Datasheet

LTC4263-1
14
42631fa
APPLICATIONS INFORMATION
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 C
DET
, R
DET
and C
PSE
is strongly
discouraged. Contact the Linear Technology Applications
department for additional support.
Internal 110Hz AC Oscillator
The LTC4263-1 includes onboard circuitry to generate
a 110Hz (typ), 2V
P-P
sine wave on its OSC pin when a
0.1μF capacitor is connected between the OSC pin and
V
SS
. This sine wave is synchronized to the controller
inside the LTC4263-1 and should not be externally driven.
Tying the OSC pin to V
SS
shuts down the oscillator and
enables DC disconnect.
Power-On Reset and Reset/Backoff Timing
Upon startup, the LTC4263-1 waits four seconds before
starting its fi rst detection cycle. Depending on the results
of this detection it will either power the port, repeat detec-
tion, or wait 3.2 seconds before attempting detection again
if in midspan mode.
The LTC4263-1 may be reset by pulling the SD pin low.
The port is turned off immediately and the LTC4263-1 sits
idle. After SD is released there will be a 4-second delay
before the next detection cycle begins.
V
DD5
Logic-Level Supply
The V
DD5
supply for the LTC4263-1 can either be supplied
externally or generated internally from the V
DD48
supply.
If supplied externally, a voltage between 4.5V and 5.5V
should be applied to the V
DD5
pin to cause the internal
regulator to shut down. If V
DD5
is to be generated inter-
nally, the voltage will be 4.4V (typ) and a 0.1μF capacitor
should be connected between V
DD5
and V
SS
. Do not
connect the internally generated V
DD5
to anything other
than a bypass capacitor and the logic control pins of the
same LTC4263-1.
LED Flash Codes
The LTC4263-1 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 LTC4263-1 blinks a code to communicate
the status to the user as shown in Table 1. One fl ash indi-
cates low signature resistance, two fl ashes indicates high
resistance and fi ve fl ashes indicates an overload fault.
When active, the LED fl ash codes are repeated every 1.2
seconds. The duration of each LED fl ash is 75ms. Multiple
LED fl ashes occur at a 300ms interval.
The LTC4263-1 includes a feature for effi ciently driving
the LED from a 56V power supply without the wasted
power caused by having to drop over 52V in a current limit
resistor. When operating the V
DD5
supply internally, the
LTC4263-1 drives the LED pin with a 6% duty cycle PWM
signal. This allows use of the simple LED drive circuit in
Figure 7 to minimize power dissipation. The modulation
frequency of the LED drive is 28kHz, making the on period
Figure 6. LTC4263-1 Using AC Disconnect
42631 F06
0.1μF
100V
0.1
μF
NC
0.1μF
X7R
C
DET
0.47μF
X7R, 100V
C
PSE
0.1μF
X7R, 100V
SMAJ58A
LED
LEGACY
MIDSPAN
V
SS
V
SS
V
SS
OSC ACOUT
LTC4263-1
CMLSH05-4
500k
ISOLATED
56V SUPPLY
+
–
R
DET
1k
D
AC
1A
V
DD5
V
SS
SD
V
DD48
OUT
OUT