RC5033 RAYTHEON | Alldatasheet

Document overview

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Technical content

Features

  • >85% Efficiency
  • 350uA quiescent current in shutdown
  • Fast transient response
  • Soft control power-up
  • Over-V oltage Protection
  • Output voltage range from 2.0V to 3.6V
  • Factory trimmed low TC reference voltage
  • Adjustable oscillator frequency
  • Drives N-Channel MOSFETs
  • 16 pin SOIC package

Applications

  • 3.3V power supply for Pentium™ based CPU motherboards
  • 3.45V power supply for AMD-K5™ CPU
  • 2.5V or 3.6V power supply for PowerPC™

Description

The RC5033 is a synchronous mode DC-DC controller IC dedicated to providing a 5V to 2.0V up to 3.6V conversion for various types of CPU power . It can be configured in both the synchronous and non-synchronous modes and with the proper applications circuitry can be used to deliver load cur- rent greater than 10 Amps. The RC5033 is designed to oper- ate in a standard PWM control mode under heavy load conditions and as a PFM controller in light load conditions. Its highly accurate low TC reference eliminates the need for precision external components in order to achieve tight tolerance voltage regulation. Through the use of external resistors, the RC5033 can generate accurate output voltages from 2.0V up to 3.6V . An integrated Over-V oltage protection function constantly monitors the output voltage and shuts down the power to the CPU in the event of a out-of- tolerance voltage situation, thereby protecting the CPU. The programmable oscillator can operate from 200KHz to greater than 1MHz to provide for flexibility in choosing external components such as inductors, capacitors, and Power MOSFETs. Block Diagram DIGITAL CONTROL VREF 65-5033-01 OSC VREF – I– – I VIN VO RC5033 Adjustable Synchronous DC-DC Converter Rev. 0.9.5

PRODUCT SPECIFICATION RC5033 Preliminary Information Pin Assignments Pin Definitions Note: 1. See voltage adjust table for function Output Voltage Selection Table Note: 1. See Figure 3 for resistor connection. 2. Indicated short pins together. Pin Name Pin Number Pin Function Description On/Off 1 A low level on this pin will power down; tie to VCCD if not used. IFB 2 Current Feedback Input. VFB 3 Voltage Feedback Input. VCCA 4 Analog VCC. VCCD 5 Digital VCC. VCCP 6 VCC for synchronous FET output drivers. LODRV 7 Synchronous FET driver output. GNDP 8 Power ground for high current drivers. HIDRV 9 High side FET driver output. VCCQP 10 VCC for High side FET output driver ADJ1 11 VREF adjust pin. ADJ2 12 VREF adjust pin. GNDD 13 Digital ground. ADJ3 14 VREF adjust pin. GNDA 15 Analog ground. CEXT 16 External capacitor for setting oscillator frequency. VOUT ADJ1 ADJ2 ADJ3 3.5V N/C N/C N/C 3.35V N/C 2 2 3.3V N/C 2.9V 3.9K N/C N/C 2.5V 2K N/C N/C 2.0V W N/C N/C CEXT GNDA ADJ3 GNDD ADJ2 ADJ1 HIDRV VCCQP ON/OFF IFB VFB VCCA VCCD VCCP GNDP LODRV 65-5033-02

