SI9140DY-T1

Si9140 Vishay Siliconix MP Controller For High Performance Process Power Supplies FEATURES D Runs on 3.3- or 5-V Supplies D Adjustable, High Precision Output Voltage D High Frequency Operation (>1 MHz) D Full Set of Protection Circuitry D High Efficiency Synchronous D 2000-V ESD Rating (Si9140CQ/DQ) Switching DESCRIPTION Siliconix’ Si9140 Buck converter IC is a high-performance, surface-mount switchmode controller made to power the new generation of low-voltage, high-performance microprocessors. The Si9140 has an input voltage range of 3 to 6.5 V to simplify power supply designs in desktop PCs. Its high-frequency switching capability and wide bandwidth feedback loop provide tight, absolute static and transient load regulation. Circuits using the Si9140 can be implemented with low-profile, inexpensive inductors, and will dramatically minimize power supply output and processor decoupling capacitance. The Si9140 is designed to meet the stringent regulation requirements of new and future high-frequency microprocessors, while improving the overall efficiency in new “green” systems. down. These simultaneous changes have made dedicated, high-frequency, point-of-use buck converters an essential part of any system design. These point-of-use converters must operate at higher frequencies and provide wider feedback bandwidths than existing converters, which typically operate at less than 250 kHz and have feedback bandwidths of less than 50 kHz. The Si9140’s 100-kHz feedback loop bandwidth ensures a minimum improvement of one-half the required output/decoupling capacitance, resulting in a tremendous reduction in board size and cost of implementation. With the microprocessing power of any PC representing an investment of hundreds of dollars, designers need to ensure that the reliable operation of the processor will not be affected by the power supply. The Si9140 provides this assurance. A demo board, the Si9140DB, is available. Si9140CQ-T1 and Si9140DQ-T1 are available in lead free. Today’s state-of-the-art microprocessors run at frequencies over 100 MHz. Processor clock speeds are going up and so are current requirements, but operating voltages are going APPLICATION CIRCUIT VIN + C1 R1 R2 VCCP R3 C3 2 x Si4435DY L1 VOUT D1 C2 + 2 x Si4410DY R4 Power-Good U1 C4 Si9140 1 2 R5 3 4 5 6 R6 7 C7 8 VDD MON VGOOD COMP FB NI VREF GND VS DR 16 15 14 R13 C8 R7 C5 C6 DS 13 PGND 12 UVLOSET 11 COSC 10 ROSC 9 ENABLE C9 R9 R8 R10 0.1% R12 0.1% C10 R11 Document Number: 70026 S-40699—Rev. H, 19-Apr-04 www.vishay.com 1 Si9140 Vishay Siliconix ABSOLUTE MAXIMUM RATINGS Voltages Referenced to GND. VDD, VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 V PGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "0.3 V VDD to VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V Linear Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V to VDD +0.3 V Logic Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V to VDD +0.3 V Peak Output Drive Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350 mA Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −65 to 150_C Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150_C Power Dissipation (Package)a 16-Pin SOIC (Y Suffix)\b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900 mW 16-Pin TSSOP (Q Suffix)c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925 mW Operating Temperature C Suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0_ to 70_C D Suffix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −40_ to 85_C Notes a. Device mounted with all leads soldered or welded to PC board. b. Derate 7.2 mW/_C above 25_C. c. Derate 7.4 mW/_C above 25_C. Thermal Impedance (QJA) 16-Pin SOIC (Y Suffix) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140_C/W 16-Pin TSSOP (Q Suffix) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135_C/W * . Exposure to Absolute Maximum rating conditions for extended periods may affect device reliability. Stresses above Absolute Maximum rating may cause permanent damage. