Xiaomi Buds 4 is Xiaomi’s first semi-in-ear headset that supports active noise cancelling, and supports adaptive noise cancelling function – it can adjust the noise cancelling depth in real time by identifying the ear canal structure, wearing style and surrounding environmental noise – thereby balancing ear pressure and providing a comfortable noise cancelling experience. Supports 3Mic+AI call noise cancelling, which can effectively filter out most scene noise and provide clear calls. It supports AI anti-wind noise algorithm and has a unique T-shaped air duct structure design, so you can get clear voice even in windy environments.

Xiaomi Buds 4 is equipped with a custom-made graphene dual-magnetic sound driver unit – the treble is naturally bright and the bass is surging. It supports LHDC5.0 ultra-clear transmission protocol, bringing high-definition audio and ultra-low distortion, and has passed the Hi-Res Audio Wireless Gold Label certification. Supports dynamic head tracking spatial audio function, bringing immersive audio effects. Supports dynamic adaptive EQ compensation to improve sound leakage problems.

Also, the earbuds have a single battery life of up to 6 hours and a total battery life of up to 30 hours. Supports dual-device connection and fast charging – 10 minutes of charging allows you to listen to music for 2.5 hours.

We have also teardown the Xiaomi products before, including: Xiaomi Buds 3, Xiaomi Buds 3 Pro, Redmi Buds 5 Pro, Redmi Buds 4 Pro, Redmi Buds 4, Xiaomi Sound, Xiaomi Sound Move, Xiaomi Watch S1, Redmi Watch 3, Xiaomi Band 8 Pro, Xiaomi Band 7, Redmi Brand 2 and more.

01/ Xiaomi Buds 4 Charging Case Teardown

Disassemble the charging case shell and take out the charging bin structure. There is an FPC for charging the earbuds inside the charging bin, which is fixed by a metal pressure plate. There are also magnets to hold the earbuds in place.

The internal structure of the cavity, with all components fixed on the internal white bracket.

Take out the bracket inside the cavity. There is a black indicator light hood at the bottom of the headphone cavity.

The bottom structure of the white bracket fixes the motherboard with screws.

There is a battery inside the bracket, which plays a very good protective role.

Remove the FPC on the back of the charging bin, and take out the motherboard and battery from the bracket.

FPC circuit for charging the earbuds.

Pogo Pin connector on the FPC to connect the earbuds.

The Hall element with “AR3n7” silk-printed on the end of the FPC is used to sense the magnetic field changes when the charging case cover is opened/closed, and then notify the charging case MCU and earbuds to pair or disconnect from the connected device.

The circuit on one side of the earbud motherboard.

The circuit on the other side of the earbud motherboard.

The motherboard connects to the FPC connector.

TPS SY8809 bluetooth headset charging case solution integrates charging module and discharge module inside the chip. The charging module adopts NVDC architecture, and the battery charging current can be adjusted by I2C. The discharge module output voltage I2C can be adjusted. Integrating two output current-limiting switches provides independent load presence detection and load insertion detection, and supports output current detection. The chip integrates NTC protection function to charge and discharge the battery more safely.

SY8809 integrates a standard I2C interface and interrupt signal to facilitate communication between the chip and MCU and control the charging/discharging function. SY8809 integrates a communication port, which can realize high-speed communication from the MCU to the headset. It is very suitable for the design of bluetooth headset charging case – the high integration greatly simplifies the peripheral circuits and components, providing an easy-to-use solution for charging case applications. The package format used by SY8809 is QFN4x4-24.

3.3μH power inductor works with the power management chip.

Three LED indicators of different colors are used to feedback charging and bluetooth pairing status.

Silk screen GD IC.

The silk screen CC2538 BP08899 MCU is responsible for the overall control of the charging case.

Silk screen H24 004 TVS protection tube for input overvoltage protection.

XySemi XB5152J2SZ integrated lithium battery protection IC. The XB5152 ZR series of products is a highly integrated solution for lithium-ion/polymer battery protection, including advanced power MOSFETs, high-precision voltage detection circuits and delay circuits. It adopts ultra-small SOT23-5 package and has only two peripheral devices, making it an ideal solution for limited space in the battery pack.

Prisemi P14C5N overvoltage and overcurrent protection chip. P14C5N supports input overvoltage and undervoltage protection, and overcurrent protection after circuit startup. When the input voltage exceeds the input overvoltage protection threshold, the device turns off the built-in MOSFET to disconnect the input and output.

P14C5N supports up to 30V input voltage and 3A output current. Built-in 55mΩ resistance switch tube, with 50ns ultra-fast overvoltage response time. Supports programmable overcurrent protection, overvoltage protection supports the 4.5-16V range, and can be set using an external voltage divider resistor, or the voltage setting pin is grounded to use a fixed 6.8V overvoltage protection. The chip has built-in overheat protection function and supports control pin control switch.

Function button for bluetooth pairing.

The information on the battery label built into the charging case is that the rechargeable lithium-ion battery, model: BW50, rated capacity: 480mAh/1.824Wh, nominal voltage: 3.8V, charging limit voltage 4.35V, comes from Chongqing VDL Electronics Co., Ltd.

02/ Xiaomi Buds 4 Earbuds Teardown

Remove the earbud stem back cover. There is a bracket printed LDS laser antenna under the cover, and a pickup hole is set on the concave surface in the middle, which forms a “T” shaped air duct structure with the holes on both sides of the shell.

