ISL6297 Intersil Corporation, ISL6297 Datasheet - Page 13

• Manufacturer Part Number: ISL6297
• Description: Li-ion/Li Polymer Battery Charger
• Manufacturer: Intersil Corporation

Ambient Temperature Sensing
The TEMP pin sets the allowable ambient temperature
range for charging the battery. Typically, an NTC (negative
temperature coefficient) resistor is mounted on the printed
circuit board (PCB) to monitor the ambient temperature. Due
to the self-heating of the PCB during charging, the ISL6297
provides the DT pin to set a higher temperature threshold
during the charge operation.
Figure 9 shows the internal circuit for the ambient
temperature sensing function. Two comparators form a
window comparator whose high-threshold is V
threshold is V
Electrical Specifications. The two MOSFETs (Q1 and Q2)
create a hysteresis for each comparator, respectively. The
DT pin is shorted to GND via the internal Q3 MOSFET when
the charger is not charging, resulting in the equivalent circuit
shown in Figure 10 (A). The on-resistance of Q3 is typically
50Ω and is negligible compared to the external resistors.
When the charger starts to charge, Q3 is turned off to set a
higher temperature range determined by the external
resistor R
The DT pin provides a higher shut down ambient
temperature during the charger operation.
Over
Temp
FIGURE 9. THE INTERNAL AND EXTERNAL CIRCUIT FOR
Under
Temp
D
CP1
CP2
. The equivalent circuit is shown in Figure 10 (B).
TMAX
THE NTC INTERFACE
+
+
-
-
. These two thresholds are given in the
V
TMAX
V
To TEMP Pin
TMIN
CHG
Q1
13
Q2
2.9V
Q3
R1
100K
R2
75K
R4
4K
R3
25K
V2P9
TEMP
DT
GND
TMIN
R
R
T
and low-
R
U
D
ISL6297
When the TEMP pin voltage is “out of the window,” as
determined by the V
charging and indicates a fault condition. When the
temperature returns to the set range, the charger continues
the charge cycle.
As the temperature falls, the TEMP pin voltage rises. When
it exceeds the 2.0V V
condition exists. This condition does not clear until the TEMP
pin voltage falls back below the threshold minus the
hysteresis voltage (V
condition exists when the TEMP pin voltage falls below the
0.714V V
temperature operation until the voltage rises above the
threshold plus the hysteresis voltage (V
accuracy of the 2.9V supply voltage is not important
because all the thresholds and the TEMP pin voltage are
ratios determined by the resistor dividers, as shown in
Figure 9.
V
FIGURE 10. EQUIVALENT CIRCUITS FOR THE NTC DIVIDER
FIGURE 11. CRITICAL VOLTAGE LEVELS FOR TEMP PIN
TMAX+
V
V
TMAX
V
TMIN-
TMIN
(0.788V)
(0.714V)
R
(1.83V)
Under
(2.0V)
Temp
Temp
Over
Q3
2.9V
0V
TMAX
V2P9
TEMP
(A)
DT
GND
(A) BEFORE CHARGING STARTS
(B) DURING CHARGING
threshold and does return to normal
R
TMIN
T
TMIN-
R
TMIN
U
and V
). Similarly, an over-temperature
threshold, an under temperature
TMAX
, the ISL6297 stops
TMAX+)
V2P9
TEMP
GND
(B)
. The actual
R
T
March 20, 2007
R
R
U
D
Voltage
TEMP
Pin
FN9215.1