Sierra Wireless AIRPRIME WISMO218 - Manual (Page 69)

WA_DEV_W218_PTS_002 Rev 006 April 29, 2010 69
Product Technical Specification &
Customer Design Guidelines Interfaces
3.16. BAT-RTC (Backup Battery)
The AirPrime WISMO218 provides an input/output to connect a Real Time Clock power supply.
3.16.1. Features
This pin is used as a back-up power supply for the internal Real Time Clock. The RTC is supported by
the AirPrime WISMO218 when VBATT is available but a back-up power supply is needed to save
date and hour when VBATT is switched off.
If the RTC is not used, this pin can be left open.
If VBATT is available, the back-up battery can be charged by the internal 3.0V power supply regulator
via a 2K
 resistor implemented inside the AirPrime WISMO218.
Table 31: Electrical Characteristics of the Signal
Parameter Minimum Typ Maximum Unit
Input voltage - 3.0 - V
Input current consumption* - 2.5 - µA
Output voltage 2.82 3.0 3.18 V
Max charging current (@VBATT=3.6V) - 0.6 - mA
* Provided by an RTC back-up battery when the AirPrime WISMO218 is off and VBATT = 0V.
3.16.2. Pin Description
Table 32: BAT-RTC Pin Descriptions
Signal Pin Number I/O I/O Type Description
BAT-RTC 6 I/O Supply RTC Back-up supply
3.16.3. Application
The Back-up Power Supply can be provided by any of the following:
 A super capacitor
 A non rechargeable battery
 A rechargeable battery cell