5.20.1Real 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 200∝A 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 ∝A

 

1.45

 

1.5

 

1.55

 

V

Maximum Output Current

 

 

 

200

 

 

 

 

 

∝A

Short-circuit Current Limit

 

VRTC to GND

 

0.7

 

1.6

 

2.9

 

mA

Output Resistance

 

IOUT = 10 ∝A

 

75

 

100

 

150

 

Ω

Line Regulation

 

IOUT = 10 ∝A

 

 

 

 

 

5

 

mV

Off Reverse Leakage Current

 

 

 

 

0.1

1

 

∝A

In the backup condition the RTC block will function to as low as 1.1V on the VRTC pin. The RTC draws 10∝A typically during powered backup (15∝A max).

Figure 5.20-1 shows the VRTC connectivity arrangement.

LZT 123 1836

70