MB39C015

Document Number: 002-08364 Rev. *A

Page 20 of 43

10.7 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 through 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 through hole wiring. Use thick, short, and straight routes to wire

the net (The layout by planes is recommended.).

• Arrange a bypass capacitor for AVDD as close as possible to both the AVDD and AGND pins. Make a through hole (TH) near

the pins of this capacitor if the board has planes for power and GND.

• 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 LX1 and pin LX2 pin of this IC as far as possible.

• If applying voltage to the VREFIN1/VREFIN2 pins 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 VREFIN1/VREFIN2 resistor is close to the IC's AGND 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.

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

possible. Also arrange so that the GND pin of the VDET resistor is close to the IC's AGND 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.

• Try to make a GND plane on the surface to which this IC will be mounted. For efficient heat dissipation when using the QFN-24

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

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

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 be restarted, 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

VIN

GND

Cin

VIN

Co

Co

GND

VIN

1pin

L

L

Feedback line

Feedback line

AVDD bypass capacitor