Linear Technology DC1788B Guida rapida alla configurazione
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DEMO MANUAL DC1788B
Description
LT4275
LTPoE++, IEEE 802.3at/
IEEE 802.3af Compliant
PD Controller
Demonstrationcircuit1788BfeaturestheLT
®
4275,afourth
generation powered device (PD) controller for Power over
Ethernet (PoE) applications.
TheDC1788B isavailable inDC1788B-A, DC1788B-B,and
DC1788B-C versions to meet the power level required by
the PD application. The DC1788B-A features the LT4275A
PD controller. This controller supports the IEEE 802.3at
(Type 2, PoE+), IEEE 802.3af (Type 1, PoE) and LTPoE++™
specification. LTPoE++ adds four power levels to the ex-
isting IEEE standard with 38.7W, 52.7W, 70W, and 90W
of delivered PD power at the RJ45 jack. The DC1788B-B
features the LT4275B PD controller and is compliant with
the IEEE 802.3at and IEEE 802.3af specifications. The
DC1788B-C features the LT4275C PD controller and is
compliant with the IEEE 802.3af specification.
The DC1788B includes an RJ45 Ethernet port, a high
power Ethernet magnetic, a discrete active bridge recti-
fier, a surge protector, an external N-channel FET, and the
LT4275. The discrete active bridge rectifier is used to
achieve higher efficiency than a conventional diode bridge
rectifier. Many of the main features from the previous gen-
eration PD controller are included in this generation PD
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
LTPoE++ and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
controller. These include a power good indicator, a power
sourcing equipment (PSE) type indicator, and support
for an auxiliary power input. The major difference from
the previous generation PD controller is that the LT4275
drives an external N-channel Hot Swap™ FET at the PoE
high side voltage rail. This allows the user to choose a low
RDS(ON) N-channelMOSFETto maximizepower efficiency,
reduce heat dissipation, and ease thermal design. An LED
status indicator is included to indicate the Hot Swap FET
is fully turned on and the PSE is powering the PD. A suf-
ficient load to sink more than 10mA is also included to
assure the PSE maintains power to the PD and to meet
the DC maintain power signature current required by the
IEEE 802.3at/IEEE 802.3af specification.
Simply connect the output of the DC1788B to the DC/DC
converterthatisrightfortheapplication.LinearTechnology
offers a variety of DC/DC converter solutions that can be
used with the DC1788B (eg DC894, DC1317, etc).
Design files for this circuit board are available at
http://www.linear.com/demo
Table 1. Summary of Features Supported by the DC1788B Assemblies
ASSEMBLY PoE STANDARD
MAXIMUM POWER
LEVEL
POWER GOOD
INDICATOR (PWRGD)
PSE TYPE INDICATOR
(T2P)
AUXILIARY SUPPLY
SUPPORT
DC1788B-A LTPoE++
PoE+
PoE
90W Yes Yes No
DC1788B-B PoE+
PoE 25.5W Yes Yes Yes
DC1788B-C PoE 13W Yes No Yes
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DEMO MANUAL DC1788B
Table 2. DC1788B Performance Summary
PARAMETER CONDITION VALUE
PD Input Voltage After Start-Up (VPORT) At the PD Ethernet Port
LTPoE++ 38.7W 49.8V to 57V
LTPoE++ 52.7W 47.8V to 57V
LTPoE++ 70W 45.1V to 57V
LTPoE++ 90W 41.0V to 57V
IEEE 802.3at (Type 2, 25.5W) 42.5V to 57V
IEEE 802.3af (Type 1, 13W) 37V to 57V
Efficiency DC1788B-A, VPORT = 48V, ILOAD = 1.1A 99.1% (Typical)
DC1788B-B, VPORT = 48V, ILOAD = 600mA 98.9% (Typical)
DC1788B-C, VPORT = 48V, ILOAD = 350mA 99.1% (Typical)
PoE Type Switching Frequency An LTPoE++ PSE is Powering a DC1788B-A 840Hz
performance summary
theory of operation
WhenanLTPoE++PSEis connected tothe DC1788Bdemo
board RJ45 connector, J1, via a CAT5e or CAT6 Ethernet
cable, the PSE initiates the detection process. During this
process, the discrete active bridge acts as a standard
diode bridge and the PD solution presents a 25k resistive
load to the PSE. After the PD has passed the detection
process, the PSE uses an IEEE 802.3at/IEEE 802.3af or
LTPoE++ classification method to determine the power
level the PSE can deliver to the PD. The PSE turns on the
port and provides power to the PD if the classification is
successful. During turn on, the MOSFETs of the discrete
active bridge are fully enhanced with low RDS(ON) in the
highcurrentpath.Thisreducesthepowerandheatdissipa-
tion compared to the conventional diode bridge. Once the
LT4275 detects the PSE has turned on the port, it drives
an external N-channel MOSFET to ramp up the output
voltage. After a successful PD controller output turn on,
the LT4275 drives a power good indicator (PWRGD) and
a PSE Type indicator (T2P) (DC1788B-A and DC1788B-B
only).The PWRGDindicator signals the loadto startdraw-
ing current and the T2P indicator signals the load the type
of PSE powering the PD.
