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STK22C48-SF25TR bảng dữ liệu(PDF) 9 Page - Simtek Corporation

tên linh kiện STK22C48-SF25TR
Giải thích chi tiết về linh kiện  2Kx8 AutoStore nvSRAM
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nhà sản xuất  SIMTEK [Simtek Corporation]
Trang chủ  http://www.simtek.com
Logo SIMTEK - Simtek Corporation

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9
STK22C48
Feb, 2008
Document Control #ML0004 Rev 2.0
STK22C48 will operate on the stored system charge
as power goes down. The user must, however, guar-
antee that V
CC does not drop below 3.6V during the
10ms STORE cycle.
AutoStore INHIBIT MODE
If an automatic STORE on power loss is not required,
then V
CC can be tied to ground and + 5V applied to
V
CAP (Figure 3). This is the AutoStore Inhibit mode,
in which the AutoStore function is disabled. If the
STK22C48 is operated in this configuration, refer-
ences to V
CC should be changed to VCAP throughout
this data sheet. In this mode, STORE operations may
be triggered with the HSB pin. To enable or disable
AutoStore using an IO port pin, see “PREVENTING
STORES” on page 9.
In order to prevent unneeded STORE operations,
automatic STOREs as well as those initiated by
externally driving HSB low will be ignored unless at
least one WRITE operation has taken place since the
most recent STORE or RECALL cycle.
If the power supply drops faster than 20
μs/volt
before V
CC reaches VSWITCH, then a 2.2 ohm resistor
should be inserted between V
CC and the system sup-
ply to avoid momentary excess of current between
Vcc and Vcap.
HSB OPERATION
The STK22C48 provides the HSB pin for controlling
and acknowledging the STORE operations. The HSB
pin is used to request a hardware STORE cycle.
When the HSB pin is driven low, the STK22C48 will
conditionally initiate a STORE operation after t
DELAY;
an actual STORE cycle will only begin if a WRITE to
the SRAM took place since the last STORE or
RECALL
cycle. The HSB pin has a very resistive pul-
lup and is internally driven low to indicate a busy
condition while the STORE (initiated by any means)
is in progress. Pull up this pin with an external 10K
ohm resistor to VCAP if HSB is used as a driver.
SRAM READ
and WRITE operations that are in
progress when HSB is driven low by any means are
given time to complete before the STORE operation
is initiated. After HSB goes low, the STK22C48 will
continue SRAM operations for t
DELAY.
During t
DELAY,
multiple SRAM READ operations may take place. If a
WRITE
is in progress when HSB is pulled low it will
be allowed a time, t
DELAY, to complete. However, any
SRAM WRITE
cycles requested after HSB goes low
will be inhibited until HSB returns high.
The HSB pin can be used to synchronize multiple
STK22C48s while using a single larger capacitor. To
operate in this mode the HSB pin should be con-
nected together to the HSB pins from the other
STK22C48s. An external pull-up resistor to + 5V is
required since HSB acts as an open drain pull down.
The V
CAP pins from the other STK22C48 parts can
be tied together and share a single capacitor. The
capacitor size must be scaled by the number of
devices connected to it. When any one of the
STK22C48s detects a power loss and asserts HSB,
the common HSB pin will cause all parts to request a
STORE
cycle (a STORE will take place in those
STK22C48s that have been written since the last
nonvolatile cycle).
During any STORE operation, regardless of how it
was initiated, the STK22C48 will continue to drive
the HSB pin low, releasing it only when the STORE is
complete. Upon completion of the STORE operation
the STK22C48 will remain disabled until the HSB pin
returns high.
If HSB is not used, it should be left unconnected.
PREVENTING STORES
The STORE function can be disabled on the fly by
holding HSB high with a driver capable of sourcing
30mA at a VOH of at least 2.2V, as it will have to
overpower the internal pull-down device that drives
HSB low for 20
μs at the onset of a STORE. When the
STK22C48 is connected for AutoStore operation
(system V
CC connected to VCC and a 68μF capacitor
on V
CAP) and VCC crosses VSWITCH on the way down,
the STK22C48 will attempt to pull HSB low; if HSB
doesn’t actually get below V
IL, the part will stop try-
ing to pull HSB low and abort the STORE attempt.
17
1
16
32
31
30
Figure 3: AutoStore Inhibit Mode


Số phần tương tự - STK22C48-SF25TR

nhà sản xuấttên linh kiệnbảng dữ liệuGiải thích chi tiết về linh kiện
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Mô tả tương tự - STK22C48-SF25TR

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