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LMQ61460 bảng dữ liệu(PDF) 30 Page - Texas Instruments |
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LMQ61460 bảng dữ liệu(HTML) 30 Page - Texas Instruments |
30 / 55 page Table 8-2. Typical External Component Values fSW (kHz) VOUT (V) L1 (µH) COUT (RATED) RFBT (kΩ) RFBB (kΩ) CBOOT (µF) RBOOT (Ω) CVCC (µF) CFF (pF) RFF (kΩ) 2100 3.3 1 3 × 22 µF ceramic 100 43.2 0.1 0 1 10 1 400 3.3 4.7 3 × 47 µF ceramic 100 43.2 0.1 0 1 4.7 1 2100 5 1.5 2 × 22 µF ceramic 100 24.9 0.1 0 1 22 1 400 5 4.7 2 × 47 µF ceramic 100 24.9 0.1 0 1 22 1 8.2.2 Detailed Design Procedure The following design procedure applies to Figure 8-1 and Table 8-1. 8.2.2.1 Choosing the Switching Frequency The choice of switching frequency is a compromise between conversion efficiency and overall solution size. Lower switching frequency implies reduced switching losses and usually results in higher system efficiency. However, higher switching frequency allows for the use of smaller inductors and output capacitors, hence, a more compact design. When choosing operating frequency, the most important consideration is thermal limitations. This constraint typically dominates frequency selection. See Figure 8-2 for circuits running at 400 kHz and Figure 8-3 for circuits running at 2.1 MHz. These curves show how much output current can be supported at a given ambient temperature given these switching frequencies. Note that power dissipation is layout dependent so while these curves are a good starting point, thermal resistance in any design will be different from the estimates used to generate Figure 8-2 and Figure 8-3. The maximum temperature ratings are based on the LMQ61460EVM, which is approximately 100 mm x 80 mm in board area. Unless a larger copper area or cooling is provided to reduce the effective RθJA, if ambient temperature is 105°C and the switching frequency is set to 2.1 MHz, the load current should typically be limited to 4 A. Output Current (A) 3 3.5 4 4.5 5 5.5 6 85 90 95 100 105 110 115 120 125 130 snvs VIN = 13.5 V VIN = 16 V VIN = 24 V fSW = 400 kHz PCB RθJA = 25°C/W VOUT = 5 V Figure 8-2. Maximum Ambient Temperature versus Output Current Output Current (A) 2 2.5 3 3.5 4 4.5 5 5.5 6 65 75 85 95 105 115 125 135 snvs VIN = 13.5 V VIN = 16 V VIN = 24 V fSW = 2100 kHz PCB RθJA = 25°C/W VOUT = 5 V Figure 8-3. Maximum Ambient Temperature versus Output Current Two other considerations are what maximum and minimum input voltage the part must maintain for the frequency setting. Since the device adjusts its frequency under conditions in which regulation would normally be prevented by minimum on-time or minimum off-time, these constraints are only important for input voltages requiring constant frequency operation. If foldback is undesirable at high input voltage, use Equation 7: LMQ61460 SNVSBR8A – JULY 2020 – REVISED AUGUST 2020 www.ti.com 30 Submit Document Feedback Copyright © 2020 Texas Instruments Incorporated Product Folder Links: LMQ61460 |
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Mô tả tương tự - LMQ61460 |
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