ISL6298_06 Datasheet, PDF (10/17 Pages) Intersil Corporation – Li-ion/Li-Polymer Battery Charger

ISL6298
Theory of Operation
The ISL6298 is an integrated charger optimized for low-
capacity single-cell Li-ion or Li-polymer batteries. It charges
a battery with the constant current (CC) and constant voltage
(CV) profile. The charge current is trimmed to have better
than 10% accuracy at 250mA and is programmable up to
450mA. The charge voltage has 1% accuracy.
Figure 20 shows the typical operating waveforms after
power on. The power is applied at t₀. When the input voltage
reaches the power-on reset (POR) threshold at t₁, the V2P8
pin starts to output a 2.8V supply. This supply also powers
the internal control circuit. The POR initiates a charge cycle.
Six different ways can initiate a charge cycle, as listed in
Table 1.
TABLE 1. EVENTS THAT LEADS TO A NEW CHARGE CYCLE
#
EVENT
1 Power on Reset
2 The VIN pin voltage drops below the VBAT pin voltage and
then rises back above the VBAT pin voltage
3 A new battery being inserted (detected by TEMP pin)
4 The battery voltage drops below a recharge threshold after
completing a charge cycle
5 recovery from a battery over-temperature fault
6 the EN pin is toggled from GND to floating
A charge cycle goes through a trickle mode (t₁ to t₂), a
constant current (CC) mode (t₂ to t₃) and a constant voltage
(CV) mode (t₃ to t₅). The total fast charge (CC and CV) time
(t₂ to t₅) is programmed by users to prevent charging a faulty
battery for an excessively long time. At the end of the fast
charge time (t₅), the charger is terminated. The charger
must reach an end-of-charge (EOC) condition before the
termination; otherwise, the charger issues a fault indication
through the FAULT pin. The charger issues a logic low signal
VIN
V2P8
POR Threshold
Charge Cycle
Charge Cycle
STATUS
FAULT
15 Cycles to
1/8 TIMEOUT
VBAT
V_RECHRG
2.8V V_MIN
15 Cycles
I_CHARGE
I_MIN
t₀
t₁ t₂
t₃ t₄ t₅
t₆ t₇
t₈
FIGURE 20. TYPICAL OPERATING WAVEFORMS
10
at the STATUS pin at the beginning of a charge cycle. When
the EOC condition is reached, the STATUS rises to high, as
shown at t₄.
After termination, if the battery voltage drops below a
recharge threshold (t₆ in Figure 20), a re-charge cycle will
take place. The total time for the recharge cycle is the total
fast charge time (t₇ to t₈). The trickle charge time is
negligible in a recharge cycle. More detailed description for
the operation is given below.
Power on Reset (POR)
The ISL6298 resets itself as the input voltage rises above
the POR rising threshold. The V2P8 pin outputs a 2.8V
voltage, the internal oscillator starts to oscillate, the internal
timer is reset, and the charger begins to charge the battery.
The two indication pins, STATUS and FAULT, indicate a
LOW and a HIGH logic signal respectively. Figure 20
illustrates the startup of the charger between t₀ to t₂.
The ISL6298 has a typical rising POR threshold of 3.4V and
a falling POR threshold of 2.4V. The 2.4V falling threshold
guarantees charger operation with a current-limited adapter
to minimize the thermal dissipation. See more details on
using a current-limited adapter in the ISL6292 datasheet,
available at http://www.intersil.com.
Internal Oscillator
The internal oscillator (see the Block Diagram) establishes a
timing reference. The oscillation period is programmable
with an external timing capacitor, C_TIME, as shown in Typical
Applications. 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 T_OSC is:
T_OSC = 0.2 ⋅ 10⁶ ⋅ C_TIME
( sec onds)
(EQ. 1)
A 1nF capacitor results in a 0.2ms oscillation period.
Total Fast Charge Time
The total fast charge time TIMEOUT is also programmed by
the C_TIME. A 22-stage binary counter increments each
oscillation period to set the TIMEOUT, thus,
TIMEOUT
=
2²² ⋅ T_OSC=
14
⋅
-^C----^T----^I--^M----^E--
1nF
(minutes) (EQ. 2)
A 1nF capacitor leads to 14 minutes of TIMEOUT. If a user
needs to set the TIMEOUT to 3.5 hours, a 15nF capacitor is
required. The charger must reach EOC before the charger
terminates, otherwise, a TIMEOUT fault will be issued.
Trickle Charge Time
The trickle charge time is limited to 1/8 of TIMEOUT. If the
trickle charge time (t₁ to t₂) exceeds the limit, a TIMEOUT
fault will be issued. The end of trickle charger is determined
by the battery voltage staying above the trickle charge
threshold (given in the Electrical Specification) for 15
consecutive cycles of T_OSC; therefore, the minimum time
FN9173.4
March 9, 2006