How to Reset or Re-Start True Wireless Stereo Devices

A Simple Solution Using a Low-Cost Voltage Detector

True Wireless Stereo (TWS) Earbuds and Headphones are sometimes susceptible to system freezes.  For other wireless devices such as mobile phones and smart watches there is often a button which will allow you to easily reset or re-start the device.  However, due to the size constraints often associated with TWS devices a button to action this process is not always available and if buttons are present, they are often dedicated to the normal control functions of the TWS device.


Sometimes the microprocessor inside the TWS device will have an internal reset function but in the event of a system ‘freeze’ the microprocessor may not function properly to activate a system reset.


Circuit and Explanation

For cases as described above, where no reset button is available, we would like to recommend the following circuit using our XC6135 ultra-low power voltage detector.  In the example shown here an active high variant of the XC6135 is applied. It interacts with the charging cradle to overcome system freeze issues. 

To explain the operation, let’s assume that at the beginning the cradle is not plugged in and that the voltage shown in the figure above as “From Cradle” is low.

1. The TWS device is entered into the charging cradle.

2. The supply line marked “From Cradle” is now connected to input pin VSEN of the XC6135.

3. The lid of the cradle is closed and/or the cradle is plugged in.

4. The voltage on the supply line marked “From Cradle” rises suddenly to a certain DC voltage value. This can for example be 5.0 V. 

5. The VSEN pin monitors the cradle voltage and when it reaches the release voltage level of the XC6135 voltage detector the logic output signal switches from high to low.

6. This low signal is used to reset the microprocessor.

7. Later the TWS is removed from the cradle.

8. The voltage on pin VSEN drops suddenly. When the voltage has dropped below the detect voltage value the logic output switches from low to high.

9. The SoC starts up again and can reconnect with the smartphone or other device used together with the TWS.

Using this circuit, the microprocessor inside the TWS will be automatically reset each time it is placed back into its charging cradle, regardless if the system was in a frozen state or not,  and so removing the need for the device to detect a ‘freeze’ state.

XC6135 Summary

Ultra-Low Power (44nA) Voltage Detector with Separated Sense Pin
The XC6135 series is an ultra-low power voltage detector that can detect voltages down-to 0.5 V. This makes it ideal for monitoring 0.7 V and 0.8 V rails, which are the core voltages SoC made in 16 nm and 28 nm processes.

The operating voltage is from 1.1 V to 6.0 V.  With a quiescent current of only 44 nA, the XC6135 can contribute to extending the operating lifetime of battery-powered equipment, such as IoT devices, wearable devices and smart meters.

The series has a separate sense pin function which, when combined with an external voltage divider, allows it to detect a high withstand voltage.

Both CMOS and open-drain variants are available as well as both active low & active high output-logic options.  The XC6135 is available in SOT-25 and SSOT-24 packages as well as in an ultra-compact (1.0 mm x 1.0 mm x 0.33 mm) USPQ-4B05 package.




Samples of the XC6135 series mentioned above are readily available, so please ask your local Torex representative for details or contact us directly via our website.