ISL6292D Datasheet, PDF (11/13 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292D
As the TEMP pin voltage rises from low and exceeds the
1.5V threshold (when the V2P8 pin is forced with a 3V bias),
the under temperature signal rises and does not clear until
the TEMP pin voltage falls below the 1.286V falling
threshold. Similarly, the over-temperature signal is given
when the TEMP pin voltage falls below the 0.605V threshold
and does not clear until the voltage rises above 0.66V. The
actual accuracy of the 3V bias is not important because all
the thresholds and the TEMP pin voltage are ratios
determined by the resistor dividers, as shown in Figure 7.
The NTC thermistor is required to have a resistance ratio of
3.96:1 at the low and the high temperature limits, that is,
R_{-----C----O-----L---D-- = 3.96}
R_HOT
(EQ. 7)
This is because at the low temperature limit, the TEMP pin
voltage is 1.5V, which is 1/2 of the 3V bias. Thus,
R_COLD = R_U
(EQ. 8)
where R_U is the pull-up resistor as shown in Figure 7. On the
other hand, at the high temperature limit the TEMP pin
voltage is 0.605V, 20.17% of the 3V bias. Therefore,
-^R----^H----^O-----^T-
R_U
=
1^-----0–----^.-02^---.0^--2^--1-0^--7--1^---7^--
(EQ. 9)
For applications that do not need to monitor the battery
temperature, the NTC thermistor can be replaced with a
regular resistor of a half value of the pull up resistor R_U.
Another option is to connect the TEMP pin to the IREF pin
that has a 0.8V output. With such connection, the IREF pin
can no longer be programmed with logic inputs.
Battery Removal Detection
The ISL6292D assumes that the thermistor is co-packed
with the battery and is removed together with the battery.
3.4V
2.8V
V_IN
V2P8
2.4V
FIGURE 8. THE V2P8 PIN OUTPUT vs THE INPUT VOLTAGE
AT THE VIN PIN. VERTICAL: 1V/DIV,
HORIZONTAL: 100ms/DIV
STAT1
STAT2
STATUS
Temp
Fault
TIMEOUT
Fault
C_TIME
OSC
TIME
DFF1
DFF8 DFF9
(A)
TIME
OSC
Output
DFF1
Output
DFF8
Output
DFF9
Output
(B)
FIGURE 9. EQUIVALENT CIRCUIT FOR THE STAT1/STAT2
INDICATION PINS AND KEY OPERATING
WAVEFORMS
When the charger senses a TEMP pin voltage that is 2.1V or
higher, it assumes that the battery is removed. The battery
removal detection circuit is also shown in Figure 7. When a
battery is removed, the charger is stopped. When a battery
is inserted again, a new charge cycle starts.
Indications
The ISL6292D has three indication pins: V2P8, STAT1, and
STAT2. The input presence is indicated by the V2P8 pin.
Figure 8 shows the V2P8 pin voltage vs. the input voltage.
The equivalent circuit for the STAT1 and STAT2 pins are
shown in Figure 9. Both pins have ESD diodes to clamp the
pin voltage between ground and the input, as shown in the
Block Diagram. The STATUS block outputs a logic HIGH
when the charger is charging and a LOW whenever the
charger is not charging. When a fault case happens, the
charger stops charging, therefore, the STATUS block outputs
LOW. Depending on fault cause, either the eighth or the
ninth D-type flip-flop output is gated to the STAT1 pin. Both
flip-flop outputs are 50% duty ratio blinking signals. The
periods of the eighth and ninth flip-flop output are calculated
by the following equations:
T_8th = 2⁸ ⋅ T_OSC = 256 ⋅ T_OSC
(EQ. 10)
T_9th = 2⁹ ⋅ T_OSC = 512 ⋅ T_OSC
(EQ. 11)
Table 1 and 2 summarize the LED indication driven by
STAT1 and STAT2 respectively.
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