Battery; Charging Concept - Siemens A55 Repair Documentation

Functions Pin
Requirements
Audio Stereo VDDSTEREO
Mode STEREO1
STEREO2
STEREOM

6.2 Battery

As a standard battery a LiIon battery with a nominal capacity of 3,7 Volt/700mAh is
used.

6.3 Charging Concept

Charging current
Charging control signal
V1.20
A55/C55_Hitachi
Sequence
For stereo mode 2 single ended buffers are
used. These buffers will be supplied by the
additional regulator with 2.9 Volt to be more
stable against the GSM ripple on the battery
voltage. Also reference voltage for the buffers
is generated by a high precision, low noise
bandgap reference for better performance. An
external capacitor is needed to filter this
reference additionally. The gain steps for the
programmable gain amplifier is identical with
the mono amplifier. No keyclick and ringer
needed for the stereo part. Gain can be
controlled with the TWI. The connected
speaker has an impedance of typical 16 Ohm.
To guarantee an ANTI-POP noise a digital
startup is implemented. This will allow a soft
start of the VMID and creates a "clean" audio
band during the startup. For eliminating
external coupling capacitors for the speaker, an
additional amplifier creates virtual ground (for
both speakers). Accordingly to this, the max
current of the virtual ground has to be the
double of the normal output amplifier. Due to
the power amplifier offset a DC current appear
in the headset. Gain can be adjusted for each
channel separately in steps of 1.5dB in the
range of 21dB to –54 dB and in steps of 3 dB in
the range of –54dB to –75dB
Page 36 of 48
Company Confidential © Copyright Siemens AG
ICM MP CCQ GRM
04/03