ISL78693 Datasheet, PDF (13/18 Pages) Intersil Corporation – Reverse battery leakage 700nA

ISL78693
The NTC thermistor is required to have a resistance ratio of 7:1 at
the low and the high temperature limits, that is given by
Equation 6:
R_{--R---C--H--O--O---L--T-D-- = 7}
(EQ. 6)
This is because, at the low temperature limit, the TEMP pin
voltage is 1.4V, which is 1/2 of the 2.8V bias, as shown in
Equation 7:
R_COLD = R_U
(EQ. 7)
where R_U is the pull-up resistor as shown in Figure Figure 24 on
page 12. At the high temperature limit, the TEMP pin voltage is
0.35V, which is 1/8 of the 2.8V bias, as shown in Equation 8:
R_HOT = -^R--₇--^U--
(EQ. 8)
Various NTC thermistors are available for this application. Table 2
shows the resistance ratio and the negative temperature
coefficient of the curve-1 NTC thermistor from Vishay at various
temperatures. The resistance at +3°C is approximately seven
times the resistance at +47°C, which is shown in Equation 9:
R^--R---₄^--3-₇^---_^-C--_C^{-- = 7}
(EQ. 9)
If the low temperature limit is +3°C, and the high temperature
limit is around +47°C, then the pull-up resistor RU can be chosen
to be the resistance measured at +3°C.
TABLE 2. RESISTANCE RATIO OF VISHAY’S CURVE-1 NTC
TEMPERATURE (°C)
0
R_T/R_25°C
3.266
NTC (%/°C)
5.1
3
2.806
5.1
5
2.540
5.0
25
1.000
4.4
45
0.4368
4.0
47
0.4041
3.9
50
0.3602
3.9
The temperature hysteresis will now be estimated in the low and
high temperatures. At the low temperature, the hysteresis is
approximately estimated in Equation 10:
T_hysLOW  ₁--¹--_.-₄-^.-⁴--_V--^V----_-^---₀₁---_..--₀₂---₅-^V--₁--  3
C
(EQ. 10)
where 0.051 is the NTC at +3°C. Similarly, the high temperature
hysteresis is estimated in Equation 11:
T_hysHIGH  ⁰--₀--^.-_.-⁴-₃--⁰-₅--⁶--_V--^V----_^----₀₀---_..--₀₃---₃₅---₉-^V--  4
C
(EQ. 11)
where the 0.039 is the NTC at +47°C.
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. In this condition, no pull-up is
allowed for the TEMP pin.
Battery Removal Detection
The ISL78693 assumes that the thermistor is co-packed with the
battery and is removed together with the battery. 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 24. When a battery is
removed, a FAULT signal is indicated and charging is halted.
When a battery is inserted again, a new charge cycle starts.
Indications
The ISL78693 has three indications: the input presence, the
charge status, and the fault indication. The input presence is
indicated by the V2P8 pin while the other two indications are
presented by the STATUS pin and FAULT pin respectively.
Figure 25 shows the V2P8 pin voltage vs the input voltage.
Table 3 summarizes the other two pins.
3.4V
2.8V
V_IN
V2P8
2.4V
FIGURE 25. THE V2P8 PIN OUTPUT vs THE INPUT VOLTAGE AT THE
VIN PIN. VERTICAL: 1V/DIV, HORIZONTAL:
100ms/DIV
TABLE 3. STATUS INDICATIONS
FAULT STATUS
INDICATION
High High Charge completed with no fault (Inhibit) or Standby
High
Low Charging in one of the three modes
Low
High Fault
*Both outputs are pulled up with external resistors.
Shutdown
The ISL78693 can be shut down by pulling the EN pin to ground.
When shut down, the charger draws typically less than 30µA
current from the input power and the 2.8V output at the V2P8 pin
is also turned off. The EN pin has to be driven with an open-drain
or open-collector logic output. The EN pin is internally biased, so
the pin should be floated to turn the device ON once the charger
is enabled. To turn OFF the device, an open-drain/open-collector
can be used to pull the pin to its low level.
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FN8891.1
December 12, 2016