DC-DC Converters for Microprocessors with Fixed Core Voltage Requirements TM Application Note April 1997 AN9722 Introduction Intersil HIP6006 and HIP6007 Today’s high-performance microprocessors present many challenges to their power source. High power consumption, low bus voltages, and fast load changes are the principal characteristics which have led to the need for a switch-mode DC-DC converter local to the microprocessor. The Intersil HIP6006 and HIP6007 are voltage-mode controllers with many functions needed for high-performance processors. Figure 1 shows a simple block diagram of the HIP6006 and HIP6007. Each contains a high-performance error amplifier, a high-accuracy reference, a programmable free-running oscillator, and overcurrent protection circuitry. The HIP6006 has two MOSFET drivers for use in synchronous-rectified Buck converters. The HIP6007 omits the lower MOSFET driver for standard Buck configurations. A more complete description of the parts can be found in their data sheets [2, 3]. Intel has specified Voltage Regulator Modules (VRMs) for the Pentium Pro and Pentium II microprocessors [1]. These specifications detail the requirements imposed upon the input power source(s) by the Pentium Pro and Pentium II and provide the computer industry with standard DC-DC converter solutions. A common requirement of these and similar processors are decreasing supply voltages as the processor clock frequency increases. The Intersil HIP6002-5 pulse-width modulator (PWM) controllers are targeted specifically for DC-DC converters powering the Pentium Pro, Pentium II, and other highperformance microprocessors with varying core voltage requirements. The HIP6002 and HIP6003 have a 4-bit digital to analog converter (DAC) and the HIP6004-5 have a 5-bit DAC to address the ‘moving target’ processor core voltage. The HIP6006 and HIP6007 use the same basic architecture of the HIP6002-5, but have a reduced feature set. One feature removed is the DAC, which allows the HIP6006 and HIP6007 to be packaged in a smaller 14 lead SOIC. These chips provide cost-effective solutions for point-of-use switchmode. DC-DC converters for many applications. This application note details the HIP6006 and HIP6007 in DC-DC converters for high-performance microprocessors with a fixed core voltage. VCC OCSET MONITOR AND PROTECTION SS HIP6006/7 Reference Designs The HIP6006/7EVAL1 is an evaluation board which highlights the operation of the HIP6006 or the HIP6007 in an embedded motherboard application. The evaluation board can be configured as either a synchronous Buck (HIP6006EVAL1) or standard Buck (HIP6007EVAL1) converter. HIP6006EVAL1 The HIP6006EVAL1 is a synchronous Buck converter capable of providing up to 9A of current at a fixed 2.5V output voltages. Simple resistor value changes allow for outputs as low as 1.3V. The schematic and bill-of-materials for this design can be found in the appendix. Efficiency Figure 2 displays the HIP6006EVAL1 efficiency versus load current for both 5V and 12V inputs with 100 linear feet per minute (LFM) of airflow. For a given output voltage and load, the efficiency is lower at higher input voltages. This is due primarily to higher MOSFET switching losses and is displayed in Figure 2. EN BOOT RT OSC UGATE HIP6006 PHASE