LTC4088 LINER [Linear Technology], LTC4088 Datasheet - Page 13

• Manufacturer Part Number: LTC4088
• Description: High Effi ciency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

OPERATIO
Battery Charger
The LTC4088 includes a constant-current/constant-volt-
age battery charger with automatic recharge, automatic
termination by safety timer, low voltage trickle charging,
bad cell detection and thermistor sensor input for out of
temperature charge pausing.
When a battery charge cycle begins, the battery charger
fi rst determines if the battery is deeply discharged. If the
battery voltage is below V
trickle charge feature sets the battery charge current to
10% of the programmed value. If the low voltage persists
for more than 1/2 hour, the battery charger automatically
terminates and indicates, via the ⎯ C ⎯ H ⎯ R ⎯ G pin, that the bat-
tery was unresponsive.
Once the battery voltage is above V
charging in full power constant-current mode. The current
delivered to the battery will try to reach 1031V/R
Depending on available input power and external load
conditions, the battery charger may or may not be able to
charge at the full programmed rate. The external load will
always be prioritized over the battery charge current. The
USB current limit programming will always be observed
and only additional power will be available to charge the
battery. When system loads are light, battery charge cur-
rent will be maximized.
Charge Termination
The battery charger has a built-in safety timer. Once the
voltage on the battery reaches the pre-programmed fl oat
voltage of 4.200V, the charger will regulate the battery
voltage there and the charge current will decrease naturally.
Once the charger detects that the battery has reached
4.200V, the 4-hour safety timer is started. After the safety
timer expires, charging of the battery will discontinue and
no more current will be delivered.
Automatic Recharge
Once the battery charger terminates, it will remain off
drawing only microamperes of current from the battery.
If the portable product remains in this state long enough,
the battery will eventually self discharge. To ensure that
the battery is always topped off, a charge cycle will au-
tomatically begin when the battery voltage falls below
U
TRKL
, typically 2.85V, an automatic
TRKL
, the charger begins
PROG
.
V
is running when the battery voltage falls below V
will reset back to zero. To prevent brief excursions below
V
must be below V
cycle and safety timer will also restart if the V
cycles low and then high (e.g., V
replaced) or if the charger is momentarily disabled using
the D2 pin.
Charge Current
The charge current is programmed using a single resistor
from PROG to ground. 1/1031th of the battery charge cur-
rent is delivered to PROG, which will attempt to servo to
1.000V. Thus, the battery charge current will try to reach
1031 times the current in the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
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. The
charge current can be determined at any time by monitoring
the PROG pin voltage and using the following equation:
In many cases, the actual battery charge current, I
be lower than the programmed current, I
input power available and prioritization to the system load
drawn from V
Charge Status Indication
The ⎯ C ⎯ H ⎯ R ⎯ G pin indicates the status of the battery charger.
Four possible states are represented by ⎯ C ⎯ H ⎯ R ⎯ G which include
charging, not charging (or fl oat charge current less than
programmed end of charge indication current), unrespon-
sive battery and battery temperature out of range.
The signal at the ⎯ C ⎯ H ⎯ R ⎯ G pin can be easily recognized
as one of the above four states by either a human or a
RECHRG
RECHRG
I
R
BAT
PROG
=
from resetting the safety timer, the battery voltage
(typically 4.1V). In the event that the safety timer
R
V
=
PROG
PROG
1031
I
CHG
OUT
RECHRG
• 1031
.
V
,
I
CHG
for more than 1.5ms. The charge
=
R
1031
PROG
BUS
V
is removed and then
CHG
LTC4088
, due to limited
BUS
RECHRG
13
BAT
UVLO
, will
4088f
, it