LTC4098EUDC-3.6 查看數據表（PDF） - Linear Technology

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LTC4098EUDC-3.6

USB Compatible Switching Power Manager/LiFePO4 Charger with Overvoltage Protection

Linear Technology 

LTC4098-3.6

OPERATION

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 LTC4098-3.6 will pause charging when the resistance

of the NTC thermistor drops to 0.25 times the value of R25

or approximately 25k (for a Vishay curve  1 thermistor, this

corresponds to approximately 60°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 LTC4098-3.6 is also designed

to pause charging when the value of the NTC thermistor

increases to 3.26 times the value of R25. For a Vishay

curve 1 thermistor, this resistance, 326k, corresponds to

approximately 0°C. The hot and cold comparators each

have approximately 3°C of hysteresis to prevent oscilla-

tion 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 LTC4098-3.6.

Thermal Regulation

To prevent thermal damage to the LTC4098-3.6 or sur-

rounding components, an internal thermal feedback loop

will automatically decrease the programmed charge current

if the die temperature rises to approximately 110°C. Ther-

mal regulation protects the LTC4098-3.6 from excessive

temperature due to high power operation or high ambi-

ent 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 LTC4098-3.6

or external components. The benefit of the LTC4098-3.6

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 LTC4098-3.6 is 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.

409836f

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