LTC4098-1 datasheet(20/32 Pages) LINER

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LTC4098/LTC4098-1

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NTC Thermistor

The battery temperature is measured by placing a nega-

tive temperature coefﬁcient (NTC) thermistor close to

the battery pack. The NTC circuitry is shown in the Block

Diagram.

To use this feature, connect the NTC thermistor, RNTC,

between the NTC pin and ground and a bias resistor, RNOM,

from NTCBIAS to NTC. RNOM should be a 1% resistor with

a value equal to the value of the chosen NTC thermistor

at 25°C (R25).

The LTC4098/LTC4098-1 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 LTC4098/

LTC4098-1 are 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.

Figure 6 is a ﬂow chart representation of the battery charger

algorithm employed by the LTC4098/LTC4098-1.

Thermal Regulation

To prevent thermal damage to the LTC4098/LTC4098-1 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 LTC4098/LTC4098-1 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

LTC4098/LTC4098-1 or external components. The beneﬁt

of the LTC4098/LTC4098-1 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 automatically

reduce the current in worst-case conditions.

Shutdown Mode

The USB switching regulator is enabled whenever VBUS

is above the UVLO voltage and the LTC4098/LTC4098-1

are not in one of the two USB suspend modes (500μA or

2.5mA). When power is available from both the USB and

high voltage inputs, the high voltage regulator is prioritized

and the USB switching regulator is disabled.

The ideal diode is enabled at all times and cannot be

disabled.

OPERATION

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