Redmi Buds 4 continues the design language of Redmi AirDots 3 Pro in appearance. The charging case adopts a vertical oval shape, and the earbuds are bean-shaped in-ear designs. In terms of functional configuration, it is equipped with a 10mm dynamic driver, which is customized and adjusted by the Xiaomi acoustic laboratory. It supports three levels of adaptive 35dB intelligent active noise cancellation/dual transparency mode, supports dual-mic AI call noise cancellation, and has a comprehensive battery life of 30 hours.
We have also teardown Xiaomi’s products before including: Xiaomi Buds 3 Pro, Xiaomi FlipBuds Pro, Xiaomi Air 2 Pro, Xiaomi Air 2 SE, Xiaomi Air 2S, Xiaomi Air 2, Redmi AirDots 3 Pro, Redmi AirDots 3, Redmi AirDots 2, Redmi AirDots and Xiaomi Xiaoai Play speaker etc. Let’s take a look at the internal structure of this product.
$26 – Redmi Buds 4 Review
01/ Redmi Buds 4 charging case teardown
Enter the earbuds section below to see the internal structure configuration information.
Pry open the charging case cockpit, fix the battery and the main board at the bottom of the cavity, and connect to the small board at the bottom of the cockpit to charge the earbud through the cable.
The small plate at the bottom of the cockpit that charges the earbud is fastened with screws.
The circuit on the side of the small board that charges the earbud.
On the other side of the small board, solder the Hall element and protect the TVS tube.
The ZIF connector used to connect the motherboard cable, as far as we know, comes from Yaqi Electronics, model OK-F501-10325.
Pogo Pin connector for charging earbud.
The hall element of silk screen 4002N is used to sense the magnetic field change of the charging case switch cover and realize the function of opening the cover.
The bottom structure of the cockpit is equipped with four magnets to attract the charging case cover and earbuds.
Take out the frame that holds the battery and the motherboard in the cavity.
The main board on the frame is fixed by screws, and the battery wires are welded on the main board.
Remove the motherboard and battery from the frame.
The overall structure of the frame.
The charging case has a built-in rechargeable lithium-ion battery Model: BW60, rated capacity: 620mAh/2.294Wh, nominal voltage: 3.7V, charging limit voltage: 4.2V.
The other side of the battery shows BIS India certification.
QR code information is silk-screened on the cell.
The circuit on one side of the charging case motherboard.
The circuit on the other side of the charging case motherboard.
Thermistor used to detect battery temperature.
SinhMicro SS881A POWER MCU is an AD type Flash MCU with integrated charge and discharge management. Power management unit and charging management unit are integrated to provide full software real-time configurable charging voltage and current settings.
The SS881X series is one of the products of the SinhMicro POWR MCU series, with rich interface functions and flexible configuration modes. Different low power consumption options are supported, suitable for portable electronic products that require battery charging and intelligent control, and the charging voltage and current of the battery can be flexibly configured through software. At the same time, it also has built-in perfect protection functions, and the chip itself has passed the IEC62368 certification. Using SinhMicro’s microcontroller can bring a streamlined peripheral, excellent performance and flexible and convenient development to TWS earbuds.
As far as we know, many models including Xiaomi, OPPO, 1MORE, Edifier, Redmi, ZMI, realme, FIIL, Anker, Lenovo, Nubia, Razer, HTC, Soundcore, JBL, UGREEN, Honor and other brands TWS headset charging cases have adopted SinhMicro’s solutions in large numbers.
The LPS LP5305 overvoltage and overcurrent protection IC is used to protect low voltage systems from abnormally high input voltages. During operation, the IC continuously checks the input voltage, input current and battery voltage. When the protection state occurs, the power MOS will be turned off at the same time.
