Rainbow Electronics MAX1507 - Manual (Page 6)

MAX1507
Linear Li+ Battery Charger with Integrated Pass FET
and Thermal Regulation in 3mm x 3mm Thin DFN
6 _______________________________________________________________________________________
MAX1507
OUTPUT DRIVER,
CURRENT SENSE,
AND LOGIC
V LUVLO
V
INOVLO
IN
ON
INOK
REFOK
V LOK
REFOK
REF
VL
N
LOGIC
TEMPERATURE
SENSOR
V REF
IREF
IN
ISET
VL
0.47 µF
BATT
TEMP
EN
200k Ω
GND
IN
+90 °C
+100 °C
+130 °C
BATT
CHG
IN
Detailed Description
The MAX1507 charger uses voltage, current, and ther-
mal-control loops to charge a single Li+ cell and to pro-
tect the battery (Figure 1). When a Li+ battery with a
cell voltage below 2.5V is inserted, the MAX1507
charger enters the prequalification stage where it
precharges that cell with 10% of the user-programmed
fast-charge current. The CHG indicator output is driven
low (Figure 2) to indicate entry into the prequalification
state. Once the cell has passed 2.5V, the charger soft-
starts before it enters the fast-charge stage. The fast-
charge current level is programmed through a resistor
from ISET to ground. As the battery voltage approach-
es 4.2V, the charging current is reduced. If the battery
current drops to less than 10% of the fast-charging cur-
rent, the CHG indicator goes high impedance, signal-
ing the battery is fully charged. At this point the
MAX1507 enters a constant voltage-regulation mode to
Figure 1. Functional Diagram