ISL6298-2CR3 Datasheet, PDF (12/17 Pages) Intersil Corporation – Li-ion/Li-Polymer Battery Charger

ISL6298
pulled up to the V2P8 pin voltage, higher than the Battery
Removal Threshold V_RMV, and the charger is disabled.
Comparators CP2 and CP3 form a window comparator and
the two transistors, Q1 and Q2, create hysteresis for the two
window thresholds respectively. When the TEMP pin voltage
is “out of the window,” determined by the V_TMIN and V_TMAX,
the ISL6298 stops charging and indicates a fault condition.
When the temperature returns to within the window, the
charger re-starts a charge cycle. See the Application
Information for more details on the NTC thermistor selection.
Thermal Foldback
Over-heating is always a concern in a linear charger. The
maximum power dissipation usually occurs at the beginning
ISL6298
2.8V
V2P8
Battery
Removal
CP1 _-
+
Under
Temp
CP2 _-
+
R1
V_RMV
40K
R2
60K
R_U
V_TMIN
R3
To TEMP Pin
75K
TEMP
Q1
Over
Temp
CP3 _-
+
V_TMAX
R4
R_T
25K
Q2
R5
4K
GND
FIGURE 21. THE INTERNAL AND EXTERNAL CIRCUIT FOR
THE NTC INTERFACE
of a charge cycle when the battery voltage is at its minimum
but the charge current is at its maximum. The charge current
thermal foldback function in the ISL6298 frees users from
the over-heating concern.
Figure 22 shows the typical charge curves in a charge cycle,
using a constant voltage input. Once the internal
temperature reaches 100°C, the ISL6298 starts to reduce
the charge current to prevent further temperature rise. The
power dissipation is directly related to the thermal
impedance, which is related to the layout of the printed-
circuit board, and the ambient temperature. The dotted lines
show the power limit and the current waveforms in two cases
that the thermal foldback occurs. The current is reduced and
gradually increases to the constant charge current as the
battery voltage rises.
Usually the charge current should not drop below the EOC
current because of the thermal foldback. For some extreme
cases if that does happen, the charger does not indicate
end-of-charge unless the battery voltage is already above
the recharge threshold.
Indications
The ISL6298 has three indications: the input presence, the
charge status, and the fault indication. The input presence is
indicated by the V2P8 pin while the other two indications are
presented by the STATUS pin and FAULT pin respectively.
Figure 23 shows the V2P8 pin voltage vs. the input voltage.
The V2P8 pin outputs a 2.8V voltage (blue waveform) when
the input voltage (yellow waveform) rises above 3.4V rising
POR threshold and falls to zero volt when the input voltage
falls below the 2.4V falling POR threshold. The V2P8 pin can
be used as a logic signal for the input presence.
Trickle
Mode
Constant Current Constant Voltage
Mode
Mode
Inhibit
V_IN
V_CH
Input Voltage
Battery Voltage
V_MIN
I_REF
I_REF/5
P₁
P₂
P₃
Charge Current
Power Dissipation
TIMEOUT
FIGURE 22. TYPICAL CHARGE CURVES USING A
CONSTANT-VOLTAGE INPUT
12
3.4V
2.8V
V_IN
V2P8
2.4V
FIGURE 23. THE V2P8 PIN OUTPUT vs THE INPUT VOLTAGE
AT THE VIN PIN. VERTICAL: 1V/DIV,
HORIZONTAL: 100ms/DIV
FN9173.3
July 20, 2005