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AN8049SH Fiches technique(PDF) 25 Page - Panasonic Semiconductor |
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AN8049SH Fiches technique(HTML) 25 Page - Panasonic Semiconductor |
25 / 28 page Voltage Regulators AN8049SH 25 s Application Notes (continued) [10] Notes on power supply printed circuit board design Careful attention must be paid to the following points when designing the printed circuit board layout to achieve low noise and high efficiency. 1. Use extremely wide lines for the ground lines, and isolate the IC ground from the power system ground. In particular, during light-load operation (when the on-duty is low) switching noise can enter the system at the lower limit of the sawtooth waveform causing the operating frequency to vary every period and resulting in unstable control. Take measures described as 1) and 2) below, and assure that switching noise does not appear on the sawtooth waveform. 1) Use a ground line separate from the power system ground for the capacitor and resistor connected to the OSC pin. 2) Lower the OSC pin impedance by either decreasing the value of the resistor RT or increasing the value of the capacitor CT. (See the figures below.) 2. Position input filter capacitors as close as possible to the VCC and ground pins. If switching noise cannot be suppressed even with exceptionally large capacitors, or if there are limitations on the size of capacitors that can be used, install an CR filter in the input to reduce switching noise. Problems may occur if switching noise enters the IC by any route. 3. Keep the length of the line between the OUT pin and the switching device as short as possible to provide a clean switching waveform to the switching device. 4. Use longer lines for the low-impedance side of the output voltage detection resistors. VIN VOUT RT CT GND Common impedance VIN VOUT RT CT GND (1) Use separate lines. (2) Modify the values of the capacitor and resistor. Q1 Lower limit voltage of the sawtooth wave during stable operation Small Large The frequency changes at each period. Noise is picked up and the IC switches from charge to discharge operation. Q1 |
Numéro de pièce similaire - AN8049SH |
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Description similaire - AN8049SH |
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