User Guide

CCS Technical Documentation System Module
RH-25
Issue 1 10/2003 ©Nokia Corporation Confidential Page 17
Figure 10: Digital interface of audio amplifer
Figure 11: Block diagram of audio amplifer
The LM4855 features a 32-step digital volume control and eight distinct output modes.
The digital volume control and output modes are accessed through a 3-wire interface,
controlled by UPP. Digital volume control is needed when FM radio is activated; there is
no amplifier block in FM radio module. Output modes are needed when routing audios to
different locations; Headset or IHF.
External Audio Connector
RH-25 is designed to support fully differential external audio accessory connection by
using Tomahawk system connector. Tomahawk connector has serial data bus called (ACI)
Accessory Control Interface (ACI) for accessory insertion and removal detection and
identification and authentication. ACI line is also used for accessory control purposes.
• 4-wire fully differential stereo audio (used also FM-radio antenna connection)
• 2-wire differential mic input
UPP8M
LM4855
Enable
Clock
Data
DATA
CLK
EN
GenIO(14)
GenIO(16)
GenIO(15)
Output
Mode
Select
Digital
Volu me
Control
SPI
Bias
By pass
Ri n
Li n
EN CL K DAT A
Lout -
Lout +
Rout -
Rout +
out -
out +
VB AT
GN D
Phone
audio
Cs
=
1uF
Radio audio
IH F Speaker
Radio audio
Stereo
Headset
Amplifier
Amplifier
Amplifier
Amplif ier
Amplifier
Amplifier
LM4855