LM2638 Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers General Description Both linear controllers have under voltage latch-off. The LM2638 provides a comprehensive embedded power supply solution for motherboards hosting high performance MPUs such as Pentium™ II, M II™, K6™-2 and other similar high performance MPUs. The LM2638 incorporates a 5-bit programmable, synchronous buck switching controller and two high-speed linear regulator controllers in a 24-pin SO package. In a typical application, the switching controller supplies the MPU core, and the linear regulator controllers supply the GTL+ bus and the clock or graphics chip core. A charge pump pin helps provide the necessary voltage to power the linear sections when 12V is shut off during system standby such as STR mode. Features Switching Section — The switching regulator controller features an Intel-compatible, 5-bit programmable output voltage, over-current and over-voltage protection, a power good signal, and a logic-controlled output enable. There are two user-selectable over-current protection methods. One provides accurate over-current protection with the use of an external sense resistor. The other saves cost by taking advantage of the rDS_ON of the high-side FET. When there is an over voltage, the controller turns off the high side FET and turns on the low side. Linear Section — The two linear regulator controllers feature wide control bandwidth, N-FET and NPN transistor driving capability and an adjustable output. The wide control bandwidth makes meeting the GTL+ bus transient response requirement an easy job. In minimum configuration, the two controllers default to 1.5V and 1.25V respectively. n Provides 3 regulated voltages n Power Good flag and output enable n Charge pump pin Switching Section n Synchronous rectification n 5-bit DAC programmable down to 1.3V n Typical ± 1% DAC tolerance n Switching frequency: 50 kHz to 1 MHz n Over-voltage protection n Two methods of over-current protection n Adaptive non-overlapping FET gate drives n Soft start without external capacitor Linear Section n N-FET and NPN drive capability n Ultra fast response speed n Under voltage latch-off at 0.63V n Output voltages default to 1.5V and 2.5V yet adjustable Applications n Embedded power supplies for motherboards n Triple DC/DC power supplies n Programmable high current DC/DC power supply Pin Configuration 24-Lead SOIC DS101034-1 Top View Order Number LM2638M See NS Package Number M24B M II™ is a trademark of Cyrix Corporation a wholly owned subsidiary of National Semiconductor Corporation. Pentium™ is a trademark of Intel Corporation. K6™ is a trademark of Advanced Micro Devices, Inc. © 1999 National Semiconductor Corporation DS101034 www.national.com LM2638 Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers May 1999 Absolute Maximum Ratings (Note 1) Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Susceptibility VCC 7V VDD 17V Junction Temperature 3 kV Soldering Time, Temperature (10 sec.) 300˚C Operating Ratings (Note 1) 4.75V to 5.25V VCC 150˚C Power Dissipation (Note 2) −65˚C to +150˚C Junction Temperature Range 0˚C to +125˚C 1.6W Electrical Characteristics VCC = 5V, VDD = 12V unless otherwise specified. Typicals and limits appearing in plain type apply for TA = TJ = +25˚C. Limits appearing in boldface type apply over the 0˚C to +70˚C range. Symbol Parameter IEN EN Pin Internal Pull-up