ISL9219
FN6606 Rev 2.00 Page 8 of 12
April 7, 2010
Applications Information
Power on Reset (POR)
The ISL9219 resets as the input voltage rises above the
POR rising threshold. The internal oscillator starts to
oscillate, the internal timer is reset, and the charger begins
to charge the battery. The STAT pins, will indicate the
operating condition according to Table 1.
The ISL9219 has a typical rising POR threshold of 3.6V and
a falling POR threshold of 2.4V.
Pre-Charge
If the battery voltage is below the pre-charge threshold, the
ISL9219 charger delivers a small current to pre-charge the
battery until the voltage reaches the fast charge threshold
value. The pre-charge threshold is programmed by the
resistor connected between the PRECH pin and GND. If the
PRECH pin is left floating, a default value of 3.0V is used as
the pre-charge voltage.
Charge Cycle
A charge cycle consists of three charge modes: trickle mode,
constant current (CC) mode, and constant voltage (CV)
mode. The charge cycle always starts with the trickle mode
until the battery voltage stays above VMIN (3.0V typical). If
the battery voltage stays below VMIN, the charger stays in
the trickle mode. The charger moves to the CC mode after
the battery voltage is above VMIN. As the battery-pack
terminal voltage rises to the final charge voltage (VCH), the
CV mode begins. Since the battery terminal voltage is
regulated at the constant VCH in the CV mode, the charge
current is expected to decline as the cell voltage rises. After
the charge current drops below IMIN, which is fixed at 50mA
for any input type, the ISL9219 indicates the end-of-charge
(EOC) with STAT1 and STAT2. The charging actually does
not terminate until the internal timer completes its length of
TIMEOUT in order to bring the battery to its full capacity.
The following events initiate a new charge cycle:
•POR
• A new battery being inserted (detected by TS pin)
• Recovery from an battery over-temperature fault
•The EN
pin is toggled from HI to LO or from HI to floating
Recharge
After a charge cycle completes at a timeout event, charging
is prohibited until the recharge condition (VOUT < VRECH)
is met. Then the charging restarts with the timer reset to
zero. The STAT1 and STAT2 indication however, is
unchanged.
Internal Oscillator
The internal oscillator establishes a timing reference. The
oscillation period is programmable with an external timing
capacitor, CTIME, as shown in “Typical Application” on
page 5. The oscillator charges the timing capacitor to 1.5V
and then discharges it to 0.5V in one period, both with 10µA
current. The period tOSC is shown in Equation 3:
A 1nF capacitor results in a 0.2ms oscillation period. The
accuracy of the period is mainly dependent on the accuracy
of the capacitance and the internal current source.
Total Charge Time
The total charge time for the CC mode and CV mode is
limited to a length of TIMEOUT. A 22-stage binary counter
increments each oscillation period of the internal oscillator to
set the TIMEOUT. The TIMEOUT can be calculated as
Equation 4:
A 1nF capacitor leads to 14 minutes of TIMEOUT. For
example, a 15nF capacitor sets the TIMEOUT to be
3.5 hours. The charger has to reach the end-of-charge
condition before the TIMEOUT, otherwise, a TIMEOUT fault
is issued. The TIMEOUT fault latches up the charger. There
are two ways to release such a latch-up: either to recycle the
input power, or toggle the EN pin to disable the charger and
then re-enable it.
The trickle mode charge has a time limit of 1/8 TIMEOUT. If
the battery voltage does not reach VMIN within this limit, a
TIMEOUT fault is issued and the charger latches up. Thus,
the charger can stay in trickle mode for no more than 1/8 of
TIMEOUT interval.
Monitoring Output Current thru ISET Pin
In addition to programming the fast charge current, the ISET
can be used to monitor the actual output current for the AC
adapter input current setting. During the constant current
phase, the ISET pin voltage is fixed at 2.4V. In this case, the
output current can be calculated by using 2.4V divided by
RISET
. During the constant voltage phase, the output current
can be calculated by using the pin voltage, divided by RISET.
For USB input current setting, VISET can still be used to
monitor the charge current but since VISET is not used for
the close loop current regulation, to achieve a good
accuracy, an one-point calibration is required.
End-of-Charge (EOC) Current
The end-of-charge current IMIN sets the level at which the
charger starts to indicate the charge complete condition with
the indication pins. The charger actually does not terminate
charging until the end of the TIMEOUT interval, as described
in “Total Charge Time” on page 8. The IMIN is fixed at 50mA
for all input types, i.e. for AC adapter, USB high power and
USB low power.
tOSC 0.2 106CTIME
=ondssec (EQ. 3)
TIMEOUT 222 tOSC 14
CTIME
1nF
------------------
==minutes
(EQ. 4)