User’s Guide User’s Guide 1
EVM IMPORTANT NOTICE Texas Instruments (TI) provides the enclosed product(s) under the following conditions: This evaluation kit being sold by TI is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not considered by TI to be fit for commercial use.
DYNAMIC WARNINGS AND RESTRICTIONS It is important to operate this EVM within the input voltage range of 0 Vdc to100 Vdc. Exceeding the specified input range may cause unexpected operation and/or irreversible damage to the EVM. If there are questions concerning the input range, please contact a TI field representative prior to connecting the input power. Applying loads outside of the specified output range may result in unintended operation and/or possible permanent damage to the EVM.
SLUU195 − June 2004 TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.5-V at 100 A Systems Power Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Schematic . . . . . . . . . . . . . .
SLUU195 − June 2004 2 Features Table 1. TPS40090EVM−002 Performance Summary PARAMETER TEST CONDITIONS Input voltage range Output voltage set point Output current range MIN TYP 12.0 14.0 1.477 1.508 1.540 0 100 120 Load regulation VIN = 12 V IOUT rising from 10 A to 100 A, 10.
SLUU195 − June 2004 TRANS_EN Figure 2. TPS40090EVM−002 Schematic Part 2 − Driver Circuit and Load Transient Generator 6 TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.
SLUU195 − June 2004 + + + + + + + + 1.5V/100A Figure 3. TPS40090EVM−002 Schematic Part 3 − Power Stage 4 Component Selection 4.1 Frequency of Operation The clock oscillator frequency for the TPS40090 is programmed with a single resistor from RT (pin 16) to signal ground. Equation (1) from the datasheet allows selection of the RT resistor in kΩ for a given switching frequency in kHz. R T + R12 + K PH ǒ39.2 10 3 f *1.
SLUU195 − June 2004 4.2 Inductance Value The output inductor value for each phase can be calculated from the volt-second during off time, shown in equation (2). L+ V OUT f I RIPPLE ǒ 1* V OUT V IN(max) Ǔ (2) where • IRIPPLE is usually chosen to be between 10% and 40% of maximum phase current IPH(max). With IRIPPLE = 20% of IPH(max), there is a ripple current of 5 A, and the inductance value is found to be 0.63 µH. Using SPM12550−R62M300 inductors from TDK, each had inductance of 0.
SLUU195 − June 2004 IRMS_CIN(nom) − Normalized RMS Input − A 0.6 NPH = 1 0.5 0.4 0.3 NPH = 2 0.2 NPH = 3 NPH = 4 0.1 NPH = 6 0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle − % Figure 4. Input Ripple Current RMS Value Overload Current The maximum input ripple RMS current can be estimated as shown in (4). I ^ I OUT D I IN(nom) ǒ4, D minǓ + 3.
SLUU195 − June 2004 where • D is the duty cycle for a single phase • NPH is the number of active phases • K (NPH) is the intermediate function for calculation In this case, NPH=4 and Dmin=0.107 which yields k=0.573. The actual output ripple is calculated in equation (7) V I RIPPLE + OUT L f KǒN PH, DǓ + 1.5 V 0.6m H 420 kHz (7) 0.573 + 3.41 A IRMS_Cout(nom) − Normalized RMS Input − A 1.0 NPH = 4 0.8 0.6 NPH = 3 NPH = 1 0.4 NPH = 2 0.
SLUU195 − June 2004 3. Transient consideration. An additional consideration in the selection of the output inductor and capacitance value can be derived from examining the transient voltage overshoot which can be initiated with a load step from full load to no load. By equating the inductive energy with the capacitive energy the equation (10) can be derived. C OUT +L I2 V2 L EQ + ǒǒ I OHǓ * ǒI OLǓ ǒVOUT2Ǔ 2 2 * ǒV OUT1Ǔ Ǔ 2 2 + 0.6mH 4 (100 A) 2 ǒ(1.75 V)2 * (1.
SLUU195 − June 2004 With the chosen inductor described in Inductance Value, (section 4.2, of this document) the following values are used. • R=19.6 kΩ • C=10 nF • RNTC=100 kΩ • R1=124 kΩ • R2=22.6 kΩ L DCR VIN VDCR L DCR C R VIN VOUT R R1 C R2 VC RNTC RTHE UDG−03136 Figure 6. DCR Current Sensing Circuit with Copper Temperature Compensation 4.
SLUU195 − June 2004 4.8 Compensation Components The TPS40090 uses peak current mode control. Type II network is used here, which is implemented to provide one zero and two poles. The first pole is placed at the origin to improve DC regulation. The ESR zero of the power stage is: f ESRZ + 1 RC 2p C OUT + 354 kHz (12) The zero is placed near 3.96 kHz to produce a reasonable time constant. fZ + 2p 1 R11 (13) C11 The second pole is placed at ESR zero (354 kHz).
