Datasheet

MAX8814
28V Linear Li+ Battery Charger with
Smart Autoboot Assistant
6 _______________________________________________________________________________________
Detailed Description
The MAX8814 charger uses voltage, current, and ther-
mal-control loops to charge a single Li+ cell and pro-
tect the battery (Figure 1). When a Li+ battery with a
cell voltage below 2.5V is inserted, the MAX8814
charger enters the prequalification stage where it
precharges that cell with 10% of the user-programmed
fast-charge current (Figure 2). When the battery voltage
exceeds 2.5V, the charger soft-starts as it enters the
fast-charge stage. In the MAX8814, the fast-charge
current level is programmed through a resistor from
ISET to GND. As the battery voltage approaches 4.2V,
the charging current is reduced. Once the battery volt-
age reaches 4.2V, the IC then enters a constant voltage
regulation mode to maintain the battery at full charge.
Thermal Regulation
The thermal-regulation loop limits the MAX8814 die
temperature to +115°C by reducing the charge current
as necessary. This feature not only protects the IC from
overheating, but also allows a higher charge current
without risking damage to the IC.
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OUTPUT DRIVER,
CURRENT SENSE,
AND LOGIC
TEMPERATURE
SENSOR
VL
REGULATOR
REF
REFOK
V
IN
OVLO
VL
UVLO
V
REF
V
REF
LOGIC
BATT
ISET
ABI
ABO
EN
POK
IN
BATT
IN
BATT
POK
200kΩ
GND
EP
+115°C
Li+
C3
2.2μF
V
I/O
200kΩ
C1
1μF
R2
2.8kΩ
4.25V TO 28V
R3
1MΩ
MAX8814
V
L
V
REF
Figure 1. Functional Diagram