LTC4088-1_12 LINER [Linear Technology], LTC4088-1_12 Datasheet - Page 15

• Manufacturer Part Number: LTC4088-1_12
• 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 LTC4088-1/
LTC4088-2 and will have to be considered for USB com-
pliance.
The LTC4088-1/LTC4088-2 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 LTC4088-1/
LTC4088-2 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 LTC4088-1/LTC4088-2
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 LTC4088-1/LTC4088-2 or external components. The
benefit of the LTC4088-1/LTC4088-2 thermal regulation
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 au-
tomatically reduce the current in worst-case conditions.
Shutdown Mode
The input switching regulator is enabled whenever V
is above the UVLO voltage and the LTC4088-1/LTC4088-
2 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.
LTC4088-1/LTC4088-2
15
40881fc
BUS