AS3415 datasheet(88/102 Pages) AMSCO

88 / 102 page

AS3415/AS3435 – 88

ams Datasheet, Confidential: 2014-Jun-13 [v1-30]

P C B La y o ut Re comme nda t ion

Line Input and Headphone

The line input- and the headphone amplifier are blocks with

higher system currents; therefore it is important to separate

these high input and output currents from the rest of the

system. The example shown in Figure 109 demonstrates how to

do a proper ground layout for boths blocks. To separate the

headphone amplifier from the rest of the system it is

recommended to route a dedicated ground connection from

the headphone amplifier terminal back to the battery ground

terminal of the device. With this separate ground connection

the high output currents of the headphone amplifier do not

influence the sensitive analog ground of the chipset. The same

layout technique is applicable for the line input amplifier. The

line input amplifier also has higher input currents because of

the 150Ω termination resistors (RTERM) connected to the line

input terminal shown in Figure 10. To avoid unwanted ground

currents influencing the sensitive analog system ground of the

AS3415/35, it is recommended to route a dedicated ground

connection from the line input terminal back to the negative

battery terminal of the PCB. The example shows a local ground

plane from the battery, to the line input terminals. Such a plane

should be used for more complicated line input filters. Thus, all

line input related components like RTERM, CHP, R1 and R2 as well

as other additional filter components should be connected to

this ground plane. The ground plane must be connected to the

battery terminal, at a single point, for best grounding effect.

Another important connection is the bypass connection from

line input terminal to the BPL and BPR pins of the AS3415/35.

This connection is active if the chip is in off mode or if the device

has run out of battery. It is important to use wide signal lines

for these connections. The wider these connections are, the

better it is for the application. The same is true for the ground

connections of the headphone amplifier and the line input

amplifier. A weak signal line can directly influence the channel

separation of the system. A minimum signal width of 1mm is

typically recommended for the left and right audio channels

and 2mm for the audio ground signals.

AS3415 Datasheet(PDF) 88 Page - ams AG