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LTC4089/LTC4089-5

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If, for some reason the charge current rises back above

the threshold, the CHRG pin will not resume the strong

pull-down state. The EOC latch can be reset by a recharge

cycle (i.e., VBAT drops below the recharge threshold) or

toggling the input power to the part.

NTC Thermistor—Battery Temperature Charge

Qualiﬁcation

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 Figure 4.

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

between the NTC pin and ground and a resistor (RNOM)from

the NTC pin to VNTC. RNOM should be a 1% resistor with

a value equal to the value of the chosen NTC thermistor at

25°C (this value is 10k for a Vishay NTHS0603N02N1002J

thermistor). The LTC4089/LTC4089-5 goes into hold mode

when the resistance (RHOT) of the NTC thermistor drops

to 0.41 times the value of RNOM, or approximately 4.1k,

which should be at 50°C. The hold mode freezes the timer

and stops the charge cycle until the thermistor indicates a

return to a valid temperature. As the temperature drops,

the resistance of the NTC thermistor rises. The LTC4089/

LTC4089-5 is designed to go into hold mode when the

value of the NTC thermistor increases to 2.82 times the

value of RNOM. This resistance is RCOLD. For a Vishay

NTHS0603N02N1002J thermistor, this value is 28.2k

which 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 will disable the NTC function.

Current Limit Undervoltage Lockout

An internal undervoltage lockout circuit monitors the

input voltage and disables the input current limit circuits

until VIN rises above the undervoltage lockout threshold.

The current limit UVLO circuit has a built-in hysteresis of

125mV. Furthermore, to protect against reverse current in

the power MOSFET, the current limit UVLO circuit disables

the current limit (i.e., forces the input power path to a high

impedance state) if VOUT exceeds VIN. If the current limit

UVLO comparator is tripped, the current limit circuits will

not come out of shutdown until VOUT falls 50mV below

the VIN voltage.

Charger Undervoltage Lockout

An internal undervoltage lockout circuit monitors the VOUT

voltage and disables the battery charger circuits until

VOUT rises above the undervoltage lockout threshold. The

battery charger UVLO circuit has a built-in hysteresis of

125mV. Furthermore, to protect against reverse current

in the power MOSFET, the charger UVLO circuit keeps the

charger shut down if VBAT exceeds VOUT. If the charger

UVLO comparator is tripped, the charger circuits will

not come out of shutdown until VOUT exceeds VBAT

by 50mV.

Suspend

The LTC4089/LTC4089-5 can be put in suspend mode by

forcing the SUSP pin greater than 2.3V. In suspend mode,

the ideal diode function from BAT to OUT is kept alive. If

power is applied to the HVIN pin, then charging will be

unaffected. Current drawn from the IN pin is reduced to

50µA. Suspend mode is intended to comply with the USB

power speciﬁcation mode of the same name.

OPERATIO

Figure 4. NTC Circuit

–

RNOM

10k

RNTC

10k

NTC

VNTC

0.1V

NTC_ENABLE

4089 F04

LTC4089

TOO_COLD

TOO_HOT

0.74 • VNTC

0.29 • VNTC

–

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