REF FB PVCC + - LGATE + PGND GND COMP NOT PRESENT (PINS NC) ON HIP6007 FIGURE 1. BLOCK DIAGRAM OF HIP6006 AND HIP6007 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a trademark of Intersil Americas Inc. Copyright © Intersil Americas Inc. 2001. All Rights Reserved Pentium® is a registered trademark of Intel Corporation. Application Note 9722 Transient Response EFFICIENCY (%) 90 Figure 3 shows a laboratory oscillogram of the HIP6006EVAL1 in response to a 0-9A load transient application. The output voltage responds rapidly and is within 1% of its nominal value in less than 15µs. VIN = 5V 85 Output Voltage Ripple VIN = 12V The output voltage ripple and inductor current of the HIP6006EVAL1 is shown in Figure 4. The input voltage is 5V and the load current is 9A for this oscillogram. Peak-to-peak voltage ripple is about 20mV under these conditions. 80 75 HIP6007EVAL1 2 4 6 LOAD CURRENT (A) 8 FIGURE 2. HIP6006EVAL1 EFFICIENCY vs LOAD 10 The HIP6007EVAL1 is a standard Buck converter capable of providing up to 9A of current. The schematic and bill-ofmaterials for this design can be found in the appendix. The HIP6007EVAL1 differs from the HIP6006EVAL1 in four ways: 1. U1 is a HIP6007 2. CR3 replaces Q2 and CR2 2.50V 3. Jumper JP1 is added VOUT 50mV/DIV 4. L1 is a larger inductor COMP 2V/DIV 0V IL 5A/DIV JP1 is needed because CR3 is a dual, common-cathode device and it is replacing a MOSFET. JP1 connects one device’s anode (the MOSFET gate in the HIP6006EVAL1) to ground. The other anode and the common cathode replace the MOSFET source and drain respectively. Efficiency Figure 5 shows the efficiency data for the HIP6007EVAL1 under identical conditions as Figure 2 for the HIP6006EVAL1. Comparing the two graphs reveals that the Synchronous-Buck design is a little more efficient than the Standard-Buck design over most of the load range. 0A TIME (10ms/DIV) FIGURE 3. HIP6006EVAL1 TRANSIENT RESPONSE WITH VIN = 12V VOUT 20mV/DIV IL 1A/DIV Transient Response Figure 6 shows a laboratory oscillogram of the HIP6007EVAL1 in response to a 0-9A load transient application. The output voltage responds a little slower than the HIP6006EVAL1, but still is within 1% of its nominal value in less than 25ms. Since the HIP6007EVAL1 uses a larger output inductor and identical control loop compensation (R3, R5, C14, and C15), the closed-loop gain crossover frequency is lower than for the HIP6006EVAL1. Check the Feedback Compensation section of either data sheet for details on loop compensation design. Table 1 details simulated closed-loop bandwidth and phase margin for both reference boards at both +5V and +12V input sources. TABLE 1. CONTROL LOOP CHARACTERISTICS HIP6006EVAL1 TIME (1ms/DIV) FIGURE 4. HIP6006EVAL1 OUTPUT VOLTAGE RIPPLE 2 HIP6007EVAL1 VIN = 5V VIN = 12V VIN = 5V VIN = 12V f0dB 27KHz 61KHz 12KHz 28KHz ϕMARGIN 72o 62o 68o 71o Application Note 9722 OC Protection Both the HIP6006EVAL1 and HIP6007EVAL1 have lossless overcurrent (OC) protection. This is accomplished via the current-sense function of the HIP600x family. The HIP6006 and HIP6007 sense converter load current by monitoring the drop across the upper MOSFET (Q1 in the schematics). By selecting the appropriate value of the OCSET resistor (R6), an overcurrent protection scheme is employed without the cost and power loss associated with an external currentsense resistor. See the Over-Current Protection section of either the HIP6006 and HIP6007 data sheet for details on the design procedure for the OCSET resistor. 