ISL6292_07 Datasheet, PDF (12/20 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292
The following events initiate a new charge cycle:
• POR,
• a new battery being inserted (detected by TEMP pin),
• the battery voltage drops below a recharge threshold after
completing a charge cycle,
• recovery from an battery over-temperature fault,
• or, the EN pin is toggled from GND to floating.
Further description of these events are given later in this
data sheet.
Recharge
After a charge cycle completes, charging is prohibited until
the battery voltage drops to a recharge threshold, V_RECHRG
(see “Electrical Specifications” on page 3). Then a new
charge cycle starts at point t₆ and ends at point t₈, as shown
in Figure 19. 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
( seconds)
(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 19.
Disabling TIMEOUT Limit
The TIMEOUT limit for the fast charge modes can be disabled
by pulling the TOEN pin to LOW or shorting it to GND. When
this happens, the charger becomes a current-limited LDO
(low-dropout) supply with its voltage regulated at the final
charge voltage V_CH and the current limit determined by the
IREF pin. If the LDO load current drops below the end-of-
charge current (refer to “End-of-Charge (EOC) Current” on
page 13), the STATUS pin will indicate.
The trickle charge time limit, however, is not disabled even
when the TOEN pin is pulled to LOW. The charger operates
in the trickle mode at the beginning of a charge cycle even if
the TIMEOUT is disabled. Leaving the TOEN pin floating is
recommended to enable the TIMEOUT. Driving the TOEN
pin above 3.0V is not recommended.
Charge Current Programming
The charge current is programmed by the IREF pin. There
are three ways to program the charge current:
1. Driving the IREF pin above 1.3V
2. Driving the IREF pin below 0.4V,
3. or using the R_IREF as shown in “Typical Applications” on
page 8.
The voltage of IREF is regulated to a 0.8V reference voltage
when not driven by any external source. The charging
current during the constant current mode is 100,000 times
that of the current in the R_IREF resistor. Hence, depending
on how IREF pin is used, the charge current is:
⎧
⎪
500 m A
I_REF=
⎪
⎨
⎪
---⁰---^.--⁸----^V-----
R_IREF
×
10⁵
(
A
)
⎪
⎩
100 m A
V_IREF > 1.3V
R_IREF
V_IREF < 0.4V
(EQ. 5)
The 500mA current is a guaranteed maximum value for the
high-power USB port, with the typical value of 450mA. The
100mA current is also a guaranteed maximum value for the
low-power USB port. This design accommodates the USB
power specification.
The internal reference voltage at the IREF pin is capable of
sourcing less than 100µA current. When pulling down the
IREF pin with a logic circuit, the logic circuit needs to be able
to sink at least 100µA current.
When the adapter is current limited, it is recommended that
the reference current be programmed to at least 30% higher
than the adapter current limit (which equals the charge
current). In addition, the charge current should be at least
350mA so that the voltage difference between the VIN and
the VBAT pins is higher than 100mV. The 100mV is the
offset voltage of the input-output voltage comparator shown
in the block diagram on page 9.
12
FN9105.9
December 17, 2007