HMNR28D Datasheet, PDF (12/13 Pages) Hanbit Electronics Co.,Ltd – 5.0 or 3.3V, 16K bit (2 Kbit x 8) TIMEKEEPER NVSRAM

HANBit
HMNR28D(V)
Battery Low Warning
The HMNR28D(V) automatically performs battery voltage monitoring upon power-up and at factory-programmed time
intervals of approximately 24 hours. The Battery Low (BL) Bit, Bit D4 of Flags Register 7F0h, will be asserted if the battery
voltage is found to be less than approximately 2.5V. The BL Bit will remain asserted until completion of battery
replacement and subsequent battery low monitoring tests, either during the next power-up sequence or the next
scheduled 24hour interval. If a battery low is generated during a power-up sequence,
this indicates that the battery is below approximately 2.5V and may not be able to maintain
data integrity in the SRAM. Data should be considered suspect and verified as correct. A fresh battery should be installed.
If a battery low indication is generated during the 24-hour interval check, this indicates that the battery is near end of life.
However, data is not compromised
due to the fact that a nominal VCC is supplied. In order to insure data integrity during
Power Supply Decoupling and Undershoot Protection
Note: ICC transients, including those produced by output
switching, can produce voltage fluctuations, resulting in spikes
on the VCC bus. These transients can be reduced if capacitors
are used to store energy which stabilizes the VCC bus. The
energy stored in the bypass capacitors will be released as low
going spikes are generated or energy will be absorbed when
overshoots occur. A ceramic bypass capacitor value of 0.1uF
is recommended in order to provide the needed filtering. In
addition to transients that are caused by normal
SRAM operation, power cycling can generate negative
voltage spikes on VCC that drive it to values below VSS by as
much as one volt. These negative spikes can cause data
corruption in the SRAM while in battery backup mode. To
protect from these voltage spikes, ST recommends
connecting a schottky diode from VCC to VSS (cathode connected to VCC, anode to VSS). (Schottky diode 1N5817 is
recommended for through hole and MBRS120T3 is recommended for surface mount).
URL : www.hbe.co.kr
Rev. 0.0 (March, 2002)
12
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