LTC4097EDDB datasheet(13/20 Pages) LINER

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LTC4097

4097f

Manual Shutdown

The SUSP pin has a 3.4MΩ pulldown resistor to GND. A

logic low enables the charger and a logic high disables it

(the pulldown defaults the charger to the charging state).

The DCIN input draws 20µA when the charger is in shut-

down. The USBIN input draws 20µA during shutdown if

no power is applied to DCIN, but draws only 10µA when

VDCIN > VUSBIN.

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 of Figure 4. To use this feature, connect the NTC

thermistor, RNTC, between the NTC pin and ground and a

bias resistor, RNOM, from VNTC 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 LTC4097 will pause charging when the resistance of

the 100k NTC thermistor drops to 0.54 times the value of

R25 or approximately 54k (for a Vishay “Curve 1” therm-

istor, this corresponds to approximately 40°C). As the

temperature drops, the resistance of the NTC thermistor

rises. The LTC4097 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.

Thermal Limiting

An internal thermal feedback loop reduces the programmed

charge current if the die temperature attempts to rise

above a preset value of approximately 115°C. This feature

protects the LTC4097 from excessive temperature and

allows the user to push the limits of the power handling

capability of a given circuit board without risk of damag-

ing the device. The charge current can be set according

to typical (not worst case) ambient temperature with the

assurance that the charger will automatically reduce the

current in worst case conditions. A safety thermal shut

down circuit will turn off the charger if the die temperature

rises above a value of approximately 150°C. DFN power

considerations are discussed further in the Applications

Information section.

OPERATION

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