AN1011
Application note
Battery technology used in NVRAM
and real-time clock (RTC) products from ST

Introduction
Lithium Carbon MonoFlouride (LiCFx) batteries are used by STMicroelectronics in their
ZEROPOWER® and TIMEKEEPER® NVRAM devices and in their serial real-time clock(RTC) devices. The batteries provide the backup power to maintain the static RAM arrays
and to keep the oscillators running in the TIMEKEEPER and serial RTC devices.
When the discharge rates are low, these non-rechargeable lithium batteries are capable ofmaintaining a highly reliable voltage level for many years. Lithium batteries, therefore, areused for a variety of applications that require battery backup without need of maintenancefor many years.
To be used in electronic components, these cells also need to be composed of constituentsthat are nontoxic, non-corrosive, and non-explosive. They also must be chemically andthermally stable before, during and after discharge. STMicroelectronics utilizes the 48 mAh
BR1225X cell, and the 120 mAh BR1632 cell. The electrolyte of these cells (see Figure 1) isbased on an organic solvent, instead of a corrosive alkaline or acidic solution found in mostconventional batteries. This greatly improves the cell’s leakage resistance and guards
against the negative effects caused by leakage.
Figure 1.

Cell cross-section

(-)

(+)
Cell Can
GasketAnode CapCFx Cathode

Lithium Anode

Current CathodeSeparator and Electrolyte
AI02531

March 2012

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www.st.com

Contents

AN1011

Contents
Characterization and modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
UL 1950/60950 validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Battery status for NVRAMs and serial RTCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102/11Doc ID 6254 Rev 4

AN1011

Characterization and modelingCharacterization and modeling
STMicroelectronics has conducted extensive tests on these cells, a great proportion being
destructive testing. Three main mechanisms of battery degradation were modeled toestablish the effects under various loads, temperatures (up to 85 °C) and otherenvironmental variables:●

Active lifetime of the cell, as a result of the consumption of the lithium anode●

Shelf life (storage lifetime) of the cell, as a result of the electrolyte drying up(evaporation)●

Self-discharge, as a result of small leakage currents inherent to the battery chemistry

The weight loss proved to be a valuable measure of electrolyte evaporation. Self-discharge
is specified by the battery manufacturer to be less than 0.3% per year.
Models were then developed to predict the rate of electrolyte loss and what effectencapsulation of the cell would have. Tests on the cells, when encapsulated in the epoxy
used in the SNAPHAT process, have demonstrated a significant reduction in electrolyteevaporation.
(A) BR1225X discharge rate(B) BR1632 discharge rate

3.5

3.5

3.0

3.0

2.5
2.0

15k

30k

100k

2.52.015k

30k50k

100k

1.5

1.5
1.0Voltage (V)Voltage (V)Figure 2.

0200 400 600 800 1000 1200 1400 1600 1800 2000

1.001000

2000

3000

4000

5000

6000

Duration (Hrs.)(B)

Duration (Hrs.)(A)

AI02519

Figure 3 shows the load discharge graphs taken at 20 °C. As can be seen, both cells
produce a nominal 3 V output with a flat discharge curve until the end of their effective lives,and so confirms that both are suitable for providing battery backup to low leakage CMOSSRAMs.
The battery lifetime of individual ZEROPOWER, TIMEKEEPER and RTC devices, asdescribed in AN1012, is a function of the current load, the battery selected and the system
duty cycle. System life, which even with 100% duty cycle can still be greater than ten years,
is specified in the datasheet for each device.

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UL 1950/60950 validation

AN1011

UL 1950/60950 validation
All ZEROPOWER, TIMEKEEPER and RTC devices are recognized by the Underwriters
Laboratory Inc. UL 1950/60950 specification. The conditions for acceptance under thisinclude the following:Figure 3.

1.

That the devices are intended for use as components where the replacement of thebattery can be performed by the operator or a trained technician.

2.

That the devices are intended for use as components in low voltage, isolated,secondary circuits; where the case temperature does not exceed 100 °C, and thevoltage on any pin, relative to ground, does not exceed 7 VDC.

3.

That the devices are intended to be mounted on a printed wiring board, flame rated to aminimum of 94 V-1.

4.

That the devices are provided with an appropriate on-chip, reverse current protectioncircuit. (See Figure 3 for the circuit diagram.)

