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WA_DEV_W218_PTS_002 Rev 005 Page 73 of 109
Product Technical Specification &
Customer Design Guidelines
BAT-RTC (Backup Battery)
The WISMO218 provides an input/output to connect a Real Time Clock power supply.
Features
This pin is used as a back-up power supply for the internal Real Time Clock. The RTC is supported
by the 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 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 WISMO218 is off and VBATT = 0V.
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
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