Datasheet LTC3526L-2, LTC3526LB-2 (Analog Devices) - 10

LTC3526L-2/LTC3526LB-2 applicaTions inForMaTion
VIN > VOUT OPERATION COMPONENT SELECTION
The LTC3526L-2/LTC3526LB-2 will maintain voltage regu-
Inductor Selection
lation even when the input voltage is above the desired output voltage. Note that the efficiency is much lower in this The LTC3526L-2/LTC3526LB-2 can utilize small surface mode, and the maximum output current capability will be mount chip inductors due to their fast 2MHz switching less. Refer to the Typical Performance Characteristics. frequency. Inductor values between 1.5µH and 4.7µH are suitable for most applications. Larger values of inductance
SHORT-CIRCUIT PROTECTION
will allow slightly greater output current capability (and lower the Burst Mode threshold) by reducing the inductor The LTC3526L-2/LTC3526LB-2 output disconnect feature ripple current. Increasing the inductance above 6.8µH will allows output short circuit while maintaining a maximum increase component size while providing little improvement internally set current limit. To reduce power dissipation in output current capability. under short-circuit conditions, the peak switch current limit is reduced to 400mA (typical). The minimum inductance value is given by: V ( ) •(V – V IN MIN OUT M ( AX) IN M ( IN))
SCHOTTKY DIODE
L > 2•Ripple• VOUT M ( AX) Although not recommended, adding a Schottky diode from SW to VOUT will improve efficiency by about 2%. Note where: that this defeats the output disconnect and short-circuit Ripple = Allowable inductor current ripple (amps peak- protection features. peak)
PCB LAYOUT GUIDELINES
VIN(MIN) = Minimum input voltage The high speed operation of the LTC3526L-2/LTC3526LB-2 VOUT(MAX) = Maximum output voltage demands careful attention to board layout. A careless The inductor current ripple is typically set for 20% to layout will result in reduced performance. Figure 2 shows 40% of the maximum inductor current. High frequency the recommended component placement. A large ground ferrite core inductor materials reduce frequency depen- pin copper area will help to lower the die temperature. A dent power losses compared to cheaper powdered iron multilayer board with a separate ground plane is ideal, but types, improving efficiency. The inductor should have not absolutely necessary. low ESR (series resistance of the windings) to reduce the I2R power losses, and must be able to support the peak LTC3526L-2 SW 1 6 VOUT MINIMIZE GND 2 5 FB TRACE ON FB AND SW V 3 4 + IN SHDN VIN MULTIPLE VIAS TO GROUND PLANE 3526lb2 F02
Figure 2. Recommended Component Placement for Single Layer Board
3526lb2fa 0 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts