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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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TPS658621A датащи(PDF) 95 Page - Texas Instruments |
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TPS658621A датащи(HTML) 95 Page - Texas Instruments |
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95 / 107 page  RMSCout Vout 1 1 Vin I = Vout L f 2 3 - ´ ´ ´ ´ Vout 1 1 Vin Vout = Vout + ESR L 8 Cout - æ ö D ´ ´ ç ÷ ´ ¦ ´ ´ ¦ è ø TPS658621A www.ti.com SLVSA58 – DECEMBER 2009 If ceramic output capacitors are used the capacitor RMS ripple current rating will always meet the application requirements. Just for completeness the RMS ripple current is calculated as: (17) At nominal load current the inductive converters operate in PWM mode and the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor: (18) Where the highest output voltage ripple occurs at the highest input voltage Vin. At light load currents the converters operate in Power Save Mode and the output voltage ripple is dependent on the output capacitor value. The output voltage ripple is set by the internal comparator delay and the external capacitor. The typical output voltage ripple is less than 1% of the nominal output voltage. 4.1.3 Input Capacitor Selection Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is required for best input voltage filtering and minimizing the interference with other circuits caused by high input voltage spikes. The converters need a ceramic input capacitor of 10 μF. The input capacitor can be increased without any limit for better input voltage filtering. Table 4-2. Capacitors 22 μF 0805 TDK C2012X5R0J226MT Ceramic 22 μF 0805 Taiyo Yuden JMK212BJ226MG Ceramic 10 μF 0805 Taiyo Yuden JMK212BJ106M Ceramic 10 μF 0805 TDK C2012X5R0J106M Ceramic 4.2 XTAL OSCILLATOR PCB – GENERAL GUIDELINES Table 4-3. External Crystal Specifications EXTERNAL CRYSTAL REQUIREMENTS [TYP CRYSTAL – EPSON MC146] PARAMETER DESCRIPTION MIN TYP MAX UNIT FOSC Nominal crystal resonant frequency 32.768 kHz Frequency Tolerance ΔF/FOSC –20 20 ppm B Parabolic Temp Co 0.04×10–6 1/°C2 ESR Equivalent Series Resistance 65 k Ω CLOAD Load Capacitance 7 pF CSHUNT Shunt capacitance 0.5 0.8 1.2 pF PDRIVE Drive power 0.5 1 μW Aging –3 3 ppm/Yr The jitter observed in the OUT32K pin is heavily dependent on the board layout close to the XTAL1 and XTAL2 pins. The following layout/assembly procedures are recommended : • Layout a good ground plane around the oscillator pins. • Prevent crosstalk from other clock or data lines into oscillator pins XIN and XOUT. Copyright © 2009, Texas Instruments Incorporated APPLICATION INFORMATION 95 Submit Documentation Feedback Product Folder Link(s): TPS658621A |
Аналогичный номер детали - TPS658621A |
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Аналогичное описание - TPS658621A |
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