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

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),

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.