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time RECOMMENDED OPERATING RANGE Voltages Referenced to GND. VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 V to 6.5 V VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 V to 6.5 V fOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 kHz to 2 MHz ROSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 kW to 250 kW COSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 pF to 200 pF Linear Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to VDD Digital Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to VDD VREF Load Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >150 kW SPECIFICATIONS Test Conditions Unless Otherwise Specifieda Parameter Reference Output Voltage VREF IREF = −10 mA TA = 25_C 1.455 1.477 1.50 1.545 1.523 V Limits C Suffix 0 to 70_C D Suffix −40 to 85_C Symbol 3 V v VDD v 6.5 V, VDD = VS .5 V, GND = PGND Minb Typ Maxb Unit Oscillator Maximum Frequencyc Accuracy ROSC Voltage Voltage Stabilityc Temperature Stabilityc fMAX fOSC VROSC Df/f 4 V v VDD v 6 V, Ref to 5 V, TA = 25_C Referenced to 25_C −8 "5 VDD = 5 V, COSC = 47 pF, ROSC = 5.0 kW VDD = 5 V COSC = 100 pF, ROSC = 7.50 kW, TA = 25_C 2.0 0.85 1.0 1.0 8 1.15 MHz V % Error Amplifier (COSC = GND, OSC DISABLED) Input Bias Current Open Loop Voltage Gain Offset Voltage Unity Gain Bandwidthc Output Current Power Supply Rejectionc IFB AVOL VOS BW IEA PSRR Source (VFB = 1 V, NI = VREF) Sink (VFB = 2 V, NI = VREF) 3 V < VDD < 6.5 V 0.4 VNI = VREF VNI = VREF , VFB = 1.0 V −1.0 47 −15 55 0 10 −2.0 0.8 60 −1.0 15 1.0 mA dB mV MHz mA dB UVLOSET Voltage Monitor Under Voltage Lockout Hysteresis www.vishay.com VUVLOHL VUVLOLH VHYS UVLOSET High to Low UVLOSET Low to High VUVLOLH − VUVLOHL 0.85 1.0 1.2 175 1.15 V mV Document Number: 70026 S-40699—Rev. H, 19-Apr-04 2 Si9140 Vishay Siliconix SPECIFICATIONS Test Conditions Unless Otherwise Specifieda Parameter UVLOSET Voltage Monitor UVLO Input Current IUVLO(SET) VUVLO = 0 to VDD −100 100 nA Limits C Suffix 0 to 70_C D Suffix −40 to 85_C Symbol 3 V v VDD v 6.5 V, VDD = VS GND = PGND Minb Typ Maxb Unit Output Drive (DR and DS) Output High Voltage Output Low Voltage Peak Output Current Peak Output Current Break-Before-Make VOH VOL ISOURCE ISINK tBBM VS = VDD = 5 V, IOUT = −10 mA VS = VDD = 5 V, IOUT = 10 mA VS = VDD = 5 V, VOUT = 0 V VS = VDD = 5 V, VOUT = 5 V VDD = 6.5 V 200 4.7 4.8 0.2 −380 300 40 0.3 −260 V mA nS Logic ENABLE Turn-On Delay ENABLE Logic Low ENABLE Logic High ENABLE Input Current tdEN VENL VENH IEN ENABLE = 0 to VDD 0.8 VDD −1.0 1.0 ENABLE Delay to Output, ENLH, VDD = 5 V 1.5 0.2 VDD ms V mA VGOOD Comparator (Voltage-Good Comparator) Input Offset Voltage Input Hysteresis Input Bias Current Output Sink I Output Low Voltage VOS VINHYS IBMON ISINK VOL VIN Common Mode Voltage = VREF, VDD = 5 V VIN = VREF, VDD = 5 V VOUT = 5 V, VDD = 5 V IOUT = 2 mA, VDD = 5 V −45 −1 6 0 10 0 9 350 500 1 45 mV mA mA mV Supply Supply Current—Normal Mode Supply Current—Standby Mode IDD fOSC = 1 MHz, ROSC = 7.50 kW ENABLE < 0.4 V 1.6 250 2.3 330 mA mA Notes a. 100 pF includes CSTRAY on COSC. b. The algebraic convention whereby the most negative value is a minimum and the most positive a maximum, is used in this data sheet. c. Guaranteed by design, not subject to production testing. TYPICAL CHARACTERISTICS (25_C UNLESS OTHERWISE NOTED) 1.515 VREF vs. Supply Voltage VREF with 10 mA Load 1.510 1.505 1.500 V REF (V) VDD = 3 V 1.495 1.490 1.485 1.480 −50 VREF vs. Temperature 1.510 1.505 V REF (V) VDD = 6 V 1.500 1.495 1.490 1.485 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 −25 0 25 50 75 100 125 VDD − Supply Voltage (V) Document Number: 70026 S-40699—Rev. H, 19-Apr-04 t − Temperature (_C) www.vishay.com 3 Si9140 Vishay Siliconix TYPICAL CHARACTERISTICS (25_C UNLESS OTHERWISE NOTED) 1.515 1.510 1.505 V REF (V) 1.500 1.495 1.490 1.485 0 5 10 15 20 25 30 VREF − Sourcing Current (mA) 6.5 V 5.0 V Gain (dB) 3.0, 3.6 V VREF vs. Load Current 80 60 Error Amplifier Gain and Phase 0 Gain −30 Phase (deg) Phase −60 −90 −120 40 20 0 −20 −40 0.0001 0.001 0.01 0.1 1 f − Frequency (MHz) 10 100 −150 Supply Current vs. Supply Voltage and Temperature 1.8 CL = 10 pF f = 1 MHz 70_C Standby Current ( m A) 240 260 Standby Current vs. Supply Voltage and Temperature 70_C TA = 85_C 250 25_C 0_C 230 −40_C 220 1.6 Normal Current (mA) 1.4 TA = 85_C 25_C 1.2 −40_C 1.0 3.0 3.5 4.0 4.5 0_C 5.0 5.5 6.0 6.5 210 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 VDD − Supply Voltage (V) VDD − Supply Voltage (V) 600 DR Sourcing Current vs. Supply Voltage 600 DR Sinking Current vs. Supply Voltage 500 DR Sourcing Current (mA) DR Sinking Current (mA) 3.5 