ISL6297 Datasheet, PDF (12/16 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6297
yellow. Once the charge begins, the ISL6297 pulls the RED
pin low to drive a red indicator. Once the charge properly
finishes (either when the EOC condition is qualified or when
the TIMEOUT completes) the ISL6297 releases the RED
output and pulls the GRN pin low to drive a green indicator
while the red indicator turns off. The green LED remains on
unless the input power is recycled, or a fault occurs. During
a recharge operation, the indicator remains green.
When a temperature fault happens, both the RED and the
GRN pins turn on to indicate a yellow color. This fault is
cleared automatically when the temperature again returns to
the normal region. If the FAULT is non-temperature related,
the yellow indicator flashes. This type of fault is latched and
can only be reset by toggling the EN pin or cycling the input
power. Table 2 summarizes the LED indications.
Because the LED outputs provide a constant 10mA current
sink, no external resistors are necessary.
TABLE 2. LED INDICATION SUMMARY
STATUS
RED GRN INDICATION
Plug In Indication
L H Red (500ms)
H L Green (500ms)
L L Yellow (500ms)
H H Off (500ms)
Charging
L H Red
Full Charge (EOC) or recharging H L Green
Short circuit Error or trickle charge L
TIMEOUT error
H
L Yellow (Flashing
H ^{1Hz rate)}
Over/Under Ambient Temperature L L Yellow
Idle state
H H Off or Battery (+)
terminal not
connected
VSEN Pin
When the charger is providing a large current to the cell,
there can be significant voltage drop in the PCB trace
between the charger output and the battery positive terminal.
To minimize this effect, the VSEN pin input provides a low
current monitoring path. This provides a more accurate
reading of the battery voltage. Figure 7 shows the internal
voltage feedback circuit.
BAT
VSEN
R2
-
VA
+
V_REF
R3
Q1
Enable
FIGURE 7. THE INTERNAL VOLTAGE FEEDBACK CIRCUIT
THERMAGUARD™ Charge Current Thermal
Foldback
Over-heating is always a concern in a linear charger or in the
linear region for a dual mode charger. The charge current
thermal foldback function in the ISL6297 frees users from
the over-heating concern.
Figure 8 shows the current signals at the summing node of
the current error amplifier CA in the Block Diagram. I_R is the
reference. I_T is the current from the Temperature Monitoring
block. The I_T has no impact on the charge current until the
internal temperature reaches approximately 100°C; then I_T
rises at a rate of 1µA/°C. When I_T rises, the current control
loop forces the sensed current I_SEN to reduce at the same
rate. As a mirrored current, the charge current is 100,000
times that of the sensed current and reduces at a rate of
100mA/°C. For a charger with the constant charge current
set at 1A, the charge current is reduced to zero when the
internal temperature rises to 110°C. The actual charge
current settles between 100°C to 110°C.
I_R
I_T
I_SEN
100^OC Temperature
FIGURE 8. CURRENT SIGNALS AT THE AMPLIFIER CA INPUT
Usually the charge current should not drop below I_MIN
because of the thermal foldback. If, in some extreme case
this does happen, the charger does not indicate end-of-
charge unless the battery voltage is already above the
recharge threshold.
12
FN9215.0
September 27, 2005