Reference design of a true wireless headset charging box with ultra-low standby power consumption
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Wireless headphones have been popular in the market for more than 10 years, and the trend of replacing wired headphones is very obvious. However, most traditional wireless headphones only separate the headphones from the adapter device (such as mobile phones, computers, etc.). However, cables are still needed to connect the two earplugs to achieve signal consistency and reduce design costs. This greatly reduces the user's comfort and sharply reduces the appearance of the headphones! Especially for headphones used for leisure and sports, this design also increases the risk of personal injury caused by cable entanglement to a certain extent.
In recent years, with the advancement of technology and the maturity of Bluetooth wireless solutions, true wireless headphones as shown in Figure 1 have begun to emerge on the market, that is, two earplugs no longer need a cable to connect, and there is a trend of replacing traditional cable-type wireless headphones. This greatly improves the ornamental and portability of wireless headphones.
Figure 1. True wireless headset products
Due to the extremely small size of true wireless headphones, only very small lithium-ion batteries can be placed inside the headphones, and the capacity of such batteries is often less than 50mA·H. In addition, the strict size requirements make it impossible to integrate the traditional micro-USB charging interface inside the wireless headphones. Instead, two simple metal sheets are used as the input interface for charging the headphones. Due to the limitation of the battery capacity of the headphones, manufacturers generally provide a dedicated charging box as standard to extend the use time of the headphones. Due to the size limitation, the capacity of the charging box is generally less than 1000mA·H, which can support charging two 50mA·H wireless headphones for more than 5 times.
Figure 2. TIDA-050007 system block diagram
TIDA-050007 is a reference design developed specifically for this application. Figure 2 shows the system block diagram of the TIDA-050007 reference design. The reference design provides a complete power solution from the charging box to the earphones. TIDA-050007 includes two innovative designs to extend the use time of the charging box while reducing the PCB board size of the charging box and earphones.
First of all, the overall standby power consumption is only 18A (always enabled), which is lower than the static power consumption of almost all single chips on the market (such as charging chips, boost chips, LDO). This is due to the fact that this reference design uses TI's industry-leading ultra-low power MSP430 MCU (<1A static current), charging chip BQ25100A (75nA static current), boost chip TPS61099 (800nA static current) and LDO TPS7A05 (1A static current). Such low standby power consumption can make the static consumption of the charging box less than 1.6% of the battery capacity per month (taking 800mA·H battery capacity as an example). Most charging boxes on the market have a static consumption of more than 10%. If this type of charging box is not used or forgotten for half a year, the internal lithium battery is basically permanently damaged. The charging box based on the TIDA-050007 reference design can effectively protect the battery because this static loss is even lower than the self-discharge loss of some lithium batteries.
The second innovation lies in the boost chip TPS61099 . TPS61099 is a synchronous boost chip with an ultra-low quiescent current of 0.8A. The current limit value of TPS61099 is designed to be 1A, and it uses a 6-ball WCSP package of 1.23mm×0.88mm, making it very suitable for this charging box application. In addition, TPS61099 has a programmable voltage feedback pin and supports entering the pass-through mode when the input voltage is higher than the output voltage. This pass-through mode can make the charging efficiency as high as 90% or more when the charging box is fully charged. In addition, this reference design also adjusts the FB pin voltage by detecting the battery voltage of the earbuds, so that the charging voltage is adjusted according to the changes in the battery voltage of the earbuds. Compared with the conventional 5-V fixed voltage output OTG boost solution, this reference design can improve the overall charging efficiency by more than 15%. At the same time, the internal charging chip of the earbuds uses the high-precision BQ25100A , which supports 1mA charging current accuracy.
Figure 3 is a photo of the PCB of TIDA-050007 , and Figure 4 is the test result of the voltage tracking function (test condition: charging box voltage 4.2V). It can be seen that when the input voltage (charging box battery voltage) is higher than the output voltage (earphone battery voltage), the boost chip works in the pass-through mode. When the input voltage cannot maintain the designed charging current, the boost chip will start to enter the boost mode to meet the charging current requirements. This greatly improves the charging efficiency and reduces heat loss.
Figure 3. TIDA-050007 PCB Figure 4. TIDA-050007 voltage tracking diagram
The static charging test of TIDA-050007 shows that compared with the traditional 5V fixed output voltage charging solution, the charging energy consumption of TIDA-050007 is reduced from 3.35W·H to 2.73W·H (test conditions: the charging box battery voltage is fixed at 4.2V, and the 600mA·H lithium-ion battery is charged from 3V to 4.2V). Even within the entire battery voltage range (3.3V to 4.2V), the reference design still has an overall efficiency improvement of more than 15%. For detailed test results, please refer to the TIDA-050007 user manual [1] .
In summary, TIDA-050007 greatly extends the charging times of the charging box and is extremely suitable for portable audio/medical devices. Don't hesitate, download the design document now and start designing your own charging box
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