4.0 4.5 5.0 5.5 6.0 6.5 500 400 400 300 300 200 200 100 3.0 100 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 VDD − Supply Voltage (V) VDD − Supply Voltage (V) www.vishay.com 4 Document Number: 70026 S-40699—Rev. H, 19-Apr-04 Si9140 Vishay Siliconix TYPICAL CHARACTERISTICS (25_C UNLESS OTHERWISE NOTED) 600 DS Sourcing vs. Supply Voltage 600 DS Sinking Current vs. Supply Voltage 500 DS Sourcing Current (mA) DS Sinking Current (mA) 3.5 4.0 4.5 5.0 5.5 6.0 6.5 500 400 400 300 300 200 200 100 3.0 100 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 VDD − Supply Voltage (V) VDD − Supply Voltage (V) 1.2 Switching Frequency vs. Supply Voltage ROSC = 7.50 kW COSC = 100 pF 10.00 Frequency vs. ROSC/COSC Switching Frequency (MHz) Switching Frequency (MHz) 1.1 1.00 4.99 kW 12.1 kW 24.9 kW 1.0 0.10 49.9 kW 100 kW 249 kW 0.9 0.8 3.0 0.01 3.5 4.0 4.5 5.0 5.5 6.0 6.5 40 COSC − Capacitance (pF) 200 300 VDD − Supply Voltage (V) Enable Turn-OFF Delay to Output 70 215 UVLO Hysteresis vs. Supply Voltage 60 UVLO Hysteresis (mV) 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Output Delay (nS) 195 50 175 40 155 30 135 20 3.0 115 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 VDD − Supply Voltage (V) VDD − Supply Voltage (V) Document Number: 70026 S-40699—Rev. H, 19-Apr-04 www.vishay.com 5 Si9140 Vishay Siliconix TYPICAL CHARACTERISTICS (25_C UNLESS OTHERWISE NOTED) 20 VGOOD Sinking Current vs. Supply Voltage Power Good Sinking Current (mA) 16 12 8 4 0 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 VDD − Supply Voltage (V) PIN CONFIGURATIONS AND ORDERING INFORMATION SOIC-16 TSSOP-16 VDD 1 2 3 4 5 6 7 8 Top View 16 15 14 13 12 11 10 9 VS DR DS PGND UVLOSET COSC ROSC ENABLE VDD MON VGOOD COMP FB NI VREF GND 1 2 3 4 5 6 7 8 Top View 16 15 14 13 12 11 10 9 VS DR DS PGND UVLOSET COSC ROSC ENABLE MON VGOOD COMP FB NI VREF GND ORDERING INFORMATION−SOIC-16 Part Number Si9140CY Si9140CY-T1 Si9140CY-T1—E3 Si9140DY Si9140DY-T1 Si9140DY-T1—E3 −40_ to 85_C 0_ to 70_C ORDERING INFORMATION Part Number Si9140CQ Si9140CQ-T1 Si9140CQ-T1—E3 Si9140DQ Si9140DQ-T1 Si9140DQ-T1—E3 TSSOP-16 Temperature Range Temperature Range 0_ to 70_C −40_ to 85_C www.vishay.com 6 Document Number: 70026 S-40699—Rev. H, 19-Apr-04 Si9140 Vishay Siliconix PIN DESCRIPTION Pin 1: VDD The positive power supply for all functional blocks except output driver. A bypass capacitor of 0.1 mF (minimum) is recommended. Pin 2: MON Non-inverting input of a comparator. Inverting input is tied internally to reference voltage. This comparator is typically used to monitor the output voltage and to flag the processor when the output voltage falls out of regulation. Pin 3: VGOOD This is an open drain output. It will be held at ground when the voltage at MON (Pin 2) is less than the internal reference. An external pull-up resistor will pull this pin high if the MON pin (Pin 2) is higher than the VREF. (Refer to Pin 2 description.) Pin 4: COMP Pin 12: UVLOSET This pin is the output of the error amplifier. A compensation network is connected from this pin to the FB pin to stabilize the system. This pin drives one input of the internal pulse width modulation comparator. Pin 5: FB The inverting input of the error amplifier. An external resistor divider is connected to this pin to set the regulated output voltage. The compensation network is also connected to this pin. Pin 6: NI The non-inverting input of the error amplifier. In normal operation it is externally connected to VREF or an external reference. Pin 7: VREF This pin supplies a 1.5-V reference. Pin 8: GND (Ground) Pin 9: ENABLE A logic high on this pin allows normal operation. A logic low places the chip in the standby mode. In standby mode normal Document Number: 70026 S-40699—Rev. H, 19-Apr-04 operation is disabled, supply current is reduced, the oscillator stops and DS goes high while DR goes low. Pin 10: ROSC A resistor connected from this pin to ground sets the oscillator’s capacitor COSC, charge and discharge current. See the oscillator section of the description of operation. Pin 11: COSC An external capacitor is connected to this pin to set the oscillator frequency. fOSC ] R OSC 0.75 COSC (at VDD = 5.0 V) This pin will place the chip in the standby mode if the UVLOSET voltage drops below 1.2 V. Once the UVLOSET voltage exceeds 1.2 V, the chip operates