PS401-I/SS Microchip Technology, PS401-I/SS Datasheet - Page 12

• Manufacturer Part Number: PS401-I/SS
• Description: IC FUEL GAUGE BATTERY MGR 28SSOP
• Manufacturer: Microchip Technology

Specifications of PS401-I/SS

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PS401
To maintain accurate capacity prediction ability, the
FullCapacity value is relearned on each discharge,
which has reached a valid EOD after a previous valid
fully charged EOC. If a partial charge occurs before
reaching a valid EOD, then no relearn will occur. If the
discharge rate at EOD is greater than the ‘C-rate'
adjusted value in RelearnCurrLim, then no relearn will
occur.
When a valid EOD has been reached, then the
error calculations represented by the SBData value
of MaxError will be cleared to zero. If appropriate,
the relearned
FullChargeCapacity) will also be updated at this time.
4.3
4.3.1
As the graph in Figure 4-1 shows, available capacity in
the battery varies with temperature and discharge rate.
Since the remaining capacity will vary, the save to disk
point of a PC will also vary with temperature and
discharge rate.
Knowing the discharge rate that occurs in the system
during the save to disk process, and knowing the
temperature can pinpoint the exact save to disk point
that will always leave the perfect save to disk capacity.
The PS401 uses this information to tailor the gas gauge
to the system and the remaining capacity and RSOC
fuel gauge function will always go to zero at the efficient
save to disk point. Table 4-1 will use the voltage points
at which this happens as the error correction and FULL
CAPACITY relearn point. This will ensure a relearn
point before save to disk occurs, and will correct any
error in remaining capacity, also to ensure proper save
to disk.
The shutdown point has to equal the capacity required
to save to disk UNDER THE CONDITIONS OF SAVE
TO DISK. That is, looking at the curve that represents
the actual discharge C-rate that occurs during the
system save to disk function, we must stop discharge
and initiate save to disk when the system has used
FIGURE 4-1:
DS40238B-page 12
EOD Voltage LookUp Table
C-rate of STD function
SAVE TO DISK POINT
Voltage
value
SAVE TO DISK POINT
of
Capacity
FullCapacity
(and
Must stop at this point on all curves
capacity equal to that point on the save to disk C-rate
curve. This is because, no matter what the C-rate is
when the STD point is reached, the system will
automatically switch to the C-rate curve that represents
the actual current draw of the save to disk function. So
it doesn't matter if the system is in high discharge, or
low discharge, it will be in "save-to-disk" discharge
conditions when save to disk begins, and there must be
enough capacity left.
The graph in Figure 4-1 shows that the system will
always shut down at the same capacity point regard-
less of C-rate conditions (since the C-rate of the save
to disk procedure is a constant). Thus, we can automat-
ically have an RSOC that is compensated for C-rate; it
will go to zero when the capacity used is equal to the
point at which STD occurs.
Ignoring the effects of temperature, we could mark the
capacity used up to the shutdown point of the STD
curve. All of the shutdown voltage points would then
represent the same capacity, and RSOC would always
become zero at this capacity, and FCC would always
equal this capacity plus the residual capacity of the
save to disk curve.
To compensate for temperature, we can look at the
series of curves that represent the STD C-rate at
different temperatures. The PS401 implementation is
to measure the temperature and choose a scaled
RSOC value that will go to zero at the save to disk point
at this temperature, assuming the temperature does
not change. If it does change, then an adjustment to
RSOC will be needed to make it go to zero at STD
point.
Taking temperature into consideration, the amount of
capacity that can be used before save to disk is a
constant as C-rate changes, but not constant as
temperature changes. Thus, in the LUT, Table 4-1, the
individual temperature columns will have voltage points
that all represent the same capacity used, but the rows
across temperature points (C-rate rows) will represent
different capacity used.
Point at which STD capacity is reached
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