LTC3559 Linear Technology, LTC3559 Datasheet - Page 12

• Manufacturer Part Number: LTC3559
• Description: Linear USB Battery Charger
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
Suspend Mode
The battery charger can also be disabled by pulling the
SUSP pin above 1.2V. In suspend mode, the battery
drain current is reduced to 1.5μA and the input current is
reduced to 8.5μA.
Charge Cycle Overview
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 full-scale value.
Once the battery voltage is above 2.9V, the battery char-
ger begins charging in constant current mode. When the
battery voltage approaches the 4.2V required to maintain
a full charge, otherwise known as the fl oat voltage, the
charge current begins to decrease as the battery charger
switches into constant voltage mode.
Trickle Charge and Defective Battery Detection
Any time the battery voltage is below V
goes into trickle charge mode and reduces the charge
current to 10% of the full-scale current. If the battery
voltage remains below V
charger latches the bad-battery state, automatically termi-
nates, and indicates via the ⎯ C ⎯ H ⎯ R ⎯ G pin that the battery was
unresponsive. If for any reason the battery voltage rises
above V
charger has latched the bad-battery state, if the battery
voltage then falls below V
V
the battery is defective. To reset the charger (i.e., when
the dead battery is replaced with a new battery), simply
remove the input voltage and reapply it or put the part in
and out of suspend mode.
Charge Termination
The battery charger has a built-in safety timer that sets
the total charge time for 4 hours. Once the battery volt-
age rises above V
enters constant voltage mode, the 4-hour timer is started.
LTC3559
12
RECHRG
TRKL
fi rst, the charger will immediately assume that
, the charger will resume charging. Since the
RECHRG
TRKL
TRKL
TRKL
(typically 4.1V) and the charger
, typically 2.9V, an automatic
again but without rising past
for more than 1/2 hour, the
TRKL
, the charger
After the safety timer expires, charging of the battery will
discontinue and no more current will be delivered.
Automatic Recharge
After 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
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
DUVLO cycles low and then high (e.g., V
and then replaced) or the charger enters and then exits
suspend mode.
Programming Charge Current
The PROG pin serves both as a charge current program
pin, and as a charge current monitor pin. By design, the
PROG pin current is 1/800th of the battery charge current.
Therefore, connecting a resistor from PROG to ground
programs the charge current while measuring the PROG pin
voltage allows the user to calculate the charge current.
Full-scale charge current is defi ned as 100% of the constant
current mode charge current programmed by the PROG
resistor. In constant current mode, the PROG pin servos to
1V if HPWR is high, which corresponds to charging at the
full-scale charge current, or 200mV if HPWR is low, which
corresponds to charging at 20% of the full-scale charge
current. Thus, the full-scale charge current and desired
program resistor for a given full-scale charge current are
calculated using the following equations:
RECHRG
RECHRG
I
R
CHG
PROG
=
from resetting the safety timer, the battery voltage
(typically 4.1V). In the event that the safety timer
R
=
800
PROG
800
I
CHG
V
RECHRG
V
for more than 1.7ms. The charge
CC
CC
is removed
RECHRG
UVLO or
3559f
, it