Linear Technology DC1842B Manuale utente

dc1843bfa

DEMO MANUAL DC1843B

DESCRIPTION

DC1842B and DC1680B

LTC4290B/LTC4271

8-Port PSE with Digital Isolation

Demonstration kit DC1843B is an 8-port IEEE 802.3at

Type 2 power sourcing equipment (PSE) composed of a

DC1842B daughter card and DC1680B motherboard. The

kitisusedforevaluationoftheLTC4290BandLTC4271PSE

chipset. Up to 8 powered devices (PDs) can be connected

andpoweredfromthissystemusingasinglepowersupply.

A DC590 is connected to the DC1843 for I2C interfacing

with QuikEval™. This demonstration manual provides a

Quick Start Procedure, a DC1842B overview, a DC1680B

overview, schematics, and layout printouts. Refer to the

Layout Guide for Demonstration Circuit 1842B when

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

QuikEval is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

BOARD PHOTO

laying out the LTC4290B/LTC4271 circuit. Contact Linear

Technology for this document.

The DC1842B has increased surge protection over the

DC1842A.TheDC1680BusesdiscreteEthernettransform-

erswhiletheDC1680Ahasanintegrated12-portRJ45jack.

Design files for this circuit board are available at

http://www.linear.com/demo/DC1843B

dc1843bfa

DEMO MANUAL DC1843B

QUICK START PROCEDURE

Figure 1. DC1842 Backside. Setting AUTO and MID Jumpers

Figure 2. Inserting the DC1842 into J1 of the DC1680

Demonstration kit DC1843B includes the DC1842B

daughter card and DC1680B motherboard. The kit is set

up for evaluating the LTC4290B/LTC4271. Follow the pro-

cedure below and refer to Figures 1 through 4 for proper

equipment setup.

NOTE (DC1843B Kit): Connector J1 on the DC1680B has

four pegs blocking the unused last four pins to match the

30-pinconnectoroftheDC1842B.Dustcapsblockthefour

unused ports at each RJ45 connector on the DC1680B

for the 8-Port.

1. On the DC1842B set AUTO jumper JP1 to HI (Figure 1)

to enable AUTO pin mode.

2. On the DC1842B set MID jumper JP2 to LO (Figure 1)

to disable midspan mode.

3. Alignpin1ofthe30-pinmaleconnectorontheDC1842B

with pin 1 of the 30-pin female connector on the

DC1680B(Figure2).Pin12ispolarizedtoassistwiththe

alignment. Carefully push the DC1842B straight down

untilthetwo30-pinconnectorsareflushwitheachother.

4. On the DC1680B, connect a supply with the positive

rail to POS and negative rail to NEG (Figure 3). Use a

power supply capable of sourcing the maximum load

expected (8 ports ×850mA ≥ 6.8A). Ramp the supply

up to 51V to 57V.

5. Connect up to 8 PDs to ports 1-8 at the DC1680B, J4

(Figure 3).

6. TheDC590isoptionallyconnectedtotheDC1680Bcon-

nector J5 with a 14-pin ribbon cable (Figure 3). A GUI

for the LTC4290B/LTC4271 is brought up by QuikEval

for I2C interfacing from a PC (Figure 4).

dc1843bfa

DEMO MANUAL DC1843B

QUICK START PROCEDURE

Figure 3. DC1843B Basic Setup

Figure 4. DC1843 System Setup with the DC590, DC1680, DC1842 and 51V to 57V Power Supply

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1842B OPERATION

Figure 5. DC1842B 8-Port PSE Daughter Card with Digital Isolation Features the LTC4290B and LTC4271

8-Port PSE Daughter Card with Digital Isolation

Demonstration circuit 1842B (Figure 5) features the

LTC4290B/LTC4271 chipset on a compact daughter card

with digital isolation. The LTC4290B/LTC4271 chipset is

an 8-port power sourcing equipment (PSE) controller

designed for use in IEEE 802.3at Type 1 and Type 2 (high

power) compliant Power over Ethernet (PoE) systems. A

transformer isolated communication protocol replaces

expensiveopto-couplersandcomplexisolated3.3Vsupply

resulting in significant BOM cost savings. The LTC4290B/

LTC4271 chipset delivers lowest-in-industry heat dissipa-

tionbyutilizinglowRONexternalMOSFETsand0.25Ωsense

resistors, eliminating the need for expensive heat sinks.

