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FAN5358S718X Fiches technique(PDF) 11 Page - Fairchild Semiconductor |
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FAN5358S718X Fiches technique(HTML) 11 Page - Fairchild Semiconductor |
11 / 13 page © 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN5358 • Rev. 1.0.1 11 PCB Layout Considerations There are only three external components: the inductor and the input and output capacitors. For any buck regulator IC, including the FAN5358, it is important to place a low-ESR input capacitor very close to the IC, as shown in Figure 21. The input capacitor ensures good input decoupling, which helps reduce noise appearing at the output terminals and ensures that the control sections of the IC do not behave erratically due to excessive noise. This reduces switching cycle jitter and ensures good overall performance. It is important to place the common GND of CIN and COUT as close as possible to any of the FAN5358 GND terminals. There is some flexibility in moving the inductor further away from the IC; in that case, VOUT should be considered at the COUT terminal. Figure 21. PCB Layout Guidance Output Capacitor Table 4 suggests 0402 capacitors. 0603 capacitors may further improve performance in that the effective capacitance is higher. This improves the transient response and output ripple as shown in Table 3. Increasing COUT has no effect on loop stability and can therefore be increased to reduce output voltage ripple or to improve transient response. Output voltage ripple, ∆VOUT, is: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + • • • Δ = Δ ESR f C 8 1 I V SW OUT OUT (5) Input Capacitor The 2.2 μF ceramic input capacitor should be placed as close as possible between the VIN pin and GND to minimize the parasitic inductance. If a long wire is used to bring power to the IC, additional “bulk” capacitance (electrolytic or tantalum) should be placed between CIN and the power source lead to reduce ringing that can occur between the inductance of the power source leads and CIN. The effective capacitance value decreases as VIN increases due to DC Bias effects. This has no significant impact on regulator performance. Table 3. Effects of Changes in Inductor Value (from Recommended Value) on Regulator Performance Inductor Value IMAX(LOAD) ILIM(PK) ∆VOUT (5) Transient Response Increase Increase Decrease Decrease Degraded Decrease Decrease Increase Increase Improved Table 4. Recommended Passive Components and Their Variation Due to DC Bias Component Description Vendor Min. Typ. Max. Comment L1 2.2 μH, 2520, 100mΩ,1.3A FDK MIPF2520D 1.5 μH2.2μH Minimum value occurs at maximum current 2.2 μH, 2520, 80mΩ,1.3A Hitachi Metal:KSLI - 252010AG-2R2 Murata: LQM31PN2RM00L TOKO: MDT2520CN2R2M COUT 4.7 μF, X5R, 0402 Murata or Equivalent GRM155R60G475M GRM155R60E475ME760 1.6 μF 4.7μF 5.2μF Decrease primarily due to DC bias (VOUT) CIN 2.2 μF, X5R, 0402 Murata or Equivalent GRM155R60J225ME15 GRM188R60J225KE19D 1.0 μF 2.2μF 2.4μF Decrease primarily due to DC bias (VIN) and elevated temperature |
Numéro de pièce similaire - FAN5358S718X |
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Description similaire - FAN5358S718X |
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