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PCB Layout Guidelines

HDRV

SW

BOOT

LDRV

FB

COMP

VDD

TPS40041

GND

(Power Pad)

Locate Parts Over Signal Ground Island

Signal Ground

Power Ground

Locate Parts Over Power Ground

Output

Current

Loop

Input

Current

Loop

SR Gate

Drive

Main

Gate

Drive

VDD

Bypass

VDD Filter

(Optional)

Current

Limit Set

Resistor

VIN

Enable

Enable Bypass

(Optional)

BOOST Resistor

(Optional)

EN

VOUT

Power Component Routing

TPS40040, TPS40041

SLUS700B – MARCH 2006 – REVISED MARCH 2006

APPLICATION INFORMATION (continued)

A synchronous BUCK power stage has two primary current loops, the input current loop that carries high ac

discontinuous current and an output current loop that carries high dc continuous current. The output current loop

carries low ac inductor ripple current.

Figure 22. Synchronous BUCK Power Stage

As shown in Figure 22, the input current loop contains the input capacitors, the switching MOSFET, the inductor,

the output capacitors, and the ground path back to the input capacitors. To keep this loop as small as possible, it

is good practice to place some ceramic capacitance directly between the drain of the main switching MOSFET

and the source of the synchronous rectifier (SR) through a power ground plane directly under the MOSFETs.

The output current loop includes the filter inductor, the output capacitors, and the ground return between the

output capacitors and the source of the synchronous rectifier MOSFET. As with the input current loop, the ground

return between the output capacitor ground and the source of the SR source should be routed under the inductor

and MOSFETs to minimize the power loop area.

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