LTC4264 datasheet(21/24 Pages) LINER

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LTC4264

4264f

APPLICATIONS INFORMATION

VOUT, to avoid the possibility of leakage shutting down the

LTC4264. If not used, tie SHDN to VIN.

The load capacitor connected between GND and VOUT

of the LTC4264 can store signiﬁcant energy when fully

charged. The design of a PD must ensure that this en-

ergy is not inadvertently dissipated in the LTC4264. The

polarity-protection diodes prevent an accidental short

on the cable from causing damage. However, if the VIN

pin is shorted to GND inside the PD while the capacitor

is charged, current will ﬂow through the parasitic body

diode of the internal MOSFET and may cause permanent

damage to the LTC4264.

ELECTRO STATIC DISCHARGE AND SURGE

PROTECTION

The LTC4264 is speciﬁed to operate with an absolute

maximum voltage of –90V and is designed to tolerate brief

over-voltage events. However, the pins that interface to the

outside world (primarily VIN and GND) can routinely see

peak voltages in excess of 10kV. To protect the LTC4264,

it is highly recommended that the SMAJ58A unidirectional

58V transient voltage suppressor be installed between the

diode bridge and the LTC4264 (D3 in Figure 4).

ISOLATION

The 802.3 standard requires Ethernet ports to be electrically

isolated from all other conductors that are user accessible.

This includes the metal chassis, other connectors and

any auxiliary power connection. For PDs, there are two

common methods to meet the isolation requirement. If

there will be any user accessible connection to the PD,

then an isolated DC/DC converter is necessary to meet

the isolation requirements. If user connections can be

avoided, then it is possible to meet the safety requirement

by completely enclosing the PD in an insulated housing.

In all PD applications, there should be no user accessible

electrical connections to the LTC4264 or support circuitry

other than the RJ-45 port.

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