ltc4263cde-trpbf Linear Technology Corporation, ltc4263cde-trpbf Datasheet - Page 17

• Manufacturer Part Number: ltc4263cde-trpbf
• Description: Single Ieee 802.3af Compliant Pse Controller With Internal Switch
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
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 includes a feature for effi ciently driving the
LED from a 48V power supply without the wasted power
caused by having to drop over 45V in a current limit
resistor. When operating the V
LTC4263 drives the LED pin with a 6% duty cycle PWM
signal. This allows use of the simple LED drive circuit in
Figure 9 to minimize power dissipation. The modulation
frequency of the LED drive is 28kHz, making the on period
Figure 9. LED Drive Circuit with Single 48V Supply
DS1608C-106
10mH, 21mA
COILCRAFT
V
Table 3. Port Status and LED Flash Codes
DD48
V
PORT STATUS
Non-Powered Device
0Ω < R
Port Open
R
Port On
25kΩ
Low Signature Resistance
300Ω < R
High Signature Resistance
33kΩ < R
Port Overload Fault
Power Management
Allocation Exceeded
SS
PORT
> 1MΩ
PORT
PORT
PORT
R
1k
LED
< 200Ω
0.1μF
< 500kΩ
< 15kΩ
D1
LED
V
DD5
LTC4263
BAS19
D2
DD5
V
DD48
supply internally, the
LED FLASH CODE
4263 F09
2 Flashes
5 Flashes
9 Flashes
1 Flash
Off
Off
On
2.2μs. During the 2.2μs that the LED pin is pulled low, cur-
rent ramps up in the inductor, limited by R
completes the circuit by allowing current to circulate while
the LED pin is open circuit. Since current is only drawn
from the power supply 6% of the time, power dissipation
is substantially reduced.
When V
signal is disabled and the LED pin will pull down continu-
ously when on. In this mode, the LED can be powered from
the 5V supply with a simple series resistor.
IEEE 802.3af COMPLIANCE AND EXTERNAL
COMPONENT SELECTION
This section discusses the other elements that go along
with the LTC4263 to make an IEEE 802.3af compliant PSE.
The LTC4263 is designed to control power delivery in IEEE
802.3af compliant Power Sourcing Equipment. Because
proper operation of the LTC4263 also depends on external
components and power sources like the 48V supply, using
the LTC4263 in a PSE does not in itself guarantee IEEE
802.3af compliance. To ensure a compliant PSE design,
it is recommended to adhere closely to the example ap-
plication circuits provided. For further assistance contact
the Linear Technology Applications department.
DD5
FLASH PATTERN
is powered from an external supply, the PWM
LED Off
LED Off
LED On
LTC4263
LED
. Diode D2
17
4263fc