST CONDITONS 5V 90% GH (GL) 2V 10% 5V 90% FALL TIME RISE TIME 2V GH (GL) 10% Signals from the PWM latch (QPWM), Fault latch (FAULT), Program Logic, Zero Crossing Comparator, and 3% Window Comparators all flow into the Driver Logic. The following is a truth table for determining the state of the GH and GL voltages for given inputs: DRIVER LOGIC TRUTH TABLE NON-OVERLAP V(BST) GH Voltage 0V V(VCC) FAULT QPWM or 3% COMP NFET/PFET CONT/DISC ZERO CROSS GH GL 1 X N X X 0 0 1 X P X X 1 0 0 1 N X X 1 0 0 1 P X X 0 0 0 0 N C X 0 1 0 0 P C X 1 1 0 0 N D 0 0 1 0 0 P D 0 1 1 0 0 N D 1 0 0 0 0 P D 1 1 0 SWN Voltage GL Voltage 0V V(VCC = VIN) ~0V The QPWM and 3% Comparators are grouped together because 3% Low is the same as QPWM = 1 and 3% High is the same as QPWM = 0. ~V(Diode) V ~2V(VIN) BST Voltage ~V(VIN) TIME Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 13 APPLICATIONS INFORMATION Inductor Selection There are many factors to consider in selecting the inductor including cost, efficiency, size and EMI. In a typical SP6120HV circuit, the inductor is chosen primarily for value, saturation current and DC resistance. Increasing the inductor value will decrease output voltage ripple, but degrade transient response. Low inductor values provide the smallest size, but cause large ripple currents, poor efficiency and more output capacitance to smooth out the larger ripple current. The inductor must also be able to handle the peak current at the switching frequency without saturating, and the copper resistance in the winding should be kept as low as possible to minimize resistive power loss. A good compromise between size, loss and cost is to set the inductor ripple current to be within 20% to 40% of the maximum output current. The switching frequency and the inductor operating point determine the inductor value as follows: duce considerable ac core loss, especially when the inductor value is relatively low and the ripple current is high. Ferrite materials, on the other hand, are more expensive and have an abrupt saturation characteristic with the inductance dropping sharply when the peak design current is exceeded. Nevertheless, they are preferred at high switching frequencies because they present very low core loss and the design only needs to prevent saturation. In general, ferrite or molypermalloy materials are better choice for all but the most cost sensitive applications. The power dissipated in the inductor is equal to the sum of the core and copper losses. To minimize copper losses, the winding resistance needs to be minimized, but this usually comes at the expense of a larger inductor. Core losses have a more significant contribution at low output current where the copper losses are at a minimum, and can typically be neglected at higher output currents where the copper losses dominate. Core loss information is usually available from the magnetic vendor. The copper loss in the inductor can be calculated using the following equation: 2 PL( Cu) = I L ( RMS ) RWINDING L= VOUT (V IN (max) - VOUT ) VIN (max) FS Kr I OUT ( max) where: FS = switching frequency Kr = ratio of the ac inductor ripple current to the maximum output current The peak to peak inductor ripple current is: where IL(RMS) is the RMS inductor current that can be calculated as follows: IL(RMS) = IOUT(max) 1 + 1 3 Output Capacitor Selection I PP = VOUT (VIN (max) - VOUT ) VI N (max) FS L ( IPP IOUT(max) ) 2 Once the required inductor value is selected, the proper selection of core material is based on peak inductor current and efficiency requirements. The core material must be large enough not to saturate at the peak inductor current I PEAK = I OUT (max) + I PP 2 and provide low core loss at the high switching frequency. Low cost powdered iron cores have a gradual saturation characteristic but can intro- The required ESR (Equivalent Series Resistance) and capacitance drive the selection of the type and quantity of the output capacitors. The ESR must be small enough that both the resistive voltage deviation due to a step change in the load current and the output ripple voltage do not exceed the tolerance limits expected on the output voltage. During an output load transient, the output capacitor must supply all the additional current demanded by the load until the SP6120HV adjusts the inductor current to the new value. Therefore the capacitance