hardware design v2.00
Table Of Contents
- Contents
- Version History
- 1 Introduction
- 2 SIM908 Overview
- 3 Package Information
- 4 GSM Application Interface
- 4.1 Power Supply
- 4.2 Power on/down Scenarios
- 4.3 Power Saving Mode
- 4.4 Charging Interface
- 4.5 RTC Backup
- 4.6 Serial Interfaces
- 4.7 Audio Interfaces
- 4.8 SIM Card Interface
- 4.9 LCD Display/SPI Interface
- 4.10 Keypad Interface
- 4.11 ADC
- 4.12 RI Behaviors
- 4.13 Network Status Indication
- 4.14 General Purpose Input/Output (GPIO)
- 4.15 PWM
- 4.16 I2C Bus
- 4.17 GSM Antenna Interface
- 5 GPS Application Interface
- 6 Electrical, Reliability and Radio Characteristics
- 6.1 Absolute Maximum Ratings
- 6.2 Recommended Operating Conditions
- 6.3 Digital Interface Characteristics
- 6.4 SIM Card Interface Characteristics
- 6.5 VDD_EXT Characteristics
- 6.6 SIM_VDD Characteristics
- 6.7 VRTC Characteristics
- 6.8 Current Consumption (VBAT = 3.8V, GPS engine is powered down)
- 6.9 Electro-Static Discharge
- 6.10 Radio Characteristics
- 6.11 Module label information
- Appendix
Smart Machine Smart Decision
SIM908_Hardware Design_V2.00 2012.05.07
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Battery temperature measurement is a customization function which is supported by the software in the module.
In above figure, the R
TEMP
is a NTC thermistor, and it is recommended to use MURATA NCP15XH103F03RC.
Its impedance is 10Kohm at 25℃. Refer to the above figure for the reference circuit.
4.4.1 Battery Pack Characteristics
SIM908 has optimized the charging algorithm for the Li-Ion battery that meets the characteristics listed below.
z The maximum charging voltage of the Li-Ion battery pack is 4.2V and the recommended capacity is
1100mAh. The Battery packs with more than 1100 mAh capacity will take more time for charging.
z The battery pack should have a protection circuit to avoid overcharging, deep discharging and over-current,
and the circuit should be insensitive to pulsed current.
z The internal resistance of the battery pack including protection circuit should be as low as possible. Its
recommended value does not exceed 150mΩ.
z The battery pack must be protected from reverse pole connection.
On the SIM908, the build-in circuit of the power management chipset monitors the supply voltage constantly.
Once the Under-voltage is detected, the SIM908 will be powered down automatically.
4.4.2 Recommended Battery Pack
Following is the specification of recommended battery pack:
Table 7: Specification of recommended battery pack
Items Description
Battery type Li-ion
Manufacturer Jiade Energy Technology
Normal voltage 3.7V
Capacity NORMAL 1100mAh
Charge Voltage 4.200±0.050V
Max Charge Current 1.0C
Charge Method CC / CV (Constant Current / Constant Voltage)
Max Discharge Current 1.0C (for continuous discharging mode)
Discharge Cut-off Voltage 3.0V/ cell
Internal resistance Initial≤130mΩ
4.4.3 Implemented Charging Technique
SIM908 has battery charging function. There are three pins related to the battery charging function: there are
VCHG, VBAT and TEMP_BAT/ADC0 pins. The VCHG Pin is driven by an external voltage, system can use this
Pin to detect a charger supply and provide most charging current through SIM908 module to battery when
charging is in fast charge state. VBAT pin gives charging current to external battery from SIM908 module.
TEMP_BAT Pin is for user to measure the battery temperature. Let this Pin open if battery temperature
measurement is not user’s design concern.