SLUSBC8C December 2013 – July 2018
bq51003 includes a ratiometric external temperature sense function. The temperature sense function has two ratiometric thresholds which represent a hot and cold condition. TI recommends an external temperature sensor to provide safe operating conditions for the receiver product. This pin is best used for monitoring the surface that can be exposed to the end user (that is, place the NTC resistor closest to the user).
Figure 28 allows for any NTC resistor to be used with the given VHOT and VCOLD thresholds.
An example solution is provided:
where the chosen parameters are:
Figure 29 shows the plot of the percent VTSB vs temperature.
Figure 30 illustrates the periodic biasing scheme used for measuring the TS state. The TS_READ signal enables the TS bias voltage for 24 ms. During this period the TS comparators are read (each comparator has a 10-ms deglitch) and appropriate action is taken based on the temperature measurement. After this 24-ms period has elapsed, the TS_READ signal goes low, which causes the TS-Bias pin to become high impedance. During the next 35 ms (priority packet period) or 235 ms (standard packet period), the TS voltage is monitored and compared to 100 mV. If the TS voltage is greater than 100 mV then a secondary device is driving the TS-CTRL pin and a CTRL = ‘1’ is detected.