LTC4101
16
4101fa
OPERATION
SMBus Accelerator Pull-Ups
Both SCL and SDA have SMBus accelerator circuits
which reduce the rise time on systems with signifi cant
capacitance on the two SMBus signals. The dynamic pull-up
circuitry detects a rising edge on SDA or SCL and applies
1mA to 10mA pull-up to V
DD
when V
IN
> 0.8V until V
IN
< V
DD
– 0.8V (external pull-up resistors are still required
to supply DC current). This action allows the bus to meet
SMBus rise time requirements with as much as 250pF on
each SMBus signal. The improved rise time will benefi t
all of the devices which use the SMBus, especially those
devices that use the I
2
C logic levels. Note that the dynamic
pull-up circuits only pull to V
DD
, so some SMBus devices
that are not compliant to the SMBus specifi cations may still
have rise time compliance problems if the SMBus pull-up
resistors are terminated with voltages higher than V
DD
.
The Control Block
The LTC4101 charger operations are handled by the con-
trol block. This block is capable of charging the selected
battery autonomously or under SMBus Host control.
The control block can request communications with the
system management host (SMBus Host) by asserting
SMBALERT = 0; this will cause the SMBus Host, if present,
to poll the LTC4101.
The control block receives SMBus slave commands from
the SMBus interface block.
The control block allows the LTC4101 to meet the fol-
lowing Smart Battery-controlled (Level 2) charger
requirements:
1. Implements the Smart Battery’s critical warning mes-
sages over the SMBus.
2. Operates as an SMBus slave device that responds to
ChargingVoltage() and ChargingCurrent() commands and
adjusts the charger output parameters accordingly.
3. The host may control charging by disabling the Smart
Battery’s ability to transmit ChargingCurrent() and
ChargingVoltage() request functions and broadcast-
ing the charging commands to the LTC4101 over the
SMBus.
4. The LTC4101 will still respond to Smart Battery critical
warning messages without host intervention.
Wake-up Charging Mode
The following conditions must be met in order to allow
wake-up charging of the battery:
1. The SafetySignal must be RES_COLD, RES_IDEAL, or
RES_UR.
2. AC must be present. This is qualifi ed by DCDIV > V
ACP
.
Wake-up charging initiates when a newly inserted battery
does not send ChargingCurrent() and ChargingVoltage()
functions to the LTC4101.
The following conditions will terminate the Wake-up
Charging Mode.
1. A T
TIMEOUT
period is reached when the SafetySignal is
RES_COLD or RES_UR.
2. The SafetySignal is registering RES_OR.
3. The successful writing of the ChargingCurrent() AND
ChargingVoltage() function. The LTC4101 will proceed
to the controlled charging mode after these two func-
tions are written.
4. The SafetySignal is registering RES_HOT.
5. The AC power is no longer present. (DCDIV < V
ACP
)
6. The ALARM_INHIBITED becomes set in the Charger-
Status() function.
7. The INHIBIT_CHARGE is set in the ChargerMode()
function.
8. The CHGEN pin is pulled low by an external device. The
LTC4101 will resume wake-up charging, if the CHGEN
pin is released by the external device. Toggling the
CHGEN pin will not reset the T
TIMEOUT
timer.
9. There is insuffi cient DCIN voltage to charge the battery.
The LTC4101 will resume wake-up charging when there
is suffi cient DCIN voltage to charge the battery. This
condition will not reset the T
TIMEOUT
timer.
