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MC34163 bảng dữ liệu(PDF) 9 Page - ON Semiconductor |
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MC34163 bảng dữ liệu(HTML) 9 Page - ON Semiconductor |
9 / 16 page MC34163 MC33163 9 MOTOROLA ANALOG IC DEVICE DATA Figures 11 and 12 show that the Current Sense comparator threshold is tightly controlled over temperature and has a typical input bias current of 1.0 µA. The propagation delay from the comparator input to the Output Switch is typically 200 ns. The parasitic inductance associated with RSC and the circuit layout should be minimized. This will prevent unwanted voltage spikes that may falsely trip the Current Limit comparator. Internal thermal shutdown circuitry is provided to protect the IC in the event that the maximum junction temperature is exceeded. When activated, typically at 170 °C, the Latch is forced into the “Set” state, disabling the Output Switch. This feature is provided to prevent catastrophic failures from accidental device overheating. It is not intended to be used as a replacement for proper heatsinking. Driver and Output Switch To aid in system design flexibility and conversion efficiency, the driver current source and collector, and output switch collector and emitter are pinned out separately. This allows the designer the option of driving the output switch into saturation with a selected force gain or driving it near saturation when connected as a Darlington. The output switch has a typical current gain of 70 at 2.5 A and is designed to switch a maximum of 40 V collector to emitter, with up to 3.4 A peak collector current. The minimum value for RSC is: RSC(min) + V A + 0.25 3.4 0.0735 Ω When configured for step–down or voltage–inverting applications, as in Figures 20 and 24, the inductor will forward bias the output rectifier when the switch turns off. Rectifiers with a high forward voltage drop or long turn–on delay time should not be used. If the emitter is allowed to go sufficiently negative, collector current will flow, causing additional device heating and reduced conversion efficiency. Figure 9 shows that by clamping the emitter to 0.5 V, the collector current will be in the range 10 µA over temperature. A 1N5822 or equivalent Schottky barrier rectifier is recommended to fulfill these requirements. A bootstrap input is provided to reduce the output switch saturation voltage in step–down and voltage–inverting converter applications. This input is connected through a series resistor and capacitor to the switch emitter and is used to raise the internal 2.0 mA bias current source above VCC. An internal zener limits the bootstrap input voltage to VCC +7.0 V. The capacitor’s equivalent series resistance must limit the zener current to less than 100 mA. An additional series resistor may be required when using tantalum or other low ESR capacitors. The equation below is used to calculate a minimum value bootstrap capacitor based on a minimum zener voltage and an upper limit current source. C B(min) + I ∆ t ∆V + mA ton V + ton 4.0 4.0 0.001 Parametric operation of the MC34163 is guaranteed over a supply voltage range of 2.5 V to 40 V. When operating below 3.0 V, the Bootstrap Input should be connected to VCC. Figure 15 shows that functional operation down to 1.7 V at room temperature is possible. Package The MC34163 is contained in a heatsinkable 16–lead plastic dual–in–line package in which the die is mounted on a special heat tab copper alloy lead frame. This tab consists of the four center ground pins that are specifically designed to improve thermal conduction from the die to the circuit board. Figures 16 and 17 show a simple and effective method of utilizing the printed circuit board medium as a heat dissipater by soldering these pins to an adequate area of copper foil. This permits the use of standard layout and mounting practices while having the ability to halve the junction–to–air thermal resistance. These examples are for a symmetrical layout on a single–sided board with two ounce per square foot of copper. APPLICATIONS The following converter applications show the simplicity and flexibility of this circuit architecture. Three main converter topologies are demonstrated with actual test data shown below each of the circuit diagrams. |
Số phần tương tự - MC34163 |
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Mô tả tương tự - MC34163 |
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