The LP5305 is a safety device that ensures accident prevention. If the input voltage exceeds the OVP threshold voltage level, the power MOS will turn off within 1μs. The current limit is adjustable with an external resistor between ISET and GND. And the current is also limited to prevent the battery from charging too much current. The LP5305 also monitors the Li-Ion battery voltage, when the battery voltage exceeds 4.35V, the IC will turn off the MOS. Additional features include overtemperature protection and undervoltage lockout (UVLO). The LP5305 is available in a space saving DFN-8 package.
As far as we know, audio products of Xiaomi, Honor, OPPO, Huawei, Redmi, realme, Lenovo, Sony, Nokia, Motorola, Edifier, Soundcore, 1MORE, QCY, UGREEN, Razer and many other brands have adopted LPS power management chip.
Screen-printed 23P TVS for input overvoltage protection.
Type-C charging interface female socket, engraving information “L24134”.
Bluetooth pairing function button.
The ZIF connector used to connect to the earbud charging board, also from Yaqi Electronics, model OK-118RF010/2-35.
The LPS LP6261 ultra-low static current synchronous boost converter is used to boost the built-in battery in the charging case to charge the earbud.
The LP6261 has a TRUE shutdown function, which can disconnect the input and output under shutdown and output short-circuit conditions, and the 1.2MHZ switching frequency can use small volume inductors and capacitors. The switch pin adopts a high-voltage 9V process, which can effectively absorb the high-voltage peak of the production capacity when the earphone is unplugged and plugged. At the same time, LP6261 has no whistling sound in the range of full load capacity (especially light load).
The LP6261 consumes only 1UA of quiescent current under light load conditions. Up to 75% efficiency can be achieved at 20uA load, and 93% conversion efficiency from 3.3V to 5V at 200mA load.
Cooperate with the boost chip to be the power inductor of the earbud chip.
XYsemi XB5152I2SZ single-cell lithium battery protection IC is used for battery overcharge, overdischarge and overcurrent protection.
02/ Redmi Buds 4 earbuds teardown
Go to the earbuds teardown section. The main board is fixed in the back cover of the headset stem.
The main board unit is fixed by a large amount of glue on the inside of the cover.
The FPC cable in the cavity is connected to the motherboard through the BTB connector.
Take out the main board and cover the structure on the inside of the cover. Fixed with touch detection and bluetooth antenna patch, exposed copper is connected to the motherboard.
The acoustic structure of the noise cancellation microphone for calls is set up with a foam pad to seal it to improve the radio performance.
Call microphone pickup hole, anti-wind noise design, improve the call effect.
Open the inner cable of the cavity, and set the soft pack battery in the cavity.
Take out the battery, the internal structure of the cavity. Covered with magnetic shielding stickers.
Inside of black magnetic shielding sticker.
Speaker structure inside the cavity.
Take out the cable inside the cavity and the connected components, and a feedback noise cancellation microphone is fixed on the speaker.
The side of the wiring circuit.
The other side of the wiring circuit.
The BTB connector male socket connecting the end of the cable to the motherboard, model OK-118RM010/2-35, from Yaqi.
The back of the Redmi Buds 4 earbud speaker.
The front of the earbud speaker is provided with a metal cover, and the feedback noise cancellation microphone is fixed in the middle.
After actual measurement, the speaker size is 10mm.
The MEMS noise cancellation microphone of SCB31 is used to pick up the ambient noise inside the ear canal.
Optical in-ear detection sensor Ambient light filtering structure while protecting the sensor inside.
Optical in-ear detection sensor, used to automatically pause when the earbud is removed, and automatically resume playback when worn.
The metal copper column that charges the earbud, and the bottom is provided with a rubber pad cushioning seal.
The headset has a built-in rechargeable lithium-ion soft pack battery Model: 441012, rated capacity: 40mAh/0.148Wh, nominal voltage: 3.7V, charging limit voltage: 4.2V.
The factory QR code is silk-screened on the battery core.
The circuit on one side of the earbud motherboard, and the microphone is equipped with an acoustic rubber cover seal to improve the radio performance.
The circuit on the other side of the earbud motherboard.
Remove the microphone rubber cover.