Advanced power management features in the LTC4290B/

LTC4271 chipset include: per port 12-bit current monitor-

ing ADCs, DAC programmable current limit, and versatile

quick shutdown of preselected ports. PD discovery uses a

proprietarydualmode4-pointdetectionmechanismensur-

ing excellent immunity from false PD detection. Midspan

PSEs are supported with 2-event classification and a two

second backoff timer. The LTC4290B/LTC4271 includes

an I2C serial interface operable up to 1MHz.

The DC1842B demonstrates proper LTC4290B/LTC4271

board layout that is approximately the height and width

of a 2 × 4 RJ45 connector. The compact layout is made

possiblebythesmall packagesizeofkey components.The

LTC4290B is in a 6mm × 6mm QFN, while the LTC4271 is

ina 4mm × 4mm QFN. Each port has a PSMN075-100MSE

MOSFET in a 3mm × 3mm LFPAK33 package.

The daughter card inserts in the DC1680B motherboard

through J1, a polarized 30-pin connector. Isolated 3.3V

and logic control signals are brought in on this connec-

tor. Also connected at J1 is the PoE VEE supply from the

motherboard and 8 PSE controlled outputs.

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1842B OPERATION

Board Layout

Proper board layout is crucial for proper LTC4290B/

LTC4271 chipset operation, robustness, and accuracy.

When laying out, pay attention to parts placement, Kelvin

sensing, power paths, and copper fill. It is imperative to

follow the LTC4290B/LTC4271 Layout Guide document

when laying out the board. Contact Linear Technology

Corporation for this document.

Figure 6. DC1842B Digital and Analog Isolation

Isolation and Power Supplies

The LTC4290B/LTC4271 chipset provides communication

across an isolation barrier through a data transformer

(Figure 6). This eliminates the need for expensive opto-

couplers. All digital pins reside on the digital ground refer-

ence and are isolated from the analog PoE supply. A 3.3V

supply for VDD and an isolated VEE supply are connected

to the DC1842B through the 30-pin connector.

VDD33

DND

CPD

CND

DPD

AGND

VEE

DNA

VEE

ISOLATION

WÜRTH 7490100143

CPA

30-PIN

CONNECTOR

DC1842A SIDE DC1680B SIDE

VDD33 SUPPLY

VEE

SUPPLY

CNA

DPA

TX+

RX–

CT(4)

CT(2)

RX+

TX–

TD+

RD–

CT(3)

RD+

TD–

LTC4271

LTC4290

C23

1µF

C21

0.1µF

R13

100Ω

DC1843A F06

DGND

C19

1µF

100V

SMAJ58A

R14

100Ω

C22

1µF

R15

100Ω

R16

100Ω

R21

100Ω R35

10Ω

R22

100Ω

R23

100Ω

R24

100Ω

C24, 2nF

2kV

TVSBULK

CBULK

–

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1842B OPERATION

Figure 7. DC1842B, LTC4271 I2C and Address Connections

I2C Communication and Addressing

TheLTC4271internal registersare accessedvia I2Ctoread

and/or write configuration, status, and interrupt registers.

The I2C lines SDAOUT, SDAIN and SCL connect to the

30-pin connector (Figure 7). Subsequently, the I2C bus

is accessed on the DC1680B.

The LTC4290B/LTC4271 chipset has an address of

(A610A3A2A1A0b), where A6, A3, A2, A1, and A0are the

logic state of the AD6, AD3, AD2, AD1, and AD0 pins

respectively. On the DC1842B, AD0 and AD1 are tied low

with pull-down resistors. AD2, AD3 and AD6 are brought

out to the 30-pin connector (Figure 7) and set with three

switches on the DC1680B.

I/O LED Indicators

The DC1842B features four LEDs to indicate the states

of the LTC4290B/LTC4271 chipset general purpose input

outputpins.Thesepinsareconfiguredasinputsoroutputs

via I2C. GP1 and GP0 are referenced to DGND and driven

by the LTC4271 when set as outputs (Figure 8). XIO0 and

XIO1arereferenced toVEE and aredrivenbytheLTC4290B

when set as outputs (Figure 9). J2 provides test points

for access to these I/Os.

