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 3.3 Vdc to 9.0 Vdc and the output of 3.3 V ± 5%. 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.
SLUU111 – June 2002 1-MHz, 3.3-V, High-Efficiency Synchronous Buck Converter With TPS43000 PWM Controller Systems Power Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 Test Results . . . . . . . . . . . . . . . . . . . . .
SLUU111 – June 2002 + Figure 1. TPS43000–001EVM Schematic 2 Design Procedure 2.1 Frequency Setting The TPS43000 can operate either in constant frequency, or in an automatic PFM mode. In the automatic PFM mode, the gate driver turns off when the inductor current goes discontinuous, and turns on when the output voltage has fallen by 2%. This pulse skipping can decrease gate-drive losses and significantly improve the efficiency at light load. (Refer to the TPS43000 Data Sheet, TI Literature No.
SLUU111 – June 2002 2.2 Inductance Value The inductance value can be calculated as shown in equation (2). L (min) + ǒ V OUT f I RIPPLE 1* V OUT V IN(max) Ǔ (2) IRIPPLE is the ripple current flowing through the inductor, which affects the output voltage ripple and core losses. According to the specification, the converter enters PFM mode at 200 mA, so the desired ripple current it 0.4 A. Based on this and the 1-MHz operating frequency, the inductance value is calculated at 5.0 µH. 2.
SLUU111 – June 2002 The transfer function for the compensator is calculated as: (1 ) s A(s) + s R1 C1 C1 R2) Ǔ)s ǒ1 ) ǒC2 C1 (1 ) s C3 (R1 ) R3)) C2 R2 (1 ) s Ǔ R3) C3 The compensator values are calculated as: C1 = 270 pF, C2 = 3.0 pF, C3 = 560 pF, R1 = 100 kΩ, R2 = 115 kΩ, and R3 = 5.76 kΩ. POWER STAGE GAIN AND PHASE vs FREQUENCY 50 25 0 Gain – dB –25 GAIN –50 –75 –100 PHASE –125 –150 –175 –200 10 100 1k 10 k 100 k 1M f – Output Frequency – Hz Figure 2. 2.
SLUU111 – June 2002 2.6 Current Limiting Two types of current limiting can be selected from the controller. Detailed information is available in the datasheet (TI Literature No. SLUS489). A jumper, JP2, is used to choose different current limiting. By tying the CCS pin to VIN, the controller enters pulse-by-pulse current limiting and the current-limiting threshold is calculated by equation (6): I MAX ǒp*pǓ + 150 mV R DS(on) (6) in which RDS(on) is the on-resistance of Q2.
SLUU111 – June 2002 3 Test Results 3.1 Efficiency Curves Efficiency tested at different loads and input voltages is shown in Figure 4. The maximum efficiency is as high as 94% at 0.5 A output. The light-load efficiency is improved due to the PFM operation mode. 3.2 Typical Operation Waveform Typical operating waveforms are shown in Figure 5 with VIN = 4.5 V and IOUT = 2 A. EFFICIENCY vs LOAD CURRENT AND INPUT VOLTAGE OPERATING WAVEFORMS DURING OVERLOAD VIN = 4.
SLUU111 – June 2002 3.3 Output Ripple Voltage and Transient Response The output ripple is approximately 28.8 mV peak-to-peak with a 1.5 A output and is shown in Figure 4. Figure 5 shows load changes from 0.5 A to 1.5 A, where the overshooting voltage is approximately 10 mV. IOUT = 5 A VOUT (10 mV/div) VOUT(ac) (10 mV/div) IOUT (1 A/div) t – Time – 500 µs / div t – Time – 500 ns / div Figure 5. Output Ripple 4 Figure 6. Transient Response PCB Layout Figures 7 through 9 show the PCB layout .
SLUU111 – June 2002 Figure 8. Top Layer Figure 9. Bottom Layer 1-MHz, 3.
SLUU111 – June 2002 5 Bill of Materials Table 1 lists the board components and their values, which can be modified to meet the application requirements. .
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