DC804B - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
LTC4267
DESCRIPTION
Demonstration circuit 804 is a POWER OVER
ETHERNET
PD
INTERFACE
WITH
INTEGRATED SWITCHING REGULATOR featuring the LTC4267. It provides a complete IEEE
802.3af power device (PD) interface and isolated
3.3V power supply solution for use in Power over
Ethernet (PoE) applications.
The LTC4267 integrates the 25k signature resistor, classification current source, thermal overload
protection, signature disable and power good signal along with an undervoltage lockout optimized
for use with the IEEE required diode bridge. The
precision dual level input current limit allows the
LTC4267 to charge load capacitors and interface
with legacy PoE systems.
The LTC4267 combines the above features with a
current mode switching controller designed for
driving a 6V rated N-channel MOSFET. It features
programmable slope compensation, soft-start, and
constant frequency operation, minimizing electrical
noise even with light loads.
The DC804 demo board comes in 3 variants, -A, B and -C, which output 3, 5 and 8.5 watts, respectively. There is also optional circuitry to provide
alternative secondary side regulation with the
LT4430, a high performance Secondary Side Optocoupler Driver.
Design files for this circuit board are available.
Call the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Minimum Turn-on Voltage
Input from PSE
-39V
Maximum Turn-off Voltage
Input from PSE
-33V
Auxiliary input voltage range
Input from 24V auxiliary power
+38V to +57V
Minimum operating voltage
Iout = Maximum rated load
-36V
Maximum Input Current
Input from PSE
400 mA
Version -A, Vout=3.3V
1.0A
Version -B, Vout=3.3V
1.6A
Version -C, Vout=3.3V
2.6A
Vin=48VDC, from PSE, Iout=max output current
3.3V, typical
Line (50% to 100% full load)
±2%, typical
Load (0% to 100% of rated full load)
±2%, typical
Basic Insulation
250VDC
Maximum Output Current
Output Voltage
Output Regulation
Isolation Voltage
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
OPERATING PRINCIPLES
Demonstration circuit 804 interfaces with a customer’s Power-Over-Ethernet test setup per Figure 1. The front end of the demo circuit implements the required Ethernet input interface transformer coupling and common-mode termination
through the integrated connector J1. The demonstration circuit is setup to allow data to pass in and
back out of the board while the DC804 performs
IEEE 802.3af interface functions. The Power
Sourcing Equipment (PSE) is connected to J1 and
the PHY is optionally connected to J2.
While every demonstration circuit is equipped with
a jumper and the appropriate resistors to select
any of the four classes defined as of this printing,
not every demonstration circuit can perform as if
it were any one of the four classes. That is,
DC804B-A is designed to produce 3.3V power for
a class 1 PD, DC804A-B for a class 2 device and
DC804A-C for a class 3. A DC804B-A, for example, cannot deliver sufficient power for a class 3
device, regardless of the classification jumper position.
The PD is required to have 0.1uF of capacitance
during detection and this is provided by C2. It is
also required to have at least 5uF of capacitance
after the in-rush circuit, provided by capacitors C1
and C9.
After detection and classification, the PD is powered up when the input voltage exceeds the
LTC4267 turn-on under-voltage lock out (UVLO)
through a dual-level current-limited power switch.
While the voltage between POUT and VPORTN is
above the Power Good trip point, the amperage
through the power switch is held below the lowlevel current limit. When the voltage between
POUT and VPORTN falls below the Power Good
trip point, the Power Good signal goes active low
and the amperage through the power switch is
held below the high-level current limit.
This demo circuit allows detection and power
classification of the PD per the IEEE 802.3af specification. During the detection process of a PD,
the LTC4267 displays the proper 25k signature
resistor. Signature detection may be disabled, if
so desired, by appropriately setting the jumper at
JP5. If signature detection is disabled, all interface functions of the LTC4267 are also disabled.
Signature detection, classification, the internal
power MOSFET switch and POWER GOOD are
all disabled. As this demonstration circuit uses the
POWER GOOD signal, the power regulator is disabled, as well.
Classification is programmed by the selection of a
single external resistor connected to the RCLASS
pin. The classification can easily be set in this
demo circuit with the placement of a single jumper
on JP0, JP1, JP2, JP3, or JP4.
For the PD to remain powered on, it must present
to the PSE both AC and DC components of the
Maintain Power Signature (MPS). The PD must
hold the DC MPS by drawing at least 10mA or the
PSE may disconnect power. The DC804 demo
circuit can be made to draw the requisite 10mA by
enabling the minimum load at JP6.
The synchronous flyback converter operates at a
typical switching frequency of 200kHz, controlled
by the current mode controller portion of the
LT4267. Galvanic isolation is achieved through
transformer T1 and opto-isolator ISO2.
