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Serial EERAM

EERAM combines the reliability of an EEPROM with the performance of an SRAM. It is a nonvolatile SRAM with a shadow EEPROM backup.

I²C™ Serial EERAM Family

4Kbit
47x04
16Kbit
47x16
What is EERAM?

EERAM is a standalone SRAM memory with shadow EEPROM backup that helps retain the contents of the SRAM memory when system power is lost. The EERAM uses a small external capacitor to provide the energy needed to store the contents of the SRAM on to the EEPROM when system power is lost. Unlike NVSRAM, no external battery is needed. EERAM offers unlimited erase and write cycles to the memory and FRAM-like functionality at a fraction of the price.

Combines Reliability of EEPROM with Performance of SRAM
  • 4Kb - 16Kb I2C
  • Nonvolatile (with external capacitor)
  • Unlimited erase/write cycles
  • Instantaneous, random read/write
  • -40°C to +125°C
EERAM is useful in applications needing

Ultra-Fast Writes, Random Access

Unlimited Writes to Memory

Preserve Data Reliably
through Power Loss

To learn more about EERAM applications:

How does EERAM Work?

The internal circuitry of the EERAM constantly monitors system power. Upon power-down or the inadvertent loss of system power below the trip voltage (VTRIP) the contents of the SRAM is securely transferred to the EEPROM array using energy stored in an external capacitor that is connected to the VCAP pin (pin 1). On power-up, the EERAM’s Auto-Store feature enables the contents of the EEPROM to be transferred back to the SRAM array when the system voltage goes back above VTRIP. The EERAM offers unlimited writes to the SRAM array and over 1M erase/write cycles to the EEPROM.

For assistance with selecting the right capacitor for your application, click here

When VDD falls below VTRIP (Power Off):

  • Contents of SRAM are internally copied onto the EEPROM (Auto Store)

  • Capacitor provides energy to perform this operation

  • Data can also be stored manually via a software command or in hardware by toggling Pin 7 (HS).

  • Auto Store can be disabled 

When VDD Goes Back Above VTRIP (Power On):

  • At power-up, contents of EEPROM are automatically copied on the SRAM with internal on-chip circuitry (Auto Recall)

  • Device automatically performs Auto Recall on power-up

  • Recalls can also be initiated in software at any time

The EERAM also allows you to perform a manual store of the SRAM array by either using the Hardware Store (HS) Pin (pin 7) or by using the Software Store command. When a manual store is executed, the contents of the SRAM are instantly copied onto the EEPROM. If you don’t want to use an external capacitor on your board, the manual store functions provide the flexibility to store SRAM array contents to the EEPROM as, and whenever, you choose to do so.

You can also recall the contents of the EEPROM onto the SRAM array at any time using the Software Recall command. The table below summarizes the three store modes (Auto Store, Hardware Store and Software Store) and the two recall modes (Auto Recall and Software Recall). Auto Recall is always performed during power-up regardless of whether an external capacitor is used or not.

Store Function–Contents of SRAM Stored onto EEPROM

Auto Store Hardware Store Software Store
Initiated when Vdd falls below Vtrip Initiated when HS pin is pulled high Initiated via a software command
Needs capacitor No capacitor needed No capacitor needed
Automatic Manual Manual
Only enabled if array is modified Enabled when the array is modified Enabled at all times

Recall Function–Contents of EEPROM Written to SRAM

Auto Recall Software Recall
Initiated when VDD is restored above VTRIP Initiated via a software command
Automatic Automatic
What Problem does EERAM Solve?

EERAM offers unlimited writes to the SRAM array, allowing you to constantly write to the device. Since power loss events are typically random or unpredictable, EERAM offers applications that need to constantly update data a safe and reliable solution to automatically store data during a power loss event. It provides designers of data logging/black box or monitoring systems with a safe and accurate way to safely, reliably and automatically store the last data bytes prior to the power loss event. The capacitor connected to the VCAP pin provides the necessary energy to safely copy the RAM’s contents to the secure EEPROM backup on power loss. Upon power-up, data is recalled automatically from the EEPROM to the SRAM.

Benefits of EERAM?
  • Reliably preserves data through power loss event
    • Automatically and safely stores data on power loss
  • No battery needed
  • Unlimited endurance:  
    • Write to the memory as often as you choose
    • Useful in data logging/black box applications
  • Instantaneous writes to the array
    • Zero write cycle times and random access writes
    • Useful for applications that need instant data transfer
  • Lowest-cost solution
    • Significantly less expensive than competing FRAM and NVSRAM technologies
  • Low power
    • lower power consumption than NVSRAM

Benefits of EERAM over NVSRAM:

  1. No battery needed
  2. Lower power consumption
  3. Lower cost

Benefits of EERAM Over FRAM:

  1. Lower cost
  2. Truly unlimited write cycles – FRAM has destructive read and writes
Tabs / Design Centers / Memory2
Memory Product Comparison
 
Serial EERAM
Serial EEPROM
Serial Flash
Parallel Flash
Serial SRAM
Serial NVSRAM
Density 
4 Kb - 16 Kb
128b - 1 Mb
1 Mb - 64 Mb
1 Mb - 64 Mb
64 Kb - 1 Mb
512 Kb - 1 Mb
Endurance
Unlimited
1,000,000+
100,000+
100,000+
Unlimited
Unlimited
Bus
I2C
I2C, SPI, Microwire,
UNI/O® Bus
SPI, Dual, SQI™ Flash
Parallel
SPI, SDI, SQI
SPI, SDI
Clock Freq
1 MHz
0.4 - 20 MHz
20 - 104 MHz
45 - 70 ns
16 - 20 MHz
16 - 20 MHz
Cost Per Bit
Low
High
Low
Low
Medium
Medium
Read Times
Medium
Medium
Fast
Medium
Medium
Medium
Write Times
Instantaneous
Medium
Medium
Fast
Instantaneous
Instantaneous
Pin Count
8 pins
8 pins
8 pins
32 and 48 pins
8 pins
8 pins
Data Retention
200+ Years
200+ Years
100+ Years
100+ Years
Volatile
20+ Years (with battery)
Typ. Standby Current
~40 µA
1 µA
~15 µA
~30 µA
~4 µA
~4 µA
Voltage
2.7V - 3.6V
4.5V - 5.5V
1.8V - 5.5V
1.65V - 1.95V,
2.7V - 3.6V,
2.3V - 3.6V
1.65V - 1.95V,
2.7V - 3.6V,
4.5V - 5.5V
1.65V - 1.95V,
2.5V - 5.5V
2.5V - 5.5V
Temperature
-40°C to +85°C
-40°C to +125°C
-40°C to +105°C
-40°C to +85°C
-40°C to +125°C
-40°C to +85°C

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