LTC4099 Linear Technology Corporation, LTC4099 Datasheet - Page 20

• Manufacturer Part Number: LTC4099
• Description: I2C Controlled USB Power Manager/Charger
• Manufacturer: Linear Technology Corporation

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LTC4099
OPERATION
Overtemperature Battery Conditioner
Since Li-Ion batteries deteriorate with full voltage and
high temperature, the LTC4099 contains an automatic
battery conditioner circuit that reduces the battery volt-
age if both high temperature and high voltage are present
simultaneously.
Recall that battery charging is inhibited if the thermistor
temperature reaches 45°C. If the thermistor temperature
climbs above 60°C, and the battery conditioner circuit is
enabled, an internal load of approximately 180mA is ap-
plied to BAT. Once the battery voltage drops to 3.9V, or the
thermistor reading drops below 58°C, the internal load is
disabled. Battery charging resumes once the thermistor
temperature drops below 42°C.
When activated via the I
operates whether or not external power is available,
charging has terminated or charging has been disabled
by I
Note that this circuit can dissipate signifi cant power inside
the LTC4099. To prevent an excessive temperature rise
of the LTC4099, the LTC4099 reduces discharge current
as needed to prevent a junction temperature rise above
120°C.
Thermal Regulation
To prevent thermal damage to the LTC4099 or surrounding
components during normal charging, an internal thermal
feedback loop will automatically decrease the programmed
charge current if the die temperature rises to 105°C. This
thermal regulation technique protects the LTC4099 from
excessive temperature due to high power operation or high
ambient thermal conditions, and allows the user to push
the limits of the power handling capability with a given
circuit board design. The benefi t of the LTC4099 thermal
regulation loop is that charge current can be set according
to actual, rather than worst-case, conditions for a given
application with the assurance that the charger will auto-
matically reduce the current in worst-case conditions.
The thermal regulation set-point can be adjusted down to
85°C from the default 105°C setting using the I
explained in the Input Data section.
20
2
C control.
2
C port, the battery conditioner
2
C port, as
Overvoltage Protection
The LTC4099 can protect itself from the inadvertent ap-
plication of excessive voltage to V
two external components: an N-channel MOSFET and a
6.2k resistor. The maximum safe overvoltage magnitude
will be determined by the choice of the external FET and
its associated drain breakdown voltage.
The overvoltage protection circuit consists of two pins. The
fi rst, OVSENS, is used to measure the externally applied
voltage through an external resistor. The second, OVGATE,
is an output used to drive the gate pin of the external FET.
When OVSENS is below 6V, an internal charge pump will
drive OVGATE to approximately 1.88 • OVSENS. This will
enhance the N-channel FET and provide a low impedance
connection to V
the LTC4099. If OVSENS should rise above 6V due to a
fault or use of an incorrect wall adapter, OVGATE will be
pulled to GND, disabling the external FET and, therefore,
protecting the LTC4099. When the voltage drops below
6V again, the external FET will be re-enabled.
See the Applications Information section for examples of
multiple input protections, reverse input protection and
recommended components.
Suspend LDO
The LTC4099 provides a small amount of power to V
in suspend mode by including an LDO from V
This LDO will prevent the battery from running down when
the portable product has access to a suspended USB port.
Regulating at 4.6V, this LDO only becomes active when
the internal switching converter is disabled. To remain
compliant with the USB specifi cation, the input to the LDO
is current-limited so that it will not exceed the low power
or high power suspend specifi cation. If the load on V
exceeds the suspend current limit, the additional current
will come from the battery via the ideal diodes. The sus-
pend LDO sends a scaled copy of the V
CLPROG pin, which will servo to a maximum voltage of
approximately 100mV. Thus, the high power and low power
suspend settings are related to the levels programmed by
the same CLPROG resistor for the 100mA, 500mA and
other switching power path settings. Command bits, I
BUS
or WALL which will, in turn, power
BUS
or WALL with just
BUS
current to the
BUS
to V
OUT
LIM2
OUT
OUT
4099f
.