BQ24640 Datasheet, PDF (15/25 Pages) Texas Instruments – High-Efficiency Synchronous Switch-Mode Super Capacitor Charger

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VREF
VREF
bq24640
SLUSA44 – MARCH 2010
CHARGE SUSPENDED
VLTF
VLTFH
TEMPERATURE RANGE
TO INITIATE CHARGE
CHARGE SUSPENDED
VLTF
VLTFH
TEMPERATURE RANGE
DURING A CHARGE
CYCLE
VHTF
CHARGE SUSPENDED
CHARGE SUSPENDED
VTCO
GND
GND
Figure 11. TS Pin, Thermistor Sense Thresholds
Assuming a 103AT NTC thermistor is selector, the value RT1 and RT2 can be determined by using the following
equations:
RT2 =
V_VREF
´ RTH_COLD
´ RTH_HOT
´
æ1
ç
è ^VLTF
-
1ö
÷
V_{TCO ø}
RTH_HOT
´
æ
ç
V_VREF
è ^VTCO
-
ö
1_÷
ø
-
RTH_COLD
´
æ
ç
V_VREF
è ^VLTF
-
ö
1_÷
ø
(4)
V_{VREF - 1}
RT1 =
V_LTF
1
1
+
RT2 RTH_COLD
(5)
VREF
bq24640
TS
RT 1
RT 2
RTH
103 AT
Figure 12. TS Resistor Network
CE (Charge Enable)
The CE digital input is used to disable or enable the charge process. A high-level signal on this pin enables
charge, provided all the other conditions for charge are met (see Enabling and Disabling Charge). A high to
low transition on this pin also resets all timers and fault conditions. There is an internal 1 MΩ pulldown resistor on
the CE pin, so if CE is floated the charge will not turn on.
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