90 EFFICIENCY (%) VIN = 5V 85 VIN = 12V 80 75 2 4 6 LOAD CURRENT (A) 8 10 FIGURE 5. HIP6007EVAL1 EFFICIENCY vs LOAD VOUT 50mV/DIV 2.50V COMP 2V/DIV 0V IL 5A/DIV Customization of Reference Designs The HIP6006EVAL1 and HIP6007EVAL1 reference designs are solutions for Pentium-class microprocessors with current demands of up to 9A. The two designs share much common circuitry and the same printed circuit board. Other than the four items listed under the HIP6007EVAL1 section, one basic design is employed to meet many different applications. The evaluation boards can be powered from +5V or +12V and a standard Buck or a synchronous Buck topology may be employed. Employing one basic design for numerous applications involves some trade-offs. These trade-offs are discussed below to help the user optimize for a given application. Control Loop Bandwidth/Transient Response 0A TIME (10ms/DIV) FIGURE 6. HIP6007EVAL1 TRANSIENT RESPONSE WITH VIN = 12V VOUT 20mV/DIV IL 1A/DIV TIME (1µs/DIV) FIGURE 7. HIP6007EVAL1 OUTPUT VOLTAGE RIPPLE Output Voltage Ripple The output voltage ripple and inductor current of the HIP6007EVAL1 is shown in Figure 7. The input voltage is 5V and the load current is 9A for this oscillogram. Peak-to-peak voltage ripple is less than that for the HIP6006EVAL1 (about 15mV), since the output inductor is larger. 3 Table 1 shows how the control loop characteristics vary with line voltage and topology. The line voltage determines the amount of DC gain, which directly affects the modulator (control-to-output) transfer function. The topology (standard buck or synchronous buck) is important because we have chosen to use a larger output inductor for the standard buck (HIP6005) design. This lowers the boundary of continuous conduction mode (ccm) and discontinuous conduction mode (dcm) operation. Staying in ccm at light loads can have an adverse affect on transient response of the converter. The HIP6006EVAL1 design will not go into dcm operation because the lower MOSFET conducts current even at light or zero load conditions. From Table 1, we see that the highest control loop bandwidth is the HIP6006EVAL1 with VIN = 12V. The transient response of the converter for this case is shown in Figure 3. The other three cases have slower responding loops and can be improved with value changes in the compensation components. Table 2 details suggested changes and the improved control loop characteristics for the three applications with slower control loops. Application Note 9722 TABLE 2. MODIFICATIONS TO CONTROL LOOP HIP6006EVAL1 HIP6007EVAL1 VIN = 5V VIN = 12V VIN = 5V VIN = 12V R5 30.1K no change 80.6K 30.1K C14 no change no change 10p no change f0dB 47kHz 61kHz 44kHz 48kHz ϕMARGIN 53o 62o 40o 52o The RFP25N05 (used on the HIP6006/7EVAL1) has a rDS(ON) equal to 47mΩ (maximum at 25oC) versus 28mΩ for the RFP45N06. In comparison to the RFP25N05, the RFP45N06 MOSFETs increased switching losses are greater than its decreased conduction losses at load currents up to about 7A with a 5V input and about 9A with a 12V input. VIN = 5V, RFP25N05 Ripple Voltage VIN = 5V, RFP45N06 The amount of ripple voltage on the output of the DC-DC converter varies with input voltage, switching frequency, output inductor, and output capacitors. For a fixed switching frequency and output filter, the voltage ripple increases with higher input voltage. The ripple content of the output voltage can be estimated with the following simple equation: EFFICIENCY (%) 90 85 VIN = 12V, RFP25N05 80 VIN = 12V, RFP45N06 75 ∆V OUT = ∆IL • ESR where 2 V OUT ( VIN – VOUT ) • ---------------- • Ts VIN ∆IL = ----------------------------------------------------------------------L OU T 4 6 LOAD CURRENT (A) 8 10 FIGURE 8. HIP6006EVAL1 EFFICIENCY WITH EITHER RFP25N05 MOSFETs OR RFP45N06 MOSFETs ESR = equivalent series resistance of output capacitors Conclusion Ts = switching period (1/Fs) The HIP6006EVAL1 and HIP6007EVAL1 are DC-DC converters reference designs for microprocessors with fixed core voltages and current requirements of up to 9A. In addition, the designs can be modified for applications with different requirements. The printed circuit board is laid out to accommodate the necessary components for operation at currents up to 15A. LOUT = output inductance Therefore, for equivalent output ripple performance at VIN = 12V as at 5V, the output filter or switching frequency must change. Assuming 200KHz operation is desired, either the output inductor value should increase or the number of parallel output capacitors should increase (to decrease the effective ESR). Increased Output Power Capability The HIP6006/7EVAL1 printed circuit board is laid out with flexibility to increase the power level of the DC-DC converter beyond 9A. Locations for additional input capacitors and output capacitors are provided. In conjunction with higher current MOSFETs, Schottky rectifiers, and inductors, the evaluation board can be tailored for applications requiring upwards of 15A. The HIP6006 and HIP6007 data sheets’ Component Selection Guidelines sections help the user with the design issues for these applications. Of course, the HIP6006/7EVAL1 can be modified for more cost-effective solutions at lower currents as well. MOSFET Selection As a supplement to the data sheets’ application information on MOSFET Selection Considerations, this section shows graphically that a larger, lower rDS(ON) MOSFET does not always improve converter efficiency. Figure 8 shows that smaller RFP25N05 MOSFETs are more efficient over most of the line and load range than larger RFP45N06 MOSFETs. 4 References For Intersil documents available on the web, see http://www.intersil.com/ [1] Pentium-Pro Processor Power Distribution Guidelines, Intel Application Note AP-523, November, 1995. [2] HIP6006 Data Sheet, Intersil Corporation, Doc. No. 4306. [3] HIP6007 Data Sheet, Intersil Corporation, Doc. No. 4307. Application Note 9722 12VCC VIN C1-3 3 x 680µF C17-18 2 x 1µF 1206 RTN C12 1µF 1206 R7 10K C19 VCC EN 6 SS 3 ENABLE CR1 4148 1000pF 14 2 OCSET MONITOR AND PROTECTION R6 3.01k PHASE TP2 10 BOOT RT 1 Q1 C13 0.1µF U1 R1 SPARE C14 C15 R5 0.01µF C16 15K SPARE R3 1K 33pF Q2 12 LGATE + 11 PGND 4 R2 1K VOUT 13 PVCC + - FB 5 L1 8 PHASE HIP6006 REF C20 0.1µF 9 UGATE OSC CR2 MBR 340 C6-9 4 x 1000µF RTN 7 COMP GND JP1 COMP TP1 R4 SPARE FIGURE 