BQ4010YMA-200 datasheet(3/18 Pages) TI

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FUNCTIONAL DESCRIPTION

bq4010/Y/LY

SLUS116A – MAY 1999 – REVISED APRIL 2007

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 VCC supply for a power-fail-detect threshold VPFD.

The bq4010 monitors for VPFD = 4.62 V typical for use in 5-V systems with 5% supply tolerance. The bq4010Y

monitors for VPFD = 4.37 V typical for use in 5-V systems with 10% supply tolerance. The bq4010LY monitors for

VPFD = 2.90 V (typ) for use in 3.3-V systems.

When VCC falls below the VPFD 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 tWPT,

write-protection takes place.

As VCC falls past VPFD and approaches VSO, 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 (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 VCC, 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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