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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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CS5151GD16 Fiches technique(PDF) 11 Page - Cherry Semiconductor Corporation |
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CS5151GD16 Fiches technique(HTML) 11 Page - Cherry Semiconductor Corporation |
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11 / 14 page  Applications Information: continued 11 COFF timing capacitor: COFF = , where: Period = “Droop” Resistor for Adaptive Voltage Positioning Adaptive voltage positioning is used to reduce output volt- age excursions during abrupt changes in load current. Regulator output voltage is offset +40mV when the regula- tor is unloaded, and -40mV at full load. This results in increased margin before encountering minimum and maxi- mum transient voltage limits, allowing use of less capaci- tance on the regulator output (see Figure 7). To implement adaptive voltage positioning, a “droop” resistor must be connected between the output inductor and output capacitors and load. This is normally imple- mented by a PC board trace of the following value: RDROOP = Adaptive voltage positioning can be disabled for improved DC regulation by connecting the VFB pin directly to the load using a separate, non-load current carrying circuit trace. Input and Output Capacitors These components must be selected and placed carefully to yield optimal results. Capacitors should be chosen to pro- vide acceptable ripple on the input supply lines and regula- tor output voltage. Key specifications for input capacitors are their ripple rating, while ESR is important for output capacitors. For best transient response, a combination of low value/high frequency and bulk capacitors placed close to the load will be required. Output Inductor The inductor should be selected based on its inductance, current capability, and DC resistance. Increasing the induc- tor value will decrease output voltage ripple, but degrade transient response. Thermal Considerations for Power MOSFETs and Diodes In order to maintain good reliability, the junction tempera- ture of the semiconductor components should be kept to a maximum of 150°C or lower. The thermal impedance (junc- tion to ambient) required to meet this requirement can be calculated as follows: Thermal Impedance = A heatsink may be added to TO-220 components to reduce their thermal impedance. A number of PC board layout techniques such as thermal vias and additional copper foil area can be used to improve the power handling capability of surface mount components. EMI Management As a consequence of large currents being turned on and off at high frequency, switching regulators generate noise as a consequence of their normal operation. When designing for compliance with EMI/EMC regulations, additional com- ponents may be added to reduce noise emissions. These components are not required for regulator operation and experimental results may allow them to be eliminated. The input filter inductor may not be required because bulk filter and bypass capacitors, as well as other loads located on the board will tend to reduce regulator di/dt effects on the cir- cuit board and input power supply. Placement of the power component to minimize routing distance will also help to reduce emissions. Figure 16: Filter components Figure 17: Input Filter Layout Guidelines 1. Place 12V filter capacitor next to the IC and connect capacitor ground to pin 11 (PGnd). 2. Connect pin 11 (PGnd) with a separate trace to the ground terminals of the 5V input capacitors. 3. Place fast feedback filter capacitor next to pin 8 (VFFB) and connect its ground terminal with a separate, wide trace directly to pin 14 (LGnd). 4. Connect the ground terminals of the Compensation capacitor directly to the ground of the fast feedback filter capacitor to prevent common mode noise from effecting the PWM comparator. 5. Place the output filter capacitor(s) as close to the load as possible and connect the ground terminal to pin 14 (LGnd). 6. To implement adaptive voltage positioning, connect both slow and fast feedback pins 16 (VFB) and 8 (VFFB) to the regulator output right at the inductor terminal. Connect inductor to the output capacitors via a trace with the fol- lowing resistance: + 2µH 1200µF x 3/16V 33Ω 1000pF 2µH TJUNCTION(MAX) - TAMBIENT Power Thermal Management 80mV IMAX 1 switching frequency Period × (1 - duty cycle) 4848.5 |
Numéro de pièce similaire - CS5151GD16 |
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Description similaire - CS5151GD16 |
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