Current ICC Operating VCC Current IQ_VCC VCC Shutdown Current IQ_VDD RDS_CP Conditions Min Typ Max 60 90 140 Units µA 6 7.5 mA 1.5 3 mA VDD Shutdown Current EN = 5V, VID = 10111 EN = 0V, VID Pins Floating EN = 0V, VID Pins Floating 4 µA CP Pin Resistance High Side FET 100 Low Side FET 10 Ω SWITCHING SECTION VDACOUT 5-Bit DAC Output Voltage IVID VID Pins Internal Pull-up Current fOSC Oscillator Frequency (Note 3) RT = 100 kΩ RT = 25 kΩ N−1.5% N N+1.5% V 60 90 140 µA 245 286 204 1000 kHz DMAX Maximum Duty Cycle 100 % DMIN Minimum Duty Cycle 0 % RSNS1 SNS1 Pin Resistance to Ground RDS_SRC Gate Driver Resistance When Sourcing Current 6 Ω RDS_SINK Gate Driver Resistance When Sinking Current 1.5 Ω VCC_TH1 VCC Power-On-Reset Threshold 4.0 8.5 10 13 4.3 V VCC_TH2 VCC Shutdown Threshold 3.0 VDAC_IH DAC Input High Voltage 3.5 VDAC_IL DAC Input Low Voltage GA Error Amplifier DC Gain 76 dB BWEA Error Amplifier Unity Gain Bandwidth 5 MHz VRAMP_L Ramp Signal Valley Voltage 1.25 V VRAMP_H Ramp Signal Peak Voltage 3.25 V tSS Soft Start Time 4096 Clock Cycles DSTEP_SS Duty Cycle Step Change during Soft Start 12.5 % tPWGD PWGD Response Time SNS1 Rises from 0V to Rated Output Voltage 2 8.4 15 µs tPWBAD PWGD Response Time SNS1 Falls from Rated Output Voltage to 0V 2 3.4 10 µs www.national.com 3.6 kΩ V V 1.3 2 V Electrical Characteristics VCC = 5V, VDD = 12V unless otherwise specified. Typicals and limits appearing in plain type apply for TA = TJ = +25˚C. Limits appearing in boldface type apply over the 0˚C to +70˚C range. (Continued) Symbol Parameter Conditions Min Typ Max 11.5 13 7 9 2.6 6 9.5 13 Units SWITCHING SECTION VPWGD_HI PWGD High Trip Point % Above Rated Output Voltage When Output Voltage↑ % Above Rated Output Voltage When Output Voltage ↓ (Note 4) VPWGD_LO PWGD Low Trip Point % Below Rated Output Voltage When Output Voltage↑ % Below Rated Output Voltage When Output Voltage ↓ (Note 4) VOVP_TRP Over-Voltage Trip Point ICS+ CS+ Pin Sink Current VOCP Over-Current Trip Point (CS+ and CS− Differential Voltage) % 5 % SNS1 Above Rated Output CS+ = 5V, CS− = 4.8V CS+ = 2V, CS− Drops from 2V % 6 15 25 35 % 126 185 244 µA 41 55 69 mV 1.5 1.538 1.5V LDO CONTROLLER SECTION VDD = 12V, VCC = 4.75V to 5.25V, IG2 = 0 mA to 20 mA VSNS2 SNS2 Voltage ROUT2 Output Resistance ISNS2 SNS2 Pin Bias Current When Regulating VPWGD_HI PWGD High Trip Point (Note 4) VPWGD_LO PWGD Low Trip Point (Note 4) 0.44 V 1.463 V 200 Ω 21 µA 0.63 V 1.25V LDO CONTROLLER SECTION VDD = 12V, VCC = 4.75V to 5.25V, IG3 = 0 mA to 20 mA VSNS3 SNS3 Voltage ROUT3 Output Resistance ISNS3 SNS3 Pin Bias Current When Regulating VPWGD_HI PWGD High Trip Point VPWGD_LO PWGD Low Trip Point 1.219 1.25 1.281 V 200 Ω 0 µA (Note 4) 0.63 V (Note 4) 0.44 V Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating ratings are conditions under which the device operates correctly. Operating Ratings do not imply guaranteed performance limits. Note 2: Maximum allowable power dissipation is a function of the maximum junction temperature, TJMAX, the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using: PMAX = (TJMAX − TA)/θJA. The junction-to-ambient thermal resistance, θJA, for LM2638 is 78˚C/W. For a TJMAX of 150˚C and TA of 25˚C, the maximum allowable power dissipation is 1.6W. Note 3: The letter N stands for the typical output voltages appearing in italic boldface type in Table 1. Note 4: The output level of the PWGD pin is a logic AND of the power good function of the switching section, the 1.5V section and the 1.25V section. For the switching section, the power good is a window. For the two linear sections, the power good is a threshold with some hysteresis. 