ISL6298_06 Datasheet, PDF (11/17 Pages) Intersil Corporation – Li-ion/Li-Polymer Battery Charger

ISL6298
the charger stays in the trickle mode is 15 cycles. Usually for
a recharge cycle, the trickle charge time is 15 cycles (t₆ to t₇
in Figure 20). If the battery voltage falls below the trickle
charge threshold during the 15 cycles, the 15-cycle counter
is reset (not the total-trickle-charge-time counter) and the
charger remains in the trickle mode.
Disabling TIMEOUT Limit
The TOEN pin allows the user to disable the fast charge
TIMEOUT limit by pulling the TOEN pin to LOW or shorting it
to GND. When this happens, the charger never terminates.
The STATUS pin still issues the EOC indication when the
EOC condition is reached. The EOC indication is latched
and does not change until a new charge cycle starts,
initiated by the events listed in Table 1. Leaving the TOEN
pin floating is recommended to enable the TIMEOUT. Driving
the TOEN pin above 3.0V is not recommended. The trickle
charge time limit can never be disabled. For the 3x3 DFN
package option, the TOEN pin is left floating internally and,
therefore, the TIMEOUT cannot be disabled.
CC Mode 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 the Typical Applications.
The voltage of IREF is regulated to a 0.8V reference voltage
when not driven by any external source. The charging
current during the CC mode is 25,000 times that of the
current in the R_IREF resistor. Hence, depending on how the
IREF pin is used, the charge current is,


255 m A
I_CHARGE=



---⁰---^.--⁸----^V-----
R_IREF
×
25000
(A)


100 m A
V_IREF > 1.3V
R_IREF
V_IREF < 0.4V
(EQ. 3)
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.
The actual charge current may be affected by the thermal
foldback function. See the Thermal Foldback section for
more details.
Trickle Mode Current
The charge current in the trickle mode is 20% of the
programmed CC mode charge current, that is:
I_TRICKLE = 0.2 ⋅ I_CHARGE
(EQ. 4)
where I_CHARGE is the charge current given in EQ. 3.
End-of-Charge (EOC) Current
The EOC current I_EOC 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 I_EOC is set in two ways:
1. By connecting a resistor between the IMIN pin and
ground,
2. Or by connecting the IMIN pin to the V2P8 pin.
When programming with the resistor, the I_EOC is set in the
equation below:
I_EOC
=
2500
⋅
-^V----^R-----^E---^F---
R_IMIN
=
2500
⋅
---⁰---^.--⁸---^V-----
R_IMIN
(
A)
(EQ. 5)
where R_IMIN is the resistor connected between the IMIN pin
and the ground, as shown in the Typical Application Circuit.
When connected to the V2P8 pin, the I_EOC is set to 1/10 of
I_CHARGE given in EQ. 3, except when the IREF pin is
shorted to GND. Under this exception, I_EOC is 5mA. For the
ISL6298 in the 3x3 DFN package, the IMIN pin is connected
internally to the V2P8 pin.
EOC Conditions
The EOC indication is asserted when the following
conditions are satisfied simultaneously:
1. The battery voltage is above the recharge threshold, and
2. The charge current is lower than the EOC current.
The two conditions can prevent prematurely indicating EOC
due to thermal foldback or other transient events.
Recharge
After a charge cycle is completed, 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 20.
The safety timer is reset at t₆.
2.8V Voltage Regulator
The V2P8 pin is the output of an internal 2.8V linear regulator.
The 2.8V is the voltage supply for the internal control circuit
and can also be used by external circuits, such as the NTC
thermistor circuit. The external load is not recommended to
exceed 2mA. The V2P8 pin is recommended to be decoupled
with a 1µF ceramic capacitor.
NTC Thermistor Interface
The TEMP pin offers an interface to an external NTC
thermistor. This pin has two functions: to monitor the battery
ambient temperature or to monitor the insertion of the battery.
The ISL6298 assumes that the NTC thermistor is inside the
battery pack. The battery and the NTC thermistor are inserted
or removed together. Removing the NTC thermistor disables
the charger.
Figure 21 shows the implementation of the TEMP pin. The
comparator CP1 monitors the existence of the NTC thermistor.
When the thermistor is removed, the TEMP pin voltage is
11
FN9173.4
March 9, 2006