STK15C88
Document Number: 001-50593 Rev. ** Page 4 of 15
Hardware Protect
The STK15C88 offers hardware protection against inadvertent
STORE operation and SRAM WRITEs during low voltage
conditions. When V
CAP
<V
SWITCH
, all externally initiated
STORE operations and SRAM WRITEs are inhibited.
Noise Considerations
The STK15C88 is a high speed memory. It must have a high
frequency bypass capacitor of approximately 0.1 µF
connected between V
CC
and V
SS,
using leads and traces that
are as short as possible. As with all high speed CMOS ICs,
careful routing of power, ground, and signals reduce circuit
noise.
Low Average Active Power
CMOS technology provides the STK15C88 the benefit of
drawing significantly less current when it is cycled at times
longer than 50 ns. Figure 2 and Figure 3 show the relationship
between I
CC
and READ or WRITE cycle time. Worst case
current consumption is shown for both CMOS and TTL input
levels (commercial temperature range, VCC = 5.5V, 100%
duty cycle on chip enable). Only standby current is drawn
when the chip is disabled. The overall average current drawn
by the STK15C88 depends on the following items:
1.T he duty cycle of chip enable
2.The overall cycle rate for accesses
3.T he ratio of READs to WRITEs
4.CMO S versus TTL input levels
5.T he operating temperature
6. T he V
CC
level
7.IO lo ading
Figure 2. Current Versus Cycle Time (WRITE)
Figure 3. Current Versus Cycle Time (READ)
Best Practices
nvSRAM products have been used effectively for over 15
years. While ease-of-use is one of the product’s main system
values, experience gained working with hundreds of applica-
tions has resulted in the following suggestions as best
practices:
■
The nonvolatile cells in an nvSRAM are programmed on the
test floor during final test and quality assurance. Incoming
inspection routines at customer or contract manufacturer’s
sites, sometimes, reprogram these values. Final NV patterns
are typically repeating patterns of AA, 55, 00, FF, A5, or 5A.
End product’s firmware should not assume a NV array is in
a set programmed state. Routines that check memory
content values to determine first time system configuration
and cold or warm boot status should always program a
unique NV pattern (for example, complex 4-byte pattern of
46 E6 49 53 hex or more random bytes) as part of the final
system manufacturing test to ensure these system routines
work consistently.
■
Power up boot firmware routines should rewrite the nvSRAM
into the desired state. While the nvSRAM is shipped in a
preset state, best practice is to again rewrite the nvSRAM
into the desired state as a safeguard against events that
might flip the bit inadvertently (program bugs and incoming
inspection routines).
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