Classification Signaling
The resistors at RCLS and RCLS++ determine the clas-
sification signature and sequence. The DC1788B-A in-
cludes user-selectable jumpers to support IEEE 802.3af,
IEEE 802.3at, and LTPoE++ power levels from 3.84W to
90W. Refer to Table 3 for the power levels. If an LTPoE++
power level is selected, an IEEE 802.3af or IEEE 802.3at
compliant PSE will classify this PD as a Class 4 PD. The
DC1788B-BincludesapreselectedRCLS resistortosupport
IEEE802.3at2-eventclassificationandthisboarddoesnot
contain jumper blocks. The DC1788B-C includes multiple
jumpers to support all IEEE 802.3af power levels. Table 3
showseachshuntpositionanditsassociatedclassnumber
and power level for the DC1788B-A and -C boards. Use
Table3 as a selection guide to choose a suitable power
level for the load.
Table 3. DC1788B-A and DC1788B-C Shunt Positions for PoE
Power Levels
ASSEMBLY
PoE
CLASS
POWER LEVEL AT
THE PD INPUT RCLASS JUMPERS
DC1788B-A & -C 0 13W JP1 JP2
DC1788B-A & -C 1 3.84W JP3 JP4
DC1788B-A & -C 2 6.49W JP5 JP6
DC1788B-A & -C 3 13W JP7 JP8
DC1788B-A 4 25.5W JP9 JP10
DC1788B-A 4* 38.7W JP11 JP12
DC1788B-A 4* 52.7W JP13 JP14
DC1788B-A 4* 70W JP15 JP16
DC1788B-A 4* 90W JP17 JP18
*An LTPoE++ PD will be classified as Class 4 by an IEEE 802.3at/af
compliant PSE.
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DEMO MANUAL DC1788B
Power Good Indicator and Power Supply Start-Up
The LT4275 limits the inrush current to the output bulk
capacitor by controlling the output voltage slew rate
during turn-on. The slew rate is preprogrammed via a
resistor and a capacitor at the LT4275 HSGATE pin on the
DC1788B to limit the inrush current to the bulk capacitor
on board. If more capacitance is desired at the output,
refer to Inrush and Powered On section in the LT4275
data sheet to recalculate the inrush current and ensure it
is below the IEEE requirement of approximately 100mA.
The inrush current limit will cause startup problems if an
attached load draws more than 100mA of current during
inrush. Therefore, it is strongly recommended to use the
PWRGD indicator on the DC1788B to interface to a load
such as a DC/DC converter as shown in Figures 1, 2 and 4.
PSE Type Indicator
Refer to Table 4 for the summary of T2P indicator signals
supported by the DC1788B assembly. The T2P signal is
validafterPWRGDisactive.Thisindicatorisnotconnected
on the DC1788B-C.
Table 4. Summary of T2P Signals Supported by the DC1788B
Assemblies
ASSEMBLY PSE TYPE T2P SIGNAL
DC1788B-A LTPoE++ 840Hz, 50% Duty Cycle
IEEE 802.3at (Type 2, PoE+) Logic Low
IEEE 802.3af (Type 1, PoE) Logic High
DC1788B-B LTPoE++ Logic Low
IEEE 802.3at (Type 2, PoE+) Logic Low
IEEE 802.3af (Type 1, PoE) Logic High
DC1788B-C Any PSE Not Supported
theory of operation
Auxiliary Supply Support
The DC1788B-B and DC1788B-C versions support an
auxiliary supply input. The auxiliary supply input has pri-
ority over the PoE input. When the PD controller detects
a valid voltage from the auxiliary supply input, it turns off
the N-channel MOSFET (Q2) to cut the power from the
PSE and lets the auxiliary supply take over powering the
load. The PSE may detect the disconnected PD and turn
off the port. The PWRGD indicator outputs a logic high
signal when an auxiliary supply is present. The T2P indi-
cator outputs a logic low signal on the DC1788B-B board
when an auxiliary supply is present. The auxiliary supply
input is an assembly option on the DC1788B-A board.
DC1788B Companion PSE Demo Boards
Linear Technology offers a variety of PSE solutions to
evaluate with DC1788B. Refer to Table 5 to select a PSE
demo board based on the DC1788B assembly and the
application power requirement.
Table 5. Selection of Companion PSE Demo Board depending
on the DC1788 Assembly and the PoE Power Level
DC1788
ASSEMBLY
PoE POWER
LEVEL
COMPANION PSE DEMO
BOARD
DC1788B-A 90W DC1814A-D
70W DC1814A-C
52.7W DC1814A-B
38.7W DC1814A-A
DC1788B-B 25.5W DC1567A
DC1788B-C 13W DC981A/B
**Contact Linear for multi-port PSE demo board options.
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DEMO MANUAL DC1788B
Dc1788B-a quick start proceDure
NOTE: Handle the DC1788B-A by the edge of the board.
