ISL6292B Datasheet, PDF (10/12 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292B
V2P9
R_U
TEMP
R_T
DT
R_Q3
GND
V2P9
R_U
TEMP
R_T
R_D
GND
(A)
(B)
FIGURE 7. EQUIVALENT CIRCUITS FOR THE NTC DIVIDER
(A) BEFORE CHARGING STARTS
(B) DURING CHARGING.
create a hysteresis for each comparator respectively. The
DT pin is shorted to GND via the internal Q3 MOSFET when
the charger is not charging, resulting in the equivalent circuit
shown in Figure 7 (A). The on-resistance of Q3 is typically
50Ω and is negligible compared to the external resistors.
When the charger starts to charge, Q3 is turned off to set a
higher temperature range determined by the external
resistor R_D. The equivalent circuit is shown in Figure 7 (B).
The DT pin allows the user to set up a higher shut down
ambient temperature after the charger starts up.
The selection of R_U and R_T uses the same procedure
described in the ISL6292 datasheet. The selection R_D
follows the following equation:
R_D = R_T,@45°C - R_{T,@(45°C + ∆T)}
where R_T,@45°C is the thermistor resistance at 45°C and the
R_{T,@(45°C + ∆T)} is the resistance at 45°C + ∆T. Figure 8
shows the temperature windows before, during, and after
charging. Before and after charging, the temperature window
is -5°C to 45°C with 5°C hysteresis. During charging, the
high temperature limit changes to 45°C + ∆T. If this limit is
exceeded, the charger is stopped and the temperature has
to come back to below 40°C for the charging to be allowed
again. The low temperature limit is also increased. However,
the R_D typically has a much lower resistance than the NTC
at low temperature, therefore, the influence on the
temperature threshold is not as much as at high
temperature. Typically, the low temperature threshold is
raised by less than 2°C, as shown in Figure 8.
Charge Current Thermal Foldback
The thermal foldback function monitors the die temperature
and reduces the charge current when the die temperature
rises above 100°C to prevent further temperature rise. The
charge current reduces at a rate of 100mA/°C after
exceeding 100°C. For a charger with the constant charge
current set at 1A, the charge current is reduced to zero when
NOTCHARGE
45^oC + ∆T
45^oC
40^oC
0^oC
-5^oC
CHARGE
NOTCHARGE
Less than2 ^°C
FIGURE 8. BOARD TEMPERATURE MONITORING WHEN
THE CHARGE IS NOT CHARGING, THE
TEMPERATURE WINDOW IS -5°C AND 45°C.
ONCE THE CHARGER STARTS, THE
TEMPERATURE WINDOW IS 1.X°C TO 45°C+ ∆T.
the internal temperature rises to 110°C. The actual charge
current settles between 100°C to 110°C.
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.
2.9V Bias Voltage
The ISL6292B provides a 2.9V 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.
EN Pin
The EN pin allows direct interface to the battery ID pin of a
battery pack. The battery ID pin is connected with a resistor
of a value less than 27kΩ to ground inside the battery pack.
When the battery is not attached, the EN pin is pulled up by
an internal source to the V2P9 pin to disable the charger.
The 2.9V internal regulator is on as long as the input power
is applied, independent of the EN input. Table 2 summarizes
the status of each pin when the IC is disabled.
TABLE 2. SUMMARY OF PIN BEHAVIOR WHEN THE IC IS
DISABLED BY THE EN PIN
PIN
BEHAVIOR
V2P9
Outputs 2.9V.
RED
High impedance
GRN
High impedance
DT
Low impedance
IREF
Outputs 0.8V
IMIN
Outputs 0.8V
TEMP The temperature monitoring circuit remains functioning.
10
FN9139 .1
April 19, 2005