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LTC4100

4100fb

OPERATION

The RES_COLD bit is set only when the SafetySignal re-

sistance value is greater than 28.5kΩ. The SafetySignal

indicates a cold battery. The RES_COLD bit will be set

whenever the RES_OR bit is set.

The RES_HOT bit is set only when the SafetySignal resis-

tance is less than 3150Ω, which indicates a hot battery.

The RES_HOT bit will be set whenever the RES_UR bit

is set.

The RES_UR bit is set only when the SafetySignal resis-

tance value is less than 575Ω.

ALARM_INHIBITED bit is set if a valid AlarmWarning()

message has been received and charging is inhibited as

a result. This bit is cleared if both ChargingVoltage() and

ChargingCurrent() are rewritten to the LTC4100, power is

removed (DCDIV < VACP), or if a battery is removed. The

setting of the ALARM_INHIBITED will activate the LTC4100

SMBALERT pull-down.

POWER_FAIL bit is set if the LTC4100 does not have suf-

ﬁcient DCIN voltage to charge the battery or if an external

device is pulling the CHGEN input signal low. Charging is

disabled whenever this bit is set. The setting of this bit

does not clear the values in the ChargingVoltage() and

ChargingCurrent() function values, nor does it necessarily

affect the charging modes of the LTC4100.

BATTERY_PRESENT is set if a battery is present other-

wise it is cleared. The LTC4100 uses the SafetySignal

in order to determine battery presence. If the LTC4100

detects a RES_OR condition, the BATTERY_PRESENT

bit is cleared immediately. The LTC4100 will not set the

BATTERY_PRESENT bit until it successfully samples the

SafetySignal twice and does not detect a RES_OR condi-

tion on either sampling. If AC is not present (e.g. DCDIV

< VACP), this bit may not be set for up to one-half second

after the battery is connected to the SafetySignal. The

ChargingCurrent() and ChargingVoltage() function val-

ues are immediately cleared whenever this bit is cleared.

Charging will never be allowed if this bit is cleared. A

change in BATTERY_PRESENT will activate the LTC4100

SMBALERT pull-down.

AC_PRESENT is set if the voltage on DCDIV is greater than

VACP. This does not necessarily indicate that the voltage

on DCIN is sufﬁcient to charge the battery. A change in

AC_PRESENT will activate the LTC4100 SMBALERT pull-

down.

ChargingCurrent() (‘h14)

Description: The Battery, System Host or other master

device sends the desired charging current (mA) to the

LTC4100 .

Purpose: The LTC4100 uses RILIM, the granularity of the

IDAC, and the value of the ChargingCurrent() function to

determine its charging current supplied to the battery. The

charging current will never exceed the maximum current

permitted by RILIM. The ChargingCurrent() value will be

truncated to the granularity of the IDAC. The charging cur-

rent will also be reduced if the battery voltage exceeds the

programmed charging voltage.

• SMBus Protocol: Write Word.

Input: The CHARGING_CURRENT is an unsigned 16 bit

integer specifying the requested charging current in mA.

The following table deﬁnes the maximum permissible

value of CHARGING_CURRENT that will not set the CUR-

RENT_OR in the ChargerStatus() function for a given

value of the RILIM:

RILIM

ChargingCurrent()

Current

Short to GND

0x0000 through 0x03FF 0mA through 1023mA

10kΩ ±1%

0x0000 through 0x07FF 0mA through 2047mA

33kΩ ±1%

0x0000 through 0x0BFF 0mA through 3071mA

Open (or Short to VDD) 0x0000 through 0x0FFF 0mA through 4095mA

ChargingVoltage() (‘h15)

Description: The Battery, SMBus Host or other master

device sends the desired charging voltage (mV) to the

LTC4100.

Purpose: The LTC4100 uses RVLIM, the granularity of the

VDAC, and the value of the ChargingVoltage() function to

determine its charging voltage supplied to the battery. The

charging voltage will never be forced beyond the voltage

permitted by RVLIM. The ChargingVoltage() value will be

truncated to the granularity of the VDAC. The charging

voltage will also be reduced if the battery current exceeds

the programmed charging current.

• SMBus Protocol: Write Word.

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