BQ500414Q Datasheet, PDF (14/34 Pages) Texas Instruments – Qi Compliant Wireless Power Transmitter Manager

bq500414Q
SLUSBE4B – JANUARY 2014 – REVISED JUNE 2014
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8.3.9 Shut Down via External Thermal Sensor or Trigger
Typical applications of the bq500414Q do not require additional thermal protection. This shutdown feature is
provided for enhanced applications and is not limited to thermal shutdown. The key parameter is the 1.0-V
threshold on pin 2 T_SENSE. Voltage below 1.0-V on pin 2 causes the device to shut down.
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 bq500414Q 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 restores 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 T_SENSE must always be terminated, otherwise erratic behavior may occur.
3V3_VCC
Optional
Temperature
Sensor
R_Setpoint
2 T_SENSE
AGND
AGND
Figure 6. Negative Temperature Coefficient (NTC) Application
14
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