11.1 Layout Guidelines

Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines (in Figure 15 and Figure 21) must be wide printed-circuit traces and must be kept as short as possible. For best results, external components must be placed as close to the switcher IC as possible using ground plane construction or single point grounding.

If open core inductors are used, take special care as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect sensitive feedback, IC ground path, and C_OUT wiring can cause problems.

When using the adjustable version, take special care as to the location of the feedback resistors and the associated wiring. Physically place both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor.

11.2 Layout Examples

C_IN = 15-μF, 25-V Solid Tantalum Sprague, 594D series
C_OUT = 68-μF, 10-V Solid Tantalum Sprague, 594D series
D1 = 1-A, 40-V Schottky Rectifier, surface mount
L1 = 47-μH, L13 Coilcraft DO3308
C_B = 0.01-μF, 50-V ceramic

Figure 27. Typical Surface Mount PCB Layout, Fixed Output (4x Size)

C_IN = 15 μF, 50 V Solid Tantalum Sprague, 594D series
C_OUT = 33 μF, 25 V Solid Tantalum Sprague, 594D series
D1 = 1-A, 40-V Schottky Rectifier, surface mount
L1 = 100-μH, L20 Coilcraft DO3316
C_B = 0.01-μF, 50-V ceramic
R1 = 1 kΩ, 1%
R2 = Use formula in Detailed Design Procedure

Figure 28. Typical Surface Mount PCB Layout, Adjustable Output (4x Size)