Datasheet LTC3526L, LTC3526LB (Analog Devices) - 10

LTC3526L/LTC3526LB ApplicAtions inForMAtion
VIN > VOUT OPERATION COMPONENT SELECTION
The LTC3526L/LTC3526LB wil maintain voltage regulation
Inductor Selection
even when the input voltage is above the desired output voltage. Note that the efficiency is much lower in this mode, The LTC3526L/LTC3526LB can utilize small surface mount and the maximum output current capability will be less. chip inductors due to their fast 1MHz switching frequency. Refer to the Typical Performance Characteristics. Inductor values between 3.3µH and 6.8µH are suitable for most applications. Larger values of inductance will allow
SHORT-CIRCUIT PROTECTION
slightly greater output current capability (and lower the Burst Mode threshold) by reducing the inductor ripple cur- The LTC3526L/LTC3526LB output disconnect feature al- rent. Increasing the inductance above 10µH will increase lows output short circuit while maintaining a maximum component size while providing little improvement in internally set current limit. To reduce power dissipation 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 > Ripple • VOUT(MAX) 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/LTC3526LB 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 dependent pin copper area will help to lower the die temperature. A power losses compared to cheaper powdered iron types, multilayer board with a separate ground plane is ideal, but improving efficiency. The inductor should have low ESR not absolutely necessary. (series resistance of the windings) to reduce the I2R power LTC3526L 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 3526l F02
Figure 2. Recommended Component Placement for Single Layer Board
3526lfc 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