User's Manual
Table Of Contents
- Contents
- Figures
- Tables
- Document history
- Introduction
- Product concept
- GSM application interface
- GSM/GPRS operating modes
- Power supply
- Power up / down scenarios
- Automatic GPRS Multislot Class change
- Charging control of the GSM part
- Power saving
- Summary of state transitions (except SLEEP mode)
- RTC backup for GSM part of XT55/56
- Serial interfaces of the XT55/56 GSM part
- Audio interfaces
- SIM interface
- Control signals
- GPS application interface
- GSM and GPS antenna interfaces
- Electrical, reliability and radio characteristics
- Mechanics
- Reference approval
- Example applications
- List of parts and accessories
XT55/56 Hardware Interface Description
Confidential / Released
s
XT55/56_hd_v02.06a Page 45 of 125 17.12.2004
3.5.3 Implemented charging technique
If the external charging circuit follows the recommendation of Figure 7, the charging process
consists of trickle charging and processor controlled fast charging. For this solution, the fast
charging current provided by the charger or any other external source must be limited to
500mA.
Trickle charging
• Trickle charging starts when the charger is connected to the charger input of the external
charging circuit and the module’s GSM_POWER pin. The charging current depends on
the voltage difference between the charger input of the external charging circuit and
GSM_BATT+ of the module.
• Trickle charging stops when the battery voltage reaches 3.6V.
Fast charging
• After trickle charging has raised the battery voltage to 3.2V within 60 minutes +
10% from
connecting the charger, the power ASIC turns on and wakes up the baseband processor.
Now, processor controlled fast charging begins.
If the battery voltage was already above 3.2V, processor controlled fast charging starts
just after the charger was connected to the charger input of the external charging circuit
and the module’s GSM_POWER pin. If the GSM part of the XT55/56 was in POWER
DOWN mode, it turns on and enters the Charge-only mode along with fast charging (see
also Chapter 3.3.1.3).
Fast charging delivers a constant current until the battery voltage reaches 4.2V and then
proceeds with varying charge pulses. As shown in Figure 5, the pulse duty cycle is
reduced to adjust the charging procedure and prevent the voltage from overshooting
beyond 4.2V. Once the pulse width reaches the minimum of 100ms and the duty cycle
does not change for 2 minutes, fast charging is completed.
After the end of charging the battery voltage falls due to discharging. Once the voltage
falls below 4.0V (approximately), the charging process begins again.
• Fast charging can only be accomplished in a temperature range from 0°C to +45°C.
4.3
4.2
3.8
Voltage
3.4
3.0
Constant current
t
OFF
= 100 ms
t
ON
= 100 ms
Time
100ms
2 ... 0.1s
100ms
0.1 ... 2s
End of
charging
Figure 9: Charging process