Q.
A.
NVRAM stands for "Non-Volatile RAM." Most RAMs are volatile;
when power is removed, they lose their contents. ROM technologies such
as EPROM, EEPROM and Flash retain their contents when power is removed.
An NVRAM is a battery-backed RAM which uses a small Lithium battery to
power a Low-Power SRAM when system power is not available thereby creating
non-volatile storage like a ROM, but high-speed writeable unlike a ROM.
A special circuit called an "NVRAM Supervisor" controls the
application of battery power to the LPSRAM.
The Supervisor may be integral to the LPSRAM as in a monolithic, or it
may be a separate IC as in a hybrid.
For a short primer on NVRAM, refer to the Application Note AN1012, "Predicting
the Battery Life and Data Retention Period of NVRAMs."
Q.
A.
ZEROPOWER is the trademark name for ST's NVRAMs without clocks.
What
is a ZEROPOWER®?
Q.
A.
TIMEKEEPER is the trademark name for ST's NVRAMs with on-board "Real-Time
Clocks." We also have a line of serial access RTCs with small amounts
of NVRAM on board. These are sometimes called "Serial TIMEKEEPERs."
Also, refer to the following page:
What
is a TIMEKEEPER®?
Q.
A.
An NVRAM Supervisor provides a switch between the main power supply (Vcc)
and a second source of energy (often a lithium battery) in order to supply
enough current to a stand-alone SRAM to generate data retention in the
event of a power loss. It is said that an NVRAM supervisor "non-volatizes"
a stand-alone SRAM.
This concept allows the user to create a customized NVRAM (see the question,
"How
do I create a high density, surface-mount (> 1Mbit) NVRAM?").
What
is an NVRAM Supervisor?
Q.
A.
See AN1012,
Predicting the Battery Life and Data Retention Period of NVRAMs. Also,
refer to the following pages:
Serial
RTC Battery Life Data
ZEROPOWER®
Battery Life Data
TIMEKEEPER®
Battery Life Data
Supervisor
Battery Life Data
Q.
A.
The /INT pin (pin 1) is an open drain output and must be connected to Vcc through a pull-up resistor, even if the interrupt function is not being used.
Q.
A.
See AN934,
TIMEKEEPER® Calibration.
Also, check out the Calibration
Calculator.
Q.
A.
The ST web site provides all of the information, including schematics and a back-up lifetime calculator to help you determine SuperCap size requirements on our SuperCap Calculator page.
Q.
How do I create a high density, surface-mount (>1Mbit) NVRAM?
A.
For high density, the solution is always a hybrid (multi-chip) solution.
In a hybrid DIP package, functionally it operates as if there is only
one silicon chip inside, but in fact, if you were to open it up, you could
see a small board with several components soldered onto it.
For a surface-mount solution, an NVRAM supervisor and one (or more) SRAM(s)
are necessary. ST's broad offering of NVRAM Supervisors allows combinations
that create NVRAMs not available in our standard ZEROPOWER®
and TIMEKEEPER® portfolio.
ST's
NVRAM Supervisor Combinations
Q.
A.
As part of ST's ECOPACK® program, all NVRAM
and Serial RTC products are switching to Lead-free packages.
For more information on this transition to environmentally friendly components
and programs, see our Lead Free/RoHS
Program web page.
For more details specific to NVRAM and Serial RTC products:
NVRAM
Strategy (100K PDF)
NVRAM
Qualification Plan (92K PDF)
NVRAM
Ordering Information (100K PDF)
Q.
Are STMicroelectronic's battery-backed devices UL certified?
A.
Yes, all ST parts are UL certified.
Details are available on the NVRAM
UL Information web page (this link, along with other useful links,
is also located on most pages under "Product Support" on the
NVRAM
web site).
Q.
What is the difference between devices with part numbers starting with "MK" versus those starting with "M"?
A.
In 1994 a new package (the CAPHAT™) was introduced which replaced the old TOPHAT package. The new package is slightly longer and slightly wider than the old package. Products using this new package had the "M" prefix. The "MK" prefix is relevant now to mostly out-of-production products. All new ST NVRAM products use the "M" prefix.
Q.
A.
The "MKI" prefix was for industrial temperature devices. The current designation scheme has the temperature designation in the suffix (usually number "6").
Q.
A.
One of the types of NVRAM made by ST is the TIMEKEEPER family. These
products incorporate a real time clock/calendar which is battery powered
when the external supply is not present.
All of our TIMEKEEPER products are Year 2000 compliant. Those which do
store the year as only two digits are guaranteed to roll-over correctly
from 99 to 00. However, the system software must take into account that
these products store only the last two digits of the year. The code should
be checked to make sure that the system cannot confuse the indication
00 for the year 1900 instead of the year 2000.
Newer TIMEKEEPER products are designed with a four digit reference for
the year and roll-over correctly from 1999 to 2000. Application Note "AN923"
explains in detail the solutions to be implemented to avoid Y2K problems
in application systems.