normally. There is a built-in hysteresis of 165 mV. Pin 13: PGND The negative return for the VS supply. Pin 14: DS This CMOS push-pull output pin drives the external p-channel MOSFET. This pin will be high in the standby mode. A break-before-make function between DS and DR is built-in. Pin 15: DR This CMOS push-pull output pin drives the external n-channel MOSFET. This pin will be low in the standby mode. A break-before-make function between the DS and DR is built-in. Pin 16: VS The positive terminal of the power supply which powers the CMOS output drivers. A bypass capacitor is required. www.vishay.com 7 Si9140 Vishay Siliconix FUNCTIONAL BLOCK DIAGRAM VREF VREF VUVLO GND VUVLO ENABLE VS COMP Error Amp NI FB + − + − Logic and BBM Control COSC ROSC Oscillator Driver PGND VS Driver PGND VS VDD UVLOSET UVLO 1.5-V Reference Generator DS DR PGND MON VREF VGOOD + − TIMING WAVEFORMS 5V ENABLE 0V 1.5 V VCOMP VCOSC 1V tBBM DS DR www.vishay.com 8 Document Number: 70026 S-40699—Rev. H, 19-Apr-04 Si9140 Vishay Siliconix DESCRIPTION OF OPERATION Schematics of the Si9140 dc-to-dc conversion solutions for high-performance PC microprocessors are shown in Figure 1 and 2 respectively. These solutions are geared to meet the extremely demanding transient regulation and power requirements of these new microprocessors at minimal cost 5V (VIN) + C1 2 x 220 mF 10 V OS-CON R1 20 k R4 24.9 k 1 2 C5, 180 pF R5 240 k 3 4 5 6 R6 C6 0.1 mF 4.99 k C7 0.1 mF 7 8 R2 10 k Power-Good U1 Si9140 VDD MON VGOOD COMP FB NI VREF GND VS DR 16 15 14 R13 C8 10 k 1 mF R7 100 k VCCP and with a minimal parts count. The two solutions are nearly identical, except for slight variations in output voltage, load transient amplitude, and specified power. Figure 3 is a schematic diagram for a 3.3-V logic converter. R3 100 C3 0.1 mF 2 x Si4435DY L1 1.5 mH D1 D1FS4 C2 3 x 330 mF 6.3V OS-CON Coiltronics CTX07-12877 2.9 V (VOUT) 2 x Si4410DY + C4, 5.6 pF DS 13 PGND 12 UVLOSET 11 COSC 10 ROSC 9 ENABLE C9 220 pF R9 11 k R12 13.3 k, 0.1% R8 40.2 k C10, 180 pF R10 14.2 k 0.1% R11, 4.7 k FIGURE 1. 2.9 V @ 10 A 5V (VIN) + C1 2 x 220 mF 10 V OS-CON VCCP R1 20 k R4 40.2 k R2 10 k Power-Good U1 Si9140 1 2 R5 240 k 3 VDD MON VGOOD R3 100 C3 0.1 mF 2 x Si4435DY L1 1.5 mH D1 D1FS4 C2 3 x 330 mF 6.3V OS-CON Coiltronics CTX07-12877 2.5 V (VOUT) + Si4410DY C4, 5.6 pF VS DR 16 15 R13 C8 10 k 1 mF R7 100 k C5, 180 pF R6 C6 0.1 mF 4.99 k C7 0.1 mF 14 DS 4 13 PGND COMP 5 12 UVLOSET FB 6 11 COSC NI 7 10 ROSC VREF 9 8 ENABLE GND C9 220 pF R9 11 k R12 13.3 k, 0.1% R8 40.2 k C10, 180 pF R10 20 k 0.1% R11, 4.7 k FIGURE 2. 2.5 V @ 8.5 A Document Number: 70026 S-40699—Rev. H, 19-Apr-04 www.vishay.com 9 Si9140 Vishay Siliconix 5V (VIN) + C1 2 x 220 mF TPS Tantalum R3 100 C3 0.1 mF L1 10 mH D1 D1FS4 C2 3 x 330 mF TPS Tantalum R7 100 k Coiltronics CTX07-12891 3.3 V (VOUT) Si4435DY Si4410DY + U1 Si9140 C4, 330 pF C5, 1000 pF R5 16.2 k 1 2 3 4 5 6 R6 C6 0.1 mF 4.99 k C7 0.1 mF 7 8 VDD MON VGOOD COMP FB NI VREF GND VS DR 16 15 14 R13 C8 10 k 1 mF DS 13 PGND 12 UVLOSET 11 COSC 10 ROSC 9 ENABLE C9 220 pF R9 20 k R12, 13.3 k R8 40.2 k C10 1000 pF R10 11 k R11 4.7 k FIGURE 3. 3.3 V@ 5 A 5V (VIN) + C1 2 x 220 mF TPS Tantalum R3 100 C3 0.1 mF Si4435DY L1 10 mH D1 D1FS4 C2 3 x 330 mF TPS Tantalum Coiltronics CTX07-12891 1.5 V (VOUT) Si4410DY + U1 Si9140 C4, 330 pF R5 16.2 k 1 2 C5, 1000 pF 3 4 5 6 R6 4.99 k C6 0.1 mF C7 0.1 mF 7 8 VDD MON VGOOD COMP FB NI VREF GND VS DR 16 15 14 R13 C8 10 k 1 mF R7 100 k DS 13 PGND 12 UVLOSET 11 COSC 10 ROSC 9 ENABLE C9 220 pF R9 20 k R12, 13.3 k R8 40.2 k C10 1000 pF R11 4.7 k FIGURE 4. 1.5-V Converter for GTL+ Bus @ 5 A Figure 4 is a schematic diagram of a converter which produces 1.5 V for a GTL bus. Each of these dc-to-dc converters has four major sections: D PWM Controller—regulates the output voltage www.vishay.com D Switch and Synchronous Rectification MOSFETs—delivers the power to the load D Inductor—filters and stores the energy D Input/Output Capacitor—filters the ripple Document Number: 70026 S-40699—Rev. H, 19-Apr-04 10 Si9140 Vishay Siliconix The functions of each circuit are explained in detail below. Design equations are provided to optimize each application circuit. The error amplifier of the PWM controller plays a major role in determining the output voltage, stability, and the transient response of the power supply. In