MAX8856
Detailed Description
The MAX8856 charger uses current, voltage, and ther-
mal control loops to charge and protect a single Li+
battery cell. It can start the system even when the bat-
tery is in deep saturation. The MAX8856 provides a
SYS output that supplies the external system with a
minimum 3.5V at 1A.
Two active-low enable inputs (EN1 and EN2) are sup-
plied to set the SYS and charging current limits. During
prequal and fast-charge modes, the CHG output status
flag is pulled low. As the battery voltage approaches
4.2V, the charging current is reduced. When the charging
current drops below 50mA and the battery voltage equals
4.2V, the CHG output goes high impedance, signaling a
full battery. At any time during charging, if both EN1 and
EN2 are driven high, the MAX8856 enters suspend mode,
charging stops, and CHG goes high impedance.
EN1
and
EN2
Inputs
EN1 and EN2 are logic inputs that enable the charger
and select the charging current (see Table 1). Drive
EN1 and EN2 high to place the IC in suspend mode.
USB/AC Adapter, Li+ Linear Battery Charger
with Integrated 50m
Ω
Battery Switch in TDFN
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1, 2 BAT
Batter y C onnecti on. The IC d el i ver s char g i ng cur r ent and m oni tor s b atter y vol tag e usi ng BAT. C onnect
b oth BAT outp uts tog ether exter nal l y. D ur i ng susp end m od e, BAT i s i nter nal l y connected to S Y S .
3IN
Supply Voltage Input. Connect IN to a 4.25V to 5.5V supply. Charging is suspended if V
IN
exceeds 6V.
Bypass IN to GND with a 4.7µF or larger ceramic capacitor.
4V
L
+3.3V Output Voltage and Logic Supply. V
L
is regulated to +3.3V and is capable of sourcing 500µA to
provide power for external circuits. Bypass V
L
to GND with a 0.1µF or larger ceramic capacitor.
V
L
is internally pulled to GND during suspend mode.
5 THM
Thermistor Input. Connect a 47kΩ NTC thermistor from THM to GND in close proximity to the battery to
monitor the battery temperature. The IC suspends charging when the temperature is outside the hot
and cold limits. Connect THM to GND to disable the thermistor monitoring function. See the THM Input
section for more details.
6 CHG
Charging Status Output. CHG is an open-drain output that goes low when the battery is charging. CHG
goes high impedance when the charge current drops below 50mA (typ) and the battery voltage is 4.2V
(typ). CHG is high impedance when the IC is in suspend mode.
7 POK P ower - OK M oni tor . P O K i s an op en- d r ai n outp ut that pul l s l ow w hen a val id char g ing sour ce i s d etected at IN .
8 GATE
MOSFET Enable/Disable Input. Drive GATE high to turn off the MOSFET between SYS and BAT,
resulting in opening of the connection between SYS and BAT. Drive GATE low to enable automatic
control of the MOSFET switch, as described in the Gate Input and SYS Output section.
9 EN2
Charge-Current Selection Input. Drive EN_ high or low to select the charge current or to put the
MAX8856 into suspend mode (see Table 1).
10 EN1
Charge-Current Selection Input. Drive EN_ high or low to select the charge current or to put the
MAX8856 into suspend mode (see Table 1).
11 GND Ground. Connect directly to exposed paddle under the IC.
12 SETI
Charge-Current Programming Input. Connect a resistor from SETI to GND to set the maximum charging
current. R
SETI
must be between 17.68kΩ and 35.36kΩ.
13, 14 SYS
System Supply Output. SYS delivers up to 1A
RMS
to power an external system. Bypass SYS to GND
with a 4.7µF or larger ceramic capacitor. SYS is connected to BAT through an internal 50mΩ switch
when V
BAT
exceeds 3.5V or when the MAX8856 is in suspend mode.
—EP
Exposed Paddle. Connect to GND under the IC. Connect to a large ground plane to improve power
dissipation.