After removing the bracket, the internal PCB structure of the earbud stem is connected to the side pressure sensing sensor FPC through a connector.

Open the connector and take out the PCB board. On the side of the cavity is the pressure sensor structure.

The BTB connector connected to the PCB is from OCN, model: OK-114GM004-35.

The pressure sensor used in the earbud supports single-pinch, double-pinch, triple-pinch three times and long press control.

The circuit on one side of the PCB.

The circuit on the other side of the PCB.

The MEMS microphone of Lasdiao G445 3ZNJ is a feed-forward noise cancelling microphone, used to pick up external environmental noise.

The MEMS microphone of Laser Engraving G491 3ZMF is a call microphone, used for voice call function to pick up vocals.

BTB connector to connect to the pressure sensing sensor FPC, from OCN, model: OK-114GF004-35.

Metal dome for connecting bluetooth antenna.

Disassemble the headphone head and fix the speaker to the bracket in the front cavity.

The back cavity is provided with a cover plate for isolation, and the FPC inside the front cavity is connected to the FPC inside the front cavity through a BTB connector.

Take out all the components inside the back cavity and earbud stem.

The circuit on one side of the earbud motherboard.

The circuit on the other side of the earbud motherboard.

BES BES2600YP bluetooth audio SoC. Bluetooth + noise cancelling + in-ear detection three-in-one single-chip solution supports dual-mode Bluetooth 5.3 and multi-point connections. Internally integrated dual-core ARM STAR-MC1 CPU and ultra-low power Sensor Hub subsystem have powerful application processing capabilities. Supports open adaptive noise cancelling and AI noise cancelling. Supports assistive listening function and spatial audio. Support voice wake-up and interactive functions.

A 24.000MHz crystal oscillator provides the clock for the bluetooth chip.

Silk screen printed IC.

BTB connector to connect the battery FPC, from OCN, model: OK-114GF106-35.

The 6-axis acceleration sensor with silk screen “I426C” comes from TDK and is used to collect the user’s motion data when using the handle.

TPS SY5501 power management PMIC – is a chip specially designed for TWS earbuds, providing a perfect solution for charging and isolated communication. The chip integrates linear charging management, discharge protection, single-line two-way data communication and I2C communication interface to facilitate users to realize headset charge and discharge management and protocol communication.

The maximum charging current of SY5501 is adjustable with an external resistor and supports constant current charging ICC and float charging voltage VFLOAT gear I2C adjustment. The chip integrates NTC detection and protection functions to manage battery charge and discharge more safely. SY5501 has battery discharge protection and shipmode functions, which can meet the low power consumption requirements of the headphone system. The chip integrates private control instructions. The charge bin can send instructions through VIN to control the SY5501 to realize the power on and reset operations of the headphone main control.

Silk screen 18 TVS tube for input overvoltage protection.

The battery FPC board circuit, the main IC is protected by black hard glue, no detailed information can be obtained.

The FPC board is connected to the BTB connector of the speaker FPC inside the front cavity.

The BTB connector that connects the battery FPC to the motherboard is from OCN, model number: OK-114GM016-35.

The earbuds have a built-in steel shell button battery, model: M1040S2, nominal voltage: 3.85V, energy: 0.135Wh, from MIC-POWER.

Take out the internal components of the front cavity. The sound hole and tuning hole at the bottom of the front cavity are protected by fine dust-proof nets.

The structure on one side of the speaker bracket.

The structure on the other side of the speaker bracket has an in-ear detection sensor.

Take out the speaker and FPC, and there is a feed-back noise cancelling microphone inside the bracket.

Take out the microphone and speaker FPC circuit.

The BTB connector that connects the speaker FPC to the battery FPC.

The MEMS microphone of Laser Engraving G446 3ZPA is a feed-back noise cancelling microphone, used to pick up noise from inside the ear canal.

The front of the headphone speaker. According to the official introduction, an ultra-thin graphene diaphragm is used.

The back of the speaker. A dual magnetic driver unit is used internally to provide high dynamic amplitude, reduce distortion, and improve bass effect.

After actual measurement, the speaker size is approximately 11mm.

All components of Xiaomi Buds 4 true wireless noise cancelling earphones.

03/ Summary

The Xiaomi Buds 4 charging case adopts a “pebble” shape design and an open charging bin structure. The earbudsadopt a long-stem semi-in-ear design, with an ergonomically designed body curve that fits the auricle comfortably and securely.

The charging case has a built-in VDL 480mAh lithium battery and adopts the TPS SY8809 bluetooth headset charging bin solution. Integrated charging module and discharging module, integrating two output current limiting switches and NTC protection functions, as well as standard I2C interface and interrupt signal – to facilitate communication between the chip and MCU, and control charging and discharging functions. It also uses Xysemi XB5152J2SZ integrated lithium battery protection IC and Prisemi P14C5N overvoltage and overcurrent protection chip, etc.

The earbud is equipped with an 11mm graphene dual-magnetic sound driver unit, feedforward + feedback + three microphones for calls. Built-in MIC-POWER 0.135Wh steel shell button battery, using TPS SY5501 power management PMIC to be responsible for charging and isolation communication. The main control chip is BES BES2600YP bluetooth audio SoC, which supports bluetooth+ noise cancelling + in-ear detection; supports dual-mode Bluetooth 5.3 and multi-point connection, and has powerful application processing capabilities.

PS: Translated from 52audio

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