Datasheet

MAX8814
Applications Information
Charge-Current Selection
The maximum charging current is programmed by an
external resistor connected from ISET to GND (R
ISET
).
Calculate R
ISET
as follows:
where I
FAST-CHARGE
is in amperes and R
ISET
is in
ohms. ISET can be used to monitor the fast-charge cur-
rent level. The output current from ISET is 877.2µA per
ampere of charging current. The output voltage at ISET
is proportional to the charging current:
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 or as the thermal-regu-
lation circuitry activates.
Capacitor Selection
Connect a ceramic capacitor from BATT to GND for
proper stability. Use a 2.2µF X5R ceramic capacitor for
most applications. Connect a 1µF ceramic capacitor
from IN to GND. Use a larger input bypass capacitor
for high charging currents to reduce supply noise.
Thermal Considerations
The MAX8814 is available in a thermally enhanced
TDFN package with an exposed paddle. Connect the
exposed paddle to a large copper ground plane to pro-
vide a thermal contact between the device and the cir-
cuit board for increased power dissipation. The exposed
paddle transfers heat away from the device, allowing the
IC to charge the battery with maximum current, while
minimizing the increase in die temperature.
DC Input Sources
The MAX8814 operates from a well-regulated DC
source. The full charging input voltage range is 4.25V
to 7V. The device can withstand up to 28V on the input
without damage to the IC. If V
IN
is greater than 7V, the
internal overvoltage-protection circuitry disables charg-
ing until the input falls below 7V. An appropriate power
supply must provide at least 4.25V at the desired peak
charging current.
V
IR
ISET
CHARGE ISET
=
×
1140
R
V
I
ISET
FAST CHARGE
=
−
1596
28V Linear Li+ Battery Charger with
Smart Autoboot Assistant
8 _______________________________________________________________________________________
IN
ABI
ISET
ABO
BATT
GND
EP
VI/O
EN
GPIO
GPIO
ADC
POWER
SUPPLY
ON
SYSTEM
POK
GND
FACTORY TEST
FIXTURE
OR
AC ADAPTER
C3
2.2μF
Li+
R3
1MΩ
R4
10kΩ
C4
0.1μF
R2
2.8kΩ
C1
1μF
R1
10kΩ
C2
0.1μF
MAX8814
Figure 3. Microprocessor-Interfaced Li+ Battery Charger