must be Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 14 large enough so that the output voltage is held up while the inductor current ramps up or down to the value corresponding to the new load current. Additionally, the ESR in the output capacitor causes a step in the output voltage equal to the ESR value multiplied by the change in load current. Because of the fast transient response and inherent 100% and 0% duty cycle capability provided by the SP6120HV when exposed to output load transient, the output capacitor is typically chosen for ESR, not for capacitance value. The output capacitor's ESR, combined with the inductor ripple current, is typically the main contributor to output voltage ripple. The maximum allowable ESR required to maintain a specified output voltage ripple can be calculated by: is a solid electrolytic chip capacitor that has low ESR and high capacitance. For the same ESR value, POSCAP has lower profile compared with tantalum capacitor. Input Capacitor Selection RESR where: VOUT I PP The input capacitor should be selected for ripple current rating, capacitance and voltage rating. The input capacitor must meet the ripple current requirement imposed by the switching current. In continuous conduction mode, the source current of the high-side MOSFET is approximately a square wave of duty cycle VOUT/VIN. Most of this current is supplied by the input bypass capacitors. The RMS value of input capacitor current is determined at the maximum output current and under the assumption that the peak to peak inductor ripple current is low, it is given by: ICIN(rms) = IOUT(max) D(1 - D) The worse case occurs when the duty cycle D is 50% and gives an RMS current value equal to IOUT /2. Select input capacitors with adequate ripple current rating to ensure reliable operation. The power dissipated in the input capacitor is: 2 P = ICIN ( rms ) R ESR( CIN ) CIN VOUT = peak to peak output voltage ripple IPP = peak to peak inductor ripple current The total output ripple is a combination of the ESR and the output capacitance value and can be calculated as follows: VOUT = IPP (1 - D) COUTFS where: ( ) 2 + (IPPRESR)2 This can become a significant part of power losses in a converter and hurt the overall energy transfer efficiency. The input voltage ripple primarily depends on the input capacitor ESR and capacitance. Ignoring the inductor ripple current, the input voltage ripple can be determined by: VIN = I out (max) RE SR (CIN ) + I OUT ( MAX )VOUT (VI N - VOUT ) FS C INV IN 2 FS = switching frequency D = duty cycle COUT = output capacitance value Recommended capacitors that can be used effectively in SP6120HV applications are: lowESR aluminum electrolytic capacitors, OS-CON capacitors that provide a very high performance/ size ratio for electrolytic capacitors and lowESR tantalum capacitors. AVX TPS series and Kemet T510 surface mount capacitors are popular tantalum capacitors that work well in SP6120HV applications. POSCAP from Sanyo The capacitor type suitable for the output capacitors can also be used for the input capacitors. However, exercise extra caution when tantalum capacitors are considered. Tantalum capacitors are known for catastrophic failure when exposed to surge current, and input capacitors Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 15 are prone to such surge current when power supplies are connected `live' to low impedance power sources. Certain tantalum capacitors, such as AVX TPS series, are surge tested. For generic tantalum capacitors, use 2:1 voltage derating to protect the input capacitors from surge fall-out. MOSFET Selection synchronous buck converters of efficiency over 90%, allow no more than 4% power losses for high or low side MOSFETs. For input voltages of 3.3V and 5V, conduction losses often dominate switching losses. Therefore, lowering the RDS(ON) of the MOSFETs always improves efficiency even though it gives rise to higher switching losses due to increased Crss. Top and bottom MOSFETs experience unequal conduction losses if their on time is unequal. For applications running at large or small duty cycle, it makes sense to use different top and bottom MOSFETs. Alternatively, parallel multiple MOSFETs to conduct large duty factor. RDS(ON) varies greatly with the gate driver voltage. The MOSFET vendors often specify RDS(ON) on multiple gate to