Laser carving SG01’s MEMS call pickup microphone.
Metal dome that connects to the bluetooth antenna.
The feedforward noise cancellation microphone of the laser carving SCB31 on the other end of the motherboard is used for the noise cancellation function to pick up the external environmental noise.
Two Pogo Pin connectors.
TI TPS7A0315 nanopower LDO with fast transient response, input voltage 6V, output voltage 1.5V.
Screen printing 318P touch detection IC.
LPS LP4070E is a 300mA linear charging chip, which adopts DFN1*1 ultra-small package and supports low-current charging. At the same time, the bottom of the chip has a heat sink, which can more effectively reduce the operating temperature of the chip. The leakage current of the battery terminal is lower than 1uA, which effectively reduces the consumption of the battery, and is very suitable for wearable products such as earbuds that require very high size.
Lithium battery protection IC.
BES BES2500IH bluetooth Audio SoC. Single-chip integrated RF, PMU, bluetooth and dual-core star-mc1 cpu, built-in 2MB/4MB Nor flash. Support dual-mode Bluetooth 5.2, voice interaction and adaptive hybrid noise cancellation. The built-in temperature sensor is a cost-effective bluetooth master control solution launched by BES.
As far as we know, the audio products of Huawei, Xiaomi, Samsung, OPPO, Honor, Soundcore, UGREEN, ZTE, Nokia, JBL, 1MORE, Baidu, OnePlus and many other brands have adopted the BES bluetooth audio solution.
The periphery of the main control chip is equipped with three power inductors, which are the Scientic SDHC1608F4R7M magnetically shielded precision winding inductors, which are one of the SDHC1608 series. Low DCR, improve efficiency and prolong standby time, the top is high-density magnetic powder, which has higher permeability than traditional precision wound inductors. Both sides are also magnetic shielding structures to optimize spatial interference to surrounding devices.
The entire SDHC series has a very high cost performance, better magnetic shielding effect, and DCR is superior to traditional precision wire wound inductors.
As far as we know, Scientic responds to three models and dozens of high-quality inductor products launched in the TWS headset market. At present, TWS earbuds of Redmi, QCY, HAYLOU, OnePlus, Soundcore, MONSTER and other brands have adopted Scientific full magnetic shielding precision winding inductors.
The crystal oscillator that provides the clock for the bluetooth chip.
BTB connector female for connecting flat cable, model OK-118RM010/2-35, from Archi Electronics.
All components of Redmi Buds 4 true wireless noise cancellation earbuds.
The Redmi Buds 4 charging case is small and round in size, and the vertical oval design can be easily opened and closed with one hand. The earbuds use a combination of two processes of smooth glossy surface and matte texture, which improves the texture of the product to a certain extent. The lightweight bean-shaped in-ear design with three soft silicone eartips in different sizes provides a comfortable fit.
In terms of internal structure and configuration, the internal circuit of the charging case consists of a battery, a main board and a small board for charging the earbud. The charging case has a built-in VDL 620mAh high-capacity battery and is equipped with XySemi XB515212SZR single-cell lithium battery protection IC. The SinhMicro SS881A POWER MCU is used on the motherboard to be responsible for power management and charging management, and supports full software real-time configurable charging voltage and current settings. The LPS LP6261 ultra-low static current synchronous boost converter boosts the built-in battery to charge the earbud. LPS LP5305 overvoltage and overcurrent protection IC, etc.
The earbud uses a 10mm dynamic driver, a 40mAh soft pack battery, optical in-ear detection and touch detection sensors, and three MEMS microphones for calls and noise cancellation. The motherboard adopts BES BES2500IH bluetooth audio SoC, which supports dual-mode Bluetooth 5.2, voice interaction and adaptive hybrid noise cancellation. The periphery is equipped with three Scientic SDHC1608F4R7M magnetically shielded precision wire wound inductors to achieve longer standby battery life. It adopts LPS LP4070E linear charging chip, TI TPS7A0315 nano-power LDO, etc.