QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1366A
IEEE802.3AF/AT POWER-OVER-ETHERNET POWER SOURCING EQUIPMENT CONTROLLER
LTC4266
DESCRIPTION
Demonstration circuit DC1366A features the
LTC
®
4266CUHF, a quad network power controller with
I
2
C™ interface, designed for use in IEEE 802.3at™-
compliant Power Sourcing Equipment (PSE). Inte-
grated into a tiny 5mm×7mm 38-pin QFN package are
four independent ports controlling external N-channel
power MOSFETs. Each port features:
■
Reliable 4-point PD detection
■
Selectable 1 or 2-event classification
■
Inrush current limiting
■
Extremely fast short-circuit protection with
programmable foldback current threshold
■
Programmable cutoff current threshold for
class power enforcement
■
Voltage and current readback
■
DC disconnect sensing
The DC1366A board is configured like a midspan
PSE with two RJ45 connectors for each port such
that gigabit Ethernet data can pass through the
board at full line rates while dc power is injected by
the LTC4266 on the PD side of the board.
Often one of the most challenging aspects of de-
signing a PSE system is the power management
software; Linear Technology makes the job easier
with the fully-featured LTC4266 register set and an
advanced GUI software application. The GUI allows
the user full and easy access to the LTC4266 regis-
ter set with detailed contextual help info. The GUI
also includes a host computer emulator to demon-
strate basic power management techniques: the
user selects various system parameters such as PSE
type (endspan or midspan), 1 or 2-event classifica-
tion, total system power budget, and fault handling
rules; then with the click of a button the host com-
puter emulator takes control of the system, manag-
ing the power budget as PDs are connected and dis-
connected, and logging all events.
The DC1366A demo boards, CAD files, and GUI soft-
ware are available only under a non-disclosure
agreement (NDA).
Contact your local Linear Tech-
nology sales person or field applications engineer.
L,
LT, LTC, and QuickEval are trademarks of Linear Technology
Corporation; I2C is a trademark of Phillips Electronics N.V.; all other
trademarks are the property of their respective owners.
QUICK START PROCEDURE
Figure 1 shows the basic setup. The LTC4266 requires
two power supply rails: V
DD
(nominally 3.3V) and V
EE
(nominally -54V). The V
DD
supply can be provided by
the DC590B board or an external bench supply.
When running the GUI application on a Windows
computer, the DC590B board from Linear Tech is
used to interface a USB port on the PC to the I
2
C bus
on the DC1366A board. The DC590B also provides
optoisolation of the I
2
C bus, and an isolated 3.3V
supply to run the LTC4266 chip; the user need only
provide the V
EE
supply.
Alternatively, the user can omit the DC590B and
connect some other I
2
C master device to the
DC1366A board. If the DC590B is omitted then a
bench power supply must provide V
DD
.
For applications where power management is not
required, the LTC4266 features an AUTO mode al-
lowing it to operate completely autonomously.
Choose one of the setup procedures shown on the next
page, depending on whether or not the GUI application
software is required.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1366A
IEEE802.3AF/AT POWER-OVER-ETHERNET POWER SOURCING EQUIPMENT CONTROLLER
LTC4266
Setup Procedure to Run the GUI Software
1. Install the GUI software on the PC according to
the instructions in the README.txt file included
with the GUI software.
2. On the DC590B board:
a. Set both sides (ISO and SW) of JP5 to ON.
b. Set JP6 to 5V. (This will be regulated down
to 3.3V on the DC1366A board.)
3. Connect the DC590B board to the PC with a stan-
dard USB A-B cable.
a. Verify the computer recognized the USB de-
vice. (The first time the DC590B board is
connected the Hardware Wizard may ask for
help to locate the driver. Direct it to the loca-
tion specified in the README.txt that came
with the GUI software.)
b. Verify the ISO PWR LED on the DC590B
board is lit.