9. HIP6006EVAL1 SCHEMATIC 12VCC VIN C17-18 2 x 1µF 1206 C1-3 3 x 680µF RTN C12 1µF 1206 R7 10K C19 VCC 1000pF 14 ENABLE EN 6 SS 3 2 OCSET MONITOR AND PROTECTION CR1 4148 R6 3.01k PHASE TP2 10 BOOT RT 1 Q1 C13 0.1µF U1 R1 SPARE FB 5 VOUT 13 NC + + - 12 NC 4 R2 1K L1 8 PHASE HIP6007 REF C20 0.1µF 9 UGATE OSC 7 COMP C14 CR3 11 NC GND RTN JP1 33pF C15 0.01µF R5 COMP TP1 15K C16 SPARE R3 1K R4 SPARE FIGURE 10. HIP6007EVAL1 SCHEMATIC 5 C6-9 4 x 1000µF Application Note 9722 Bill of Materials for HIP6006EVAL1 PART NUMBER DESCRIPTION PACKAGE QTY REF VENDOR 25MV680GX 680µF, 25V Aluminum Capacitor Radial 10 x 22 3 C1 - C3 Sanyo 6MV1000GX 1000µF, 6.3V Aluminum Capacitor Radial 8 x 20 4 C6 - C9 Sanyo 1206YZ105MAT1A 1.0µF, 16V, X7S Ceramic Capacitor 1206 3 C12, C17-C18 AVX 1000pF Ceramic 1nF, X7R Ceramic Capacitor 0805 1 C19 Various 0.1uF Ceramic 0.1µF, 25V X7R Ceramic Capacitor 0805 2 C13, C20 AVX/Panasonic 0.01uF Ceramic 0.01µF, X7R Ceramic Capacitor 0805 1 C15 Various 33pF Ceramic 33pF, X7R Ceramic Capacitor 0805 1 C14 Various Spare Spare Ceramic Capacitor 0805 1N4148 Rectifier 75V DO35 1 CR1 Various MBR340 3A, 40V, Schottky Axial 1 CR2 Motorola CTX09-13313-X1 PO343 5.3µH, 12A Inductor T50-52B Core, 10 Turns of 16 AWG Wire Wound Toroid 1 L1 Coiltronics Pulse RFP25N05 47mΩ, 50V MOSFET TO220 2 Q1, Q2 Intersil HIP6006 Synchronous Rectified Buck Controller SOIC-14 1 U1 Intersil 10kΩ 10kΩ, 5% 0.1W, Resistor 0805 1 R7 Various Spare Spare 0.1W, Resistor 0805 15kΩ 15kΩ, 5%, 0.1W, Resistor 0805 1 R5 Various 1kΩ 1kΩ, 5%, 0.1W, Resistor 0805 2 R2-R3 Various 3.01kΩ 3.01kΩ, 1%, 0.1W, Resistor 0805 1 R6 Various 576802B00000 TO-220 Clip-on Heatsink 2 1514-2 Terminal Post 6 VIN, 12VCC, VOUT, RTN Keystone 1314353-00 Scope Probe Test Point 1 V OUT Tektronics SPCJ-123-01 Test Point 3 ENABLE, TP1, TP2 Jolo 6 C16 R1,R4 AAVID Application Note 9722 Bill of Materials for HIP6007EVAL1 PART NUMBER DESCRIPTION PACKAGE QTY REF VENDOR Radial 10 x 22 3 C1 - C3 Sanyo Radial 8 x 20 4 C6 - C9 Sanyo 25MV680GX 680µF, 25V Aluminum Capacitor 6MV1000GX 1000µF, 6.3V Aluminum Capacitor 1206YZ105MAT1A 1.0µF, 16V, X7S Ceramic Capacitor 1206 3 C12, C17-C18 AVX 1000pF Ceramic 1nF, X7R Ceramic Capacitor 0805 1 C19 Various 0.1µF Ceramic 0.1µF, 25 V X7R Ceramic Capacitor 0805 2 C13, C20 AVX/Panasonic 0.01µF Ceramic 0.01µF, X7R Ceramic Capacitor 0805 1 C15 Various 33pF Ceramic 33pF, X7R Ceramic Capacitor 0805 1 C14 Various Spare Spare Ceramic Capacitor 0805 1N4148 Rectifier 75V DO35 1 CR1 Various MBR1535CT 15A, 35V, Schottky TO220 1 CR3 Motorola CTX09-13337-X1 PO345 7µH, 12A Inductor T60-52 Core, 14 turns of 17 AWG wire Wound Toroid 1 L1 Coiltronics Pulse RFP25N05 47mΩ, 50V MOSFET TO220 1 Q1 Intersil HIP6007 Synchronous Rectified Buck Controller SOIC-14 1 U1 Intersil 10kΩ 10kΩ, 5%, 0.1W, Resistor 0805 1 R7 Various Spare Spare 0.1W, Resistor 0805 15kΩ 15kΩ, 5%, 0.1W, Resistor 0805 1 R5 Various 1kΩ 1kΩ, 5%, 0.1W, Resistor 0805 2 R2-R3 Various 3.01kΩ 3.01kΩ, 1%, 0.1W, Resistor 0805 1 R6 Various 576802B00000 TO-220 Clip-on Heatsink 2 1514-2 Terminal Post 6 V IN, 12VCC, VOUT, RTN Keystone 1314353-00 Scope Probe Test Point 1 VOUT Tektronics SPCJ-123-01 Test Point 3 ENABLE, TP1, TP2 Jolo 7 C16 R1, R4 AAVID Application Note 9722 All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com 8