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LTC3526B Datasheet(PDF) 10 Page - Linear Integrated Systems |
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LTC3526B Datasheet(HTML) 10 Page - Linear Integrated Systems |
10 / 16 page LTC3526/LTC3526B 0 3526bfd VIN > VOUT OPERATION The LTC3526/LTC3526B will maintain voltage regulation even when the input voltage is above the desired output voltage.Notethattheefficiencyismuchlowerinthismode, and the maximum output current capability will be less. Refer to the Typical Performance Characteristics. SHORT-CIRCUIT PROTECTION The LTC3526/LTC3526B output disconnect feature allows output short circuit while maintaining a maximum inter- nally set current limit. To reduce power dissipation under short-circuit conditions, the peak switch current limit is reduced to 400mA (typical). SCHOTTKY DIODE Although it is not required, adding a Schottky diode from SW to VOUT will improve efficiency by about 2%. Note that this defeats the output disconnect and short-circuit protection features. PCB LAYOUT GUIDELINES The high speed operation of the LTC3526/LTC3526B demands careful attention to board layout. A careless layout will result in reduced performance. Figure 2 shows the recommended component placement. A large ground pin copper area will help to lower the die temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. COMPONENT SELECTION Inductor Selection The LTC3526/LTC3526B can utilize small surface mount chip inductors due to their fast 1MHz switching frequency. Inductor values between 3.3µH and 6.8µH are suitable for most applications. Larger values of inductance will allow slightly greater output current capability (and lower the Burst Mode threshold) by reducing the inductor ripple cur- rent. Increasing the inductance above 10µH will increase size while providing little improvement in output current capability. The minimum inductance value is given by: L V V V Ripple V IN MIN OUT MAX IN MIN OUT > ( ) ( ) ( ) ( ) ( • – • M MAX) where: Ripple = Allowable inductor current ripple (amps peak- peak) VIN(MIN) = Minimum input voltage VOUT(MAX) = Maximum output voltage The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. High frequency ferrite core inductor materials reduce frequency depen- dent power losses compared to cheaper powdered iron types, improving efficiency. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be able to support the peak Figure 2. Recommended Component Placement for Single Layer Board + SW LTC3526 1 GND MINIMIZE TRACE ON FB AND SW 2 VIN MULTIPLE VIAS TO GROUND PLANE VIN VOUT FB SHDN 3526 F02 3 6 5 4 applicaTions inFormaTion |
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Similar Description - LTC3526B |
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