Battery control circuit

VCCP(OFF when VCC is below(2)
the switchover voltage)

RA(1)

RB

VSO

(1)

BATTERY

INTERNAL VCC
PVSO(ON when VCC is below
the switchover voltage)(2)AI02520

1. RA is the ESD protection resistor and RB is the battery protection resistor required by UL.
2. Depending on the device, switchover will be a function of battery voltage or set by a fixed reference.

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AN1011

Battery status for NVRAMs and serial RTCs

Battery status for NVRAMs and serial RTCs
For the devices listed in Table 1 and 2, the battery can be internal or external to the ICpackage. In the external cases, the battery will either be a user-supplied battery or it may
be incorporated into ST's SNAPHAT package which mates to the underlying IC as depicted
in Figure 6 on page 6.
Figure 4 shows the CAPHAT IC package with the battery integrated with the IC. In thispackage, the battery is encapsulated within the device.
Figure 5 is representative of several IC packages all of which use a customer-supplied,external battery. None of these device types include the battery in the IC package.
Figure 6 on page 6 shows ST's SNAPHAT SOH28 (SOIC) package with mating SNAPHATbattery top. Here, there is no battery in the IC package. Instead, it is a separate,
removable/replaceable unit stacked on top of the IC which reduces board space.
Figure 4.

CAPHAT IC package

CAPHAT andHybrid DIPs:
Internal battery
encapsulated indevice package

Figure 5.

External battery, user supplied

External,
user suppliedbattery
Serial RTC

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Battery status for NVRAMs and serial RTCs
Figure 6.

AN1011

External battery, SNAPHAT battery top

SNAPHATBattery top

RTC AM
NVR

Table 1.

SOH28
SNAPHAT SOIC

Battery status for serial RTCs
Part number

Package

Battery status

SO-16

External, user supplied

SOH28 (330 mil)External, SNAPHATSOX28 (300 mil)External, user supplied

SOX28 (300 mil)External, user supplied

SSOP20External, user supplied

SOX28 (300 mil)External, user supplied

SOX28 (300 mil)External, user supplied

M41T00AUDD1F

DFN16External, user supplied

M41T00CAPPC1CAPHAT DIP-24

M41ST84WMQ6E
M41ST84WMQ6F
M41ST85WMH6E
M41ST85WMH6F
M41ST85WMX6M41ST85WMX6TR
M41ST87WMX6M41ST87WMX6TR
M41ST87WSS6F
M41ST87YMX6M41ST87YMX6TR
M41ST95WMX6M41ST95WMX6TR

Internal, BR1632

M41T00M6E
SO-8

External, user supplied

SO-8

External, user supplied

SO-8

External, user supplied

SOH28 (330 mil)External, SNAPHAT

SO-8

External, user supplied

M41T00M6F
M41T00SM6E
M41T00SM6F
M41T11M6E
M41T11M6F
M41T11MH6E
M41T11MH6F
M41T56M6E
M41T56M6F

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AN1011

Battery status for NVRAMs and serial RTCs
Table 1.

Battery status for serial RTCs (continued)
Part number

Package

Battery status

M41T81M6E
SO-8External, user supplied

SO-8External, user supplied

SOX18 (300 mil)External, user supplied

SO-8External, user supplied

SOX18 (300 mil)External, user supplied

QFN16

External, user supplied

SOX18 (300 mil)External, user supplied

QFN16

External, user supplied

SOX18 (300 mil)External, user supplied

QFN16

External, user supplied

SOX18 (300 mil)External, user supplied

QFN16

External, user supplied

SOX18 (300 mil)External, user supplied

QFN16

External, user supplied

SOX18 (300 mil)External, user supplied

QFN16

External, user supplied

SOH28 (330 mil)External, SNAPHAT

SO-16

External, user supplied

M41T81M6F
M41T81SM6E
M41T81SM6F
M41T81SMY6E
M41T81SMY6F
M41T82RM6E
M41T82RM6F
M41T82SM6E
M41T82SM6F
M41T82ZM6E
M41T82ZM6F
M41T83RMY6E
M41T83RMY6F
M41T83RQA6F
M41T83SMY6E
M41T83SMY6F
M41T83SQA6F
M41T83ZMY6E
M41T83ZMY6F
M41T83ZQA6F
M41T93RMY6E
M41T93RMY6F
M41T93RQA6F
M41T93SMY6E
M41T93SMY6F
M41T93SQA6F
M41T93ZMY6E
M41T93ZMY6F
M41T93ZQA6F
M41T94MH6E
M41T94MH6F
M41T94MQ6E
M41T94MQ6F

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Battery status for NVRAMs and serial RTCs

Table 2.

