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Power Supply Concept; Overvoltage Conditions - Siemens S25 Service Manual

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Power Supply Concept

The S25 has two main power inputs:
1) Battery Voltage (3.6 Volts) connected at the battery contacts
2) Charging Voltage (6.5 Volts) delivered by the different charger types (see accessory list)
via the Lumberg connector at the bottom of the telephone.
Since the battery voltage is supplying the power supply asic, it is always needed to
operate the phone. You cannot switch on the handset if the battery voltage is not present
or if no battery is inserted.
From the battery voltage all other supply voltages of the S25 are derived, controlled by the
power supply ASIC.
The RF power amplifier needs an operation voltage of 5,4Volts, which is generated by a DC-
DC step-up converter.
The logic module uses 2.9 V, generated by a regulator inside the ASIC.
Furthermore the ASIC generates the supply voltage for the SIM card and the RESET signal
for the logic devices.
The ASIC also checks the presence of the watchdog signal from the µP and provides the
switching on functionality (ON_OFF button or Ignition signal).
During testing ist is advisable to use a battery dummy, connected to a power supply delivering
+4V, max 3A.
Make sure that you connect the battery dummy with the right polarity, the red plug to +4V
and the blue plug to ground.
If you use a voltage higher than +7V, or with wrong polarity, the phone can be damaged!

Overvoltage Conditions

a) Battery Voltage:
b) Charging Current:
Service Manual S25 / S2588
Information and Communication Products
If the supply voltage rises above 6.2 Volts, the phone will
switch off and it cannot be switched on again before the
voltage is lower than 6.2 Volts.
If the supply voltage rises above 7 Volts the phone can be
The charging current must not rise above 1 A or the phone
(fuse) will be inoperable, meaning that charging the
battery will not be possible anymore.
V 1.0
Page 21 of 35
Mobile Phones
R. Fleuren



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