поискавой системы для электроныых деталей |
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LM3401 датащи(PDF) 9 Page - Texas Instruments |
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LM3401 датащи(HTML) 9 Page - Texas Instruments |
9 / 27 page 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 0 250 500 750 1000 1250 1500 = calculated value 68 PH 22 PH L = D fSW - (2 x delay) x RSNS x (VIN - VANODE) 2 x SNSHYS fSW = 2 x SNSHYS x L RSNS x (VIN - VANODE) D + (2 x delay) 50 110 175 255 340 425 505 VHYS (mV) 0 300 600 900 1200 1500 1800 0 300 600 900 1200 1500 1800 22 PH freq 68 PH freq 68 PH rip 22 PH rip LM3401 www.ti.com SNVS516C – AUGUST 2007 – REVISED MAY 2013 Figure 16. Switching Frequency and Ripple Current vs Hysteresis SWITCHING FREQUENCY Although hysteretic control is a simple control method, the switching frequency depends on application conditions and components. If the inductance, input voltage, or LED forward voltage is changed, there will be a change in the switching frequency. Therefore, care must be taken to select components which will provide the desired frequency range. Usually, the best approach is to determine a nominal switching frequency for the application and then select the inductor accordingly. Once the inductor is selected, VHYS can be adjusted to set the frequency range more precisely. This design process usually involves a few iterations to select appropriate standard values that will result in the desired frequency and ripple current. Switching frequency can be approximately calculated using the formula: (8) Where D is the duty cycle, defined as (VOUT + VDIODE) / VIN, VANODE is 200 mV plus the sum of LED forward voltages, and delay is the sum of the LM3401 propagation delay time and the PFET delay time. The LM3401 propagation delay is 46 ns typically (See the Propagation Delay curve). Alternately, the inductor value can be calculated from a known frequency by re-arranging the same equation: (9) Switching frequency for a typical application is shown in Figure 17 along with the calculated frequency. Figure 17. Frequency vs Input Voltage Maximum switching frequency will typically occur around the input voltage which corresponds to 25% duty cycle. Copyright © 2007–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3401 |
Аналогичный номер детали - LM3401 |
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Аналогичное описание - LM3401 |
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