FM1808-120-P ETC [List of Unclassifed Manufacturers], FM1808-120-P Datasheet - Page 5

• Manufacturer Part Number: FM1808-120-P
• Description: 256Kb Bytewide FRAM Memory
• Manufacturer: ETC [List of Unclassifed Manufacturers]

Ramtron
Figure 3. Row and Column Organization
Applications
As the first truly nonvolatile RAM, the FM1808 fits
into many diverse applications. Clearly, its monolithic
nature and high performance make it superior to
battery-backed SRAM in most every application. This
applications guide is intended to facilitate the
transition from BBSRAM to FRAM. It is divided into
two parts. First is a treatment of the advantages of
FRAM memory compared with battery-backed
SRAM. Second is a design guide, which highlights
the simple design considerations that should be
reviewed in both retrofit and new design situations.
FRAM Advantages
Although battery-backed SRAM is a mature and
established solution, it has numerous weaknesses.
These stem, directly or indirectly from the presence of
the battery. FRAM uses an inherently nonvolatile
storage mechanism that requires no battery. It
therefore eliminates these weaknesses. The major
considerations in upgrading to FRAM are as follows.
Construction Issues
1.
The
manufacturing overhead of battery-backed SRAM is
high. FRAM with its monolithic construction is
inherently a lower cost solution. In addition, there is
no ‘built-in’ rework step required for battery
attachment when using surface mount parts.
Therefore assembly is streamlined and more cost
effective. In the case of DIP battery-backed modules,
the user is constrained to through-hole assemb ly
techniques and a board wash using no water.
2.
A typical battery-backed SRAM module is qualified at
60º C, 90% Rh, no bias, and no pressure. This is
because
vulnerable to moisture, not to mention dirt. FRAM is
27 July 2000
A0-A7
A9-A8
11b
10b
01b
00b
Cost
Humidity
cost
00h
the
01h 02h 03h
of
multi-component
both
the
FCh
component
FDh
FEh
assemblies
FFh
and
A14-A10
00100b
Block 4
the
are
qualified using HAST – highly accelerated stress test.
This requires 120º C at 85% Rh, 24.4 psia at 5.5V.
3.
Data integrity must be in question when using a
battery-backed
vulnerable to shock and vibration. If the battery
contact comes loose, data will be lost. In addition a
negative voltage, even a momentary undershoot, on
any pin of a battery-backed SRAM can cause data
loss. The negative voltage causes current to be drawn
directly from the battery. These momentary short
circuits can greatly weaken a battery and reduce its
capacity over time. In general, there is no way to
monitor the lost battery capacity. Should an
undershoot occur in a battery backed system during a
power down, data can be lost immediately.
4.
Certain disadvantages of battery-backed, such as
susceptibility to shock, can be reduced by using the
old fashioned DIP module. However, this alternative
takes up board space, height, and dictates through-
hole assembly. FRAM offers a true surface-mount
solution that uses 25% of the board space.
No multi-piece assemblies, no connectors, and no
modules. A real nonvolatile RAM is finally
available!
Direct Battery Issues
5.
Batteries, no matter how mature, are a built-in
maintenance problem. They eventually must be
replaced. Despite long life projections, it is impossible
to know if any individual battery will last considering
all of the factors that can degrade them.
6.
Lithium batteries are widely regarded as an
environmental problem. They are a potential fire
hazard and proper disposal can be a burden. In
addition, shipping of lithium batteries may be
restricted.
7.
Backing up an SRAM with a battery is an old-
fashioned approach. In many cases, such modules are
the only through-hole component in sight. FRAM is
the latest memory technology and it is changing the
way systems are designed.
FRAM is nonvolatile and writes fast -- no battery
required!
System reliability
Space
Field maintenance
Environmental
Style!
SRAM.
They
are
FM1808-70
inherently
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