RC5033 PRODUCT SPECIFICATION Preliminary Information Absolute Maximum Ratings (beyond which the device may be damaged) Note: 1. Functional operation under any of these conditions is NOT implied. Operating Conditions CC = 5V, fosc = 650 KHz, and T A = +25˚C unless otherwise noted) Notes: 1. Functional operation under any of these conditions is not implied. Performance is guaranteed only if Operating Conditions are not exceeded. 2. Output Voltage accuracy, Tempco, load regulation, ripple, and transient performance determine the Cumulative Accuracy. Parameter Conditions Min Typ Max Units V CCP Driver Voltage 13 V V CCQP High Driver Supply 13 V T J Junction Temperature 175 C T A Ambient Operating Temperature 0 70 C T S Storage Temperature -65 150 C T L Lead Soldering Temperature (10 seconds) 300 C Parameter Conditions Min Typ Max Units V CC Supply Voltage 4.5 5 7 V V CCP Low Driver Supply 4.5 5 12 V V CCQP High Driver Supply 9 13 V V IH Input Voltage, Logic HIGH 2 V V IL Input Voltage, Logic LOW 0.8 V Parameter Conditions Min Typ Max Units V O Output Voltage Nominal, Pin 12 conn. Pin 14, T A = 0–70 C 3.135 3.3 3.465 V I O Output Current See Figure for application 5 A Vref Acc Voltage Reference Accuracy 1 % VTC Output Voltage Tempco -40 ppm LDR Load Regulation 0.5 to 7A 1 %V o LIR Line Regulation V CC 5% 0.14 %V o V R Output Voltage Ripple 30 mV Cum Acc Cumulative Accuracy T A = 0–70 C 3 % Eff Efficiency Synchronous mode > 1A 80 85 % Iodr Output Driver I Open Loop 0.5 0.7 A PD Power Dissipation 0.1 0.2 W

PRODUCT SPECIFICATION RC5033 Preliminary Information A = +25˚C unless otherwise noted) Note: 1. Guaranteed by design, not 100% total. Parameter Conditions Min Typ Max Units Tr Response Time Il=0.5A to 5.5A 10 m s Fosc Oscillator Range 0.2 1.2 MHz Osc Acc Fosc Accuracy 10 % Dtc Max Duty Cycle PWM mode 90 95 % Dtcm Min Duty Cycle PFM mode 100 ns Imax Imax Threshold 30 mV Iscp Short Circuit Prot 80 mV Ovp Over Voltage Prot 20 %Vo Trimax Response to Imax 15 30 ns Tssp Soft start response 10 m s

RC5033 PRODUCT SPECIFICATION Preliminary Information Typical Operating Characteristics Note: 1. Data taken with circuit of Figure 1. Efficiency vs Output Current (FOSC = 400 KHz) Efficiency (%) Output Current (A) 100 0 2 4 6 Efficiency vs Output Current (FOSC = 650 KHz) Efficiency (%) Output Current (A) 100 0 2 4 6 Efficiency vs Output Current (FOSC = 1 MHz) Efficiency (%) Output Current (A) 100 0 2 4 6 Load Regulation (FOSC = 1 MHz) VOUT Output Current (A) Output Current (A) 3.36 3.35 3.34 3.33 3.32 3.31 3.3 0 2 4 6 65-5033-03 Load Regulation (FOSC = 650 KHz) VOUT 3.37 3.36 3.35 3.34 3.33 3.32 3.31 3.3 0 2 4 6 8 Output Current (A) Load Regulation (FOSC = 400 KHz) VOUT 3.38 3.37 3.36 3.35 3.34 3.33 3.32 3.31 3.3 0 2 4 6 8

PRODUCT SPECIFICATION RC5033 Preliminary Information Typical Operating Characteristics (continued) Line Regulation vs. Output Load (FOSC = 400 KHz) Line Reg (%) Output Current (A) 0.3 0.25 0.2 0.15 0.1 0.05 0 2 4 6 8 Reference Tempco VREF Temp 3.5 3.495 3.49 3.485 3.48 3.475 3.47 0 50 100 Line Regulation vs. Output Load (FOSC = 650 KHz) Line Reg (%) Output Current (A) 0.3 0.25 0.2 0.15 0.1 0.05 0 2 4 6 8 Line Regulation vs. Output Load (FOSC = 1 MHz) Line Reg (%) Output Current (A) 0.25 0.2 0.15 0.1 0.05 -0.05 -0.1 65-5033-04 0 2 4 6 8 CEXT vs. Oscillator Frequency CEXT (pF) Frequency (Hz) 200 150 100 0 4 8

