STHS4257A データシートの表示（PDF） - STMicroelectronics

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STHS4257A

IEEE 802.3af PoE Powered Device (PD) interface controller with integrated signature resistor

STMicroelectronics 

STHS4257A, STHS4257A1, STHS4257L, STHS4257L1

1

Summary description

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

t(s devices include an open drain Power Good (PWRGD) signal to indicate normal steady

c operation (see Figure 1 on page 6 and Table 2 on page 6). The STHS4257 family also

u incorporates a 1.5V voltage offset (two series diodes) to accommodate the input diode

d bridge used to make the PD polarity insensitive.

Pro 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

te maintaining compatibility with the current IEEE 802.3af specification.

ole Each of the two basic part types, the STHS4257A/L and the STHS4257A1/L1, is available

s either with Latched Operation (L) Mode or with Automatic Retry (A) Mode after fault

Obsolete Product(s) - Ob conditions. For product options overview see Table 1 on page 1.

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