PS401-I/SS Microchip Technology, PS401-I/SS Datasheet - Page 11

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

Specifications of PS401-I/SS

• Lead Free Status / RoHS Status: Request inventory verification / Request inventory verification

 2003 Microchip Technology Inc.
4.0
The PS401 internal CPU uses the voltage, current and
temperature data from the A/D converter, along with
parameters and cell models from the EEPROM and
OTP EPROM, to determine the state of the battery and
to process the SBData function instruction set.
By integrating measured current, monitoring voltages
and temperature, adjusting for self-discharge and
checking for end-of-charge and end-of-discharge
conditions, the PS401 creates an accurate fuel gauge
under all battery conditions.
4.1
The PS401 calculates state-of-charge and fuel gauging
functions using a ‘coulomb counting’ method, with
additional inputs from battery voltage and temperature
measurements.
measuring all the current into and out of the battery
cells, along with accurate three dimensional cell
models, the PS401 is able to provide run-time accuracy
with less than 1% error.
The capacity calculations consider two separate states:
charge acceptance or capacity increasing (CI) and
discharge or capacity decreasing (CD). The CI state
only occurs when a charge current larger than OTP
EPROM NullCurr value is measured. Otherwise, while
at rest and/or while being discharged, the state is CD.
Conditions must persist for at least NChangeState
measurement periods for a valid state change between
CD and CI. A minimum value of 2 is suggested for
NChangeState.
Regardless of the CI or CD state, self-discharge is
also calculated and subtracted from the integrated
capacity values. Even when charging, there is still a
self-discharge occurring in the battery.
To compensate for known system errors in the capacity
calculations, a separate error term is also continuously
calculated. This term is the basis for the SBData value
of MaxError. Two error values are located in OTP
EPROM. The CurrError value is the inherent error in
current measurements and should be set based on the
selection of a sense resistor and calibration results.
The SelfDischrgErr value is the error in the parameter
tables for self-discharge and depends on the accuracy
of the cell chemistry model for self-discharge.
Since the PS401 electronics also drain current from the
battery system, another OTP EPROM value allows
even this minor drain to be included in the capacity
calculations. The PwrConsumption value represents
the drain of the IC and associated circuitry, including
additional safety monitoring electronics, if present. A
typical value of 77 represents the PS401's nominal
power consumption of 300 A.
CAPACITY MONITORING
Capacity Calculations
By continuously and
accurately
The total capacity added or subtracted from the battery
(change in charge) per measurement period is
expressed by the following formula:
The error terms are always subtracted, even though
they are +/- errors, so that the fuel gauge value will
never be overestimated. Current draw of the PS401
and the self-discharge terms are also always
subtracted. The SBData value MaxError is the total
accumulated error as the gas gauge is running.
The battery current will be precisely measured and
integrated at all times and for any current rate, in order
to calculate total charge removed from or added to the
battery. Based on lookup table access, the capacity is
adjusted with self-discharging rates depending on
actual capacity and temperature, and residual capacity
corrections depending on the discharging current rate
and temperature.
4.2
Discharge capacity is determined based on the End-
Of-Discharge (EOD) voltage point. This voltage can be
reached at different times based on the discharge rate.
The voltage level at which this point occurs will also
change depending on the temperature and discharge
rate, since these factors affect the voltage curve
and total capacity of the battery. The EOD voltage
parameter table predicts the voltage point at which this
EOD will be reached based on discharge rate and
temperature.
The PS401 will monitor temperature and discharge rate
continuously and update the EOD voltage in real-time.
When the voltage measured on the cell is below EOD
voltage for duration of EODRecheck x periods, a valid
EOD has occurred.
When
TERMINATE_DISCHARGE_ALARM bit (bit 11) in
BatteryStatus will be set. This will cause an
AlarmWarning condition with this bit set.
Additionally, the REMAINING_TIME_ALARM and/or
REMAINING_CAPACITY_ALARM bits can be set first
to give a user defined early warning prior to the
TERMINATE_DISCHARGE_ALARM.
Charge = i t (the current integrated over time)
- CurrError (Current Meas. Error)
- PwrConsumption * t (PS401 I
- % of Self-Discharge * FCC
- SelfDischrgErr (Self-Disch. Error)
a
Discharge Termination and
Capacity Relearn
valid
EOD
has
been
DS40238B-page 11
PS401
DD
reached,
)
the