BQ4024 Datasheet, PDF (2/12 Pages) List of Unclassifed Manufacturers – 128Kx16 Nonvolatile SRAM

bq4024/bq4024Y
Functional Description
When power is valid, the bq4024 operates as a standard
CMOS SRAM. During power-down and power-up cycles,
the bq4024 acts as a nonvolatile memory, automatically
protecting and preserving the memory contents.
Power-down/power-up control circuitry constantly moni-
tors the VCC supply for a power-fail-detect threshold
VPFD. The bq4024 monitors for VPFD = 4.62V typical for
use in systems with 5% supply tolerance. The bq4024Y
monitors for VPFD = 4.37V typical for use in systems
with 10% supply tolerance.
When VCC falls below the VPFD threshold, the SRAM
automatically write-protects the data. All outputs be-
come high impedance, and all inputs are treated as
“don’t care.” If a valid access is in process at the time of
power-fail detection, the memory cycle continues to com-
pletion. If the memory cycle fails to terminate within
time tWPT, write-protection takes place.
As VCC falls past VPFD and approaches 3V, the control
circuitry switches to the internal lithium backup supply,
which provides data retention until valid VCC is applied.
When VCC returns to a level above the internal backup
cell voltage, the supply is switched back to VCC. After
VCC ramps above the VPFD threshold, write-protection
continues for a time tCER (120ms maximum) to allow for
processor stabilization. Normal memory operation may
resume after this time.
The internal coin cells used by the bq4024 have an ex-
tremely long shelf life and provide data retention for
more than 10 years in the absence of system power.
As shipped from Benchmarq, the integral lithium cells
are electrically isolated from the memory. (Self-
discharge in this condition is approximately 0.5% per
year.) Following the first application of VCC, this isola-
tion is broken, and the lithium backup provides data re-
tention on subsequent power-downs.
Truth Table
Mode
CE
WE
OE
I/O Operation
Power
Not selected
H
X
X
High Z
Standby
Output disable
L
H
H
High Z
Active
Read
L
H
L
DOUT
Active
Write
L
L
X
DIN
Active
Absolute Maximum Ratings
Symbol
Parameter
Value
Unit
Conditions
VCC
DC voltage applied on VCC relative to VSS
VT
DC voltage applied on any pin excluding VCC
relative to VSS
TOPR
Operating temperature
TSTG
Storage temperature
TBIAS
Temperature under bias
TSOLDER Soldering temperature
-0.3 to 7.0
-0.3 to 7.0
0 to +70
-40 to +70
-10 to +70
+260
V
V
VT ≤ VCC + 0.3
°C
°C
°C
°C
For 10 seconds
Note:
Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional operation
should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Exposure to con-
ditions beyond the operational limits for extended periods of time may affect device reliability.
Sept. 1992
2