MAX8971
Industry's Smallest 1.55A
1-Cell Li+ DC-DC Charger
Charger-Disabled State
When DC is low or the input voltage is out of range, the IC
disables the charger. To exit this state, the input voltage
must be within its valid range.
Dead-Battery State
When a deeply discharged battery is inserted with a
voltage of less than V PQLTH , the IC disables the switch-
ing charger and linearly charges with I DBAT . Once V BAT
increases beyond V PQLTH , the IC clears the prequalifica-
tion timer, and transitions to the dead battery + prequali-
fication state. This state prevents the IC from dissipating
excessive power in the event of a shorted battery. The
dead-battery linear charge remains on, except when
in the charger disabled state, timer fault state, thermal
shutdown and V BAT > V DBAT .
Dead-Battery + Prequalification State
The dead battery + prequalification state occurs when
the battery voltage is greater than V PQLTH, and less
than V DBAT . In this state, both the linear dead-battery
charger and the switching charger are on, delivering
current to the battery. The total battery current is I DBAT
+ I PQ . If the IC remains in this state for longer than
t PQ , the IC transitions to the timer fault state. A normal
battery typically stays in this state for several minutes
or less. When the battery voltage rises above V DBAT
the IC transitions to the prequalification states. The
dead-battery linear charger remains on except when
in the charger disabled state, timer fault state, thermal
shutdown and V BAT > V DBAT .
Prequalification State
The prequalification state occurs when the battery
voltage is greater than V DBAT and less than V PQUTH .
In this state, the linear dead-battery charger is turned
off. Only the switching charger is on and delivering
current to the battery. The total battery current is I PQ . If
the IC remains in this state for longer than t PQ , then the
IC transitions to the timer fault state. A normal battery
typically stays in the prequalification state for several
minutes or less. When the battery voltage rises above
V PQUTH , the IC transitions to the fast-charge constant-
current state.
Fast-Charge Constant-Current State
The fast-charge constant-current state occurs when
the battery voltage is greater than V PQUTH and less
than V BATREG . In this state, the switching charger is on
and delivering current to the battery. The total battery
current is I FC . If the IC remains in this state and
Maxim Integrated
the fast-charge constant voltage state for longer than
t FC , then the IC transitions to the timer fault state.
When the battery voltage rises to V BATREG , the IC
transitions to the fast-charge constant voltage state.
The fast-charge constant-current is set to 50% of
programmed value when 0 N C < THM <+15 N C, and 100%
of programmed value when +15 N C < THM <+60 N C.
The MAX8971 dissipates the most power in the fast-
charge constant-current state. This power dissipation
causes the internal die temperature to rise. If the die
temperature exceeds T REG , I FC is reduced.
If there is low input-voltage headroom (V IN - V BAT ), then
I FC decreases due to the impedance from IN to BAT.
Fast-Charge Constant Voltage State
The fast-charge constant voltage state occurs when the
battery voltage is at the V BATREG , and the charge cur-
rent is greater than I TOPOFF . In this state, the switching
charge is on and delivering current to the battery. The IC
maintains V BATREG and monitors the charge current to
detect when the battery consumes less than the TOPOFF
current. When the charge current decreases below the
TOPOFF threshold, the IC transitions to the top-off state.
If the IC remains in the fast-charge constant-current state
for longer than t FC , then it transitions to the timer fault
state.
Top-Off State
The top-off state occurs when the battery voltage is
at V BATREG and the battery current decreases below
TOPOFF current. In this state, the switching char-
ger is on and delivers current to the battery. The IC
maintains V BATREG for a specified time. When this
time expires, the IC transitions to the DONE state.
If the charging current increases to I TOPOFF + 200mA
before this time expires, then the charge reenters the
fast-charge constant voltage state.
Done State
The IC enters its done state after the charge has been in
the top-off state for t TOPOFF . In this state, the switching
charger is off and no current is delivered to the battery. If
the system load presented to the battery is low << 10 F A,
then a typical system can remain in the done state for
many days. If left in the done state long enough, the bat-
tery voltage decays below the restart threshold and the
IC transitions back into the fast-charge state. There is no
soft-start (di/dt limiting) during the done-to-fast-charge
state transition.
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