12.1 Layout Guidelines

As in any switching regulator, layout is very important. Rapid switching currents associated with wiring inductance can generate voltage transients, which can cause problems. For minimal inductance and ground loops (see Test Circuits), the wires indicated by heavy lines 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 lC 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, lC groundpath, 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.

12.2 Layout Examples

C_IN = 470-μF, 50-V, aluminum electrolytic Panasonic HFQ Series
C_OUT = 330-μF, 35-V, aluminum electrolytic Panasonic HFQ Series
D1 = 5-A, 40-V Schottky rectifier, 1N5825
L1 = 47-μH, L39, Renco through hole
R_{PULL UP} = 10k
C_DELAY = 0.1 μF
C_SD/SS = 0.1 μF
Thermalloy heat sink #7020

Figure 33. Typical Through-Hole PCB Layout, Fixed Output (1x Size), Double-Sided

C_IN = 470-μF, 50-V, aluminum electrolytic Panasonic, HFQ Series
C_OUT = 220-μF, 35-V, aluminum electrolytic Panasonic, HFQ Series
D1 = 5-A, 40-V Schottky Rectifier, 1N5825
L1 = 47-μH, L39, Renco, through-hole
R₁ = 1 kΩ, 1%
R₂ = Use formula in Detailed Design Procedure
R_FF = See Feedforward Capacitor
R_{PULL UP} = 10k
C_DELAY = 0.1 μF
C_SD/SS= 0.1 μF
Thermalloy heat sink #7020

Figure 34. Typical Through-Hole PCB Layout, Adjustable Output (1x Size), Double-Sided