ISL78693 Datasheet, PDF (12/18 Pages) Intersil Corporation – Reverse battery leakage 700nA

ISL78693
End-of-Charge (EOC) Current
The end-of-charge 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 21 on page 11. The charger actually does
not terminate charging until the end of the TIMEOUT, as
described in “Total Charge Time” on page 11. The I_EOC is set to
60mA (typical) internal to the device by tying the I_EOC node to
V2P8.
Charge Current Thermal Foldback
Overheating is always a concern in a linear charger. The
maximum power dissipation usually occurs at the beginning of a
charge cycle when the battery voltage is at its minimum, but the
charge current is at its maximum. The charge current thermal
foldback function in the ISL78693 frees users from the
overheating concern.
Figure 22 shows the current signals at the summing node of the
current error amplifier in “Block Diagram” on page 2. I_R is the
reference and 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 (+85°C
Min) 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.
The charge current should not drop below I_EOC because of the
thermal foldback. For some extreme cases (if that does happen),
the charger does not indicate end-of-charge unless the battery
voltage is already above the recharge threshold.
IR
IT
NTC Thermistor
The ISL78693 uses two comparators (CP2 and CP3) to form a
window comparator, as shown in Figure 24. When the TEMP pin
voltage is “out of the window,” determined by the V_TMIN and
V_TMAX, the ISL78693 stops charging and indicates a fault
condition. When the temperature returns to the set range, the
charger restarts a charge cycle. The two MOSFETs, Q1 and Q2,
produce hysteresis for both upper and lower thresholds. The
temperature window is shown in Figure 23.
2.8V
V_TMIN (1.4V)
VTMIN- (1.2V)
TEMP
PIN
VOLTAGE
VTMAX+ (0.406V)
V_TMAX (0.35V)
0V
UNDER-
TEMPERATURE
OVER-
TEMPERATURE
FIGURE 23. CRITICAL VOLTAGE LEVELS FOR TEMP PIN
ISL78693
2.8V
V2P8
BATTERY _CP1
REMOVAL
-
+
UNDER- CP2
TEMPERATURE
-
+
V_RMV
R₁
40K
R2
R_U
V_TMIN
60K
TO TEMP PIN
R₃
75K
TEMP
Q1
I _SEN
+100°C
TEMPERATURE
FIGURE 22. CURRENT SIGNALS AT THE AMPLIFIER AC INPUT
2.8V Bias Voltage
The ISL78693 provides a 2.8V voltage for biasing the internal
control and logic circuit. This voltage is also available for external
circuits such as the NTC thermistor circuit. The maximum
allowed external load is 2mA.
OVER-
CP3
TEMPERATURE
-
+
V_TMAX
R4
25K
RT
Q2
R₅
4K
GND
FIGURE 24. THE INTERNAL AND EXTERNAL CIRCUIT FOR THE NTC
INTERFACE
As the TEMP pin voltage rises from low and exceeds the 1.4V
threshold, the under-temperature signal rises and does not clear
until the TEMP pin voltage falls below the 1.2V falling threshold.
Similarly, the over-temperature signal is given when the TEMP pin
voltage falls below the 0.35V threshold and does not clear until the
voltage rises above 0.406V. The actual accuracy of the 2.8V is not
important because all the thresholds and the TEMP pin voltage are
ratios determined by the resistor dividers, as shown in Figure 24.
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FN8891.1
December 12, 2016