BQ4010_07 Datasheet, PDF (3/18 Pages) Texas Instruments – 8 k x 8 NONVOLATILE SRAM (5 V, 3.3 V)

bq4010/Y/LY
www.ti.com
SLUS116A – MAY 1999 – REVISED APRIL 2007
FUNCTIONAL DESCRIPTION
When power is valid, the bq4010/Y/LY operates as a standard CMOS SRAM. During power-down and power-up
cycles, the bq4010/Y/LY acts as a nonvolatile memory, automatically protecting and preserving the memory
contents.
Power-down/power-up control circuitry constantly monitors the V_CC supply for a power-fail-detect threshold V_PFD.
The bq4010 monitors for V_PFD = 4.62 V typical for use in 5-V systems with 5% supply tolerance. The bq4010Y
monitors for V_PFD = 4.37 V typical for use in 5-V systems with 10% supply tolerance. The bq4010LY monitors for
V_PFD = 2.90 V (typ) for use in 3.3-V systems.
When V_CC falls below the V_PFD threshold, the SRAM automatically write-protects the data. All outputs become
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 completion. If the memory cycle fails to terminate within time t_WPT,
write-protection takes place.
As V_CC falls past V_PFD and approaches V_SO, the control circuitry switches to the internal lithium backup supply,
which provides data retention until valid V_CC is applied.
When V_CC returns to a level above the internal backup cell voltage, the supply is switched back to V_CC. After V_CC
ramps above the V_PFD threshold, write-protection continues for a time t_CER (120 ms maximum in 5-V system,
85 ms maximum in 3.3-V system) to allow for processor stabilization. Normal memory operation may resume
after this time.
The internal coin cells used by the bq4010/Y/LY have an extremely long shelf life and provide data retention for
more than 10 years in the absence of system power.
As shipped from TI, the integral lithium cells of the MT-type module are electrically isolated from the memory.
(Self-discharge in this condition is approximately 0.5% per year.) Following the first application of V_CC, this
isolation is broken, and the lithium backup provides data retention on subsequent power-downs. The LIFETIME
LITHIUM package option is shipped as two devices, which must be ordered separately.
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