
11
FN6430.0
February 14, 2007
Recharge
After a charge cycle completes, the charger continues to
regulate the output at the constant voltage; but the STATUS
pin indicates that the charging is completed. The STATUS pin
stays high until the battery voltage drops to below the
recharge threshold, V
RECHRG
(see Electrical Specifications).
Then the STATUS pin goes low and a new charge cycle starts
at point t
6
. The charge cycle ends at point t
7
with the STATUS
pin again going high, as shown in Figure 20.
Internal Oscillator
The internal oscillator 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 10
μ
A current.
The period T
OSC
is:
(EQ. 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.
Charge Current Programming
The charge current in the CC mode is programmed by the
IREF pin. The voltage of IREF is regulated to a 0.8V
reference voltage. The charging current during the constant
current mode is 100,000 times that of the current in the
R
IREF
resistor. Hence, the charge current is,
(EQ. 4)
Table 1 shows the charge current vs. selected R
IREF
values.
The typical trickle charge current is 10% of the programmed
constant charge current. Table 2 shows the trickle charge
current tolerance guidance at given R
IREF
values, when the
battery voltage is between 0V to 2.5V.
NOTE: The values in table 2 and table 1 are not tested and are only
for guidance in selecting resistor values for mass production tests or
in customer’s products.
End-of-Charge (EOC) Current
The EOC current I
MIN
sets the level at which the charger
starts to indicate the end of the charge with the STATUS pin,
as shown in Figure 20. The charger actually does not
terminate charging. In the ISL9203A, the EOC current is
internally set to 1/10 of the CC charge current, that is:
(EQ. 5)
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. The tolerance guidance for the EOC current at
selected R
IREF
values are given in Table 3.
NOTE: The values in table 3 are not tested and are only for guidance
in selecting resistor values for mass production tests or in customer’s
products.
FIGURE 20. OPERATION WAVEFORMS
VIN
V2P8
STATUS
VBAT
ICHARGE
AT LEAST 15
CYCLES
POR THRESHOLD
2.8V VMIN
V
RECHRG
t0
t1t2t3
t4
t5
CHARGE CYCLE
IMIN
t6
t7
CHARGE CYCLE
T
OSC
0.2 10
6
C
TIME
=
onds
sec
(
)
I
REF
IREF
-----------------
10
5
×
A
( )
=
TABLE 1. CHARGE CURRENT vs R
IREF
VALUES
R
IREF
(k
Ω
)
CHARGE CURRENT (mA)
MIN
TYP
MAX
267 ~ 160
17% lower than
TYP Value
= I
REF
in EQ. 5
17% higher than
TYP Value
160
450
500
550
100
720
800
880
88.9
810
900
990
80
900
1000
1100
TABLE 2. TRICKLE CHARGE CURRENT vs R
IREF
VALUES
R
IREF
(k
Ω
)
TRICKLE CHARGE CURRENT (mA)
MIN
TYP
MAX
267
15
30
60
160
30
50
80
100
40
80
120
88.9
45
90
135
80
70
100
150
TABLE 3. EOC CURRENT vs R
IREF
VALUES
R
IREF
(k
Ω
)
EOC CURRENT (mA)
MIN
TYP
MAX
267
15
30
60
160
30
50
80
100
40
80
120
88.9
45
90
135
80
70
100
150
I
MIN
------
I
REF
=
ISL9203A