Electronic Components Datasheet Search |
|
FAN5362UC25X Datasheet(PDF) 10 Page - Fairchild Semiconductor |
|
FAN5362UC25X Datasheet(HTML) 10 Page - Fairchild Semiconductor |
10 / 14 page © 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN5362 • Rev. 1.0.1 10 Thermal Shutdown When the die temperature increases, due to a high load condition and/or a high ambient temperature, the output switching is disabled until the temperature on the die has fallen sufficiently. The junction temperature at which the thermal shutdown activates is nominally 150°C with a 20°C hysteresis. Minimum Off-Time Effect on Switching Frequency tOFF(MIN) is 35ns. This imposes constraints on the maximum IN OUT V V that the FAN5362 can provide, or the maximum output voltage it can provide at low VOUT while maintaining a fixed switching frequency in PWM mode. When VIN is high, fixed switching is maintained as long as 7 . 0 1 ) ( ≈ • − ≤ SW MIN OFF IN OUT f t V V . The switching frequency drops when the regulator cannot provide sufficient duty cycle at 3MHz to maintain regulation. This occurs when VIN is below 3.3V at nominal load currents. The calculation for switching frequency is given by: ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = MHz 3 , t 1 min f ) MAX ( SW SW (4) where: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − • − • + + • = OUT ON OUT IN OFF OUT OUT ) MAX ( SW V R I V R I V 1 ns 35 t (5) where: OFF R = L N _ DSON DCR R + ON R = L P _ DSON DCR R + Applications Information Selecting the Inductor The output inductor must meet both the required inductance and the energy handling capability of the application. The inductor value affects the average current limit, the PWM-to-PFM transition point, the output voltage ripple, and the efficiency. The ripple current (∆I) of the regulator is: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ • − • ≈ Δ SW OUT IN IN OUT f L V V V V I (6) The maximum average load current, IMAX(LOAD) is related to the peak current limit, ILIM(PK) by the ripple current: 2 I I I ) PK ( LIM ) LOAD ( MAX Δ − = (7) The FAN5362 is optimized for operation with L=1 μH, but is stable with inductances up to 1.5 μH (nominal) and down to 470nH. The inductor should be rated to maintain at least 80% of its value at ILIM(PK). Failure to do so lowers the amount of DC current that the IC can deliver. Efficiency is affected by the inductor DCR and inductance value. Decreasing the inductor value for a given physical size typically decreases the DCR; but since ∆I increases, the RMS current increases, as do the core and skin effect losses. 12 I I I 2 2 ) DC ( OUT RMS Δ + = (8) The increased RMS current produces higher losses through the RDS(ON) of the IC MOSFETs as well as the inductor ESR. Increasing the inductor value produces lower RMS currents, but degrades transient response. For a given physical inductor size, increased inductance usually results in an inductor with lower saturation current and higher DCR. Inductor Current Rating The FAN5362’s current limit circuit can allow a peak current of 1.25A to flow through L1 under worst-case conditions. If it is possible for the load to draw that much continuous current, the inductor should be capable of sustaining that current or failing in a safe manner. Output Capacitor While 4.7 μF capacitors are available in 0402 package size, 0603 capacitors are recommended due to the severe DC voltage bias degradation in capacitance value that the 0402 exhibits. 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 (9) If values greater than 24 μF of COUT are used, the regulator may fail to start. See the sections on Enable and Soft Start for more information. Input Capacitor The 2.2 μF ceramic input capacitor should be placed as close as possible to 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. |
Similar Part No. - FAN5362UC25X |
|
Similar Description - FAN5362UC25X |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |