DC1415A - Demo Manual

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D E S C R IP T IO N
Demonstration circuit DC1415A features the
LTC®4265CEDE, a third-generation Powered Device
(PD) controller for Power over Ethernet (PoE) applications.
The LTC4265 is compliant to IEEE Standard 802.3at. It
can handle up to 25.5W and recognizes 2-event classification.
The LTC4265 includes the PD controller circuitry and
power M OSFET integrated into a tiny 3mm×4mm 12pin DFN package.
The DC1415A board includes the entire front end of
a typical PD; R J45 connector, Ethernet magnetics,
bridge rectifiers, surge protection, and PD controller, all in a 1”×2” board. Two status indicator LEDs
are also included: one shows the PSE is powering
the PD; and the other shows the PSE performed 2event classification. A small load sufficient to as-
sure the PSE maintains power to the PD is also included.
The LTC4265 features complementary PW R G D and
PWRGD outputs to facilitate interface to a wide
range of off-the-shelf DC/DC converters.
Simply connect the outputs of the DC1415A to the
DC/DC converter that’s right for your application.
Linear Technology offers many DC/DC converter
demo boards that can be used with the DC1415A.
To obtain CAD files for the DC1415A demo board,or
inquire about DC/DC converter demo boards, contact your local Linear Technology sales person or
field applications engineer.
L, LT, and LTC are trademarks of Linear Technology Corporation;
allother trademarks are the property of their respective owners.
Q U IC K S T A R T P R O C E D U R E
1. To evaluate the LTC4265 without a load,skip to
step 3.
b. Use Figure 2 or Figure 3 if the startup delay
could be an issue.
2. To evaluating the LTC4265 with a load,choose the
connection diagram based on the type of load desired and wire the DC1415A board to the load as
shown.
c. Use Figure 4 if the load is resistive.
a. Use Figure 1 if the DC/DC converter has sufficient built-in startup delay. The LTC4265 limits the current to 100mA during startup;if the
DC/DC converter tries to draw more than
100mA during this time then startup willfail.
The required delay depends on the input capacitance and U nder-Voltage Lock Out
(UVLO ) threshold of the particular converter.
3. Connect the output of the PSE to J1 on the
DC1415A board with a CAT5e or CAT6 cable.
4. Verify LED2 is lit,indicating the PSE has successfully detected and powered the PD. LED1 may
also be lit if the PSE performed 2-event classification.
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QUICK START GUIDE FOR DEM ON STRATION CIRCUIT 1 4 1 5A
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DC1415A
LED2
DC/DC Converter
J1
LED1
VIN
Figure 1. Basic Connection to a D C/D C Converter.
DC/DC Converter
DC1415A
J1
VIN
RUN
PW RGD (TP5)
Figure 2. Connecting to a D C/D C Converter w ith Active-H igh RU N pin.
DC/DC Converter
DC1415A
J1
VIN
RU N
10k
PWRGD (TP4)
Figure 3. Connecting to a D C/D C Converter w ith Active-Low RU N pin.
DC1415A
Power R esistors
J1
100k
PW RGD (TP5)
12V
(Optional)
IRFM 120A
Figure 4. Connecting to a Resistive Load.
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QUICK START GUIDE FOR DEM ON STRATION CIRCUIT 1 4 1 5A
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O P E R A T IO N
Classification Signature
Pow er Supply Startup
The R CLASS resistor (R 3) determines the classification signature. The DC1415A board comes with
R 3=30.9Ω for class 4. If a different class signature is desired, simply change R 3 according to
Table 1.
The LTC4265 limits the current to 100mA during
startup. If the DC/DC converter attempts to draw
more than 100mA while the LTC4265 is still limiting the current then startup willfail.
Table 1. RCLASS Resistor Values.
PD CLASS
RCLASS (Ω , 1% )
0
1
2
3
4
O pen (no resistor)
124
69.8
45.3
30.9
LED Indicators
There are two LEDs on the front of J1 as shown in
Figure 1. In a typical PD application a PHY chip
would drive these LEDs to indicate the status of
the Ethernet link or traffic activity; however, on the
DC1415A board the LTC4265 drives the LEDs to
indicate PoE status.
The PWRGD pin of the LTC4265 drives LED2.
LED2 is lit continuously while the PD is powered
by the PSE. To disable LED2 remove R 2.
The T2PSE pin drives LED1. LED1 willbe lit if the
PSE performed 2-event classification, indicating
the PSE is Type 2. To disable LED1 remove R 1.
M any DC/DC converters include startup delay sufficient to prevent this situation. Such a converter
may be connected to the DC1415A board as
shown in Figure 1.
However, some DC/DC converters have short
startup delays. To avoid startup problems it is
recommended to use either the PW R G D or
PWRGD output to inhibit startup of the DC/DC
converter until the LTC4265 finishes limiting the
inrush current.
U se PW R G D if the DC/DC converter has an activehigh controlinput,as shown in Figure 2.
U se PWRGD if the DC/DC converter has an activelow control input, as shown in Figure 3. A 10k
resistor limits the current between PWRGD and
RU N in the event of a voltage transient at the J1
input.A resistive load may be used to evaluate the
thermal properties of the LTC4265; in this case
use a series M O SFET to prevent startup problems,
as shown in Figure 4. PW R G D holds the M O SFET
gate low until the LTC4265 is ready to supply full
current.
CAU TIO N : The M O SFET may be destroyed if its gate is pulled all the way to VO U T+ by the pull-up resistor.
The M O SFET is protected by a 14V clamp inside the LTC4265; however, if the wire to PW R G D were disconnected – or mistakenly connected to PWRGD – then the M O SFET would not be protected. Therefore it is
recommended to use a zener diode connected directly across the gate and source pins of the M O SFET as
shown in Figure 4.
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M inim um LO AD
The PSE may discontinue power if the load current is below 10mA. The DC1415A includes a 3k load (R M PS)
across its outputs to prevent the PSE from turning off power. R PM S may be removed is the DC1415A is
connected to a load that draws at least 10mA continuously.
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QUICK START GUIDE FOR DEM ON STRATION CIRCUIT 1 4 1 5A
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