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STHS4257L1 Datasheet(PDF) 5 Page - STMicroelectronics |
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STHS4257L1 Datasheet(HTML) 5 Page - STMicroelectronics |
5 / 18 page Obsolete Product(s) - Obsolete Product(s) STHS4257A, STHS4257A1, STHS4257L, STHS4257L1 Summary description 5/18 1 Summary description The STHS4257 is an IEEE802.3af-compliant family of interface controllers for Power over Ethernet (PoE) Powered Device (PD) applications. The devices consist of two main sections: ● The IEEE802.3af interface to the PoE powered RJ-45 wall socket, and ● the Hot Swap Controller (HSC) functions required to protect the PD during insertion, operation, and withdrawal from the RJ-45 socket. These devices have an integrated high voltage power MOSFET (low-side switch) with low RON and the capability to accept transients as high as 100V. Since the pins (such as GND and VIN) which interface to the RJ-45 socket can routinely see high peak voltages in excess of 100V, it is strongly recommended that board designers protect the PD device with a transient voltage suppressor, such as the SMAJ58A (available from STMicroelectronics), connected between the GND and VIN pins (see Figure 4 on page 8). The IEEE802.3af-compliant interface includes the basic PD detection and Classification functions, whereas the ‘Hot Swap’ functions include other basic features, such as Inrush Current Limiting, Undervoltage Lockout (UVLO), and Thermal Overload Protection. All of the devices include an open drain Power Good (PWRGD) signal to indicate normal steady operation (see Figure 1 on page 6 and Table 2 on page 6). The STHS4257 family also incorporates a 1.5V voltage offset (two series diodes) to accommodate the input diode bridge used to make the PD polarity insensitive. The STHS4257A1/L1 includes a dual level current limit circuit. This allows the STHS4257A1/L1 to interface with legacy Power over Ethernet (LAN) systems while maintaining compatibility with the current IEEE 802.3af specification. Each of the two basic part types, the STHS4257A/L and the STHS4257A1/L1, is available either with Latched Operation (L) Mode or with Automatic Retry (A) Mode after fault conditions. For product options overview see Table 1 on page 1. |
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