Figure 1. Standard 7A Application Schematic

Table 1. Components for RC5033 Table 2. Alternate Components Selection

PRODUCT SPECIFICATION RC5033 Preliminary Information Dual Power Supply Application In some CPU power applications there may be a need for a split voltage converter. The circuit in Figure 4 addresses this need with only minimal component count. The basic RC5033 non-synchronous DC-DC converter is augmented with an op-amp, a power MOSFET , and some 1% resistors to provide a dual power supply with one voltage set to 3.3V and the other, slaved off of the 3.3V, set to 2.9V. In this con- figuration, the RC5033 converts the 5V to 3..3V with high efficiency. By using the op-amp, power FET, and the resis- tors, a low-dropout linear regulator is realized that can be run off of the 3.3V. The 2.9V linear regulator has a relatively high efficiency just due to the fact that the ratio of 2.9V/3.3V is close to 88%. The power FET is a low Rdson n-channel MOSFET , and thus it is reasonably inexpensive. The opamp can be a garden variety, though the input bias current and output slew rate need to be considered to optimize accuracy and transient response. The overall efficiency of this power supply system will very much depend upon the percentage of power used on each power output. Overall, the efficiency of this system will be lower than if both supplies were imple- mented as switchers; howe ver, the added savings of the part count reduction may more than compensate for the overall lower efficiency. Standard Application Circuit The circuit shown in Figure 1 along with its components and values has been designed as representative of the typical application involving the RC5033 for a Pentium™ CPU. Use of the standard application circuit will deliver the perfor- mance curves shown under the Typical Operating Character- istics section of the data sheet. Many users will want to develop their own DC-DC con verter solution that is uniquely tailored to a specific application requirement. In that case, the users should review the detailed information in the Design Procedure and Applications Information section of the data sheet. Detailed Description The RC5033 is a programmable voltage synchronous con- troller. When designed around the appropriate external com- ponents, it can be configured to deliver more than 10A of output current. During heavy loading conditions the RC5033 functions as a current-mode PWM step down regulator. Under light loading conditions, the regulator functions in the PFM or pulse skipping mode, thereby increasing its effi- ciency under light loads. Applications Discussion VCCP 200µF DS2 EC10QS02 RC5033 C13 4.7µF GND 0.1µF +12V 47pF 12K 88K LM308A– MTD20N03HDL DS1 MBRB1545CT 330µF 65-5033-08 1µF 1.5µH 0.012Ω VO MTD20N03HDL VO2 2.9V 47pF

