LTC4263CS datasheet(16/24 Pages) LINER

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LTC4263

4263fe

APPLICATIONS INFORMATION

being shorted by the LTC4263’s power control MOSFET.

The 500k resistor across DAC allows the port voltage to

decay after disconnect occurs.

Sizing of capacitors is critical to ensure proper function

of AC disconnect. CPSE (Figure 8) controls the connection

impedance on the PSE side. Its capacitance must be kept

low enough for AC disconnect to be able to sense the PD.

On the other hand, CDET has to be large enough to pass

the signal at 110Hz. The recommended values are 0.1μF

for CPSE and 0.47μF for CDET. The sizes of CPSE, CDET,

and RDET are chosen to create an economical, physically

compact and functionally robust system. Moreover, the

complete Power over Ethernet AC disconnect system (PSE,

transformers, cabling, PD, etc.) is complex; deviating from

the recommended values of CDET,RDETandCPSEisstrongly

discouraged. Contact the Linear Technology Applications

department for additional support.

Internal 110Hz AC Oscillator

The LTC4263 includes onboard circuitry to generate a

110Hz (typ), 2VP-P sine wave on its OSC pin when a

0.1μF capacitor is connected between the OSC pin and

VSS. This sine wave is synchronized to the controller

inside the LTC4263 and should not be externally driven.

Tying the OSC pin to VSS shuts down the oscillator and

enables DC disconnect.

Power-On Reset and Reset/Backoff Timing

Upon start-up, the LTC4263 waits four seconds before

starting its ﬁrst detection cycle. Depending on the re-

sults of this detection it will either power the port, repeat

detection, or wait 3.2 seconds before attempting detection

again if in midspan mode.

The LTC4263 may be reset by pulling the SD pin low. The

port is turned off immediately and the LTC4263 sits idle.

After SD is released there will be a 4-second delay before

the next detection cycle begins.

VDD5 Logic-Level Supply

The VDD5 supply for the LTC4263 can either be supplied

externally or generated internally from the VDD48 supply.

If supplied externally, a voltage between 4.5V and 5.5V

should be applied to the VDD5 pin to cause the internal

regulator to shut down. If VDD5 is to be generated inter-

nally, the voltage will be 4.4V (typ) and a 0.1μF capacitor

should be connected between VDD5 and VSS. Do not

connect the internally generated VDD5 to anything other

than a bypass capacitor and the logic control pins of the

same LTC4263.

LED Flash Codes

The LTC4263 includes a multi-function LED driver to inform

the user of the port status. The LED is turned on when the

port is connected to a PD and power is applied. If the port

is not connected or is connected to a non-powered device

with a 150Ω or shorted termination, the port will not be

powered and the LED will be off. For other port conditions,

the LTC4263 blinks a code to communicate the status

to the user as shown in Table 3. One ﬂash indicates low

signature resistance, two ﬂashes indicates high resistance,

ﬁve ﬂashes indicates an overload fault, and nine ﬂashes

indicates that power management is preventing the port

from turning on.

Figure 8. LTC4263 Using AC Disconnect

4263 F08

0.1μF

100V

0.1μF

CDET

0.47μF

X7R, 100V

CPSE

0.1μF

X7R, 100V

SMAJ58A

LED

LEGACY

MIDSPAN

PWRMGT

VSS

OSC

ACOUT

LTC4263

DAC

CMLSH05-4

500k

ISOLATED

48V SUPPLY

–

RDET

VDD5

ENFCLS

VDD48

OUT

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