LTC4040_15 Datasheet, PDF (11/26 Pages) Linear Technology – 2.5A Battery Backup Power Manager

LTC4040
Pin Functions
OVSNS (Pin 16): Overvoltage Protection Sense Input. If
the overvoltage feature is used, the OVSNS pin should be
connected through a 6.2k resistor to an input power con-
nector and the drain of an N-channel MOS pass transistor.
If not, this pin should be shorted to V_IN. When voltage is
detected on OVSNS, it draws a small amount of current to
power a charge pump which then provides gate drive to
IGATE to energize the external transistor. When the voltage
on this pin exceeds typically 6V, IGATE is pulled to GND
to disable the pass transistor and protect the LTC4040
from high voltage.
NTC (Pin 17): Input to the Thermistor Monitoring Circuits.
The NTC pin connects to a battery’s thermistor to deter-
mine if the battery is too hot or too cold to charge. If the
battery’s temperature is out of range, charging is paused
until it re-enters the valid range. A low drift bias resistor
is required from V_IN to NTC and a thermistor is required
from NTC to ground. If the NTC function is not desired,
the NTC pin should be grounded.
BSTFB (Pin 18): Feedback Input for the Backup Boost
Regulator. During steady-state backup operation, voltage
on this pin servos to 0.8V.
PFI (Pin 19): Power-Fail Input. High impedance input to
an accurate comparator (power-fail) with a 1.19V falling
threshold and 30mV hysteresis. PFI controls the state of
the PFO output pin and sets the input voltage threshold
below which the boost backup is initiated. This threshold
voltage also represents the minimum voltage above which
the step-down battery charger is enabled and the part al-
lows power to flow from the input to the output through
the external pass transistors.
PFO (Pin 20): Open-Drain Power-Fail Status Output. This
pin is pulled to ground by an internal N-channel MOSFET
when the PFI input is below the falling threshold of the
power-fail comparator. Once the PFI input rises above
the rising threshold, this pin becomes high impedance.
SW (Pins 21, 22): Power Transmission Pin for the Buck
Switching Charger and the Boost Switching Backup
Converter. A 1µH to 2.2µH inductor should be connected
from SW to BAT.
BAT (Pin 23): Single Cell Li-Ion or LiFePO₄ Battery Pin.
Depending on the availability of input power, the battery
will either deliver power to V_SYS via the boost converter
or be charged from V_SYS via the buck charger. BAT should
be bypassed with a low ESR ceramic capacitor of at least
10µF to GND.
GND (Exposed Pad Pin 25): The exposed pad must be
soldered to the PCB to provide a low electrical and ther-
mal impedance connection to the printed circuit board’s
ground. A continuous ground plane on the second layer of
a multilayer printed circuit board is strongly recommended.
For more information www.linear.com/LTC4040
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