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ILC6383CIR33X датащи(PDF) 6 Page - Fairchild Semiconductor |
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ILC6383CIR33X датащи(HTML) 6 Page - Fairchild Semiconductor |
6 / 15 page ILC6383 PRODUCT SPECIFICATION 6 REV. 1.2.6 6/13/02 Applications Information The ILC6383 performs boost DC-DC conversion by control- ling the switch element as shown in the simplified circuit in Figure 3 below. Figure 3. Basic Boost Circuit When the switch is closed, current is built up through the inductor. When the switch opens, this current is forced through the diode to the output. As this on and off switching continues, the output capacitor voltage builds up due to the charge it is storing from the inductor current. In this way, the output voltage is boosted relative to the input. In general, the switching characteristic is determined by the output voltage desired and the current required by the load. The energy transfer is determined by the power stored in the coil during each switching cycle. PL = ƒ(tON, VIN) Synchronous Rectification The ILC6383 also uses a technique called “synchronous rectification” which removes the need for the external diode used in other circuits. The diode is replaced with a second switch or in the case of the ILC6383, an FET as shown in Figure 4 below. Figure 4. Simplified ILC6382 block diagram The two switches now open and close in opposition to each other, directing the flow of current to either charge the induc- tor or to feed the load. The ILC6383 monitors the voltage on the output capacitor to determine how much and how often to drive the switches. PWM Mode Operation The ILC6383 uses a PWM or Pulse Width Modulation technique. The switches are constantly driven at typically 300kHz. The control circuitry varies the power being deliv- ered to the load by varying the on-time, or duty cycle, of the switch SW1 (see Fig. 5). Since more on-time translates to higher current build-up in the inductor, the maximum duty cycle of the switch determines the maximum load current that the device can support. The minimum value of the duty cycle determines the minimum load current that can main- tain the output voltage within specified values. There are two key advantages of the PWM type controllers. First, because the controller automatically varies the duty cycle of the switch's on-time in response to changing load conditions, the PWM controller will always have an opti- mized waveform for a steady-state load. This translates to very good efficiency at high currents and minimal ripple on the output. Ripple is due to the output cap constantly accept- ing and storing the charge received from the inductor, and delivering charge as required by the load. The “pumping” action of the switch produces a sawtooth-shaped voltage as seen by the output. The other key advantage of the PWM type controllers over pulse frequency modulated (PFM) type is that the radiated noise due to the switching transients will always occur at the (fixed) switching frequency. Many applications do not care much about switching noise, but certain types of applica- tions, especially communication equipment, need to mini- mize the high frequency interference within their system as much as possible. Use of the PWM converter is those cases is desirable. PFM Mode Operation For light loads the ILC6383 can be switched to PFM technique at low currents. This technique conserves power loss by only switching the output if the current drain requires it. As shown in the Figure 5, the waveform actually skips pulses depending on the power needed by the output. This technique is also called “pulse skipping” because of this characteristic. In the ILC6383, the switchover from PWM to PFM mode is determined by the user to improve efficiency and conserve power. Figure 5. PFM Waveform VOUT POK LBO LB/SD SEL GND LX VIN ILC6383 PWM/PFM CONTROLLER SHUTDOWN CONTROL VREF DELAY + + - - SW1 SW2 VSET VOUT Switch Waveform |
Аналогичный номер детали - ILC6383CIR33X |
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Аналогичное описание - ILC6383CIR33X |
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