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參數(shù)資料
| 型號： | bq2502 |
| 廠商： | Benchmark Technology Group |
| 英文描述： | Integrated Backup Unit(完整的后備單元) |
| 中文描述： | 綜合備份單元（完整的后備單元） |
| 文件頁數(shù)： | 2/12頁 |
| 文件大?。?/td> | 88K |
| 代理商： | BQ2502 |
As the supply continues to fall past V
PFD
, an internal
switching device forces V
OUT
to the internal backup en-
ergy source. CE
CON1
and CE
CON2
are held high by the
V
OUT
energy source.
During power-up, V
OUT
is switched back to the 5V sup-
ply as V
CC
rises above the backup cell input voltage
sourcing V
OUT
. Outputs CE
CON1
and CE
CON2
are held
inactive for time t
CE R
(120ms maximum) after the
power supply has reached V
PFD
, independent of the CE
input, toallow for processor stabilization.
The reset output (RST) goes active within t
R
(150
μ
s
maximum) after V
PFD,
and remains active for a mini-
mum of 40ms (120ms maximum) after power returns
valid. The RST output can be used as the power-on re-
set for a microprocessor.
Access to the external RAM
may begin when RST returns inactive.
During power-valid operation, the CE input is passed
through to one of the two CE
CON
outputs with a propa-
gation delay of less than 10ns. The CE input is output on
one of the two CE
CON
output pins depending on the
level of bank select input A, as shown in the Truth Ta-
ble.
Bank select input A is usually tied to a high-order address
pin so that a large nonvolatile memory can be designed
using lower-density memory devices. Nonvolatility and de-
coding are achieved by hardware hookup, as shown in Fig-
ure1.
The internal lithium cell is capable of supplying 3V on
V
OUT
for an extended period. The cumulative length of
time that the external SRAMs retain data in the ab-
sence of power is a function of the data-retention cur-
rent of the SRAMs used. The initial capacity of the in-
ternal lithium cell is 130mAh. Typically, if the data- re-
tention currents for two external SRAMs are 1
μ
A per
SRAM at room temperature, nonvolatility is calculated
to be for more than 7 years. If only one external SRAM
is used, the data-retention time increases to more than
13 years.
The bq2502 battery life is a function of the time spent in
battery-backed mode and the data-retention current of
the external SRAM.
For example, office equipment is
generally powered on for 8 hours and powered off for 16
hours. Under these conditions, a single bq2502 provides
SRAMs drawing 2
μ
A total data-retention current with
morethan 10 years of nonvolatility.
2
FG250201.eps
VCC
CE
THS
VSS
VOUT
bq2502
VCC
CE
CMOS
SRAM
5V
CECON2
RST
CECON1
A
VCC
CE
CMOS
SRAM
To Microprocessor
Figure 1. Hardware Hookup (5% Supply Operation)
Apr. 1991
bq2502
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