L7292 datasheet(51/60 Pages) STMICROELECTRONICS

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L7292

PCB design rules guideline

13.1

Basic principles

A step-down converter reduces an incoming voltage to a lower output voltage. A switching

element, typically a bipolar or a MOSFET is switched on and off. When the switch is on, the

input supply charges the inductor and capacitor and delivers power to the load. During this

time, the magnitude of the inductor current ramps up as it flows through the loop 1.

When the MOSFET turns off, the input is disconnected from the output, and the inductor

and output capacitor support the load. The magnitude of the inductor current ramps down as

it flows through the recirculating element, following the direction indicated in the loop 2. The

recirculating element can be a diode, but recently a more efficient synchronous rectification

system is used where a second switching element takes over the function of the diode.

Figure 19. Current loops

13.2

Layout rules

A multilayer board is preferred using the top layer to contain all power routing for the

devices, and inner layer 1 as a ground return plane.

Figure 20. Layer stack

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