DC1351B - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
LTC4269IDKD-2
DESCRIPTION
Demonstration circuit 1351B is a high-power
supply featuring the LTC®4269IDKD-2. This
board acts as an IEEE 802.3at compliant, high
power Power-over-Ethernet (PoE), Powered
Device (PD) and connects at the RJ45 to a
compatible high power Power Sourcing
Equipment (PSE) device, such as the
DC1366A.
The LTC4269IDKD-2 provides IEEE802.3at
standard (PoE+) PD interfacing and power
supply control. When the PD is fully powered,
the PD interface switches power over from the
PSE to the switcher through an internal, low
resistance, high power MOSFET. The highly
integrated LTC4269IDKD-2 controls a high-
Table 1.
power, small-sized power supply that utilizes a
highly-efficient isolated forward topology with
synchronous rectification. The DC1351B supplies a 5V output at up to 5A.
DC1351B also demonstrates the use of an
auxiliary 48V wall adapter. When present, the
auxiliary supply becomes the dominant supply
over PoE to provide power.
Design files for this circuit board are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Port Voltage (VPORT)
At Ethernet port
37V – 57V
Auxiliary Voltage (VAUX)
From Aux- to Aux+ terminals
44V – 57V
Output Voltage (VOUT) Initial Set-point
VPORT = 37V to 57V, IOUT = 0A to 5A
5.05V ± 1%
Maximum Output Current
VPORT = 42V
4.6A (min)
Typical Output Voltage Ripple
VIN = 50V, IOUT = 4.6A
40mVP–P (typ)
Output Regulation
Over Entire Input Voltage and Output Current Range < ±0.1% (typ)
Peak to Peak Deviation with Load Step of 2.5A to 5A ±120mV (< ±2.5%) (typ)
Load Transient Response
Settling Time (within 1% of VOUT)
Switching Frequency
Efficiency
150us (typ)
225kHz (typ)
VPORT = 42V, IOUT = 5A, not incl. diode bridge
92.5% (typ)
OPERATING PRINCIPLES
A compatible high power PSE board, such as
the DC1366A, is connected to the DC1351B at
the RJ45 connector J2 (see the schematic). As
required by IEEE802.3at, a diode bridge is used
across the data pairs and signal pairs. Schottky
diodes (D5-8, D12-15) are used at the input to
improve efficiency over standard diode bridges.
The LTC4269IDKD-2 provides an IEEE802.3at
standard PoE 25k signature resistance and is
set for a power class 4. When the PD is pow-
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
ered and voltage is above the PoE “On Voltage”, the LTC4269IDKD-2 switches the port
voltage over to the power supply controller
through its internal MOSFET which lies between the VPORTN and VNEG pins. This voltage
charges C11 through a trickle charge resistor,
R3 to power the bias pin, Vin, of the power supply controller. Once the bias power gets to its
VIN(ON) threshold, the IC begins a controlled
soft-start of the output. As this voltage rises,
bias power is taken over by T2, D1/2, and L1.
When the soft-start period is over, the output
voltage is regulated by the combination of the
optoisolator (U2) and the reference/error amplifier (D21) pulling down on the COMP pin. The
OUT and SOUT pins which drive Q3 and Q2,
respectively, are Pulse Width Modulated (PWM)
in order to keep the output voltage constant.
The synchronous rectifiers (Q4 and Q5) on the
secondary side are self-driven by T2. This reduces the gate drive part’s count and complexity since no external driver ICs or delay circuits
are needed to achieve synchronous rectification. The high efficiency that is expected with
synchronous rectification is maintained.
QUICK START PROCEDURE
Demonstration circuit 1351B is easy to set up to
evaluate the performance of the LTC4269IDKD2 in a PoE+ PD application. Refer to Figure 1
for proper equipment setup and follow the procedure below:
NOTE: When measuring the input or output volt-
age ripple, care must be taken to avoid a long
ground lead on the oscilloscope probe. Measure the output (or input) voltage ripple by touching the probe tip and probe ground directly
across the +VOUT and –VOUT (or VPORT_P
and VPORT_N) terminals. See Figure 2 for
proper scope probe technique.
1. Place test equipment (voltmeter, ammeter,
and electronic load) across output.
a. Connect a PoE+ capable PSE with a CAT-5
cable to the RJ45 connector, J2. See Figure
1.
b. Or, connect a 37V to 57V capable power
supply (“Power Supply” in Figure 1) across
VPORT_P and VPORT_N.
c. If evaluating the auxiliary power supply
(“Auxiliary Supply” in Figure 1) capability,
connect a 44V to 57V capable power supply
across AUX+ to AUX-.
3. Check for the proper output voltage of 5V.
4. Once the proper output voltage is confirmed,
adjust the load within the operating range and
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
2. Input supplies:
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
MEASURED DATA
Figures 3 through 12 are measured data for a typical DC1351B.
94
92
90
88
86
42Vport
50Vport
82
57Vport
80
78
76
74
72
70
68
66
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Output Current (A)
Figure 3. Efficiency
0.03%
0.02%
0.01%
Regulation (%)
Efficiency (%)
84
42Vport
50Vport
57Vport
0.00%
-0.01%
-0.02%
-0.03%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Output Current (A)
Figure 4. Regulation
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
Figure 5. Output Voltage Ripple (37Vport, 5A)
Figure 6. Load Transient Response (48Vport, 2.5A to 5A to 2.5A)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
Figure 7. Temp Data (37Vport, 5A, Top)
Figure 8. Temp Data (37Vport, 5A, Bottom)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
Figure 9. Loop Plot (5A out)
Figure 10. Loop Plot (0A out)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
Figure 11. Stresses (57Vport, 5A)
Figure 12. Stresses (37Vport, 5A)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351B
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
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