MB39C014 datasheet(17/32 Pages) CYPRESS

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Document Number: 002-08361 Rev. *C

Page 17 of 32

MB39C014

10.6 Board Layout, Design Example

The board layout needs to be designed to ensure the stable operation of this IC.

Follow the procedure below for designing the layout.

■ Arrange the input capacitor (Cin) as close as possible to both the VDD and GND pins. Make a thru-hole (TH) near the pins of this

capacitor if the board has planes for power and GND.

■ Large AC currents flow between this IC and the input capacitor (Cin), output capacitor (CO), and external inductor (L). Group these

components as close as possible to this IC to reduce the overall loop area occupied by this group. Also try to mount these components

on the same surface and arrange wiring without thru-hole wiring. Use thick, short, and straight routes to wire the net (The layout by

planes is recommended.).

■ The feedback wiring to the OUT should be wired from the voltage output pin closest to the output capacitor (CO). The OUT pin is

extremely sensitive and should thus be kept wired away from the LX pin of this IC as far as possible.

■ If applying voltage to the VREFIN pin through dividing resistors, arrange the resistors so that the wiring can be kept as short as

possible. Also arrange them so that the GND pin of the VREFIN resistor is close to the IC's GND pin. Further, provide a GND

exclusively for the control line so that the resistor can be connected via a path that does not carry current. If installing a bypass

capacitor for the VREFIN, put it close to the VREFIN pin.

■ Try to make a GND plane on the surface to which this IC will be mounted. For efficient heat dissipation when using the SON-10

package, Cypress recommends providing a thermal via in the footprint of the thermal pad.

10.7 Layout Example of IC SW Components

10.8 Notes for Circuit Design

■ The switching operation of this IC works by monitoring and controlling the peak current which, incidentally, serves as form of short-

circuit protection. However, do not leave the output short-circuited for long periods of time. If the output is short-circuited where VIN

< 2.9 V, the current limit value (peak current to the inductor) tends to rise. Leaving in the short-circuit state, the temperature of this

IC will continue rising and activate the thermal protection.

Once the thermal protection stops the output, the temperature of the IC will go down and operation will resume, after which the

output will repeat the starting and stopping.

Although this effect will not destroy the IC, the thermal exposure to the IC over prolonged hours may affect the peripherals surrounding

it.

Cin

GND

1 Pin

VIN

Feedback line

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