the Si9140, the non-inverting input of the error amplifier is available for use with an external precision reference for tighter tolerance regulation. With a two-pair lead-lag compensation network, it is easy to create a stable 100-kHz closed loop converter with the Si9140 error amplifier. The Si9140 achieves the 5-mS transient response by generating a 100-kHz closed-loop bandwidth. This is possible only by switching above 400 kHz and utilizing an error amplifier with at least a 10-MHz bandwidth. The Si9140 controller has a 25-MHz unity gain bandwidth error amplifier. The switching frequency must be at least four times greater than the desired closed-loop bandwidth to prevent oscillation. To respond to the stimuli, the error amplifier bandwidth needs to be at least 10 times larger than the desired bandwidth. PWM Controller There are generally two types of controllers, voltage mode or current mode. In voltage mode control, an error voltage is generated by comparing the output voltage to the reference voltage. The error voltage is then compared to an artificial ramp, and the result is the duty cycle necessary to regulate the output voltage. In current mode, an actual inductor current is used, in place of the artificial ramp, to sense the voltage across the current sense resistor. The logic and timing sequence for voltage mode control is shown in Figure 5. The Si9140 offers voltage mode control, which is better suited for applications requiring both fast transient response and high output current. Current mode control requires a current sense resistor to monitor the inductor current. A 10-mW sense resistor in a 10-A design will dissipate 1 W, decreasing efficiency by 3.5%. Such a design would require a 2-W resistor to satisfy derating criteria, besides requiring additional board space. Voltage mode control is a second-order LC system and has a faster natural transient response compared to current mode control (first-order RC system). Current mode has the advantage of providing an inherently good line regulation. But the situations where line voltage is fixed, as in the point-of-use conversion for microprocessors, this feature is wasted. Current mode control also provides automatic pulse-to-pulse current limiting. This feature requires a current sense resistor as stated above. These characteristics make voltage mode control ideal for high-end microprocessor power supplies. Phase Phase (deg) www.vishay.com Gain (dB) Gain Frequency (Hz) FIGURE 6. 100-kHz BW Synchronous Buck Converter OSC COMP DS DR The Si9140 solution requires only three 330-mF OS-CON capacitors on the output of power supply to meet the 10-A transient requirement. Other converter solutions on the market with 20- to 50-kHz closed loop bandwidths typically require two to five times the output capacitance specified above to match the Si9140’s performance. The theoretical issues and analytical steps involved in compensating a feedback network are beyond the scope of this application note. However, to ease the converter design for today’s high-performance microprocessors, typical component values for the feedback network are provided in Table 1 for various combinations of output capacitance. Figure 6 shows the Bode plot (frequency domain) of the 2.9-V converter shown schematically in Figure 1. 11 FIGURE 5. Voltage Mode Logic and Timing Diagram Document Number: 70026 S-40699—Rev. H, 19-Apr-04 Si9140 Vishay Siliconix FEEDBACK NETWORK COMPONENT VALUES Total Output and Decoupling Capacitance 3 x 330 . . . . . . . . . Os-con 6 x 100 mFb . . . . . . . . . Tantalum 25 x 1 mFb . . . . . . . . . . Ceramic 2 x 330 mFa . . . . . . . . . Os-con 4 x 100 mFb . . . . . . . . . Tantalum 25 x 1 mFb . . . . . . . . . . Ceramic 3 x 330 mFa . . . . . . . . . Tantalum 4 x 100 mFb . . . . . . . . . Tantalum 25 x 1 mFb . . . . . . . . . . Ceramic a. b. Power supply output capacitance. mprocessor decoupling capacitance. m Fa TABLE 1. reference and 3.5% transient load regulation safely complies with the "5% regulation requirement. If additional margin is desired, an external precision reference can be used in place of the internal 1.5-V reference. C4 5.6 pF C5 180 pF R5 240 k Switching and Synchronous Rectification MOSFETs The synchronous gate drive outputs of Si9140 PWM controller drive the high-side p-channel switch MOSFET and