HANBit
HMNR1288D(V)
Battery Low Warning
The HMNR1288D(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 1FFF0h, 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).
Figure 8. Supply Voltage Protection
URL : www.hbe.co.kr
Rev. 1.0 (April, 2002)
14
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