Figure 8. DC1842B, LTC4290B General Purpose I/O LED Indicators

Figure 9. DC1842B, LTC4271 General Purpose I/O LED Indicators

Figure 10. DC1842B AUTO and MID Jumpers

DGND

SDAOUT

SDAIN

SCL

INT

SDAOUT

SDAIN

SCL

INT

AD6

AD3

AD2

AD1

AD0

AD6

AD3

AD2

TO 30-PIN

CONNECTOR

LTC4271

0Ω

DC1843A F07

0Ω R9

0Ω

VDD33

GP1

GP0

DGND

J2, PIN 5

J2, PIN 6

LTC4271

DC1843A F09

R28

560Ω R29

560Ω

GRN

GP0

GRN

GP1

VDD33

AUTO

MID

DGND

J2, PIN 3

J2, PIN 4

LTC4271

DC1843A F10

JP1 JP2

AUTO

MID

AGND

XIO1

XIO0

VEE

J2, PIN 9

J2, PIN 10

VEE

LTC4290

DC1843A F08

R30

27k R31

27k

GRN

XIO0

GRN

XIO1

Q13B

BC846AS

Q13A

BC846AS R33

220k

R32

220k

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1842B OPERATION

AUTO and MID Jumpers

The AUTO and MID pins of the LTC4271 are set by

jumpers JP1 and JP2 respectively on the DC1842B

(Figure 10). Setting JP1 to HI enables the AUTO pin mode

in the LTC4290B/LTC4271 chipset. J2 provides test points

for access to AUTO and MID.

In AUTO pin mode (JP1 high), the LTC4290B/LTC4271

chipset internal I2C registers default to the AUTO pin

high state after a software or hardware reset, or system

power on. The LTC4290B/LTC4271 chipset autonomously

detects,powers onanddisconnects power toPDs without

the need for I2C host control.

Setting JP1 to LO disables AUTO pin mode and sets the

LTC4290B/LTC4271 chipset to a low current shutdown

mode. An I2C host controller can then be used to config-

ure the LTC4290B/LTC4271 chipset to semi-auto mode

for controlled PSE operation or to manual mode for test

purposes.

Setting JP2 to HI enables the midspan mode detection

backoff timer in the LTC4290B/LTC4271 chipset. For

endpoint PSEs, set JP2 to LO to disable midspan mode.

For quick PSE evaluation in AUTO pin mode with

MIDSPANdisabled,setJP1HIandJP2LOontheDC1842B.

Surge Protection

Ethernet ports can be subject to significant cable surge

events.Tokeep PoEvoltagesbelowasafe leveland protect

the application against damage, protection components,

as shown in Figure 11, are required at the main supply,

at the LTC4270 supply pins and at each port.

Bulk transient voltage suppression (TVSBULK) and bulk

capacitance (CBULK) are required across the main PoE

supply and should be sized to accommodate system level

surge requirements.

EachLTC4290requires a 10Ω, 0805 resistor (R1) in series

from supply AGND to the LTC4290 AGND pin. Across the

LTC4290 AGND pin and VEE pin are an SMAJ58A, 58V

TVS (D1) and a 1μF, 100V bypass capacitor (C19). These

components must be placed close to the LTC4290 pins.

Finally, each port requires a pair of S1B clamp diodes:

one from OUTn to supply AGND and one from OUTn to

supply VEE. The diodes at the ports steer harmful surges

into the supply rails where they are absorbed by the surge

suppressors and the VEE bypass capacitance. The layout

of these paths must be low impedance. These S1B diodes

are placed on the DC1680 mother board of the DC1843 kit.

Figure 11. DC1842B, 1 of 8 Port Outputs. Surge Protection

30-PIN

CONNECTOR

DC1842B SIDE DC1680B SIDE

DC1843A F11

VEE

VEE VEE

S1B

PROTECTION

S1B

VSSK

C19

1µF

100V

D26

B1100

4 × 1.00

PSM075-100MSE

OUTn OUTn

PORT

SENSEn

RSENSEn

GATEn OUTn

LTC4290

AGND

SMAJ58A

R35

10Ω

C26

0.1µF

0.22µF

X7R

100V

VEE TVSBULK

CBULK

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1680B OPERATION

Demonstration circuit 1680B is configured as an 8-Port,

IEEE802.3at Type 1 and Type 2 PoE PSE motherboard in

theDC1843Bkit.Thisboard acceptsvariousPSEdaughter

cards featuring Linear Technology PSE controllers. The

DC1680B is capable of powering up to 8 PDs.