the low-side n-channel synchronous rectifier MOSFET. The physical difference between the non-synchronous to synchronous rectification requires an additional MOSFET across the free-wheeling diode (D1). The inductor current will reach 0 A if the peak-to-peak inductor current equals twice the output current. In synchronous rectification mode, current is allowed to flow backwards from the inductor (L1) through the synchronous MOSFET (Q3) and to the output capacitor (C2) once the current reaches 0 A. Refer to schematic on Figure 1. In non-synchronous rectification, the diode (D1) prevents the current from flowing in the reverse direction. This minor difference has a drastic affect on the performance of a power supply. By allowing the current to flow in the reverse direction, it preserves the continuous inductor current mode, maintaining the wide converter bandwidth and improving efficiency. Also, maintaining the continuous current mode during light load to full load guarantees consistent transient response throughout a wide range of load conditions. The transition from stop clock and auto halt to active mode is a perfect example. The microprocessor current can vary from 0.5 A to 10 A or greater during these transitions. If the converter were to operate in discontinuous current mode during the stop clock and auto halt modes, the transfer function of the converter would be different compared to operation in the active mode. In discontinuous current mode, the converter bandwidth can be 10 to 15 times lower than the continuous current mode (Figure 8). Therefore, the response time will also be 10 to 15 times slower, violating the microprocessor’s regulator requirements. This could result in unreliable operation of the microprocessor. 10 pF 220 pF 200 k 10 pF 100 pF 100 k Figure 7 is the measured transient response (time domain) for the 10-A step response. The measured transient response shows the processor voltage regulating to 70 mV, well within the 0.145-V regulation. The Si9140’s switching frequency is determined by the external ROSC and COSC values, allowing designers to set the switching frequency of their choice. For applications where space is the main constraint, the switching frequency can be set as high as 2 MHz to minimize inductor and output capacitor size. In applications where efficiency is the main concern, the switching frequency can be set low to maximize battery life. The switching frequency for high-performance processors applications circuits are set for 400 kHz. The equation for switching frequency is: fOSC [ 0.75 ROSC COSC (at VDD = 5.0 V) The precision reference is set at 1.5 V"1.5%. The reference is capable of sourcing up to 1 mA. The combination of 1.5% mP Voltage 2.9 V mP Current 10 A 5A 0A a) Transient Response from 0- to 10-A Step Load b) Transient Response from 10- to 0-A Step Load FIGURE 7. www.vishay.com Document Number: 70026 S-40699—Rev. H, 19-Apr-04 12 Si9140 Vishay Siliconix For these reasons, synchronous rectification is a must in today’s microprocessors power supply design. Pulseskipping modes are undesirable in high-performance microprocessor power supplies, especially when the minimum load current is as high as 500 mA. This pulse-skipping mode disables the synchronous rectification during light load and generates a random noise spectrum which may produce EMI problems. Worst case current of 10 A can be handled with two paralleled Si4435DY and two paralleled Si4410DY MOSFETs, which results in the efficiency levels shown in Figure 9. 100 VIN = 5 V VOUT = 2.9 V Efficiency (%) Siliconix’ TrenchFETt technology has resulted in 20-mW n-channel (Si4410DY) and 35-mW p-channel (Si4435DY) MOSFETs in the SO-8 surface-mount package. These LITTLE FOOTr products totally eliminate the need for an external heatsink. 