source voltages (VGS), as well as provide typical curve of RDS(ON) versus VGS. For 5V input, use the RDS(ON) specified at 4.5V VGS. At the time of this publication, vendors, such as Fairchild, Siliconix and International Rectifier, have started to specify RDS(ON) at VGS less than 3V. This has provided necessary data for designs in which these MOSFETs are driven with 3.3V and made it possible to use SP6120HV in 3.3V only applications. Thermal calculation must be conducted to ensure the MOSFET can handle the maximum load current. The junction temperature of the MOSFET, determined as follows, must stay below the maximum rating. The losses associated with MOSFETs can be divided into conduction and switching losses. Conduction losses are related to the on resistance of MOSFETs, and increase with the load current. Switching losses occur on each on/off transition when the MOSFETs experience both high current and voltage. Since the bottom MOSFET switches current from/to a paralleled diode (either its own body diode or a Schottky diode), the voltage across the MOSFET is no more than 1V during switching transition. As a result, its switching losses are negligible. The switching losses are difficult to quantify due to all the variables affecting turn on/off time. However, the following equation provides an approximation on the switching losses associated with the top MOSFET driven by SP6120HV. PSH (max) = 12C rssV IN (max) I OUT (max) FS where Crss = reverse transfer capacitance of the top MOSFET Switching losses need to be taken into account for high switching frequency, since they are directly proportional to switching frequency. The conduction losses associated with top and bottom MOSFETs are determined by: TJ ( max) = T A (max) + where PMOSFET (max) R JA PCH (max) = RDS (ON ) I OUT (max) D PCL(max) = R DS (ON ) I OUT (max) (1 - D) where PCH(max) = conduction losses of the high side MOSFET PCL(max) = conduction losses of the low side MOSFET RDS(ON) = drain to source on resistance. The total power losses of the top MOSFET are the sum of switching and conduction losses. For Date: 5/25/04 2 2 TA(max) = maximum ambient temperature PMOSFET(max) = maximum power dissipation of the MOSFET RJA = junction to ambient thermal resistance. RJA of the device depends greatly on the board layout, as well as device package. Significant thermal improvement can be achieved in the maximum power dissipation through the proper design of copper mounting pads on the circuit board. For example, in a SO-8 package, placing (c) Copyright 2004 Sipex Corporation SP6120HV Low Voltage, Synchronous Buck Controller 16 two 0.04 square inches copper pad directly under the package, without occupying additional board space, can increase the maximum power from approximately 1 to 1.2W. For DPAK package, enlarging the tap mounting pad to 1 square inches reduces the RJA from 96C/W to 40C/W. Schottky Diode Selection Loop Compensation Design The goal of loop compensation is to manipulate loop frequency response such that its gain crosses over 0db at a slope of -20db/dec. The SP6120HV has a transconductance error amplifier and requires the compensation network to be connected between the COMP pin and ground, as shown in Figure 18. The first step of compensation design is to pick the loop crossover frequency. High crossover frequency is desirable for fast transient response, but often jeopardize the system stability. Since the SP6120HV is equipped with 3% window comparator that takes over the control loop on transient, the crossover frequency can be selected primarily to the satisfaction of system stability. Crossover frequency should be higher than the ESR zero but less than 1/5 of the switching frequency. The ESR zero is contributed by the ESR associated with the output capacitors and can be determined by: 1 fZ(ESR) = 2COUTRESR Crossover frequency of 20kHz is a sound first try if low ESR tantalum capacitors or poscaps are used at the output. The next step is to calculate the complex conjugate poles contributed by the LC output filter, 1 fP(LC) = 2 LCOUT The open loop gain of the whole system can be divided into the gain of the error amplifier, PWM modulator, buck converter, and feedback resistor divider. In order to crossover at the selected frequency fco, the gain of the error amplifier has to compensate for the attenuation caused by the rest of