PS501 datasheet(14/42 Pages) MICROCHIP

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PS501

DS21818C-page 14

 2004 Microchip Technology Inc.

5.1

Full Charge Detection Methods

For a typical Lithium Ion constant-current/constant-

voltage charge system, the PS501 will monitor the

taper current that enters the battery once the battery

has reached the final voltage level of the charger. Once

the taper current falls to a certain level, indicating that

the battery is full, the End-Of-Charge (EOC) will be trig-

gered. Different taper currents will be used for different

temperatures. See the parameter explanation in

Section 9.0 “Parameter Setup” for details.

When a valid fully charged EOC condition is detected,

the following actions occur:

• The FULLY_CHARGED status bit (bit 5) in the

SBData value of BatteryStatus is set to ‘1’ to

indicate a full condition. (This will remain set until

RelativeStateOfCharge drops below the

ClrFullyChrg value in EEPROM.)

• RelativeStateOfCharge is set to 100%.

• ChargingCurrent is set to ChrgCurrOff value.

• SBData value for MaxError is cleared to zero

percent (0%).

• The TERMINATE_CHARGE_ALARM bit (bit 14)

is set in BatteryStatus and an AlarmWarning

broadcast is sent to the SMBus Host and Smart

Battery Charger addresses.

•The OverChrg value is incremented for any

charge received above 100% after a valid fully

charged EOC condition.

• Control flags for internal operations are set to

indicate a valid full charge condition was

achieved.

• Other BatteryStatus or AlarmWarning flag bits

may also be set depending on the conditions

causing the EOC.

- The charge timer, EOCTimer, is exceeded

- Cell voltage is higher than TCAVolt

5.2

Temperature Algorithms

The PS501 SMBus Smart Battery IC provides multiple

temperature alarm set points and charging conditions.

The following EEPROM parameters control how the

temperature alarms and charging conditions operate.

HighTempAl: When the measured temperature is

greater than HighTempAl, the OVER_TEMP_ALARM

set.

the

battery

charging,

then

the

TERMINATE_CHARGE_ALARM is also set.

ChrgMinTemp, DischrgMaxTemp and ChrgMaxTemp:

If the measured temperature is less than ChrgMinTemp,

the ChargingCurrent is set to ChrgCurrOff and the

ChargingVoltage is set to ChrgVolt to communicate to

the charger that the non-charging state of current and

voltage should be given. When measured temperature

is greater than ChrgMaxTemp and the system is charg-

ing, or greater than DischrgMaxTemp and the system is

discharging, then ChargingCurrent is set to ChrgCurrOff

and

the

ChargingVoltage

set

to ChrgVoltOff

also. Otherwise, ChargingCurrent = ChrgCurr and

ChargingVoltage = ChrgVolt.

6.0

CELL BALANCING

The PS501 has internal cell balancing loads with which

to draw extra current away from higher voltage cells.

There are internal 500 ohm resistors, which will draw

up to 8.4 mA of current from each cell, depending on

the cell voltage. The cell balancing algorithm will moni-

tor individual cell voltages and the difference between

them. When the difference between any cells exceeds

the EEPROM parameter, VcelldiffMax, the resistor

load will be applied to the higher cell until it is within

VcelldiffresetMax of the lowest. Cell balancing will

only be applied during the charging state to maintain

run time during discharge.

Determination of cell balance requirement will be made

near End-Of-Charge, when the capacity difference

results in a cell voltage difference. Once this determina-

tion is made, cell balancing will commence on the

charge cycle and remain in effect for the entire charge

cycle. Upon discharging, cell balancing will be disabled

to preserve run time. Once the near empty point is

reached again, determination will be made as to

whether correct hysteresis has been reached to disable

the cell balancing for the next charge cycle.

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