BQ500412 Datasheet, PDF (15/28 Pages) Texas Instruments – Low System Cost, Wireless Power Controller for WPC TX A6

bq500412
www.ti.com
SLUSBO2A – NOVEMBER 2013 – REVISED DECEMBER 2013
Shut Down via External Thermal Sensor or Trigger
Typical applications of the bq500412 will not require additional thermal protection. This shutdown feature is
provided for enhanced applications and is not only limited to thermal shutdown. The key parameter is the 1.0 V
threshold on pin 2. Voltage below 1.0 V on pin 2 for longer than 150ms causes the device to shutdown.
The application of thermal monitoring via a Negative Temperature Coefficient (NTC) sensor, for example, is
straightforward. The NTC forms the lower leg of a temperature dependant voltage divider. The NTC leads are
connected to the bq500412 device, pin 2 and GND. The threshold on pin 2 is set to 1.0 V, below which the
system shuts down and a fault is indicated (depending on LED mode chosen).
To implement this feature follow these steps:
1) Consult the NTC datasheet and find the resistence vs temperature curve.
2) Determine the actual temperature where the NTC will be placed by using a thermal probe.
3) Read the NTC resistance at that temperature in the NTC datasheet, that is R_NTC.
4) Use the following formula to determine the upper leg resistor (R_Setpoint):
R _ Setpoint = 2.3 ´ R _ NTC
(1)
The system will restore normal operation after approximately five minutes or if the receiver is removed. If the
feature is not used, this pin must be pulled high.
NOTE
Pin 2 must always be terminated, else erratic behavior may result.
3V3_VCC
Optional
Temperature
Sensor
R_Setpoint
2 T_SENSE
AGND
AGND
Figure 4. Negative Temperature Coefficient (NTC) Application
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