Charger Requirements; Rtc Backup - SimCom SIM808 Hardware Design

4.4.5

Charger Requirements

Following is the requirements of charger for SIM808:
Simple transformer power plug
Output voltage: 5.0V~7V
Minimum supply current: 800mA
A 10V peak voltage is allowed for maximum 1ms when charging current is switched off.
A 1.6A peak current is allowed for maximum 1ms when charging current is switched on.
4.5

RTC Backup

Current input for RTC when the VBAT is not supplied for the system. Current output for backup battery when
the VBAT power supply is in present and the backup battery is in low voltage state. The RTC power supply of
module can be provided by an external capacitor or a battery (non-chargeable or rechargeable) through the VRTC.
The following figures show various reference circuits for RTC back up.
External capacitor for RTC
Non-chargeable battery for RTC
Rechargeable battery for RTC
SIM808_Hardware Design_V1.00
Figure 18: RTC supply from capacitor
Figure 19: RTC supply from non-chargeable battery
Figure 20: RTC supply from rechargeable battery
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Smart Machine Smart Decision
2014.03.27