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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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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