3 www.national.com Electrical Characteristics VCC = 5V, VDD = 12V unless otherwise specified. Typicals and limits appearing in plain type apply for TA = TJ = +25˚C. Limits appearing in boldface type apply over the 0˚C to +70˚C range. (Continued) TABLE 1. 5-Bit DAC Output Voltage Table (VCC = 5V, VDD = 12V ± 5%, TA = 25˚C, Test Mode) Symbol VDACOUT Parameter 5-Bit DAC Output Voltages for Different VID Codes Conditions VID4:0 = 01111 VID4:0 = 01110 Typical Units 1.30 V VID4:0 = 01101 VID4:0 = 01100 1.40 VID4:0 = 01011 VID4:0 = 01010 VID4:0 = 01001 1.50 VID4:0 = 01000 VID4:0 = 00111 VID4:0 = 00110 1.55 1.60 1.65 1.70 1.75 1.80 VID4:0 = 00011 VID4:0 = 00010 VID4:0 = 00001 1.90 1.85 1.95 2.00 2.05 (shutdown) 2.1 VID4:0 = 11101 VID4:0 = 11100 2.2 VID4:0 = 11011 VID4:0 = 11010 VID4:0 = 11001 2.4 VID4:0 = 11000 VID4:0 = 10111 VID4:0 = 10110 4 1.45 VID4:0 = 00101 VID4:0 = 00100 VID4:0 = 00000 VID4:0 = 11111 VID4:0 = 11110 www.national.com 1.35 2.3 2.5 2.6 2.7 2.8 2.9 VID4:0 = 10101 VID4:0 = 10100 VID4:0 = 10011 3.0 VID4:0 = 10010 VID4:0 = 10001 VID4:0 = 10000 3.3 3.1 3.2 3.4 3.5 Pin Description Pin Pin Name Pin Function 1 LG Low side N-FET gate driver output. 2 PGND Ground for the two FET drivers of the switching section. 3 VDD Supply for the FET gate drivers. Usually tied to +12V. 4 SNS2 Feedback pin for the 1.5V linear regulator. 5 G2 Gate drive output for the external N-MOS of the fast 1.5V linear regulator. 6 SGND Ground for internal signal circuitry and system ground reference. 7 VCC Supply voltage. Usually +5V. 8 SNS1 Output voltage monitor input for the switching regulator. 9 CS+ Switching regulator current sense input, positive node. 10 CS− Switching regulator current sense input, negative node. 11 CP Charge pump. Output is a square wave with 50% duty cycle. Amplitude is close to VCC voltage. 12 FREQ Switching frequency adjustment pin. An external resistor is needed to set the desired frequency. 13 EAO Output of the error amplifier. Used for compensating the switching regulator. 14 FB Inverting input of the error amplifier. Used for compensating the switching regulator. 15 PWGD Open collector Power Good signal. 16 VID4 5-Bit DAC input, MSB. 17 VID3 5-Bit DAC input. 18 VID2 5-Bit DAC input. 19 VID1 5-Bit DAC input. 20 VID0 5-Bit DAC input, LSB. 21 G3 Gate drive pin for the external N-MOS of the 1.25V linear regulator. 22 SNS3 Feedback pin for the 1.25V linear regulator. 23 EN Output Enable. A logic low shuts the whole chip down. 24 HG High side N-FET gate driver output. 5 www.national.com Block Diagram DS101034-3 Test Circuit DS101034-4 FIGURE 1. LDO Controller Test Circuit www.national.com 6 FIGURE 2. Using LM2638 to Supply GTL+ Bus (VTT, 1.5V, 5.6A), 2.5V Standby (VCC2_5SBY, 2A Full Power and 180 mA Suspend) and 3.3V Standby (VCC3_3SBY, 1.5A Full Power, 0.5A Suspend) DS101034-2 Typical Application 7 www.national.com LM2638 Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers Physical Dimensions inches (millimeters) unless otherwise noted 24-Lead Small Outline Package Order Number LM2638M NS Package Number M24B LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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