ISL6292D Datasheet, PDF (10/13 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292D
End-of-Charge (EOC) Current
The end-of-charge current I_MIN sets the level at which the
charger indicates the end of the charge with the STAT1 and
STAT2 pins, as shown in Figure 4. The charger terminates at
this moment. The I_MIN is set in two ways, by connecting a
resistor between the IMIN pin and ground, or by connecting
the IMIN pin to the V2P8 pin. When programming with the
resistor, the I_MIN is set in the equation below.
I_MIN
=
10000 ⋅ -^V----^R-----^E----^F-- =
R_IMIN
---0---.--8---V----- ^×104 ( A )
R_IMIN
(EQ. 6)
where R_IMIN is the resistor connected between the IMIN pin
and the ground. When connected to the V2P8 pin, the I_MIN
is set to 1/10 of I_REF, except when the IREF pin is shorted to
GND. Under this exception, I_MIN is 5mA.
Charge Current Thermal Foldback
Over-heating is always a concern in a linear charger. The
maximum power dissipation usually occurs at the beginning
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 ISL6292D frees users from
the over-heating concern.
Figure 5 shows the current signals at the summing node of
the current error amplifier CA in the Block Diagram. I_R is the
reference. I_T is the current from the Temperature Monitoring
block. The I_T has no impact on the charge current until the
internal temperature reaches approximately 100°C; then I_T
rises at a rate of 1µA/°C. When I_T rises, the current control
loop forces the sensed current I_SEN to reduce at the same
rate. As a mirrored current, the charge current is 100,000
times that of the sensed current and reduces at a rate of
100mA/°C. For a charger with the constant charge current
set at 1A, the charge current is reduced to zero when the
internal temperature rises to 110°C. The actual charge
current settles between 100°C to 110°C.
I_R
I_T
I_SEN
100^OC Temperature
FIGURE 5. CURRENT SIGNALS AT THE AMPLIFIER CA INPUT
Usually the charge current should not drop below I_MIN
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.
2.8V Bias Voltage
The ISL6292D provides a 2.8V voltage for biasing the
internal control and logic circuit. This voltage is also
available for external circuits such as the NTC thermistor
circuit. The maximum allowed external load is 2mA.
NTC Thermistor
The ISL6292D uses two comparators (CP2 and CP3) to form
a window comparator, as shown in Figure 7. When the TEMP
pin voltage is “out of the window,” determined by the V_TMIN
and V_TMAX, the ISL6292D stops charging and indicates a
fault condition. When the temperature returns to the set range,
the charger re-starts a charge cycle. The two MOSFETs, Q1
and Q2, produce hysteresis for both upper and lower
thresholds. The temperature window is shown in Figure 6.
3.0V
V_TMIN (1.50V)
V_TMIN-
(1.286V)
TEMP
Pin
Voltage
V_TMAX+ (0.660V)
V_TMAX (0.605V)
0V
Under
Temp
Over
Temp
FIGURE 6. CRITICAL VOLTAGE LEVELS FOR TEMP PIN
ISL6292D
2.8V
V2P8
R1
Battery
Removal
CP1 _-
+
Under
Temp
CP2 _-
+
V_RMV
R2
R_U
V_TMIN
R3
To TEMP Pin
TEMP
Q1
Over
Temp
CP3 _-
+
V_TMAX
R4
R_T
Q2
R5
GND
FIGURE 7. THE INTERNAL AND EXTERNAL CIRCUIT FOR
THE NTC INTERFACE
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