4. On the DC1366A board:
a. Set JP5 to the USB VDD position.
b. Set JP3 to the TIE position.
c. Set JP4 (AUTO) to the HI position.
d. If midspan operation is desired set JP2 to
HI, for endspan set to LO.
5. Connect the DC590B board to the DC1366A board
with the 14-conductor ribbon cable supplied with
the DC590B board. Verify the VDD LED on the
DC1366A board is lit.
6. Before connecting the main power supply to the
DC1366A board verify the voltage is between 51V
and 57V,
and that the main supply is turned off.
7. Connect the main power supply to the DC1366A
board with two banana patch cords as shown in
Figure 1.
Verify the polarity is correct before
turning on the power; positive goes to GND and
negative to VEE.
Setup Procedure without the GUI Software
1. On the DC1366A board:
a. Set JP5 to EXT VDD.
b. Set JP3 to the TIE position.
c. Set JP4 (AUTO) to the HI position.
d. If midspan operation is desired set JP2 to
HI, for endspan set to LO.
2. Connect a 3.3V power supply to the TP16 and
TP30 test points as shown in Figure 1. Turn on
the 3.3V supply and verify the VDD LED on the
DC1366A board is lit.
3. Before connecting the main power supply to the
DC1366A board verify the voltage is between 51V
and 57V,
and that the main supply is turned off.
4. Connect the main power supply to the DC1366A
board with two banana patch cords as shown in
Figure 1.
Verify the polarity is correct before
turning on the power; positive goes to GND and
negative to VEE.
5. Turn on the main power supply and verify the VEE
LED on the DC1366A board is lit.
6. Connect PDs to any of the ports on the ICM and
verify they turn on.
8. Turn on the main power supply and verify the VEE
LED on the DC1366A board is lit.
9. Connect PDs to any of the ports on the DC1366A
board and verify they turn on.
10. Launch the GUI application. Refer to the GUI us-
ers’ manual for instructions.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1366A
IEEE802.3AF/AT POWER-OVER-ETHERNET POWER SOURCING EQUIPMENT CONTROLLER
LTC4266
Figure 1. DC1366A Board Setup.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1366A
IEEE802.3AF/AT POWER-OVER-ETHERNET POWER SOURCING EQUIPMENT CONTROLLER
LTC4266
OPERATION
Introduction
The DC1366A demonstrates the features and capa-
bilities of the LTC4266, a quad controller for
IEEE802.3at Power Sourcing Equipment (PSE). The
DC1366A provides a quick and simple, fully compli-
ant PSE solution requiring only a V
EE
supply when
used in conjunction with the DC590B USB-to-I
2
C
interface board.
Supply Voltages
The IEEE802.3at standard requires the output volt-
age of a Type 2 PSE to be in the range of 51V to
57V. (The positive side is GND and the negative
side is V
EE
.) Obviously the V
EE
supply voltage should
be in this range for the sake of compliance; how-
ever, the LTC4266 is capable of operating with V
EE
down to 30V, the max undervoltage lockout (UVLO)
threshold.
Make sure to choose a V
EE
supply with enough
power to sustain all four ports at maximum load; if
the total load is too great for the power supply its
voltage may drop below the UVLO threshold, reset-
ting the LTC4266 and shutting off all the ports. The
worst case is when all four PDs are class 4: each
class 4 PD may draw up to 600mA, totaling 2.4A.
Therefore a V
EE
supply rated for at least 2.6A is rec-
ommended.
The V
DD
supply should nominally be 3.3V but the
LTC4266 is capable of operating over the range of
3.0V to 4.3V. (The UVLO threshold for the V
DD
sup-
ply is typically 2.2V.) The LTC4266 chip typically
draws only 1.1mA from the V
DD
supply; however,
LEDs and other components on the DC1366A board
also draw current from V
DD
, so the total load is typi-
cally 9mA to 26mA @ 3.3V depending on which
LEDs are lit.
Modes of Operation
The LTC4266 has four modes of operation:
■
Shutdown:
Power is off, detection and classifi-
cation cycles are suspended.