AN1011

Battery status for TIMEKEEPER and ZEROPOWER NVRAMs
Part number

Package

Battery status

M40Z111MH6E
M40Z111MH6F
SOH28 (330 mil)External, SNAPHAT

SO-16

External, user supplied

SOH28 (330 mil)External, SNAPHAT

SO-16

External, user supplied

M40Z111WMH6E
M40Z111WMH6F
M40Z300AVMQ6TR
M40Z300WMH6EM40Z300WMH6F
M40Z300WMQ6E
M40Z300WMQ6F
M48T02-150PC1
CAPHAT DIP-24

Internal, BR1225

CAPHAT DIP-28

Internal, BR1225

SOH28 (330 mil)External, SNAPHATCAPHAT DIP-24

Internal, BR1225

Hybrid DIP-32

Internal, BR1632

CAPHAT DIP-28

Internal, BR1632

SOH28 (330 mil)External, SNAPHATCAPHAT DIP-28

Internal, BR1632

SOH28 (330 mil)External, SNAPHATCAPHAT DIP28Internal, BR1632

SOH28 (330 mil)External, SNAPHAT

M48T02-70PC1
M48T08-100PC1
M48T08-150PC1
M48T08Y-10MH1E
M48T08Y-10MH1F
M48T12-150PC1
M48T12-70PC1
M48T128Y-70PM1
M48T129V-85PM1
M48T129Y-70PM1
M48T18-100PC1
M48T18-150PC1
M48T201V-85MH1E
M48T201V-85MH1F
M48T201Y-70MH1E
M48T201Y-70MH1F
M48T35-70PC1
M48T35Y-70PC1
M48T35AV-10MH1E
M48T35AV-10MH1F
M48T35AV-10PC1
M48T35Y-70MH1E
M48T35Y-70MH1F

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AN1011

Battery status for NVRAMs and serial RTCs
Table 2.

Battery status for TIMEKEEPER and ZEROPOWER NVRAMs (continued)
Part number

Package

Battery status

M48T37V-10MH1E
M48T37V-10MH1F
SOH28 (330 mil)External, SNAPHAT

Hybrid DIP-32

Internal, BR1632

CAPHAP DIP-28Internal, BR1225

SOH28 (330 mil)External, SNAPHATCAPHAP DIP-28

Internal, BR1225

CAPHAP DIP-28

Internal, BR1632

CAPHAP DIP-28

Internal, BR1225

Hybrid DIP-32

Internal, BR1632

CAPHAP DIP-28

Internal, BR1632

Hybrid DIP-36

Internal, BR1632 (two)

CAPHAP DIP-28

Internal, BR1225

SOH28 (330 mil)External, SNAPHAT

Hybrid DIP-32

Internal, BR1632

CAPHAP DIP-28

Internal, BR1225

SOH28 (330 mil)External, SNAPHATM48T37Y-70MH1E
M48T37Y-70MH1F
M48T512Y-70PM1
M48T58-70PC1
M48T58Y-70PC1
M48T58Y-70MH1E
M48T58Y-70MH1F
M48Z02-150PC1
M48Z02-70PC1
M48Z08-100PC1
M48Z12-150PC1
M48Z12-70PC1
M48Z128-70PM1
M48Z128Y-70PM1
M48Z128Y-85PM1
M48Z129V-85PM1
M48Z18-100PC1
M48Z2M1V-85PL1
M48Z2M1Y-70PL1
M48Z35-70PC1
M48Z35Y-70PC1
M48Z35AV-10MH1E
M48Z35Y-70MH1E
M48Z35Y-70MH1F
M48Z512A-70PM1
M48Z512AV-85PM1
M48Z512AY-70PM1
M48Z512BV-85PM1
M48Z58-70PC1
M48Z58Y-70PC1
M48Z58Y-70MH1E
M48Z58Y-70MH1F

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Revision history

AN1011

Revision history
Table 3.

10/11

Document revision history

Date

Revision

ChangesDec-1998

1

Initial release.

28-Dec-2007

2

Reformatted document; updated UL 1950/60950 validation andtechnical support URL.

02-Nov-20093

Updated Introduction; Characterization and modeling; Figure 3;
reformatted document.

07-Mar-20124

Added Battery status for NVRAMs and serial RTCs, Figure 4, 5, 6
Table 1, 2; updated title of datasheet; minor textual updates.

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AN1011

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