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Axelite Confidential Materials, do not copy or distribute without written consent.

Rev.1.1 Nov.05, 2019

AX3984

AX3984

BST

SW

External 5V

10nF

Layout Consideration

For proper operation of the converter, some layout rules should be followed. It is necessary to

understand which pin of AX3984 is sensitive and which is insensitive. Please refer the following for

the location where noise comes from on the circuit and where the clear ground is for the small

signal ground.

1.) First, put the input capacitor (CIN) as close as possible to the VIN pin.

2.) Secondly, place the Cs, Rs, Cp, Css and R2 as close as AX3984 and connect these analog

grounds (Clear AGND) to AX3984’s GND pin. It is recommended to use a dot short for these

AGND pins or connect the GND pin via contact.

3.) The large current loop shown in bold lines in the above figure circuit should be routed as short

and wide as possible and the switch node is a high dv/dt. It easily couples noise to other traces

by the capacitive path. Therefore the sensitive signals like FB, COMP and AGND should be

routed away with this noise source.

4.) The feedback network resistors (R1 & R2) should be routed away from the inductor and switch

node to minimize noise and EMI issue. And the R1 resistor should be sensed the output

capacitor or device loading, not the inductor’s output node.