95 90 85 Phase 80 0 2 4 IOUT (A) 6 8 10 Gain (dB) FIGURE 9. Efficiency Phase (deg) Gain Frequency (Hz) FIGURE 8. Non-Synchronous Converter BW Good electrical designs must provide an adequate margin for the specification, but they should not be grossly overdesigned to lower costs. LITTLE FOOT power MOSFETs allow designers to balance cost and performance considerations without sacrificing either. If the design requires only an 8.5-A continuous current, for example, one Si4410DY can be eliminated. Table 2 shows the number of MOSFETs required to handle the various output current levels of today’s highperformance microprocessors. For other output power levels, the equations below should be used to calculate the power handling capability of the MOSFET. TABLE 2. CONVERTER REQUIREMENTS (FIGURES 1, 2, AND 3) IO (A) Maximum 5A 8.5 A 10 A 14.5 A Document Number: 70026 S-40699—Rev. H, 19-Apr-04 Quantity High-Side P-Channel Si4435DY 1 2 2 3 Quantity Low-Side N-Channel Si4410DY 1 1 2 2 Quantity Input (C1-C3) Capacitor Os-con 220 mF 1 2 2 3 www.vishay.com 13 Si9140 Vishay Siliconix PDissipation in switch + IRMS SW 2 RSW ) Q SW V IN 2 VO V IN Q RECT V IN 2 f OSC f OSC ) I PP VO 2 tC fOSC IRMS SW + IPEAK 2 ) IPP 2 ) I PEAK IPP 3 PDissipation in synchronous rectification + IRMS RECT2 RRECT ) I RMS RECT + I PEAK 2 ) I PP 2 ) I PEAK I PP (V IN – V ) O 3V IN IPP = IPEAK + DI DI + L V O2 f OSC V IN IPEAK + PIN – (0.5 VO VO IO DI) PIN + VO IRMSSW RSW IRMSRECT RRECT QSW QRECT VIN VO IO fOSC h tC = = = = = = = = = = = = Switch rms current Switch on resistance Synchronous rectifier rms current Synchronous rectifier on resistance Total gate charge of switch Total gate charge of synchronous rectifier Input voltage Output voltage Output current Switching frequency efficiency Crossover time h Current IO IPEAK 0A IPP time Inductor The size and value of the inductor are critical in meeting overall circuit dimensional requirements and in assuring proper transient voltage regulation. The size of the core is determined by the output power, the material of the core, and the operating frequency. To handle higher output power, the core must be larger. Luckily, a higher switching frequency will lower the inductance value, decreasing the core size. However, a higher switching frequency can also mean greater core loss. In applications where the dc flux density is high and the ac flux density swing is only 100 to 200 gauss, the core loss will be www.vishay.com negligible compared to the wire loss. Kool Mu is the best material to use at 500 kHz to deliver 30 W in the minimum volume. Ferrite has a lower core cost and loss at this frequency, but the core size is fairly large. If the power supply is designed on the motherboard and space is not a critical issue, ferrite is a better choice. The higher switching frequency reduces the core size by decreasing the amount of energy that must be stored between switching periods. It also accelerates the transient response to the load by decreasing the inductance value. The inductance is calculated with following equation: Document Number: 70026 S-40699—Rev. H, 19-Apr-04 14 Si9140 Vishay Siliconix L+ V IN V O2 DI f OSC of Sanyo (OS-CON) input capacitors required to handle various output currents are specified in Table 2. Output Capacitor To regulate the microprocessor’s input voltage within 145 mV during 10-A load transients, a large output capacitance with low ESR is required. The output capacitor of the power supply and decoupling capacitors at the microprocessor must hold up the processor voltage until the power supply responds to the change. Even with fastest known switching solution, it still takes three 330-mF OS-CON capacitors to handle the load transient. If it weren’t for the 10-A load transient, the output capacitor would not need a low ESR value. The fundamental output ripple current in a continuous step-down converter is much lower than the input ripple current. Maintaining voltage regulation during transients requires an ESR in the range of 30 mW . For microprocessors with lower transient requirements, the number of output and decoupling capacitors can be reduced. The lower transient requirements also allows greater consideration for Tantalum or Nichicon PL series capacitors. Conclusion The Si9140 synchronous Buck controller’s ability to switch up to 1 MHz combined with a 25-MHz error amplifier provides the best solution in powering high- performance microprocessors. The high switching frequency reduces inductor size without compromising output ripple voltage. The wide converter bandwidth generated with the help of a 25-MHz error amplifier reduces the amount of decoupling capacitors required to handle the extreme transient requirement. The Si9140’s synchronous fixed-frequency operation eliminates the pulse skipping mode that generates random unpredictable EMI/EMC problems in desktop and notebook