Daughter Card Insertion Precautions

When inserting or removing the daughter card into the

DC1680B, verify all supplies and LEDs are off. Push the

card straight down for insertion or pull straight up for

removal to avoid bending the connector pins. Follow the

instructions in the Quick Start Procedure for alignment.

VEE Supply

ConnectapowersupplyforVEE withthepositiverailtoPOS

and negative rail to NEG as shown in Figure 3 of the Quick

Start Procedure. Set the voltage within the range in Table 1

dependingon whethertheapplication is aType1 or Type 2.

Choose a power supply rating and set the current limit

highenoughtoprovidepowerforthemaximumnumberof

PDs connected and to meet each PD power requirements.

Table 1. DC1843B VEE Power Range for Type 1 and Type 2 PSEs

PSE TYPE

VEE SUPPLY

RANGE

MAX DELIVERED

PORT POWER

POWER

SUPPLY*

Type 1 45V to 57V 13W 200W

Type 2 51V to 57V 25.5W 400W

*Recommended DC1843B power supply minimum to avoid drooping in

a worst-case scenario with ILIM current at all 8 ports.

PD Connection

PDs are connected using an Ethernet cable to any of the

8 ports at the 2×6, RJ45 connector J4 on the DC1680B

(Figure 3). Test points for port outputs OUT1 through

OUT8 are provided.

8-Port Configuration

TheDC1680Bisconfiguredforan8-portPSEmotherboard

for the DC1843B kit. Four RJ45 dust caps at J3 and four

dust caps at J4 are inserted to block off the four unused

Ethernet ports. Additional pegs are placed in the last 4

pins of connector J1 to block off the unused pins when

the DC1842B daughter card is inserted.

DC1680B USER FEATURES

Refer to Figure 12 and Figure 13 for the following user

features.

Onboard 3.3V Supply

The DC1680B has an onboard VDD33 digital supply gen-

erated from the VEE supply. DGND is a negative voltage

referenced to AGND. If an external 3.3V supply is to be

used, contact Linear Technology Applications for proper

connection.

VEE and VDD33 LED Indicators

LEDs for VEE and VDD33 indicate if voltage is present at

these supplies. Verify these LEDs are off before inserting

or removing the daughter card.

Digital Connections

The DC1680B has connections for I2C control from a

host controller. The DC590 is optionally connected to

the DC1680B at J5 through a 14-pin ribbon cable. The

QuikEval software will automatically detect the DC1680B

and open the LTC4271 GUI. A second 14-pin ribbon cable

can be connected to J6 for I2C expansion to another

DC1680B board with slight board modifications. Contact

Linear Technology Applications for instructions.

Digital test points include SCL, SDA, DGND, INT, MSD,

and RESET. I2C address pin AD6, AD3, and AD2 are set

with a 3-bit switch SW3.

Midspan PSE

The DC1843B can be configured as a midspan PSE.

Upstream switch data comes in to J3. Data and PoE go

out to a PD at J4. Set both MID and AUTO pins logic high.

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1680B OPERATION

Figure 12. DC1680B Connections and Supply LEDs

MSD and RESET Pushbuttons

Pushbutton switch SW1, when pressed, pulls the RESET

pin of the daughter card logic low. The PSE controller is

thenheld inactivewith allportsoff andall internalregisters

reset to their power-up states. When SW1 is released,

RESET ispulledhigh,andthePSEbeginsnormaloperation.

Pushbutton switch SW2 when pressed pulls the maskable

shutdown input (MSD) pin of the daughter card logic low.

Whenpressed,allportsthathavetheircorrespondingmask

bit set in the mconfig register of the PSE controller will be

shutdown. These ports must then be manually re-enabled

via I2C or by resetting the PSE.

dc1843bfa

DEMO MANUAL DC1843B

DEMONSTRATION CIRCUIT 1680B OPERATION

Figure 13. DC1680B Address Switch, Pushbutton Switches, INT LED, and Port Power LEDs

Interrupt LED

A red LED indicates when the INT line is pulled logic low

by the daughter card. When the interrupt is cleared (high)

via I2C servicing, the LED is turned off.

Port 1 Through 8 Power LED Indicators

Each PSE port has a green LED indicator to show when

PoE power is present at the port. The LEDs are driven by

the respective port OUT voltage.

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