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Maxim > App Notes > Hot-Swap and Power Switching Circuits
Keywords: powered device, PD, power over Ethernet, PoE, IEEE 802.3af, IEEE 802.3at, Class 2 PD, Class 3 PD, IP phones, IP cameras, security cameras, WAP, wireless access point, pointof sales, POS, thin client, Ethernet repeater, active clamped forward, flyback
Feb 10, 2011
APPLICATION NOTE 4983Wide Input Flyback Converter Features 5V at 2.6A Output
Abstract: This reference design is for a highly efficient, flyback, 5V Class 3 powered device (PD) with a wide 9V to 57V auxiliary input. The design features the MAX5969Bas its controller. The design also uses the MAX5974D, which controls current-mode PWM converters and provides frequency foldback for both the auxiliary input andpower over Ethernet (PoE) applications. Using these devices, this reference design is IEEE® 802.3af/at compliant. It is also a high-performance, compact, and cost efficientsolution for a Class 3 PD. The design can also support the wide auxiliary-input voltage range to provide 10W output power.
General Description
This reference design features the MAX5969B and MAX5974D. The MAX5969B controller is fully compliant with the IEEE 802.3af/at standard in a power-over-Ethernet(PoE) system. The device can also be powered from a wall adapter (WAD). The MAX5974D controls wide 9V to 57V input-voltage, active-clamped, current-mode PWMconverters and provides frequency foldback. Using these devices, this reference design is IEEE 802.3af/at compliant. It is also a high-performance, compact, and cost-effective solution for a Class 2 PD or a Class 3 PD.
Specifications:
The 5V/2.6A PD meets the following specifications:
Input voltage: 36V to 57VWAD input voltage: 9V up to 57VVOUT: 5V/2.6AOutput ripples: ±2%Load transient VP-P: ±2% (50% step-load)Line and load regulation: ±0.2%Total efficiency with a load of 2.5A at 5V and a 48V input: 87.4% (not including input LAN transformer and diode bridge)
Top view of the reference design. Bottom view of the reference design.
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AVAILABLE
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Transient Response
VIN = 40V, IOUT2 = 1A–2.5ACh1: 100mV/div, 5V output voltageCh4: 1A/div, output currentTime base: 2ms/div
Transient Response
VIN = 16V, IOUT2 = 1A–2.5ACh2: 200mV/div, 5V output voltageCh4: 1A/div, output currentTime base: 2ms/div
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A
B
C
DD
C
B
ATitle
noisiveRrebmuNSize
Letter
fo teehS:etaDDrawn By:
DT1
DITHER/SYNC2
RT3
FFB45 6 87
PGND 10
CS 9
NDRV 11
AUXDRV 12
13141516
SS DCLMP EN VC
COMP FB SGND CSSC
U2
R1VDD1
DET2 2EC 9
N.C.4
VSS5 RTN 6
WAD 7
PG 8N.C.3
CLS 10
EPEP
U1
R4
D3
Vin
VSS
C6
+ C7
GND
5V
RTN
VC
C3
R6
C14
PG
R15
R16
R10
C15C16 R18
R19
R21
RTN
RTN
R7
R8
C4
R14
C5 C12
MAX5969B MAX5974D FL5VPD
RTN
D10
FB
VDD
RTN
C24
R26
R17
R9PG
R25RTN
V+
V-
12345 6 7
8 N3
12345
67
8
N1
R13
R2
V-
V+
2
3
1
4
AC
V+
AC
V-
D1
2
3
1
4
AC
V+
AC
V-
D2
TC1 12
TD1- 10
TD1+ 11TX1+P1
TX1-P2 Y
220
G2
18
Y119
G1
17
21 22
VC1 13
TC2 6
TD2- 5
TD2+ 4TX2+P3
TX2-P6
VC2 14
TC3 1
TD3- 2
TD3+ 3TX3+P4
TX3-P5
VC3 15
CT 7
TD4- 9
TD4+ 8TX4+P7
TX4-P8
VC4 16
J1
DA
TA &
PO
WER
IN
DA
TA O
UT
V-
V+
R29 R30
C18
C20
R33
GND
R34
R36
53
4U4
RTN
R42
C19U3
R35
5V
C21
R37
VC
R32
R31
C23
FB
C22
R39
D5D11
D6
D7
RTN
CLS
CLS
C17
L2
VDD
C13
C3012
J2
WAD
Vin
R27
R28
C27
Vin
VSS
C31
1 2
J4
C32
AUX
C34
C10A C10B
4
5
8
1
10
2
3
7
69
T1
GND
D37A
D8
D8A
R20
R22
R5
R12
R3
Q1
C1
D10A
VC
THIS OPTIONAL CIRCUIT FOR 9V to 57V WAD INPUT
Q1A
R11
C2
C9
C8
12V-57V
MAX5974D
MAX5969B
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IEEE is a registered service mark of the Institute of Electrical and Electronics Engineers, Inc.
Related PartsMAX5969B IEEE 802.3af/at-Compliant, Powered Device Interface Controllers with Integrated Power MOSFET MAX5974D Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers
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Application note 4983: www.maxim-ic.com/an4983More informationFor technical support: www.maxim-ic.com/supportFor samples: www.maxim-ic.com/samplesOther questions and comments: www.maxim-ic.com/contact
AN4983, AN 4983, APP4983, Appnote4983, Appnote 4983Copyright © by Maxim Integrated ProductsAdditional legal notices: www.maxim-ic.com/legal
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