ISL6292BCR Datasheet, PDF (8/12 Pages) Intersil Corporation – Complete Charger for Single-Cell Li-ion Batteries

ISL6292B
Applications Information
Power-On Reset (POR)
The ISL6292B has a 3.4V rising POR threshold. Before the
input voltage reaches the POR threshold, the 2.9V V2P9 pin
outputs 0V and the charger is disabled. Once the POR
threshold is reached, the V2P9 pin outputs 2.9V, the open-
drain MOSFET on the DT pin is turned on, and the ambient
temperature monitoring circuit starts to function. After a
delay and after the input voltage rises above the battery
voltage, the charger control circuit starts to work and the DT
pin impedance becomes high. Figure 3 shows the sequence
of the events at power on. The POR has a falling threshold
of 2.4V typically. At power on, all counters are reset to zero.
Charge Current and R_IREF Selection
When the ISL6292B is used as a traditional linear charger,
the R_IREF sets the constant charge current. The trickle
charge current is 10% of the CC current I_REF. When working
with a current-limited supply, the CC current is determined
by the supply limited current I_LIM. I_REF needs to be
programmed higher than I_LIM and is used as an overcurrent
protection. Taking into account the tolerance of both the I_LIM
and I_REF, it is recommended the I_REF be programmed at
least 30% higher than the I_LIM. I_REF can be found by the
following equation:
I_REF=
---⁰---^.--⁸----^V-----
R_IREF
×
10⁵
(
A
)
(EQ. 1)
The trickle charge current is 10% of IREF, that is,
I_Trickle=
---⁰---^.--⁸----^V----- × 10⁴(A)
R_IREF
(EQ. 2)
The ISL6292B has a comparator with 100mV offset voltage
to ensure the input voltage is higher than the battery voltage
before charging starts (see the Block Diagram). This
condition requires I_LIM be higher than 400mA. The upper
limit for I_LIM is 1.5A.
POR
VIN
V2P9
DT
Imped
Charger
Start
FIGURE 3. EVENT SEQUENCE AT POWER UP
EOC Current and R_IMIN Selection
The EOC current is programmed by the IMIN pin and can be
calculated by the following equation:
I_MIN=
---⁰---^.--⁸---^V-----
R_IMIN
×
10⁴
(
A
)
(EQ. 3)
The EOC current has a programming range up to 400mA.
To qualify as an EOC condition, the charge current needs to
drop below the I_MIN level and stay below the IMIN level for
more than three to four cycles of the internal oscillator;
additionally, the battery voltage rises above the recharge
threshold given in the Electrical Specification table.
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 10µA current.
The period T_OSC is:
T_OSC = 0.2 ⋅ 10⁶ ⋅ C_TIME
( seconds)
(EQ. 4)
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 and C_TIME Selection
The total charge time for the CC mode and CV mode is
limited to a length of TIMEOUT, which can be found by:
TIMEOUT=
14
⋅
-^C----^T----^I--^M----^E--
1nF
(minutes)
(EQ. 5)
VIN
V2P9
DT
Impe d.
POR
Thre shold
Charge
C yc le
Charge
C yc l e
RED
GRN
M IN
15 Cycle s to
1/8 TIM EOUT
VBAT
V _RECHRG
2.8V V _{M IN}
15
Cycle s
I _CHG
IM _IN
t0 t1 t2 t3
t4
t5
t6 t7
t8
FIGURE 4. OPERATION WAVEFORMS
8
FN9139 .1
April 19, 2005