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LTC1760

1760fa

OPERATION

2.6 LTC1760 SMBALERT Operation

The SMBALERT pin allows the LTC1760 to signal to the

SMBus Host that there has been a change of status.

This pin is asserted low whenever there is a change in

battery presence, AC presence or after a power on reset

event. This pin is cleared during an Alert Response or

any of the following reads:

BatterySystemState(),BatterySystemStateCont(), Bat-

terySystemInfo(), or LTC().

3 Charging Algorithm Overview

3.1 Wake-Up Charging Initiation

The following conditions must be met in order to allow

wake-up charging:

1. The battery thermistor must be COLD-RANGE, IDEAL-

RANGE, or UNDER-RANGE.

2. AC must be present.

3. BatterySystemStateCont(CHARGING_INHIBIT) must

be de-asserted (or low).

4. Hardware controlled charging inhibit must be

de-asserted (MODE not low with VDDS high). Refer to

“Section 6.2”.

Wake-up charging initiates when a newly inserted battery

does not respond to any LTC1760 Master read commands.

Only one battery will wake-up charge at a time. When two

batteries are inserted and both require wake-up charging,

Battery 1 will wake-up charge first. Battery 2 will only wake-

up charge when Battery 1 terminates wake-up charging.

Wake-up charging takes priority over controlled charg-

ing; this prevents one battery from tying up the charger

when it would be advantageous to dual charge two deeply

discharged batteries.

The LTC1760 will attempt to reinitiate wake-up

charging on both batteries after the SMBus Host asserts

BatterySystemStateCont(CHARGER_POR) or a power on

reset event. This will reset any wake-up charging safety

timers and is equivalent to removing and reinserting both

batteries.

The LTC1760 will attempt to reinitiate wake-up charging

on a battery if the battery is not being charged, the therm-

istor is reporting IDEAL-RANGE, and the battery fails to

respond to an SMBus query. This is an important feature

for handling deeply discharged NiMH batteries. These

batteries may begin to talk while being charged and go

silent once charging has stopped.

Wake-up charging is disabled if the battery thermistor is

COLD-RANGE or UNDER-RANGE and the battery has been

charged for longer than tTIMEOUT.

3.2 Wake-Up Charging Termination

The LTC1760 will terminate wake-up charging when any

of the following conditions are met:

1. Battery removal (thermistor indicating OVER-RANGE)

2. AC is removed.

3. The SMBus Host issues a calibration request by setting

BatterySystemStateCont(CALIBRATE) high.

4. Any response to an LTC1760 Master read of Charg-

ingCurrent(), Current(), ChargingVoltage(), or Voltage().

Note that the LTC1760 ignores all writes from the battery.

5. Any of the following AlarmWarning() bits asserted high:

OVER_CHARGED_ALARM

TERMINATE_CHARGE_ALARM

TERMINATE_CHARGE_RESERVED

OVER_TEMP_ALARM

Note that the LTC1760 ignores all writes from the battery.

Each battery’s charge alarm is cached inside the LTC1760.

This internally cached bit will be set when any of the up-

per four bits of the battery’s AlarmWarning() response

are set. The cached bit will remain set if a subsequent

AlarmWarning() fails to respond. The cached alarm will

be cleared by any of the following conditions.

a) Associated battery is removed.

b) A subsequent AlarmWarning() clears all

charge alarm bits for the associated battery.

c) A power on reset event.

d) The SMBus Host asserts

BatterySystemStateCont(CHARGER_POR) high.

LTC4100 数据表(PDF) 26 Page - Linear Technology

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