Power over Ethernet Input
1. Refer to Figure 1 to evaluate the DC1788B-A with a
DC/DCconverter.Ifaresistiveloadisusedtoevaluatethe
DC1788B-A, connect the load by hand between VOUT+
and VOUT– after the LED (D3) is lit. It is recommended
to disconnect the resistive load before powering down
theDC1788B-A,soatthenextturnontheloadisdiscon-
nected. If the load is not connected and disconnected
by hand properly, the PD may not power on. Contact
field applications engineers for further details.
2. Default class select shunt positions are at JP1 and JP2
onthe DC1788B-Aboard.Inthisconfiguration,anyPSE
will turn on this PD. Choose a power level from Table3
and select the corresponding shunt positions.
3. Check the power delivery capability of the LTPoE++
PSE to ensure it can power the PD and the load. Do
not select a jumper position corresponding to a higher
power level than the LTPoE++ PSE can provide. Oth-
erwise, the LTPoE++ PSE will not turn on the PD after
classification.
4. Connect the output of the PSE to the RJ45 connector
(J1) on the DC1788B-A board with a CAT5e or CAT6
Ethernet cable.
5. After connection has been established, verify that the
LED (D3) is lit. This indicates the PSE has successfully
detected and powered the PD
Figure 1. Setup Diagram for the DC1788B-A with a DC/DC Converter, a Microprocessor, and an LTPoE++ PSE
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DEMO MANUAL DC1788B
Dc1788B-B quick start proceDure
NOTE: Handle the DC1788B-B by the edge of the board.
Power over Ethernet Input
1. Refer to Figure 2 to evaluate the DC1788B-B with a
DC/DCconverter.Ifaresistiveloadisusedtoevaluatethe
DC1788B-B, connect the load by hand between VOUT+
and VOUT– after the LED (D3) is lit. It is recommended
to disconnect the resistive load before powering down
theDC1788B-B,soatthenextturnontheloadisdiscon-
nected. If the load is not connected and disconnected
by hand properly, the PD may not power on. Contact
field applications engineers for further details.
2. Connect the output of the PSE to the RJ45 connector
(J1) on the DC1788B-B board with a CAT5e or CAT6
Ethernet cable.
3. After connection has been established, verify that the
LED (D3) is lit. This indicates the PSE has successfully
detected and powered the PD.
Auxiliary Supply Input
1. Refer to Figure 3 to evaluate the DC1788B-B with a
DC/DC converter and an auxiliary DC power supply.
2. Connect the auxiliary supply to the AUX+ to AUX– in-
puts. Check to make sure the voltage polarity is correct
before turning on the auxiliary power supply.
3. Turn on the auxiliary power supply and verify that the
LED (D3) is lit.
Figure 2. Setup Diagram for the DC1788B-B with a DC/DC Converter, a Microprocessor, and a Type 2 PSE
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DEMO MANUAL DC1788B
Dc1788B-B quick start proceDure
Figure 3. Setup Diagram for the DC1788B-B with a DC/DC Converter, a Microprocessor, and an Auxiliary DC Power Supply
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DEMO MANUAL DC1788B
NOTE: Handle the DC1788B-C by the edge of the board.
Power over Ethernet Input
1. Refer to Figure 4 to evaluate the DC1788B-C with a
DC/DCconverter.Ifaresistiveloadisusedtoevaluatethe
DC1788B-C, connect the load by hand between VOUT+
and VOUT– after the LED (D3) is lit. It is recommended
to disconnect the resistive load before powering down
theDC1788B-C,soatthenextturnontheloadisdiscon-
nected. If the load is not connected and disconnected
by hand properly, the PD may not power on. Contact
field applications engineers for further details.
2. Connect the output of the PSE to the RJ45 connector
(J1) on the DC1788B-C board with a CAT5e or CAT6
Ethernet cable.
3. After connection has been established, verify that the
LED (D3) is lit. This indicates the PSE has successfully
detected and powered the PD.
Auxiliary Supply Input
1. Refer to Figure 5 to evaluate the DC1788B-C with a
DC/DC converter and an auxiliary DC power supply.
2. Connect the auxiliary supply to the AUX+ to AUX– in-
puts. Check to make sure the voltage polarity is correct
before turning on the auxiliary power supply.
3. Turn on the auxiliary power supply and verify that the
LED (D3) is lit.
Figure 4. Setup Diagram for the DC1788B-C with a DC/DC Converter and a Type 1 PSE
Dc1788B-c quick start proceDure
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DEMO MANUAL DC1788B
Dc1788B-c quick start proceDure
Figure 5. Setup Diagram for the DC1788B-C with a DC/DC Converter and an Auxiliary DC Power Supply
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DEMO MANUAL DC1788B
quick start proceDure
Figure 6. DC1788B-A Efficiency at Various PoE Load Currents (without LED D3)
Figure 7. Thermal Image. DC1788B-A with 90W Load. Top View
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DEMO MANUAL DC1788B
quick start proceDure
Figure 8. Thermal Image. DC1788B-A with 90W Load. Bottom View
Indice
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