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
The primary side power path is comprised of C1,
L1, C9, ½ of T1, Q2, and R11. These components
should be as close to each other as possible when
laying out the printed circuit board. The components R4 and C6 serve to damp switching spikes
on Q2. They should be placed as close as possible to Q2 in order to be effective. The secondary
side power path is made up of the other ½ of T1,
D5, C4, C5 and C18. These parts should also be
laid out as close to each other as possible, without
overlapping any of the circuitry or traces of the
primary side. The components R5 and C3 serve
to damp switching spikes on D5. They should be
placed as close as possible to D5 in order to be
effective.
In order to ensure proper operation, the designer
must ensure that the PD input current requirement
does not exceed the LTC4267 current limit over
the unit’s operating voltage range.
QUICK START PROCEDURE
Demonstration circuit 804 is easy to set up to evaluate the performance of the LTC4267. For proper
equipment setup, refer to the connection diagram
and follow the procedure below:
1. With the power source to the PSE turned off,
connect the input power supply to the board
through the J1 filtered Ethernet connector.
2. In addition to a PSE, the DC804 board can be
powered by an alternate input power supply
through the VSIG+ and VSIG- terminals. Similarly, the alternate input power supply can be
connected through the SPARE+ and SPAREterminals. Only one set of connections is necessary. Do not connect more than one power
source.
3. Install the jumper at one of the locations JP0
through JP4 determine the classification of the
power device.
4. Install the jumper at JP5 to “enable.”
5. Connect or remove the DC Maintain Power
Signature minimum load as desired by appropriately connecting a jumper at JP6.
6. Turn on the PSE or alternate input power
supply. Increase the voltage until the power
converter turns on. Be careful not to exceed
57VDC. NOTE: Make sure that the input voltage does not exceed 57VDC. If a higher input
voltage is required, power components with
higher voltage ratings should be used.
7. Verify proper classification, signature detection
and Power Good signal status.
8. Check the output voltage. It should be 3.3V,
typical. If there is no output, temporarily disconnect the load to make sure that the load is
not set too high.
9. Once the proper output voltage is established,
adjust the load current within the appropriate
range and observe the output regulation, ripple
voltage, efficiency and other parameters.
The PD interface of the LTC4267 can be bypassed by powering just the DC/DC regulator with
an optional auxiliary power source via the V+ and
–48V terminals. Even if the PD interface is bypassed, the signature detection must be enabled
in order for the POWER GOOD signal to enable
the current mode controller.
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
OPTIONAL CIRCUITRY
DC804 is equipped with optional circuitry. Their
functions fall into three major categories: existing
control loop modifications, non-isolated feedback,
and LT4430 circuitry.
The pads at locations C11 and C14 are used to
modify the existing feedback compensation. The
user is cautioned that adding components to these
locations will alter the behavior of the voltage
regulator, possibly resulting in instability.
The pads located at R1, R15 and C12 are used
only if the isolated feedback circuitry is not necessary. In such a case, disable the isolated control
circuitry by removing the components at locations
D9, ISO2, and R13. Tie the secondary side
ground reference to that of the primary by removing C15 and replacing it with a low AC impedance
short circuit.
All of the components on the bottom side of the
board are used to integrate Linear Technology’s
LT4430, a high performance secondary side optocoupler driver. The LT4430 features high performance capabilities such as a precision reference,
start-up and short circuit recovery overshoot control and high operating bandwidth. To use the
LT4430, disable the existing control circuitry by
removing R12, C10, C13 and D10 for DC804B-A,
also remove additional resistor R25 for DC804AB, -C version located on the top side, and replace
R19 with a 22.1K, 1% resistor. Install the optional
components C16, R27, C20, C21, C22 and U2 for
DC804B-A. For DC804 -B, -C version, install D13
in addition to the components listed in previous
sentence. Please consult the LT4430 data sheet
for further details about the proper application of
this device.
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
Figure 1. Setup Diagram
5
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
6
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804
POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR
SHT 1 V+
C20 OPT
U2
1
2
C21 OPT
3
VIN
OPTO
GND COMP
OC
FB
6
OPTO SHT 1
5
4
LT4430ES6 OPT
FB
SHT 1
C22
OPT
SHT 1 COMP
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
APPROVALS
PCB DES.
TECHNOLOGY
MI
APP ENG. KAUNG H.
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900 www.linear.com
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
TITLE: SCHEMATIC
RJ-45 ETHERNET OUTPUT
SIZE
N/A
SCALE = NONE
IC NO.
REV.
LTC4267CDHC
1
DEMO CIRCUIT 804B-A
DATE: Monday, February 07, 2011
SHEET 2
OF 2
7
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