LTC4065 LINER [Linear Technology], LTC4065 Datasheet - Page 15

• Manufacturer Part Number: LTC4065
• Description: High Efficiency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

operaTion
NTC Thermistor
The battery temperature is measured by placing a negative
temperature coefficient (NTC) thermistor close to the bat-
tery pack. The NTC circuitry is shown in the Block Diagram.
To use this feature, connect the NTC thermistor, R
between the NTC pin and ground and a bias resistor, R
from V
a value equal to the value of the chosen NTC thermistor
at 25°C (R25). A 100k thermistor is recommended since
thermistor current is not measured by the LTC4088 and
will have to be considered for USB compliance.
The LTC4088 will pause charging when the resistance of
the NTC thermistor drops to 0.54 times the value of R25 or
approximately 54k (for a Vishay “Curve 1” thermistor, this
corresponds to approximately 40°C). If the battery charger
is in constant voltage (float) mode, the safety timer also
pauses until the thermistor indicates a return to a valid
temperature. As the temperature drops, the resistance of
the NTC thermistor rises. The LTC4088 is also designed
to pause charging when the value of the NTC thermistor
increases to 3.25 times the value of R25. For a Vishay
“Curve 1” thermistor, this resistance, 325k, corresponds
to approximately 0°C. The hot and cold comparators each
have approximately 3°C of hysteresis to prevent oscillation
about the trip point. Grounding the NTC pin disables all
NTC functionality.
BUS
to NTC. R
NOM
should be a 1% resistor with
NOM
NTC
,
,
Thermal Regulation
To prevent thermal damage to the IC or surrounding
components, an internal thermal feedback loop will
automatically decrease the programmed charge current
if the die temperature rises to approximately 110°C.
Thermal regulation protects the LTC4088 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 without risk of damaging the LTC4088 or external
components. The benefit of the LTC4088 thermal regula-
tion loop is that charge current can be set according to
actual conditions rather than worst-case conditions for a
given application with the assurance that the charger will
automatically reduce the current in worst-case conditions.
Shutdown Mode
For autonomous battery charger operation, D2 should
be permanently grounded. However, for more control
via software the LTC4088’s battery charger can be inde-
pendently disabled by bringing the D2 pin above V
must also be brought high to enable high power (2.5mA)
suspend mode.
The input switching regulator is enabled whenever V
is above the UVLO voltage and the LTC4088 is not in one
of the two USB suspend modes (500µA or 2.5mA).
The ideal diode is enabled at all times and cannot be
disabled.
LTC4088
15
IH
. D2
4088fb
BUS