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LTC4160EPDC-PBF View Datasheet(PDF) - Linear Technology

Part Name
Description
MFG CO.
LTC4160EPDC-PBF Datasheet PDF : 32 Pages
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LTC4160/LTC4160-1
OPERATION
the battery will eventually self discharge. To ensure that
the battery is always topped off, a charge cycle will auto-
matically begin when the battery voltage falls below the
recharge threshold which is typically 100mV less than
the charger’s float voltage. In the event that the safety
timer is running when the battery voltage falls below the
recharge threshold, it will reset back to zero. To prevent
brief excursions below the recharge threshold from reset-
ting the safety timer, the battery voltage must be below
the recharge threshold for more than 1ms. The charge
cycle and safety timer will also restart if the VBUS UVLO
cycles low and then high (e.g., VBUS is removed and then
replaced), or if the battery charger is cycled on and off by
the ENCHARGER pin.
Charge Current
The charge current is programmed using a single resis-
tor from PROG to ground. 1/1030th of the battery charge
current is sent to PROG, which will attempt to servo to
1.000V. Thus, the battery charge current will try to reach
1030 times the current in the PROG pin. The program
resistor and the charge current are calculated using the
following equation:
ICHG
=
VPROG
RPROG
1030
In either the constant-current or constant-voltage charging
modes, the voltage at the PROG pin will be proportional to
the actual charge current delivered to the battery. There-
fore, the actual charge current can be determined at any
time by monitoring the PROG pin voltage and using the
following equation:
IBAT
=
VPROG
RPROG
•1030
In many cases, the actual battery charge current, IBAT, will
be lower than ICHG due to limited input power available and
prioritization with the system load drawn from VOUT.
The Battery Charger Flow Chart on the next page illustrates
the battery charger’s algorithm.
18
Charge Status Indication
The CHRG and FAULT pins can be used to indicate the status
of the battery charger. Two possible states are represented
by CHRG: charging and not charging. An open-drain output,
the CHRG pin can drive an indicator LED through a current
limiting resistor for human interfacing or simply a pull-up
resistor for microprocessor interfacing.
When charging begins, CHRG is pulled low and remains
low for the duration of a normal charge cycle. When charg-
ing is complete, i.e., the BAT pin reaches the float and the
charge current has dropped to one tenth of the programmed
value, the CHRG pin goes high. The CHRG pin does not
respond to the C/10 threshold if the LTC4160/LTC4160-1
is in VBUS input current limit. This prevents false end-of-
charge indications due to insufficient power available to
the battery charger.
Table 2 illustrates the possible states of the CHRG and
FAULT pins when the battery charger is active.
Table 2. Charge Status Readings Using the CHRG and FAULT Pins
STATUS
CHRG
FAULT
Charging/NTC Fault
Low
High
Not Charging
High
High
Bad Battery
High
Low
An NTC fault pauses charging while the battery tempera-
ture is out of range but is not indicated using the CHRG
or FAULT pins.
If a battery is found to be unresponsive to charging (i.e.,
its voltage remains below 2.85V for 1/2 hour) the CHRG
pin goes high and the FAULT pin goes low to indicate a
bad battery fault.
Note that the LTC4160/LTC4160-1 are 3-terminal
PowerPath products where system load is always priori-
tized over battery charging. Due to excessive system load,
there may not be sufficient power to charge the battery
beyond the trickle charge threshold voltage within the bad
battery timeout period. In this case, the battery charger
will falsely indicate a bad battery. System software may
then reduce the load and reset the battery charger to try
again.
The FAULT pin is also used to indicate whether there is
a short circuit condition on VBUS when the bidirectional
41601f

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