ISL6292C Datasheet, PDF (8/11 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292C
Recharge
After a charge cycle completes, charging is prohibited until
the battery voltage drops to a recharge threshold, V_RECHRG
(see Electrical Specifications). Then a new charge cycle
starts at point t₆ and ends at point t₈, as shown in Figure 5.
The safety timer is reset at t₆.
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
( sec onds)
(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.
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:
TIMEOUT
=
2²² ⋅ T_OSC=
14
⋅
-^C----^T----^I--^M----^E--
1nF
(minutes) (EQ. 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
enable it again.
The trickle mode charge has a time limit of 1/8 TIMEOUT. If
the battery voltage does not reach V_MIN within this limit, a
TIMEOUT fault is issued and the charger latches up. The
charger stays in trickle mode for at least 15 cycles of the
internal oscillator and, at most, 1/8 of TIMEOUT, as shown in
Figure 5.
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,
I_REF=
---⁰---^.--⁸----^V-----
R_IREF
×
10⁵
(
A
)
(EQ. 5)
TABLE 1. CHARGE CURRENT vs R_IREF VALUES (Note)
CHARGE CURRENT (mA)
R_IREF (kΩ)
MIN
267
250
TYP
MAX
300
350
160
450
500
550
100
720
800
880
88.9
810
900
990
80
900
1000
1100
NOTE: The limits are still preliminary. Additional samples will be
tested for the final results.
Table 1 shows the charge current vs. selected R_IREF values.
The ISL6292C is designed to be safe when the IREF pin is
accidentally short-circuited to an external source or to
ground. If the IREF pin is driven by an external source to
below 0.38V or above 1.5V for any reason, the charger is
disabled and the FAULT pin turns to LOW to indicate a fault
condition. The charger will resume charging after the fault
condition is removed. When the IREF is driven by a voltage
between 0.38V to 0.5V (typical value), the charge current is
limited to 100mA; or when driven to a voltage between 1.2V
to 1.5V, the charge current is limited to 500mA. For any
voltage between 0.5V to 1.2V, the charge current will drop to
a very low value. This feature can protect the charger from a
large charging current when IREF is accidentally shorted to
ground or to a high voltage. Figure 6 shows the charge
current when the IREF pin voltage is driven from 0V to 3V.
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 5. The charger actually does not
terminate charging until the end of the TIMEOUT, as
described in the Total Charge Time section. In the
STATUS
GND
5V/Div
GND
GND
IREF Pin Voltage
500mV/Div
Charge Current
200mA/Div
Time Scale
40s/Div
FIGURE 6. CHARGE CURRENT WHEN IREF PIN IS DRIVEN
BY AN EXTERNAL VOLTAGE SOURCE
8
FN9133.2
July 22, 2005