Datasheet

LTC4089-3
17
40893f
For more information www.linear.com/4089-3
OPERATION
resistance of the NTC thermistor rises. The LTC4089-3 is
designed to go into hold mode when the value of the NTC
thermistor increases to 2.82 times the value of R
NOM
. This
resistance is R
COLD
. For a Vishay NTHS0603N02N1002J
thermistor, this value is 28.2k which corresponds to ap-
proximately 0°C. The hot and cold comparators each have
approximately 2°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 V
IN
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 V
OUT
exceeds V
IN
. If the current limit
UVLO comparator is tripped, the current limit circuits will
not come out of shutdown until V
OUT
falls 50mV below
the V
IN
voltage.
Charger Undervoltage Lockout
An internal undervoltage lockout circuit monitors the V
OUT
voltage and disables the battery charger circuits until
V
OUT
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 V
BAT
exceeds V
OUT
. If the charger
UVLO comparator is tripped, the charger circuits will
not come out of shutdown until V
OUT
exceeds V
BAT
by 50mV.
Suspend
The LTC4089-3 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.