Datasheet

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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
SLUS700D – MARCH 2006 – REVISED DECEMBER 2007
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.
Copyright © 2006 – 2007, Texas Instruments Incorporated 17
Product Folder Link(s): TPS40040 TPS40041