SLUU195 − June 2004 5 Test Setup The HPA072 has the following input/output connections: 12-V input J1 (VIN) and J2 (GND), 1.5-V output J9 (VOUT) and J10 (GND). A diagram showing the connection points is shown in Figure 5. A power supply capable of supplying 18 A should be connected to VIN and GND through a pair of 10 AWG wires. The 1.5-V load should be connected respectively to J9 and J10 through pairs of 0 AWG wires. Wire lengths should be minimized to reduce losses in the wires.
SLUU195 − June 2004 6 Test Results and Performance Data 6.1 Efficiency and Power Loss Figure 8 shows the efficiency as the load varies from 10 A to over 100 A. The efficiency at full load is about 84.3%. Figure 7 shows the total loss versus the load current, which is approximately 28.3W at 100 A.
SLUU195 − June 2004 6.2 Closed-Loop Performance The TPS40090 uses peak current-mode control. Figure 10 shows the bode plots at 100 A of load current, where no droop function is implemented. The crossover frequency is at 89 kHz with phase margin of 40°. GAIN AND PHASE vs OSCILLATOR FREQUENCY 80 180 135 60 90 40 45 20 0 Phase − 5 Gain − dB PHASE −45 0 −90 −20 −40 100 GAIN VIN = 12 V VOUT = 1.5 V IOUT = 10 A −135 −180 1k 10 k 100 k fOSC − Oscillator Frequency − kHz 1M Figure 10.
SLUU195 − June 2004 6.4 Transient Response The on-board load transient circuit enables to check the step load transient response on the same board. Simply by putting a jumper to connect Pin1 and 2 of J3, a 90-A step load is created by three 50-mΩ resistors placed on the board. The slew rates of the transient are 200 A/µs for the load step-down and 160 A/µs for the load step-up. The transient response is shown in Figure 6 as the load is stepped from 10 to 100 A.
SLUU195 − June 2004 6.5 Start up with Pre-Biased Output In synchronous buck converter, the bottom FET discharges the pre-biased output during start-up. To avoid this, a comparator U9 and surround components are used to pull the SYNC pin of the drivers low, which keeps the bottom FET off during startup. So the output can rise smoothly. After the SS pin comes up, SYNC is pulled up high and enable the bottom FET’s driving signal. The converter goes back to normal synchronization mode.
SLUU195 − June 2004 7 Layout Considerations The PCB layout plays a critical role in the performance in a high frequency switching power supply design. Following the suggestions listed below will help to improve the performance and expedite the design. • To take full advantage of the ripple cancellation factor from interleaving, place the input capacitors before the junction where the input voltage is distributed to each phase.
SLUU195 − June 2004 8 EVM Assembly Drawing and PCB Layout Figure 15. Top Side Component Assembly Figure 16. Bottom Assembly 20 TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.
SLUU195 − June 2004 Figure 17. Top Side Copper Figure 18. Internal 1 (Ground Plane) TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.
SLUU195 − June 2004 Figure 19. Internal 2 (Power Plane) Figure 20. Internal 3 22 TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.
SLUU195 − June 2004 Figure 21. Internal 4 Figure 22. Bottom Layer Copper TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.
SLUU195 − June 2004 9 List of Materials The following table lists the TPS40090EVM−002 components corresponding to the schematic shown in Figure 1. Table 2. List of Materials Reference Designator QTY Description Size Manufacturer Part Number 2 Capacitor, OS−CON, 68 µF, 20 V, 40 mΩ, 20% 10.3mm (F8) Sanyo 20SVP68M 7 Capacitor, ceramic, 1000−pF, 25 V, X7R, ±5% 603 muRata GRM39SL102J25 5 Capacitor, dielectric, 1.0 µF, 16 V, X7R, ±10% 805 muRata GRM40B105K16 0 1 Capacitor, ceramic, 0.
SLUU195 − June 2004 Reference Designator QTY R27, R28, R29, R30 4 Size Manufacturer Part Number Resistor, chip, 2.2 Ω, 1/10−W, 1% 805 Std Std 4 Resistor, chip, 19.6 kΩ, 1/10−W, 1% 805 Std Std 8 Resistor, chip, 2.7 Ω, 1/16−W, 1% 603 Std Std R39, R40, R43, R44 4 Resistor, chip, 22.6 kΩ, 1/10−W, 1% 805 Std Std R47, R49, R51, R52 4 Resistor, chip, 124 kΩ, 1/10−W, 1% 805 Std Std 805 Vishay 805 0.25 0.25 108,800 PWP14 TSSOP 8 0.
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