computers. The synchronous rectification also allows the converter to operate in continuous current mode, independent of output load current. This preserves the wide closed-loop converter bandwidth required to meet the transient demand of the microprocessor as it transitions from stop clock and auto halt to active mode. The synchronous rectification improves the efficiency of the converter by substituting the much smaller I2R MOSFET loss for the VI diode loss. The need for heatsinking is eliminated by using low rDS(on) TrenchFETs (Si4410DY and Si4435DY). DI = desired output current ripple. Typically DI = 25% of maximum output current. Finally, the time required to ramp up the current in the inductor can be reduced with smaller inductance. A quick response from the power supply relaxes the decoupling capacitance required at the microprocessor, reducing the overall solution cost and size. Input Capacitor The input capacitor’s function is to filter the raw power and serve as the local power source to eliminate power-up and transient surge failures. The type and characteristics of input capacitors are determined by the input power and inductance of the step-down converter. The ripple current handling requirement usually dominates the selection criteria. The capacitance required to maintain regulation will automatically be achieved once it meets the ripple current requirement. The following equation calculates the ripple current of the input capacitor: IRIPPLE + IRMSSW 2 – I IN2 An aluminum-electrolytic capacitor from Sanyo (OS-CON), AVX (TPS Tantalum), or Nichicon (PL series) should be used in high-power (30-W) applications to handle the ripple current. The Sanyo capacitor is smaller and handles higher ripple current than Nichicon, but at higher cost than the Nichicon product. The AVX Tantalum capacitor has the best capacitance and current handling capability per volume ratio, but it takes extra surface area compared to OS-CON or PL series. The TPS capacitors, lead time and cost have increased drastically in the recent past due to high demand, causing designers to shy away from the TPS Tantalum capacitors. Nichicon capacitors can be used to provide an economical solution if space is available or a large bulk capacitance is already present on the input line. The number Document Number: 70026 S-40699—Rev. H, 19-Apr-04 www.vishay.com 15 Legal Disclaimer Notice Vishay Notice Specifications of the products displayed herein are subject to change without notice. Vishay Intertechnology, Inc., or anyone on its behalf, assumes no responsibility or liability for any errors or inaccuracies. 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Document Number: 91000 Revision: 08-Apr-05 www.vishay.com 1 Package Information Vishay Siliconix SOIC (NARROW): JEDEC Part Number: MS-012 16-LEAD (POWER IC ONLY) MILLIMETERS Dim A A1 B C D E e H L Min 1.35 0.10 0.38 0.18 9.80 3.80 5.80 0.50 0_ INCHES Min 0.053 0.004 0.015 0.007 0.385 0.149 0.228 0.020 0_ Max 1.75 0.20 0.51 0.23 10.00 4.00 6.20 0.93 8_ Max 0.069 0.008 0.020 0.009 0.393 0.157 0.244 0.037 8_ 16 15 14 13 12 11 10 9 E 1.27 BSC 0.050 BSC 1 2 3 4 5 6 7 8 ECN: S-40080—Rev. A, 02-Feb-04 DWG: 5912 D H C All Leads e B A1 L 0.101 mm 0.004 IN Document Number: 72807 28-Jan-04 www.vishay.com 1 Package Information Vishay Siliconix TSSOP: 16-LEAD DIMENSIONS IN MILLIMETERS Symbols A A1 A2 B C D E E1 e L L1 y θ1 ECN: S-61920-Rev. D, 23-Oct-06 DWG: 5624 Min 0.05 0.22 4.90 6.10 4.30 0.50 0.90 0° Nom 1.10 0.10 1.00 0.28 0.127 5.00 6.40 4.40 0.65 0.60 1.00 3° Max 1.20 0.15 1.05 0.38 5.10 6.70 4.50 0.70 1.10 0.10 6° Document Number: 74417 23-Oct-06 www.vishay.com 1 Legal Disclaimer Notice Vishay Disclaimer ALL PRODUCT, PRODUCT SPECIFICATIONS AND DATA ARE SUBJECT TO CHANGE WITHOUT NOTICE TO IMPROVE RELIABILITY, FUNCTION OR DESIGN OR OTHERWISE. Vishay Intertechnology, Inc., its affiliates, agents, and employees, and all persons acting on its or their behalf (collectively, “Vishay”), disclaim any and all liability for any errors, inaccuracies or incompleteness contained in any datasheet or in any other disclosure relating to any product. Vishay makes no warranty, representation or guarantee regarding the suitability of the products for any particular purpose or the continuing production of any product. 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