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LT1613 数据表(PDF) 12 Page - Linear Technology |
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LT1613 数据表(HTML) 12 Page - Linear Technology |
12 / 28 page LT3580 12 3580fg APPLICATIONS INFORMATION Using the circuit in Figure 14 as an example, Table 3 shows the parameters used to generate the bode plot shown in Figure 5. Table 3. Bode Plot Parameters PARAMETER VALUE UNITS COMMENT RL 21.8 Ω Application Specific COUT 10 μF Application Specific RESR 10 m Ω Application Specific RO 305 k Ω Not Adjustable CC 1000 pF Adjustable CF 0 pF Optional/Adjustable CPL 0 pF Optional/Adjustable RC 10 k Ω Adjustable R1 130 k Ω Adjustable R2 14.6 k Ω Not Adjustable VOUT 12 V Application Specific VIN 5 V Application Specific gma 230 μmho Not Adjustable gmp 7 mho Not Adjustable L 4.2 μH Application Specific fS 1.2 MHz Adjustable In Figure 5, the phase is –140° when the gain reaches 0dB giving a phase margin of 40°. The crossover frequency is 10kHz, which is more than three times lower than the frequency of the RHP zero to achieve adequate phase margin. Diode Selection Schottky diodes, with their low forward voltage drops and fast switching speeds, are recommended for use with the LT3580. The Microsemi UPS120 is a very good choice. Where the input-to-output voltage differential exceeds 20V, use the UPS140 (a 40V diode). These diodes are rated to handle an average forward current of 1A. Oscillator The operating frequency of the LT3580 can be set by the internal free-running oscillator. When the SYNC pin is driven low (< 0.4V), the frequency of operation is set by a resistor from RT to ground. An internally trimmed timing capacitor resides inside the IC. The oscillator frequency is calculated using the following formula: f OSC = 91.9 (R T + 1) where fOSC is in MHz and RT is in kΩ. Conversely, RT (in k Ω) can be calculated from the desired frequency (in MHz) using: R T = 91.9 f OSC − 1 Clock Synchronization The operating frequency of the LT3580 can be synchronized to an external clock source. To synchronize to the external source, simply provide a digital clock signal into the SYNC pin. The LT3580 will operate at the SYNC clock frequency. The LT3580 will revert to the internal free-running oscillator clock after SYNC is driven low for a few free-running clock periods. Driving SYNC high for an extended period of time effectively stops the operating clock and prevents latch SR1 from becoming set (see the Block Diagram). As a result, the switching operation of the LT3580 will stop. The duty cycle of the SYNC signal must be between 35% and 65% for proper operation. Also, the frequency of the SYNC signal must meet the following two criteria: Figure 5. Bode Plot for Example Boost Converter FREQUENCY (Hz) 10 60 80 100 120 140 100 1k 10k 100k 1M 3580 F05 40 20 0 –20 160 180 –120 –100 –80 –60 –40 –140 –160 –180 –200 –20 0 40 AT 10kHz PHASE GAIN |
类似零件编号 - LT1613 |
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类似说明 - LT1613 |
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