Highly integrated smart Bluetooth headset power circuit (with circuit reference diagram)

The power management design of the Bluetooth headset requires few peripheral components and high integration, and also meets the requirements of the Bluetooth chip for load response and noise suppression. Wireless stereo headphones have become popular products. As more and more mobile phones support Bluetooth, Bluetooth headsets have become an indispensable option for mobile phones. At the same time, with the introduction of stereo Bluetooth headsets that support MP3 playback, Bluetooth headsets have been able to connect to Bluetooth mobile phones and music players at the same time.

The core of the Bluetooth headset is the radio frequency and baseband processing. In order to adapt to the integration of functions and the miniaturization of the design, companies such as CSR and Broadcom have integrated the radio frequency and baseband processing functions, such as CSR BlueCore4 highly integrated Bluetooth chip, the smallest package 6 & TImes; 6mm. The power management design of the entire headset requires fewer peripheral components and a high degree of integration, while meeting the Bluetooth chip's requirements for load response and noise suppression.

Figure 1: TC1303 application circuit on Bluetooth headset.

Bluetooth earphones are mostly powered by lithium batteries, with a voltage range of 2.7V to 4.2V. The battery capacity is 90mAH to 170mAH. In order to meet the needs of longer calls and music playback, the battery capacity has gradually increased. In addition, Bluetooth chips based on ARM or DSP cores require two sets of power supplies (such as 1.8V and 2.7V) to power the core and I / O, respectively. At the same time, the microphone also requires a "clean" bias voltage.

Based on the above system power requirements, Microchip has launched a highly integrated, small size power management solution, including TC1303 and MCP73855. Among them, TC1303 is a highly integrated power conversion chip, MCP73855 is a highly integrated linear lithium battery charging chip. TC1303 integrates a 500mA synchronous buck converter and a 300mA low-dropout LDO in a 3 & TImes; 3mm 10-pin DFN package, and has a voltage-good indicator pin (Power-Good). Its standard fixed voltage output combination, such as 1.8V / 2.7V, just meets the power requirements of BlueCore2. Figure 1 shows the application circuit of TC1303 on the Bluetooth headset.

The 500mA synchronous DC / DC converter in the figure integrates P-channel and N-channel MOSFETs, with a switching frequency of 2MHz, and the conversion efficiency reaches more than 92%. High switching frequency and PWM / PFM automatic switching technology enable engineers to choose surface-mount inductors and ceramic capacitors as low as 2.2μH, which can meet the ripple requirements of filtering and Bluetooth chips. The integrated LDO in the TC1303 can provide an output current of 300mA with a voltage difference of only 137mV. In order to further reduce the impact of DC / DC switching noise on the circuit design, the LDO power ground pin and the DC / DC power ground pin are separated during chip design to ensure that the LDO output can be provided to the I / O part and the microphone. Clean "voltage.

Figure 2: The application circuit of MCP73855 in the design of Bluetooth headset.

The voltage normal indication pin provided by the TC1303 can be connected to the I / O of the Bluetooth chip to monitor the status of the power supply voltage. The normal voltage indication pin can detect the DC / DC output voltage (TC1303A) or the LDO output voltage (TC1303B), and can even detect these two outputs separately to achieve sequential power-on to meet the power supply requirements of different Bluetooth chips. MCP73855 can provide lithium battery charge management function. The on-chip integrated MOSFET, current detection resistor and reverse blocking diode can provide a maximum charge current of 400mA, and the required charge current can be set through an external resistor or directly from the I / O output. . MCP73855 can automatically complete the pre-charging, constant current and constant voltage charging control of the lithium battery, and output the charging status to the LED or Bluetooth chip. With the appropriate peripheral circuit, the charging status indicator pin can drive the two-color LED to realize the separate display of the charging process and the end of charging. Figure 2 shows the application circuit of MCP73855 in the design of Bluetooth headset.

The small size package (3 & TImes; 3mm) and simple peripheral circuits of TC1303 and MCP73855 constitute a low-cost, high-performance, highly integrated Bluetooth headset power management solution, which can also be applied to the latest stereo Bluetooth headset design for MP3 playback . Engineers can use it and the Bluetooth chip to design a more comfortable, stylish, and easy-to-use, lightweight Bluetooth stereo headset, allowing users to enjoy music while moving, and never miss a call.