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BQ51003: Thermal shutdown

Part Number: BQ51003

Hi

We where trying to derive a thermal shutdown at around 60 degrees C, to that end we used the equations on page 23 of the data sheet https://www.ti.com/lit/ds/symlink/bq51003.pdf, and arrived at the two resistor values (denoted from equation 3) R1 = 1.5 kOhm and R3 = 1.2 kOhm with the beta value of 3380 K.

When testing hower the thermal shutdown happened at around 40 degrees C. So my question is if we are doing something wrong? The NTC we use is this https://product.tdk.com/system/files/dam/doc/product/sensor/ntc/chip-ntc-thermistor/catalog/tpd_commercial_ntc-thermistor_ntcg_en.pdf

With best regards
Christoffer

• Just for clarification it is specifically this one NTCG103JF103FT1 in the data sheet

• Hi Christoffer

I calculated the values using another tool that I have and would recommend R1=2k and R3=open.

0C voltage is 1.32V  (Vcold=1.2914V)

60C voltage is 0.442V  (Vhot=0.4312V)

• Thanks for the quick reply, but from our understanding the thermal shutdown happens when the voltage at the TS-CTRL pin is at 100 mV

• Hi Christoffer

The TS-CTRL pin high temp threshold is 19.6% of 2.2V or .431V.   Cold is 58.7% of 2.2V or 1.29V.

• Hi again

From our understanding those thressholds has nothing to do with when the system shuts down, We have tried (before using the values in the original post) using values such that we get those exact thresshold values. But the system did not shutoff. As per page 24 of the data sheet "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." which from our understanding means that we need to get the voltage down to less than 100 mV before the system shuts down

• Hi

Normal operation will be between 0.44V and 1.32V.

The Voltage at TS is measured with a pulse .  If there is a capacitor on the TS pin it may prevent correct measurement of the voltage

Can you try driving the TS-CTRL pin with a power supply, and confirm that between 0.44V and 1.32V the unit does not operate?