AN4319
Application note
Power over Ethernet - PD converter with 12 V 1 A output,
standard IEEE 802.3af compliant
By Antonio Rotta
Introduction
This document focuses on a reference design for a simple, low cost 12 V 1 A flyback
converter based on the PM8800A device.
The PM8800A is a highly integrated device embedding an IEEE 802.3af compliant
“Powered Device” (PD) interface together with a PWM controller.
It can be successfully used in all low power, low cost PoE applications.
Figure 1. STEVAL-TSP003V2 demonstration board photo
February 2014
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Contents
AN4319
Contents
1
2
3
Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 3
Electrical diagram and bill of material for 12 V at 1 A . . . . . . . . . . . . . . 4
Measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1
3.2
3.3
3.4
3.5
3.6
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Primary side waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Dynamic load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Short-circuit behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4
5
6
7
Loop compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Support material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
PCB layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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AN4319
Main characteristics and circuit description
1
Main characteristics and circuit description
The main characteristics (reference and electrical specifications) of the converter are listed
in
Table 2.
Table 1. Reference
Reference code
Device
Demonstration board
PM8800A
STEVAL-TSP003V2
Table 2. Electrical specification
Parameter
Input voltage supplies VIN [VDC]
Output voltage Vout [VDC]
Peak-to-peak output ripple
Efficiency DC-DC full-load
Efficiency overall peak
Transient response
Voutpk-pk
to 50% load step
V
in load line case
GLOOP bandwidth
GLOOP phase margin at 0 dB
GLOOP dB margin at 0 deg.
Specifications
From 40 to 60 V at 13 W
12 VDC ± 5% at 1 A
100 mV
> 88%
> 85%
< 200 mVpp
< 0.5%
3.5 kHz
105 deg.
-10 dB
This document details the characteristics and performances of the PM8800A demonstration
kit STEVAL-TSP003V2 which has been designed to cover a broad range of power over
Ethernet (PoE) applications.
The PM8800A is a highly integrated device embedding an IEEE 802.3af compliant powered
device (PD) interface together with a PWM controller and support for auxiliary sources.
Even though the PM8800A can be configured to work in both isolated and non-isolated
topologies, single or double output; this application note focuses on a low cost isolated
flyback converter topology with diode rectification, 12 V output voltage with up to 1 A output
current capability.
Auxiliary sources can be connected to the board on 2 input connectors. One input (AUX II)
allows prevalence of the auxiliary sources with respect to the PoE, while the other input
(AUX I) allows the usage of a wall adaptor with voltage lower than the internal PoE UVLO
threshold and still benefits from the inherent inrush and DC current limit.
The above mentioned configurations are all supported by the PM8800 demonstration kit as
options on the same PCB. The bill of material (BOM) in
Table 3
provides the list of
components to be mounted to obtain a 12 V at 1 A demonstration board.
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Electrical diagram and bill of material for 12 V at 1 A
AN4319
2
Electrical diagram and bill of material for 12 V at 1 A
Figure 2. Circuit diagram 12 V at 1 A
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AN4319
Electrical diagram and bill of material for 12 V at 1 A
Table 3. Bill of material 12 V at 1 A
Item
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Reference
C1
C2
C5
C7
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C26
C28
C29
C30
C31
C33
C35
C38
C41
C47
C48
C51
C53
C54
Description
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Elect. capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Ceramic capacitor
Elect. capacitor
Ceramic capacitor
Value
1 nF
0.1
F
10 nF
1 nF
1 nF
0.1
F
22
F
1 nF
0.1
F
0.1
F
10 nF
1
F
1 nF
1 nF
1
F
470 pF
0.1
F
0.1
F
1 nF
1 nF
1
F
1 nF
2.2 nF
1 nF
0.1
F
2.2 nF
22
F
22
F
22
F
1
F
22 nF
330
F
100 pF
PCB
footprint
C0805
C0805
C0603
C0603
C0805
C0805
C-POL8-10
C0805
C0603
C0805
C0603
C1206
C0603
C0603
C1206
C0603
C0603
C0603
C0805
C0805
C0603
C0805
C1812
C0805
C0603
C1812
C1206
C1206
C1206
C0603
C0603
C-POL8-6_3
C0603
Supplier
Several
Several
Several
Several
Several
Several
Panasonic
EEEFK2A220P
Several
Several
Several
Several
Several
Several
Several
Several
Several
Several
Several
Several
Several
TDK C1608X5R1E105K
Several
TDK 4532X7R3D222K
Several
Several
TDK 4532X7R3D222K
TDK C3216X5R1E226M
TDK C3216X5R1E226M
TDK C3216X5R1E226M
TDK C1608X5R1E105K
Several
Panasonic
EEEFK1C331P
Several
Voltage
100 V
100 V
100 V
100 V
100 V
100 V
100 V
100 V
50 V
100 V
100 V
100 V
100 V
100 V
100 V
50 V
50 V
50 V
200 V
200 V
25 V
200 V
2 KV
200 V
50 V
2 KV
16 V
16 V
16 V
25 V
50 V
16 V
50 V
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