Datasheet

26 Maxim Integrated
1.2A Switch-Mode Li+ Chargers with ±22V Input
Rating and JEITA Battery Temperature Monitoring
MAX8900A/MAX8900B/MAX8900C
Figure 11. Thermistor Monitor Detail
Thermal Foldback
Thermal foldback maximizes the battery charge current
while regulating the MAX8900_ junction temperature. As
shown in Figure 12, when the die temperature exceeds
T
REG
, a thermal limiting circuit reduces the battery
charge-current target by A
TREG
, until the charge cur-
rent reaches 25% of the fast-charge current setting. The
charger maintains 25% of the fast-charge current until
the die temperature reaches T
SHDN
. Please note that
the MAX8900_ is rated for a maximum ambient tempera-
ture of +85NC. Furthermore, although the maximum die
temperature of the MAX8900_ is +150NC, it is common
industry practice to design systems in such a way that
the die temperature never exceeds +125NC. Limiting the
maximum die temperature to +125NC extends long-term
reliability.
Thermal Shutdown
As shown in Figure 12, when the MAX8900_ die tempera-
ture exceeds T
SHDN
, the IC goes into thermal shutdown.
During shutdown, the step-down charger is off and all
internal blocks except the bias circuitry is turned off. Once
the junction has cooled by 15NC, the IC resumes operation.
Figure 12. Charge Current vs. Junction Temperature
T
COLD: T1
AVL IS THE
INTERNAL
ANALOG SUPPLY
TO DC-DC
CHARGE
CONTROLLER
AVL: E5
A. BASIC THERMISTOR CONFIGURATION B. ADVANCED THERMISTOR CONFIGURATION
AVL
BAT_T
THM: E4
R
THRM
R
TB
THERMOMETER
DECODE LOGIC
COOL: T2
WARM: T3
HOT: T4
MAX8900_
T
COLD: T1
AVL IS THE
INTERNAL
ANALOG SUPPLY
TO DC-DC
CHARGE
CONTROLLER
AVL: E5
AVL
BAT_T
THM: E4
R
THRM
R
TP
R
TS
R
TB
THERMOMETER
DECODE LOGIC
COOL: T2
WARM: T3
HOT: T4
MAX8900_
CHARGE CURRENT
vs. JUNCTION TEMPERATURE
T
J
(°C)
I
CHG
(A)
15012575 10050 175
I
FC
= 1.19A
I
FC
= 0.756A
T2 < V
THM
< T3
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0