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TVS Solution for Storage2020/07/08

With the development of storage devices, the requirements of storage application have been gradually evolved from SATA 3.0 into PCIe 4.0 (Gen4x4) U.2 SSD. As having the biggest advantage of increasing storage speed and efficiency, END customers can replace PCIe 4.0 Gen4x4 with throughput of 7.88 GB/s to improve the application demands in the 5G market. For server storage devices, PCIe 4.0 (Gen4x4) U.2 enterprise-class SSD has been adopted by providing the servers with higher data transmission speed and faster storage efficiency to reduce search time.

At present, the selection of PCIe 4.0 (Gen4x4) U.2 SSD for servers also comes with a much higher price. When upgrading the server system to PCle 4.0 (Gen4x4) U.2 SSD, it is required to perform hot swapping for replacing the storage device. In this case, the PCIe 4.0 (Gen4x4) U.2 SSD will be affected by the impact of ESD/EOS as a matter of course, which may lead to the abnormal operation of system, or even result in damage to the SSD to cause the loss of data stored in the server.

Requirements for the protection components used in SSD
A protection component such as TVS diodes used in SSD has to meet all three of the following requirements:
  • The package size of TVS diode should be carefully considered (it is recommended to install a TVS diode with size less than 2.0 mm x 2.0 mm) to avoid the protection component placement issues on the PCB of storage device.
  • When configuring TVS diode on the high-speed signal of PCle 4.0 (Gen4x4) U.2 SSD, it is very important to note that the parasitic capacitance of such protection component should be as lower as possible (ESD protection component of < 0.2pF is recommended). Otherwise, it will slow down the transmission rate while performing data transmission.
  • The last and the most important one is to limit the clamping voltage provided by the protection component during an ESD event to as lower as possible to prevent any possibility of damage inside the chip.
It is essential to meet all above three requirements, and without all three, the SSD is unable to be protected thoroughly. However, it is a difficult challenge to design the TVS diode that meets all three requirements.
The AZ5B8S-01F series adopt the package structure of DFN0603. It can be your best option for ESD/EOS protection to fit into limited and insufficient space on a PCB.
The most important thing is that the AZ5B8S-01F has extremely low ESD clamping voltage, which can effectively prevent transmission from ESD disturbance. It enables the electronic system connected to the SSD to enhance the chance of passing the Criteria A of IEC 61000-4-2, the ESD standard for system level testing. The clamping voltage provided by TLP (as shown in Figure 1) is observed after measuring the AZ5B8S-01F using TLP (transmission-line pulse).

Under the ESD impact of 8kV contact testing in the IEC 61000-4-2 standard (TLP current equivalent to 16A), the ESD clamping voltage is only 5.5V, which will effectively prevent data error, system crash, or even damage to storage system during ESD testing.
TVS Solution for Storage
Figure 1: TLP clamping voltage measurement curve of AZ5B8S-01F

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