PRODUCT SPECIFICATION RC5033 Preliminary Information Selecting the Inductor The inductor is one of the most critical components to be selected in the DC-to-DC converter application. The critical parameters are inductance (L), max DC current (Imax), and the coil resistance (Rl). The inductor core material is a criti- cal factor in determining the amount of current that the inductor will be able to handle. As with all engineering designs there are trade- offs for various types of inductor core materials. In general, Ferrites are popular because of their low cost, low EMI, and high frequency (>500kHz) characteristics. Molypermalloy powder (MPP) materials have good saturation characteristics and low EMI with low hysteresis losses; howe ver they tend to be expensive and are more efficiently utilized at frequencies below 400kHz. DC winding resistance is another critical parameter. In general, the DC resistance should be kept as low as possible. The power loss in the DC resistance will degrade the efficiency of the converter by the relationship: Power Loss = (Io)2*Rl. The value of the inductor is a function of the switching fre- quency (Ton) and the maximum inductor current. The max inductor current can be calculated from the relationship: Where: Fo is the desired clock frequency Ton is the max on time of the M1 FET Vd is the forward voltage of the schottky diode D1 Then the inductor value can be calculated with the relationship: Where: Vdson is the voltage across the drain-source of the M1 FET when switched on. (this can be calculated by RDSon * Imax) Current-Sense Resistor The current sense resistor will carry all of the peak current of the inductor. This current will be more than the designed for load current. The RC5033 will begin to limit the output cur- rent to the load by turning off the top-side FET driver when the voltage across the current-sense resistor exceeds 100mV. When this happens the output voltage will temporarily go out of regulation. As the voltage across the resistor becomes larger, the top-side FET will turn off more and more until the current limit value is reached and then the RC5033 will con- tinuously deliver the limit current at a reduced output voltage level. To insure that load transient conditions do not momen- tarily cause deregulation of the output voltage, a 20% margin in the limit voltage is advisable. Thus the resistor should be set by the relationship: R = 100 mV/ Ipeak Where: Ipeak = Imax * 1.33 IM A X 2IL FO T O N V IN V O U T– æ ö 1+ L V IN V D S O N– IM A X Since the value of the sense resistor is generally in the mil- iohm region, care should be taken in the layout of the PCB. Trace resistance can contribute significant errors. The traces to the IFB and VFB pins of the RC5033 should be Kelvin connected to the pads of the current-sense resistor as shown in the sample layout Figure 5. To minimize the influence of noise the two traces should be run next to each other and the pins should be bypassed with a .1uF to GND as close to the device pins as possible. Filter Capacitors Good ripple performance and transient response are func- tions of the filter capacitors. Since the 5V input for a PC motherboard can be located several inches aw ay from the DC-to-DC converter, input capacitance can play an impor- tant role in the load transient response of the RC5033. In general, the higher the input capacitance, the more charge storage is available for improving the current transfer through the top-side FET. A good rule of thumb is that for each watt of output power that you wish to deliver, there should be around 10uF of input capacitance. Low “ESR” capacitors are best suited for this application and can have an influence on the converter’s efficiency. The input capacitor should be placed as close to the drain of the top-side FET as possible to reduce the effect of ringing that can be caused by large trace lengths. The ESR rating of a capacitor is a difficult number to pin down. ESR or Equivalent Series Resistance, is defined at the resonant impedance of that capacitor. Since the capacitor is actually a complex impedance device having resistance, inductance and capacitance, it is quite natural for it to have an associated resonant frequency. As a rule, the lower the ESR, the better suited the capacitor is for use in switching power supply applications. Man y capacitor manufacturers do not supply ESR data. A useful estimate of the ESR can be obtained with the following equation: ESR = Pd/2pfC. Where Pd is the capacitor’s dissipation factor and f is the fre- quency of measure and C is the capacitance in farads. W ith this in mind, calculating the output capacitance cor- rectly is crucial to the performance of the DC-to-DC con- verter. The output capacitor determines the overall loop stability, output voltage ripple, and the transient load response. The calculation uses the following equation: Where: Vr is the desired output ripple voltage Schottky Diode Selection The application circuit diagram shows two schottky diodes, DS1 and DS2. DS1 is used in parallel of M2 in order to pre- vent the lossy body diode in the FET from turning on. DS2 serves a dual purpose. As it is configured, it allows the VCCQP supply pin of the RC5033 to be bootstrapped up to C m F( ) T O N V IN V O U T–( )IM A X V O U T æ ö V r

