Datasheet
22 Maxim Integrated
1.2A Switch-Mode Li+ Chargers with ±22V Input
Rating and JEITA Battery Temperature Monitoring
MAX8900A/MAX8900B/MAX8900C
Charger Disabled State
When CEN is high or the input voltage is out of range, the
MAX8900_ disables the charger. To exit this state, CEN must
be low and 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 MAX8900_ disables the
switching charger and linearly charges with I
DBAT
. If the
MAX8900_ remains in this dead-battery state for longer
than t
PQ
, then it transitions to the timer fault state. This
dead-battery state prevents the MAX8900_ from dissi-
pating excessive power in the event of a shorted battery.
Once V
BAT
increases beyond V
PQLTH,
the MAX8900_
transitions to the dead battery + prequalification state.
Dead Battery + Prequalification State
The dead battery + prequalification state occur 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 and delivering current
to the battery. The total battery current is I
DBAT
+ I
PQ
. If
the MAX8900_ remains in this state for longer than t
PQ
,
then it transitions to the timer fault state. A normal bat-
tery typically stays in the dead-battery + prequalification
state for several minutes or less and when the battery
voltage rises above V
DBAT
, the MAX8900_ transitions to
the prequalification state.
Prequalification State
The prequalification state occurs when the battery volt-
age is greater than V
DBAT
and less than V
PQUTH
.
In this state, the linear dead-battery charger is turned
off and only the switching charger is on and delivering
current to the battery. The total battery current is I
PQ
. If
the MAX8900_ remains in this state for longer than t
PQ
,
then the MAX8900_ transitions to the timer fault state. A
normal battery typically stays in the prequalification state
for several minutes or less and when the battery voltage
rises above V
PQUTH
, the MAX8900_ transitions to the
fast-charge constant current state.
As shown in Figure 10, the prequalification current and
done threshold is set to 50% of programmed value when
T1 < THM < T2, and 100% of programmed value when
T2 < THM < T4.
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 MAX8900_ remains in this state and the fast-
charge constant voltage state for longer than t
FC
, then
the MAX8900_ transitions to the timer fault state. When
the battery voltage rises to V
BATREG
, the MAX8900_
transitions to the fast-charge constant voltage state. As
shown in Figure 10, the fast-charge constant current is
set to 50% of programmed value when T1 < THM < T2,
and 100% of programmed value when T2 < THM < T4.
The MAX8900_ dissipates the most power in the fast-
charge constant current state. This power dissipation
causes the internal die temperature to rise. If the die tem-
perature exceeds T
REG
, I
FC
is reduced. See the Thermal
Foldback section for more detail.
If there is low input voltage headroom (V
IN
- V
BAT
), then
I
FC
decreases due to the impedance from IN to BAT. See
Figure 13 for more detail.
Fast-Charge Constant Voltage State
The fast-charge constant voltage state occurs when the
battery voltage is at the V
BATREG
and the charge current
is greater than I
DN
. In this state, the switching charger is
on and delivering current to the battery. The MAX8900_
maintains V
BATREG
and monitors the charge current to
detect when the battery consumes less than the I
DN
cur-
rent. When the charge current decreases below the I
DN
threshold, the MAX8900_ transitions to the top-off state.
If the MAX8900_ remains in the fast-charge constant
current state and this state for longer than t
FC
, then the
MAX8900_ transitions to the timer fault state. Please note
when the battery temperature is between T3 and T4 the
BAT regulation voltage is reduced to 4.075V.
The MAX8900_ offers an adjustable done current thresh-
old (I
DN
) from 10mA to 200mA. The accuracy of the
top-off current threshold is Q1mA when it is set for 10mA.
This accurate threshold allows the maximum amount of
charge to be stored in the battery before the MAX8900_
transitions into done state.
Top-Off State
The top-off state occurs when the battery voltage is
at V
BATREG
and the battery current decreases below
I
DN
. In this state, the switching charger is on and deliv-
ers current to the battery. The MAX8900_ maintains
V
BATREG
for a specified time (t
TO
). When t
TO
expires,
the MAX8900_ transitions to the done state. If the charg-
ing current increases to I
DN
+ 1mA before t
TO
expires,
then the charger re-enters the fast-charge constant volt-
age state.