PS501 datasheet(13/42 Pages) MICROCHIP

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 2004 Microchip Technology Inc.

DS21818C-page 13

PS501

5.0

CHARGE CONTROL

A SBS configuration normally allows the Smart Battery

to broadcast the ChargingVoltage and ChargingCurrent

values to the Smart Battery Charger (SMBus address

12 hex) to ‘control’ when to start charge, stop charge

and when to signal a valid ‘fully charged’ condition.

AlarmWarnings are also sent from the Smart Battery

(SMBus address 16 hex) to the Smart Battery Charger.

Alternately, the SMBus Host or a “Level 3” Smart

Battery Charger may simply read the SBData values

for ChargingVoltage and ChargingCurrent from the

Smart Battery directly. The Host or “Level 3” Smart

Battery Charger is also required to read the SBData

value of BatteryStatus to obtain the appropriate alarm

and status bit flags. When used in this configuration,

the ChargingCurrent and ChargingVoltage broadcasts

can be disabled from the Smart Battery by setting the

CHARGER_MODE (bit 14) in the BatteryMode regis-

ter. The PS501 ICs support all of these functions.

(Please refer to the SBS Smart Battery Charger

Specification for a definition of the “Level 3” Smart

Battery Charger.)

The ChargingCurrent and ChargingVoltage registers

contain the maximum charging parameters desired by

the particular chemistry, configuration and environmen-

tal conditions. The environmental conditions include

the measured temperature and the measured cell or

pack voltages.

For Li-based systems, ChargingVoltage should be set

to the product of the EOCVolt and Cells values from

the EEPROM:

EQUATION 5-1:

The ChargingCurrent value is set to a maximum using

the ChrgCurr value from the EEPROM. For Lithium

systems, both ChargingCurrent and ChargingVoltage

values are maximums. When the current reaches

ChrgCurr, it will be held constant at this value. Then,

when the voltage reaches ChrgVolt, the current must

be reduced so that the voltage will be constant and not

exceed the maximum. This is accomplished by setting

ChargingCurrent to ChrgCurrOff. For safety reasons,

this current change also occurs when the temperature

limits are exceeded. When temperature or voltage lim-

its are exceeded, the value of ChargingCurrent

changes to the ChrgCurrOff value from the EEPROM.

When a valid End-Of-Charge (EOC) condition is

detected and a fully charged state is reached, the

ChargingCurrent value is set equal to the ChrgCurrOff

value.

When ChargingCurrent is set to the ChrgCurrOff value,

no broadcasts of either ChargingCurrent or Charging-

Voltage will occur unless a charge current greater than

NullCurr is detected by the A/D measurements.

Temperature limits are set using the ChrgMaxTemp,

DischrgMaxTemp and ChrgMinTemp values from

EEPROM. These values represent the temperature

limits within which ChargingCurrent will be set to

ChrgCurr. Temperatures outside these limits will cause

ChargingCurrent to be set to ChrgCurrOff.

If ChargingCurrent is set to ChrgCurrOff and the mea-

sured temperature is greater than DischrgMaxTemp

and less than ChrgMaxTemp and a charge current is

measured which is significantly larger than the

ChrgCurrOff value, then ChargingCurrent will be set to

ChrgCurr unless a fully charged condition has already

been reached.

If the CHARGER_MODE bit in the BatteryMode regis-

ter is cleared (enabling broadcasts of ChargingCurrent

and ChargingVoltage), then these broadcasts will occur

every NChrgBroadcast measurement cycle.

The Smart Battery Data and Smart Battery Charger

Specifications

require

that

ChargingCurrent

and

ChargingVoltage broadcasts occur no faster than once

per 5 seconds and no slower than once per 60 seconds

when charging is occurring or desired. This requires

that the NChrgBroadcast value must be set between

10 and 120. The SMBus Specification also requires

that no broadcasts occur during the first 10 seconds

after SMBus initialization.

EXAMPLE 5-1:

CONFIGURATION

ChargingVoltage = EOCVolt x Cells

Measurement cycle is 500 msec

NChrgBroadcast

100 decimal

ChrgCurr

2500 decimal

ChrgCurrOff

=10 decimal

ChrgMaxTemp

162 decimal

DischrgMaxTemp =

137 decimal

ChrgMinTemp

=50 decimal

Results:

ChargingCurrent and ChargingVoltage broadcasts:

100 cycles of 500 msec = every 50 seconds

Broadcast delay after SMBus initialization:

10 seconds

ChargingCurrent if Temperature > 45°C: 10 mA

ChargingCurrent if Temperature < 0°C: 10 mA

ChargingCurrent if Temperature < 35°C and

> 0°C: 2500 mA

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