Mitsubishi Motors DS5000TK - Manual (Page 57)

USER’S GUIDE
050396 56/173
57
POWER SUPPLY SLEW RATE Figure 6–1
40 µ s, 130 µ s
V CC
V CCMIN
V LI
LITHIUM
CURRENT
Each time V
CC
is restored, the lithium backed functions
will remain as they were left. A result is that many of
these values are not altered on a reset condition except
for the ‘no battery reset’. In the documentation, this is
referred to as ‘No V
LI
reset’. This will occur after the first
time V
CC
is applied to the microprocessor. The ‘no bat-
tery reset’ state is documented in the section on resets.
A module user will never see the ‘no battery reset’ condi-
tion as it was cleared during assembly and test prior to
leaving the factory.
BATTERY ATTACH PROCEDURE
This section applies to microprocessor chips only, not
modules. When a microprocessor is received from the
factory, it is completely uninitialized. All nonvolatile func-
tions are absent since there is no backup source con-
nected to the chip. As mentioned above, the micropro-
cessor must place circuits in a low power state to
prepare for lithium backup. If a battery were attached to
an uninitialized chip, the backup current would be
unpredictable. For this reason, the following battery
attach procedure must be followed.
1. Apply V
CC
to the microprocessor.
2. Attach the lithium cell to the V
LI
input.
3. Configure and program the device as normal.
(Optional at this time.)
4. Power down the microprocessor (remove V
CC
)
using the guidelines discussed above while leaving
the battery attached.
The first time a battery is attached to the microprocessor
is a special event. When power is applied in the absence
of a lithium cell, the device performs a No V
LI
Reset.
This allows the microprocessor to initialize control bits
that are ordinarily nonvolatile and unaffected by a reset.
The microprocessor will never be completely in this
state again unless all power (including battery) is
removed by the user. In order to provide the extremely
low back up currents (<75 nA), the circuits must config-
ure themselves for lithium backup. This is done when
V
CC
is removed from the chip. That is, the microproces-
sor IS NOT CONFIGURED FOR LITHIUM BACKUP
when it is received. Therefore, the battery should be
attached with V
CC
at +5V. This will prevent the micropro-
cessor from placing a load on the lithium cell until V
CC
is
removed. At this time, the microprocessor performs its
power down procedure and prepares for ultra low power
data retention. Attaching the battery to an unpowered
microprocessor places an unknown load on the lithium
cell. This may drain the cell excessively and should not
be done.
BATTERY LIFETIME
The calculations of data retention lifetime are helpful for
chip or module users. They can serve as design and
system reliability guidelines. All lithium backed micro-
controller modules are rated for better than 10 years of
data retention in the absence of V
CC
at 25
°
C. Following
these guidelines, similar performance can be achieved
using chips. It is also not difficult to achieve better than