LTC4040_15 Datasheet, PDF (10/26 Pages) Linear Technology – 2.5A Battery Backup Power Manager

LTC4040
Pin Functions
V_SYS (Pins 1, 24): System Voltage Output Pin. This pin is
used to provide power to an external load from either the
primary input supply or the backup battery if the primary
input supply is not available. In addition to supplying power
to the load, this pin provides power to charge the battery
when input power is available. V_SYS should be bypassed
with a low ESR ceramic capacitor of at least 100µF to GND.
PROG (Pin 2): Charge Current Program Pin. An external
resistor from the PROG pin to ground programs the full-
scale charge current. At full scale, the PROG pin servos
to 0.8V. The ratio of BAT pin current to PROG pin current
is internally set to 2500.
CLPROG (Pin 3): V_SYS Current Monitoring Pin. The ratio
between the CLPROG pin voltage and the differential voltage
between V_IN and CLN is internally set to 32. Charge current
is reduced when the CLPROG pin voltage reaches 0.8V.
CHGOFF (Pin 4): Disable Pin for the Battery Charger. Tie
this pin to GND to enable the charger or to a voltage above
1.2V to disable it. Do not leave this pin unconnected.
BSTOFF (Pin 5): Disable Pin for the Backup Boost Con-
verter. Tie this pin to GND to enable the boost backup or
to a voltage above 1.2V to disable backup. Do not leave
this pin unconnected.
V_IN (Pin 6): Input Pin. Power can be applied directly to
this pin if the optional overvoltage protection (OVP) fea-
ture is not used. For applications where the OVP feature
is required, connect an external N-channel FET between
the power supply output V_PWR and this pin.
CLN (Pin 7): Negative terminal pin for an external cur-
rent limit sense resistor connected between V_IN and this
pin. This resistor is used to monitor the current from V_IN
to V_SYS. The LT4040 reduces charge current in order to
maintain 25mV across this sense resistor. However, it does
not limit the system current if the drop exceeds 25mV.
CHRG (Pin 8): Open-Drain Charge Status Output; typi-
cally pulled up through a resistor to a reference voltage.
During a battery charging cycle, CHRG is pulled low until
the charge current drops below C/8 when the CHRG pin
becomes high impedance.
FAULT (Pin 9): Open-Drain Fault Status Output; typically
pulled up through a resistor to a reference voltage. This
pin indicates charge cycle fault conditions during a battery
charging cycle. A temperature fault or a bad-battery fault
causes this pin to be pulled low. If no fault conditions
exist, the FAULT pin remains high impedance.
RSTFB (Pin 10): Reset Comparator Input. High Imped-
ance input to an accurate comparator with a 0.74V falling
threshold and 20mV hysteresis. This pin controls the state
of the RST output pin. An external resistor divider is used
between V_SYS, RSTFB and GND. It can be the same resistor
divider as the BSTFB divider to monitor the system output
voltage V_SYS. See the Applications Information section.
RST (Pin 11): Open-Drain Status Output of the Reset
Comparator. This pin is pulled to ground by an internal
N-channel MOSFET whenever the RSTFB pin falls below
0.74V. Once the RSTFB pin voltage recovers, the pin be-
comes high impedance after a 232ms delay.
F2 (Pin 12): Logic Input to Select Battery Chemistry. A
logic high on this pin selects Li-Ion and a logic low selects
LiFePO₄. Do not leave this pin unconnected.
F1, F0 (Pins 13, 14): Logic inputs to select one of the
four possible charge voltage settings for each battery
chemistry. Do not leave these pins unconnected.
F0
F1
F2 = 1: Li-Ion (V) F2 = 0: LiFePO₄ (V)
0
0
3.95
3.45
1
0
4.00
3.50
0
1
4.05
3.55
1
1
4.10
3.60
IGATE (Pin 15): Gate Pin for the External N-Channel FETs.
This pin is driven by an internal charge pump to develop
sufficient overdrive to fully enhance the pass transistors.
The first pass transistor is connected between the supply
output V_PWR and V_IN and is part of the optional overvolt-
age protection module. The second pass transistor, con-
nected between V_IN and V_SYS, is mandatory and is used
to disconnect the system from the input supply during
backup mode.
4040fa
10
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