RC5033 PRODUCT SPECIFICATION Preliminary Information 9V by using the bootstrap capacitor C2. When the lower FET M2 is turned on, one side of the capacitor C2 is connected to GND while the other side of the cap is being charged up through D2 to a voltage that is V in - Vd. When the lower FET turns off and the upper one turns on, the voltage that is supplied to the VCCQP pin is 2Vin - Vd. The voltage then that is applied to the gate of the FET is VCCQP - Vsat, typi- cally around 9V. It is important in the selection of DS1 and DS2 that they have a low forward voltage drop as this directly affects the regulator efficiency. The other job that DS2 performs is that of bootstrapping VCCQP during star- tup. It is possible to cause the output stage to latchup if the VCCQP supply is brought up before the other VCC supplies of the RC5033. It is therefore advisable that DS2 be con- nected even in applications that do not utilize the bootstrap- ping technique for VCCQP . An alternate application could tie the VCCQP supply pin to the +12V power supply in the PC, thus eliminating the need for C2 and forcing the Rdson of M1 even lower by increasing its Vgs. MOSFET Switches The MOSFET switches in the RC5033 applications circuit are N-channel “logic-level” FETs. This means that they will be fully on with a Vgs of 4V. Many manufacturers make logic-level FETs and the trick is to choose the one with the lowest RDSon at the given Imax current level. The value of RDSon directly enters into the efficiency equation as a power loss. Also influencing the efficiency is the gate charge of the FET and the clock frequency of the RC5033. At higher clocking rates the amount of charge needed to be delivered to the FET is going to lower the overall efficiency. In higher current applications, the upper FET can be paralleled to pro- vide greater current capability; howe ver, the lower FET doesn’t necessarily have to be doubled since it is on only a fraction of the time that the upper FET is on. PCB Layout and Grounding As is the case with most analog circuitry, good layout practices are necessary to achieve the optimum in the overall performance of the DC-to-DC converter. In general, it is alw ays a good practice to have a tight layout that attempts to minimize short low inductance wiring to the RC5033. The use of multilayer PCB is recommended. In particular, it is recommended to have a continuos ground plane beneath the circuit, 2oz copper would be preferred in high current applications. As was stated previously, the current-sense resistor, R1, should be located as close to the RC5033 as possible and the IFB and VFB traces should be Kelvin con- nected to the pads of R1. To minimize switching losses and noise, place M1, M2, L and DS2 as close together as possi- ble. Also try to keep the HIDRV and LODR V gate drive sig- nal traces as short as possible. It is recommended that the noisy switching part of the circuit be kept aw ay from the low current pins on the chip such as IFB, VFB, ADJ3, ADJ1, and CEXT . Keep the 0.1uF bypass capacitors as close to the chip pins as possible. All of the ground pins should be connected to the ground plane directly under the chip. A sample layout is provided in Figure 6.

Figure 6. Sample PCB Layout

RC5033 PRODUCT SPECIFICATION Preliminary Information Mec hanical Dimensions – 16-Lead SOIC Package A .093 .104 2.35 2.65 Symbol Inches Min. Max. Min. Max. Millimeters Notes A1 .004 .012 0.10 0.30 .020 0.51B .013 0.33 C .009 .013 0.23 0.32 E .291 .299 7.40 7.60 e .394 .419 10.00 10.65 .010 .020 0.25 0.51 H .050 BSC 1.27 BSC h L .016 .050 0.40 1.27 0° 8° 0° 8° N 16 16 α ccc .004 0.10— — D .398 .413 10.10 10.50 Notes: Dimensioning and tolerancing per ANSI Y14.5M-1982. "D" and "E" do not include mold flash. Mold flash or protrusions shall not exceed .010 inch (0.25mm). "L" is the length of terminal for soldering to a substrate. Terminal numbers are shown for reference only. "C" dimension does not include solder finish thickness. Symbol "N" is the maximum number of terminals. 16 9 1 8 D A A1 – C – ccc C LEAD COPLANARITY SEATING PLANEe B L h x 45° C α E H

PRODUCT SPECIFICATION RC5033 Preliminary Information 10/95 2.5m Stock#DS30005033 © Raytheon Company 1995 The information contained in this data sheet has been carefully compiled; howe ver, it shall not by implication or otherwise become part of the terms and conditions of any subsequent sale. Raytheon’s liability shall be determined solely by its standard terms and conditions of sale. No representation as to application or use or that the circuits are either licensed or free from patent infringement is intended or implied. Raytheon reserves the right to change the circuitry and any other data at any time without notice and assumes no liability for errors. LIFE SUPPORT POLICY: Raytheon’s products are not designed for use in life support applications, wherein a failure or malfunction of the component can reasonably be expected to result in personal injury. The user of Raytheon components in life support applications assumes all risk of such use and indemnifies Raytheon Company against all damages. Raytheon Electronics Semiconductor Division

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Ordering Information

q JA RC5033M 16 SOIC 85 C/W