
Ramtron 
FM1608 
28 July 2000 
5/12 
Figure 3. Row and Column Organization 
Applications 
As the first truly nonvolatile RAM, the FM1608 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. 
Cost 
The cost of both the component and 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 assembly 
techniques and a board wash using no water.  
2. 
Humidity 
A typical battery-backed SRAM module is qualified at 
60o C, 90% Rh, no bias, and no pressure. This is 
because 
the 
multi-component 
vulnerable to moisture, not to mention dirt. FRAM is 
assemblies 
are 
qualified using HAST – highly accelerated stress test. 
This requires 120o C at 85% Rh, 24.4 psia at 5.5V bias.  
3. 
System reliability  
Data integrity must be in question when using a 
battery-backed 
SRAM. 
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. 
Space 
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, add 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!
They 
are 
inherently 
Direct Battery Issues
5. 
Field maintenance 
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. 
Environmental 
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. 
Style! 
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!