Datasheet

MAX8808X/MAX8808Y/MAX8808Z
VL Internal Voltage Regulator
The MAX8808X/MAX8808Y/MAX8808Z linear chargers
contain an internal linear regulator to supply the power
for the IC. Bypass VL to GND with a 0.47µF ceramic
capacitor. VL is regulated to 3.0V whenever the input
voltage is above the battery voltage.
CHG Charge-Indicator Output
CHG is an open-drain output that indicates charge sta-
tus. Table 1 describes the state of CHG during different
stages of operation. CHG is suitable for driving a
charge-indication LED. If the MAX8808X/MAX8808Y/
MAX8808Z is used in conjunction with a µP, a pullup
resistor to the logic I/O voltage allows CHG to indicate
charge status to the µP instead of driving an LED.
Soft-Start
The soft-start algorithm activates when entering fast-
charge mode. In the MAX8808X, when the prequalifica-
tion state is complete (V
BATT
exceeds +2.5V), the
charging current ramps up in 1ms to the full charging
current. This reduces the inrush current on the input
supply. Note that the MAX8808Y and MAX8808Z do not
have a prequalification state and enter soft-start directly
after being enabled.
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:
R
ISET
= 1302V / I
FASTCHG
where I
FASTCHG
is in Amps and R
ISET
is in Ohms. ISET
can be used to monitor the fast-charge current level.
The output current from ISET is 1.08mA per amp of
charging current. The output voltage at ISET is propor-
tional to the charging current:
V
ISET
= (I
CHARGE
x R
ISET
) / 930
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 1µF 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.
Connect a 0.47µF ceramic capacitor from VL to GND.
Thermal Considerations
The MAX8808X/MAX8808Y/MAX8808Z are available in
a thermally enhanced TDFN package with exposed
paddle. Connect the exposed paddle to a large cop-
per ground plane to provide a thermal contact
between the device and the circuit board for increased
power dissipation. The exposed paddle transfers heat
away from the device, allowing the ICs to charge the
battery with maximum current, while minimizing the
increase in die temperature.
1A Linear Li+ Battery Chargers with Integrated Pass
FET and Thermal Regulation in 2mm x 2mm TDFN
8 _______________________________________________________________________________________
Table 1. CHG States
EN
MAX8808X
EN
MAX8808Y
EN
MAX8808Z
V
IN
V
BATT
I
BATT
CHG STATE
XXX≤V
BATT
≥V
IN
0
High-Impedance
Shutdown
Low — —
4.25V ≤ V
IN
≤ 7V
<2.4V
10% of I
FAST
Low Prequal
Low High Low
4.25V ≤ V
IN
≤ 7V
≥2.5V I
FAST
* Low
Fast-Charge
Low High Low
4.25V ≤ V
IN
≤ 7V
4.2V
<10% of I
FAST
High-Impedance
Top-off
Low High Low >7V X 0
High-Impedance
Shutdown
High Low High X X 0
High-Impedance
Disabled
X = Don’t care.
— = Prequal not applicable to MAX8808Y and MAX8808Z.
*I
FAST
is reduced as necessary to prevent the die temperature from exceeding +115°C.