EUP8086
impedance state even if C/10 has not yet been reached.
To restart the charge cycle, remove the input-voltage and
reapply it or momentarily force the EN_BAT pin below
VIL. A new charge cycle will automatically restart if the
BAT pin voltage falls below VBAT_EOC (typically 4.05V).
OPERATION
The EUP8086 is a full-featured linear battery charger
with an integrated synchronous buck converter designed
primarily for handheld applications. The battery charger
is capable of charging single-cell 4.2V Li-Ion batteries.
The buck converter is powered from the VIN pin and has
a programmable output voltage providing a maximum
load current of 600mA. The converter and the battery
charger can run simultaneously or independently of each
other.
Constant-Current / Constant-Voltage /
Constant- Temperature
The EUP8086 battery charger uses a unique architecture
to charge a battery in a constant-current, constant-voltage
and constant-temperature fashion. Figure 2 shows a
Simplified Block Diagram of the EUP8086. Three of the
amplifier feedback loops shown control the constant-
current, CA, constant-voltage, VA, and constant-
temperature, TA modes. A fourth amplifier feedback loop,
MA, is used to increase the output impedance of the
current source pair, MP1 and MP3 (note that MP1 is the
internal P-channel power MOSFET). It ensures that the
drain current of MP1 is exactly 400 times the drain
current of MP3.
Amplifiers CA and VA are used in separate feedback
loops to force the charger into constant-current or
constant voltage mode, respectively. Diodes D1 and D2
provide priority to either the constant-current or
constant-voltage loop, whichever is trying to reduce the
charge current the most. The output of the other amplifier
saturates low which effectively removes its loop from the
system. When in constant-current mode, CA servos the
voltage at the ISET pin to be precisely 1V. VA servos its
non-inverting input to 1.22V when in constant-voltage
mode and the internal resistor divider made up of R1 and
R2 ensures that the battery voltage is maintained at 4.2V.
The ISET pin voltage gives an indication of the charge
current anytime in the charge cycle, as discussed in
“Programming Charge Current” in the Applications
Information section.
If the die temperature starts to creep up above 115°C due
to internal power dissipation, the transconductance
amplifier, TA, limits the die temperature to
approximately 115°C by reducing the charge current.
Diode D3 ensures that TA does not affect the charge
current when the die temperature is below 115°C. In
thermal regulation, the ISET pin voltage continues to
give an indication of the charge current.
In typical operation, the charge cycle begins in constant-
current mode with the current delivered to the battery
equal to 400V/RISET. If the power dissipation of the
EUP8086 results in the junction temperature approaching
115°C, the amplifier (TA) will begin decreasing the
charge current to limit the die temperature to
approximately 115°C. As the battery voltage rises, the
EUP8086 either returns to constant-current mode or
enters constant-voltage mode straight from constant-
temperature mode.
BATTERY CHARGER OPERATION
Featuring an internal P-channel power MOSFET, MP1,
the battery charger uses a constant-current/constant-
voltage charge algorithm with programmable current.
Charge current can be programmed up to 500mA with a
final float voltage of 4.2V ± 1%. The STAT open-drain
status output indicates when C/10 has been reached. No
blocking diode or external sense resistor is required; thus,
the basic charger circuit requires only two external
components. An internal termination timer adheres to
battery manufacturer safety guidelines. Furthermore, the
EUP8086 battery charger is capable of operating form a
USB power source.
A charge cycle begins when the voltage at the ADP pin
rises above 3.6V and approximately 110mV above the
BAT pin voltage, a 1% program resistor is connected
form the ISET pin to ground, and the EN_BAT pin is
pulled above the enable threshold (VIH). If the battery
voltage is less than 2.95V, the battery charger begins
trickle charging at 10% of the programmed charge
current.
When the BAT pin approaches the final float voltage of
4.2V, the battery charger enters constant-voltage mode
and the charge current begins to decrease. When the
current drops to 10% of the full-scale charge current, an
internal comparator turns off the N-channel MOSFET
driving the STAT pin, and the pin becomes high
impedance.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 115℃. This feature
protects the EUP8086 from excessive temperature and
allows the user to push the limits of the power handling
capability of a given circuit board without the risk of
damaging the EUP8086 or external components. Another
benefit of the thermal limit is that charge current can be
set according to typical, rather than worst-case, ambient
temperatures for a given application with the assurance
that the battery charger will automatically reduce the
current in worst-case conditions.
An internal timer sets the total charge time, tTIMER
(typically 4.5 hours). When this time elapses, the charge
cycle terminates and the STAT pin assumes a high
DS8086 Ver 1.0 Apr. 2008
13
EUTECH [ EUTECH MICROELECTRONICS INC ]
