Rainbow Electronics MAX1508 - Manual (Page 7)

MAX1508
Li+ Linear Battery Charger with Integrated Pass FET,
Thermal Regulation, and
ACOK
in 3mm x 3mm TDFN
_______________________________________________________________________________________ 7
Applications Information
Charge-Current Selection
The maximum charging current is programmed by an
external R
ISET
resistor connected from ISET to GND.
Select the R ISET value based on the following formula:
I FAST = 1461V / R ISET
Ω
where I FAST is in amps and R ISET is in ohms. ISET can
also be used to monitor the fast-charge current level.
The output current from the ISET pin is 0.958mA per
amp of charging current. The output voltage at ISET is
proportional to the charging current as follows:
V ISET = (I CHG x R ISET ) / 1044
The voltage at ISET is nominally 1.4V at the selected
fast-charge current, and falls with charging current as
the cell becomes fully charged.
Thermal Regulation
The MAX1508 features a proprietary thermal-regulation
circuit to protect both the IC and the system from
excessive heat. When the MAX1508’s die temperature
reaches +100°C, the charge current is reduced to pre-
vent any additional increase in the die temperature. An
active thermal loop does not indicate a fault condition.
Thermal regulation allows the MAX1508 to provide con-
tinuous charge to the battery under adverse conditions
without causing excessive power dissipation.
SHUTDOWN
CHARGER = OFF
LED = OFF
PRECHARGE
100% CHARGE CURRENT
LED = ON
FAST CHARGE
100% CHARGER CURRENT
LED = ON
FULL BATT CONTINUES
TO REGULATE BATT
UP TO 4.2V
I
CHARGE
< 10%
OF ISET
V BATT > 2.5V
V BATT < 2.4V
V BATT < 2.5V
V IN
< 7V AND
V IN
> V
BA
TT
AND
EN = LOW
V IN > 7V +
V BATT > V IN +
EN = HIGH
ASYNCHRONOUS FROM
ANYWHERE
V
IN
> 7V +
V
BATT
> VIN +
EN = HIGH
I CHARGE > 20%
OF ISET
FULL BATT
LED = OFF
Figure 2. Charge State Diagram