LTC4263CS datasheet(17/24 Pages) LINER

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LTC4263

4263fe

APPLICATIONS INFORMATION

When active, the LED ﬂash codes are repeated every 1.2

seconds. The duration of each LED ﬂash is 75ms. Multiple

LED ﬂashes occur at a 300ms interval.

The LTC4263 includes a feature for efﬁciently 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 VDD5 supply internally, the

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

2.2μs. During the 2.2μs that the LED pin is pulled low, cur-

rent ramps up in the inductor, limited by RLED. Diode D2

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 VDD5 is powered from an external supply, the PWM

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.

Figure 9. LED Drive Circuit with Single 48V Supply

Table 3. Port Status and LED Flash Codes

PORT STATUS

LED FLASH CODE

FLASH PATTERN

Non-Powered Device

0Ω < RPORT < 200Ω

Off

LED Off

Port Open

RPORT > 1MΩ

Off

LED Off

Port On

25kΩ

LED On

Low Signature Resistance

300Ω < RPORT < 15kΩ

1 Flash

High Signature Resistance

33kΩ < RPORT < 500kΩ

2 Flashes

Port Overload Fault

5 Flashes

Power Management

Allocation Exceeded

9 Flashes

VDD48

10mH, 21mA

COILCRAFT

DS1608C-106

BAS19

VDD5

RLED

VDD48

LED

VSS

LTC4263

4263 F09

0.1μF

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