The eMMC chip is an embedded multimedia card (Embedded MultiMediaCard) chip that integrates a flash memory and a controller. It is mainly used in mobile devices, such as mobile phones and tablet computers, and can be used to store operating systems, applications, data and images, etc. Whether the eMMC chip supports a specific function depends on the specifications and design of the controller and flash memory chip.
Table of Contents
- What is eMMC?
- How does eMMC work?
- Main features of eMMC chip
- Where is eMMC used?
- Pins of eMMC chip
- PCB design of eMMC chip
- Design for manufacturability of eMMC Chips
What is eMMC?
eMMC, or embedded MultiMediaCard, is a type of flash storage integrated directly onto a device’s motherboard. It’s used to store data such as the operating system, applications, and user files.
eMMC provides a compact, cost-effective solution for device storage, combining the memory controller and NAND flash memory into a single package. This integration allows for quicker access to data and reduces physical space requirements compared to separate storage components.
You’ll find eMMC in a range of devices, from smartphones and tablets to budget laptops and consumer electronics. Its advantages include simplicity, affordability, and adequate performance for many everyday tasks. However, for higher performance needs, such as in high-end laptops or gaming systems, SSDs or other storage technologies are often preferred.
How does eMMC work?
eMMC, or embedded MultiMediaCard, operates as a storage solution by combining NAND flash memory with a memory controller in a single chip.
Data Storage: eMMC uses NAND flash memory to store data. This memory is organized into blocks and pages, where data is written and read. Unlike traditional hard drives, NAND flash is solid-state and does not have moving parts, making it more reliable and faster.
Memory Controller: The built-in memory controller manages read and write operations between the NAND flash and the device. It handles tasks such as wear leveling (to ensure even usage of memory cells), error correction, and data management to maintain performance and data integrity.
Integration: eMMC integrates both the NAND flash memory and the controller into a single package. This compact design reduces the physical space needed on a device’s motherboard and simplifies the design process.
Data Transfer: When you save or access data, the controller coordinates the data flow between the device’s processor and the eMMC memory. It ensures that data is written to and read from the correct locations efficiently.
Main features of eMMC chip
Highly integrated
The eMMC chip integrates a controller for managing the flash memory chip, which simplifies the product design process and accelerates product introduction.
Unified interface
eMMC adopts the MMC standard interface, which can be matched with a variety of storage devices, including NAND storage devices and MMC devices.
Larger capacity
The common capacity of eMMC is 2~256GB, which can meet the user’s demand for large-capacity storage.
High speed transmission
eMMC chips support higher data transfer rates, up to 400MB/s or higher, depending on their version and specification.
Strong compatibility
eMMC chips are compatible with a variety of mobile devices and computer systems, including Windows, Mac, Android, and more.
Where is eMMC used?
eMMC (embedded MultiMediaCard) is used in a variety of electronic devices as a compact, integrated storage solution.
Smartphones and Tablets: eMMC serves as the primary storage for operating systems, apps, and user data due to its balance of performance, capacity, and cost.
Consumer Electronics: It’s found in devices like digital cameras, GPS units, and portable media players, providing reliable and efficient storage in a small footprint.
Laptops and Netbooks: eMMC is used in budget-friendly laptops and netbooks as a cost-effective alternative to traditional hard drives or SSDs, offering adequate performance for everyday tasks.
IoT Devices: In Internet of Things (IoT) devices, eMMC provides onboard storage for firmware and data logging, thanks to its compact size and durability.
Automotive Systems: eMMC is used in infotainment systems and advanced driver-assistance systems (ADAS) for storing maps, media, and system software.
Pins of eMMC chip
The eMMC chip is a solid-state flash memory card, and its pin definition is slightly different from that of a general SIM card or SD card. Therefore, when using it, it needs to be modified appropriately according to the specific hardware device and chip specifications. At the same time, due to the wide application of eMMC chips in mobile devices, understanding their pin definitions and working principles is also helpful for better data communication and operation. Taking KLM8G1GETF as an example, briefly introduce its pins:
VCC/VCCQ
VCC is the pin that supplies power to the flash memory power supply, generally 3.3V; VCCQ is the pin that supplies power to the memory controller.
CLK
Clock input pin, sent by the main processor, enters the eMMC chip.
DATA Strobe
Data strobe pin, the strobe signal sent by eMMC to the main processor, in HS400 mode, read data and CRC response are synchronized with data strobe.
DATA0-DATA7
Data bus, bidirectional data transmission mode “pull-up”, eMMC defaults to 1-bit mode, and 4-bit or 8-bit can also be used.
RSTN
The reset pin is active at a low level, so generally a resistor will be pulled on the pin, and the default high level will not be reset.
CMD
Bi-directional signal for device initialization and command transmission, commands operate in two modes, open drain for initialization and push-pull for fast command transmission.
PCB design of eMMC chip
The PCB design of the eMMC chip needs to take into account many aspects, including power supply and interface, layout and routing, protection, heat dissipation, testing and debugging, etc., to ensure the performance and reliability of the eMMC and meet the requirements of the device.
Power and ground
Make sure stable power and ground lines for the eMMC chip. The power line should be wide enough to withstand the chip’s power consumption requirements, and the length and impedance of the power line should be minimized.
Signal line length matching
The length of the signal line of the eMMC chip should match as much as possible to reduce the delay and distortion of signal transmission, and differential pairs can be used to improve the anti-interference ability of the signal.
Signal line routing
Try to avoid signal lines crossing with high-power lines or high-frequency lines to reduce interference. You can use ground planes and power planes to isolate signal lines.
Capacitance and inductance
Add appropriate capacitors and inductors to the power and ground of the eMMC chip to provide stable power and ground. The selection of capacitors and inductors should be in line with the chip manufacturer’s recommendations.
PCB layout
Place the eMMC chip far away from other high-power or high-frequency components to reduce interference, and at the same time minimize the length of the signal line to improve signal stability.
Pin distance outlet method
Because the pin spacing of the eMMC device is relatively small, if the pins inside cannot go out, the following methods can be adopted:
① When the conventional wiring cannot be routed, the tight wiring can be adopted, that is, the minimum line width is used between the pad and the pad;
② If the wiring cannot be traced according to the minimum line width, you can also modify the pad and change the pad to an ellipse to meet the spacing of the minimum line width;
③ When it is really impossible to route the wires, it is possible to drill blind holes on the pads and change the layer routing.
Design for manufacturability of eMMC Chips
Line width and spacing
The minimum line width and line spacing is generally 3mil, and the design of the minimum line width and line spacing needs to meet the process requirements. If the minimum line width and line spacing exceeds the manufacturing capacity, the PCB board cannot be produced, or the produced board has a low yield rate and a very high cost.
Pad size
The size of the pad affects the welding quality. The pad is too small or even unsolderable. The minimum pad is generally 0.2mm. The production of a pad smaller than 0.2mm may cause the pad to be etched and the board will be scrapped.
Plate hole
The hole in the board refers to the hole on the SMT patch pad. The hole in the board generally needs resin plugging, and copper is plated on the hole to meet the welding requirements. If the hole in the board does not have a resin plug hole, the small welding area will lead to poor welding.
