ISL6292C Datasheet, PDF (9/11 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

I_R
I_T
I _SEN
ISL6292C
Indications
The ISL6292C 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 8 shows the V2P8 pin voltage vs. the input voltage.
Table 2 summarizes the other two pins.
100^OC TEMPERATURE
FIGURE 7. CURRENT SIGNALS AT THE AMPLIFIER CA INPUT.
ISL6292C, the EOC current is internally set to 1/10 of the CC
charge current, that is,
I_MIN=
--¹----
10
⋅
I_REF
(EQ. 6)
At the EOC, the STATUS signal rises to HIGH and is latched.
The latch is not reset until a recharge cycle or a new charge
cycle starts.
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 ISL6292C frees users from
the over-heating concern.
Figure 7 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.
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 ISL6292C 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.
3.4V
2.8V
V_IN
V2P8
2.4V
FIGURE 8. THE V2P8 PIN OUTPUT vs THE INPUT VOLTAGE
AT THE VIN PIN. VERTICAL: 1V/DIV,
HORIZONTAL: 100ms/DIV
TABLE 2. STATUS INDICATIONS
FAULT STATUS
INDICATION
High High
Charge completed with no fault (Inhibit) or
Standby
High Low
Charging in one of the three modes
Low High
Fault
NOTE: Both outputs are pulled up with external resistors.
Shutdown
The ISL6292C can be shutdown by pulling the EN pin to
ground. When shut down, the charger draws typically less
than 30µA current from the input power and the 2.8V output
at the V2P8 pin is also turned off. The EN pin needs be
driven with an open-drain or open-collector logic output, so
that the EN pin is floating when the charger is enabled. If the
EN pin is driven by an external source, the POR threshold
voltage will be affected.
Input and Output Capacitor Selection
Typically any type of capacitors can be used for the input
and the output. Use of a 0.47µF or higher value ceramic
capacitor for the input is recommended. When the battery is
attached to the charger, the output capacitor can be any
ceramic type with the value higher than 0.1µF. However, if
there is a chance the charger will be used as an LDO linear
regulator, a 10µF tantalum capacitor is recommended.
9
FN9133.2
July 22, 2005