13892 datasheet(53/158 Pages) FREESCALE

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FUNCTIONAL DEVICE OPERATION

CLOCK GENERATION AND REAL TIME CLOCK

Analog Integrated Circuit Device Data



Freescale Semiconductor

MC13892

data that has been provided, so occasional refreshing is recommended to ensure that any drift influencing environmental factors

have not skewed the clock beyond desired tolerances.

COIN CELL BATTERY BACKUP

The LICELL pin provides a connection for a coin cell backup battery or supercap. If the main battery is deeply discharged,

removed, or contact-bounced (i.e., during a power cut), the RTC system and coin cell maintained logic will switch over to the

LICELL for backup power. This switch over occurs for a BP below the UVDET threshold with LICELL greater than BP. A small

capacitor should be placed from LICELL to ground under all circumstances.

Upon initial insertion of the coincell, it is not immediately connected to the on chip circuitry. The cell gets connected when the

IC powers on, or after enabling the coincell charger when the IC was already on. During operation, coincells can get damaged

and their lifetime reduced when deeply discharged. In order to avoid such, the internal circuitry supplied from LICELL is

automatically disconnected for voltages below the coincell disconnect threshold. The cell gets reconnected again under the same

conditions as for initial insertion.

The coin cell charger circuit will function as a current-limited voltage source, resulting in the CC/CV taper characteristic

typically used for rechargeable Lithium-Ion batteries. The coin cell charger is enabled via the COINCHEN bit. The coin cell

voltage is programmable through the VCOIN[2:0] bits. The coin cell charger voltage is programmable in the ON state where the

charge current is fixed at ICOINHI.

If COINCHEN=1 when the system goes into Off or User Off state, the coin cell charger will continue to charge to the predefined

voltage setting but at a lower maximum current ICOINLO. This compensates for self discharge of the coin cell and ensures that

if/when the main cell gets depleted, that the coin cell will be topped off for maximum RTC retention. The coin cell charging will

be stopped for the BP below UVDET. The bit COINCHEN itself is only cleared when an RTCPORB occurs.

Table 20. Coin cell Charger Voltage Specifications

VCOIN[2:0]

Output Voltage

000

2.50

001

2.70

010

2.80

011

2.90

100

3.00

101

3.10

110

3.20

111

3.30

Table 21. Coin cell Charger Specifications

Parameter

Typ

Units

Voltage Accuracy

100

Coin Cell Charge Current in On and Watchdog modes ICOINHI

A

Coin Cell Charge Current in Off and Low-power Off modes (User Off / Memory Hold) ICOINLO

A

Current Accuracy

LICELL Bypass Capacitor

100

LICELL Bypass Capacitor as coin cell replacement

4.7

F

LICELL Bypass Capacitor

100

LICELL Bypass Capacitor as coin cell replacement

4.7

F

13892 Datasheet(PDF) 53 Page - Freescale Semiconductor, Inc

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