■
Manual:
The port does not advance automati-
cally from detection to classification, to power
on. It waits for instructions from a host control-
ler via the I
2
C interface.
■
Semiauto:
The port automatically advances to
classification after detecting a PD, but does not
turn on power to the PD until told to do so by
from a host controller via the I
2
C interface.
■
Auto:
The port does everything autonomously.
The mode of each port can be set independently of
the others after power up via I
2
C commands.
The AUTO Pin
The AUTO pin determines several aspects of the
LTC4266 initial behavior. AUTO is sensed by the
LTC4266 at power up and after a reset.
If the AUTO pin is high then:
■
All ports come up in AUTO mode. Any valid
PD will be turned on without software inter-
vention.
■
The current-sense resistors are assumed to be
0.25Ω (which they are on the DC1366A).
■
High power is enabled. After the LTC4266
classifies a PD it applies power and automati-
cally sets I
CUT
and I
LIM
appropriately for the
class. With high-power enabled a class 4 PD
will be able to draw >600mA without being cut
off.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1366A
IEEE802.3AF/AT POWER-OVER-ETHERNET POWER SOURCING EQUIPMENT CONTROLLER
LTC4266
If the AUTO pin is low then:
■
All ports come up in shutdown mode. The
software must take action in order to power up
any PDs.
■
The current-sense resistors are assumed to be
0.50Ω; the software must change this to
0.25Ω for correct operation of the DC1366A.
(This feature allows the LTC4266 to be a drop-
in replacement for the older LTC4259 with no
software changes.)
■
High power is disabled. If the software were
to simply change the operating mode to AUTO,
a class 4 PD would be treated as class 0, i.e.
limited to 15.4W in accordance with the origi-
nal 802.3af standard.
Endspan vs. Midspan
The LTC4266 can be configured either for endspan
or midspan operation without software intervention
by setting the MID pin high or low respectively.
(You must reset the LTC4266 or cycle the power for
the MID pin to be sensed.) The only difference in
the behavior of the LTC4266 is that the detection
back-off timer is enabled when midspan operation is
selected.
Each port can be configured individually as either
endspan or midspan via I
2
C commands.
The DC1366A board is wired for Alternative-A, MDI-
X (power is injected on the data pairs of the CAT5/6e
cable; positive on pins 3 and 6 of the RJ45 connec-
tor, and negative on pins 1 and 2). The original
802.3af standard required all midspans to use Alter-
native-B, but 802.3at now allows midspans to use
Alternative-A.
Disconnect Sensing
The LTC4266 employs dc disconnect sensing only.
For the sake of software backward compatibility with
Masked Shut Down
The MSD register can be used to pre-assign low-
priority to selected ports so they can be shut down
quickly when needed.
A PSE system design can utilize the MSD feature in
various ways. For example, a PSE system may in-
clude a circuit that monitors the V
EE
supply; if it be-
comes overloaded and the voltage begins to sag, the
system can dump low-priority loads by asserting the
MSD
pin. Shedding excess load quickly may allow
the V
EE
voltage to recover before it reaches the UVLO
threshold, thus avoiding shutting down higher-
priority loads.
the older LTC4259, the LTC4266 includes register
bits for enabling ac disconnect sensing, but these
bits simply enable the dc disconnect sensing.
Pushbutton Switches
The DC1366A board includes several pushbutton
switches to facilitate experimentation with the
LTC4266.
■
The
RESET
button (S6) resets all ports just as
if the power supplies were cycled.
■
The Masked Shut-Down (MSD) button (S7)
will turn off any ports that have their corre-
sponding mask bit set in the MSD register.
■
Each port has an individual shut down switch
(S2 through S5 for ports 1 through 4 respec-
tively).
I
2
C Addressing
The 7-bit I
2
C address of the LTC4266 is
010A
3
A
2
A
1
A
0
b, where A
3
through A
0
are determined
by pins AD3 through AD0 respectively. On the
DC1366A board these pins are controlled by the
quad DIP switch, S1. The LTC4266 has internal
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