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LZT 123 1836 70
5.20.1 Real Time Clock Backup Supply (VRTC)
Pin Name Direction Function
31 VRTC Input DC supply for real time clock
VRTC provides an input connection to the module which allows the user to power the
real time clock (RTC) within the GS64 by way of a coin cell or charged capacitor.
When the module is powered, an internal LDO regulator provides a 200µA source
designed to supply the microprocessor’s RTC block. It is also intended to recondition
a rechargeable coin cell that supplies the RTC module when the main battery is
removed, or has insufficient energy. Because this LDO is always on, even when the
module is powered down, it features very low quiescent current. It also offers
reverse current protection, with low leakage, when the coin cell is powering the RTC
block.
The RTC LDO is primarily designed to charge manganese-silicon lithium batteries.
Rechargeable coin cells with different chemical composition may also be charged,
provided their charging requirements are consistent with the RTC LDO’s electrical
characteristics. The VRTC output is nominally 1.5 V.
VRTC LDO characteristics
Parameter Condition
Min Typ Max Unit
Output Voltage Tolerance
IOUT
= 10 µA
1.45 1.5 1.55 V
Maximum Output Current 200
µA
Short-circuit Current Limit VRTC to GND 0.7 1.6 2.9 mA
Output Resistance
IOUT = 10 µA
75 100 150
Line Regulation
IOUT = 10 µA
5 mV
Off Reverse Leakage Current 0.1 1
µA
In the backup condition the RTC block will function to as low as 1.1V on the VRTC
pin. The RTC draws 10µA typically during powered backup (15µA max).
Figure 5.20-1 shows the VRTC connectivity arrangement.