EUP8092X
OPERATION
The EUP8092 is an integrated charger for single-cell
Li-ion or Li-polymer batteries. As a linear charger, the
EUP8092 charges a battery in the popular constant
current (CC) and constant voltage (CV) profile. The
constant charge current IREF is programmable up to 1.5A
with an external resistor or a logic input. The charge
voltage VCH has 1% accuracy over the entire
recommended
operating
condition
range.
A
thermal-regulation feature removes the thermal concern
typically seen in linear chargers. The charger reduces the
charge current automatically as the IC internal
temperature rises above +110°C to prevent further
temperature rise. The thermal-regulation feature
guarantees safe operation when the printed circuit board
(PCB) is space limited for thermal dissipation.
Figure 20 shows the typical charge curves in a traditional
linear charger powered with a constant-voltage adapter.
From the top to bottom, the curves represent the constant
input voltage, the battery voltage, the charge current and
the power dissipation in the charger. The power
dissipation PCH is given by the following equations:
Figure 20. Typical Charge Curves Using a
Constant-Voltage Adapter
P
=
V
- V
BAT
× I
(1)
CH
IN
CHARGE
where ICHARGE is the charge current. The maximum
power dissipation occurs during the beginning of the CC
mode. The maximum power the IC is capable of
dissipating is dependent on the thermal impedance of the
printed-circuit board (PCB). Figure 20 shows, with
dotted lines, two cases that the charge currents are
limited by the maximum power dissipation capability due
to the thermal regulation.
When using a current-limited adapter, the thermal
situation in the EUP8092 is totally different. Figure 20
shows the typical charge curves when a current-limited
adapter is employed.
The operation requires the IREF to be programmed higher
than the limited current ILIM of the adapter, as shown in
Figure 21. The key difference of the charger operating
under such conditions occurs during the CC mode. The
adapter current is limited, the actual output current will
never meet what is required by the current reference.
Therefore, the main MOSFET becomes a power switch
instead of a linear regulation device. The power
dissipation in the CC mode becomes:
Figure 21. Typical Charge Curves Using a
Current Limited Adapter
Battery Pre-Conditioning
During a charge cycle if the battery voltage is below the
V(MIN) threshold, the EUP8092X applies a precharge
current, ITRICKLE, to the battery. This feature revives
deeply discharged cells. The resistor connected between
the IREF and GND, RIREF, determines the precharge rate.
4
0.8V×10
I
=
(3)
REF
R
IREF
The EUP8092X activates a safety timer, ITRICKLE, during
the conditioning phase. If VMIN threshold is not reached
within the timer period, the EUP8092X turns off the
2
(2)
P
= R
× I
DS(ON) CHARGE
CH
charger and enunciates FAULT on the FAULT pins.
where RDS(ON) is the resistance when the main MOSFET
is fully turned on. This power is typically much less than
the peak power in the traditional linear mode.
DS8092X Ver 0.1 May 2008
11
EUTECH [ EUTECH MICROELECTRONICS INC ]