the loop at this frequency. In the RC network shown in Figure 18, the product of R1 and the error amplifier transconductance determines this gain. Therefore, R1 can be determined from the following equation that takes into account the typical error amplifier transconductance, reference voltage and PWM ramp built into the SP6120HV. R1 = 1300VOUT fCO fZ(ESR) VIN fP(LC)2 When paralleled with the bottom MOSFET, an optional Schottky diode can improve efficiency and reduce noises. Without this Schottky diode, the body diode of the bottom MOSFET conducts the current during the non-overlap time when both MOSFETs are turned off. Unfortunately, the body diode has high forward voltage and reverse recovery problem. The reverse recovery of the body diode causes additional switching noises when the diode turns off. The Schottky diode alleviates these noises and additionally improves efficiency thanks to its low forward voltage. The reverse voltage across the diode is equal to input voltage, and the diode must be able to handle the peak current equal to the maximum load current. The power dissipation of the Schottky diode is determined by PDIODE = 2VFIOUTTNOLFS where TNOL = non-overlap time between GH and GL. VF = forward voltage of the Schottky diode. COMP (R) R1 C2 C1 SP6120B Figure 18. The RC network connected to the COMP pin provides a pole and a zero to control loop. Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 17 In Figure 18, R1 and C1 provides a zero fZ1 which needs to be placed at or below fP(LC). If fZ1 is made equal to fP(LC) for convenience, the value of C1 can be calculated as C1 = 1 2fP(LC)R1 Current Sense The optional C2 generates a pole fP1 with R1 to cut down high frequency noise for reliable operation. This pole should be placed one decade higher than the crossover frequency to avoid erosion of phase margin. Therefore, the value of the C2 can be derived from C2 = 1 20fCOR1 Figure 19 illustrates the overall loop frequency response and frequency of each pole and zero. To fine-tune the compensation, it is necessary to physically measure the frequency response using a network analyzer. Gain The SP6120HV allows sensing current using the inductor, PCB trace or current-sense resistor. Inductor-sense utilizes the voltage drop across the ESR of the inductor, while PCB trace and current-sense resistor introduce additional resistance in series with the inductor. The resistance of the sense element determines the overcurrent protection threshold as follows, ILIM = 43mV RSEN RSEN = current-sense resistance which can be implemented as ESR of the inductor, trace or discrete resistor. The maximum power dissipation on the currentsense element is: PSEN = I OUT ( max) R SEN For the inductor-sense scheme shown in the application circuit, RS and CS are used to replicate the signal across the ESR of the inductor. RS and CS can be looked at as a low pass filter whose output represents the DC differential voltage between the switch node and the output. At steady state, this voltage happens to be the output current times the ESR of the inductor. In addition, if the following relationship is satisfied, L =RC SS ESR the output of the RsCs filter represents the exact voltage across the ESR, including the ripple. Since the SP6120HV's hiccup overcurrent protection scheme is intended to safeguard sustained overload conditions, the DC portion of the current signal is more of interest. Therefore, designing the RSCS time constant higher than L/ ESR provides reliable current sense against any premature triggering due to noise or any transient conditions. Pick Rs between 10k and 100k, and Cs can be determined by: 1 CS = 2 L ESR RS Here the time constant of RSCS is twice the value of L/ESR. In some applications, it may be desirable to extend the current sense capability of a given 2 -20db/dec -40db/dec Loop -20db/dec f -20db/dec Error Amplifier -20db/dec f fZ1 fP(LC) fZ(ESR) fCO fP1 Figure 19. Frequency response of a stable system and its error amplifier. Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 18 RSEN element (usually the inductor ESR) beyond the limit set by the 43mV threshold. A straight forward way to do this would be to add a resistor RS2 in parallel with CS, creating a voltage divider with RS. This changes the relationship with RS and CS to be 1 CS = 2 L ESR RS //RS2 Using a voltage divider across the inductor, the new relationship becomes: 43mV RS + RS2 ILIM = ESR RS2 To calculate RS2, the formula becomes RS2 = RS ISP ISN RS2 RS CS VOUT L SWN ESR Figure 20: Current Sensing Output Voltage Programming As shown in Figure 21(A), the voltage divider connecting to the VFB pin programs the output voltage according to VOUT = 1.25( 1 + R1 ) R2 /( ILIMESR -1 43mV ) where 1.25V is the internal reference voltage. Select R2 in the range of 10k to 100k, and R1 can be calculated using R1 = R2(VOUT - 1.25) 1.25 VOUT > 1.25V For output voltage less than 1.25V, a simple circuit shown in Figure 21(B) can be used in which VREF is an external voltage reference V use 1.25V greater than 1.25V. For simplicity,OUT < the same VREF resistor value for R1 and R2, then R3 is determined as follows, (R) (R) R1 R3 = SP6120B VFB SP6120B VFB (VREF - 1.25)R1 2.5 - VOUT R3 R1 R2 R2 A B Figures 21(A), a voltage divider connected to the VFB pin programs the output voltageand 21(B), a simple circuit using one external voltage reference programs the output voltages to less than 1.25V. Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 19 Layout Guideline PCB layout plays a critical role in proper function of the converters and EMI control. In switch mode power supplies, loops carrying high di/dt give rise to EMI and ground bounces. The goal of layout optimization is to identify these loops and minimize them. It is also crucial on how to connect the controller ground such that its operation is not affected by noise. The following guideline should be followed to ensure proper operation. 1. A ground plane is recommended for minimizing noises, copper losses and maximizing heat dissipation. 2. Connect the ground of feedback divider, compensation components, oscillator resistor and soft-start capacitor to the GND pin of the IC. Then connect this pin as close as possible to the ground of the output capacitor. 3. The VCC bypass capacitor should be right next to the Vcc and GND pin. 4. The traces connecting to feedback resistor and current sense components should be short and far away from the switch node, and switching components. 5. Connect the PGND pin close to the source of the bottom MOSFET, and the SWN pin to the source of the top MOSFET. Minimize the trace between GH/GL and the gates of the MOSFETs. All of these requirements reduce the impedance driving the MOSFETs. This is especially important for the bottom MOSFET that tends to turn on through its miller capacitor when the switch node swings high. 6. Minimize the loop composed of input capacitors, top/bottom MOSFETs and Schottky diode, This loop carries high di/dt current. Also increase the trace width to reduce copper losses. 7. Maximize the trace width of the loop connecting the inductor, output capacitors, Schottky diode and bottom MOSFET. Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 20 PACKAGE: PLASTIC THIN SMALL OUTLINE (TSSOP) E2 E1 D A O e B A1 L DIMENSIONS in inches (mm) Minimum/Maximum A A1 B D E1 e E2 L O 16-PIN - /0.043 (- /1.10) 0.002/0.006 (0.05/0.15) 0.007/0.012 (0.19/0.30) 0.193/0.201 (4.90/5.10) 0.169/0.177 (4.30/4.50) 0.026 BSC (0.65 BSC) 0.126 BSC (3.20 BSC) 0.020/0.030 (0.50/0.75) 0/8 Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 21 ORDERING INFORMATION Model Operating Temperature Range Package Type SP6120HVCY .......................................... 0C to +70C ........................................ 16-Pin TSSOP SP6120HVCY/TR .................................... 0C to +70C ........................................ 16-Pin TSSOP SP6120HVEY ......................................... -40C to +85C ...................................... 16-Pin TSSOP SP6120HVEY/TR .................................... -40C to +85C ...................................... 16-Pin TSSOP Available in lead free packaging. To order add "-L" suffix to part number. Example: SP6120HVEY/TR = standard; SP6120HVEY-L/TR = lead free /TR = Tape and Reel Pack quantity is 1,500 for tsSOP. Corporation SIGNAL PROCESSING EXCELLENCE Sipex Corporation Headquarters and Sales Office 22 Linnell Circle Billerica, MA 01821 TEL: (978) 667-8700 FAX: (978) 670-9001 e-mail: sales@sipex.com Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Date: 5/25/04 SP6120HV Low Voltage, Synchronous Buck Controller (c) Copyright 2004 Sipex Corporation 22 |
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