ISL6844EVAL2 Intersil, ISL6844EVAL2 Datasheet

ISL6844EVAL2

Manufacturer Part Number

ISL6844EVAL2

Description

EVALUATION BOARD 2 ISL6844

Manufacturer

Intersil

Datasheets

1.ISL6840IUZ-T.pdf (12 pages)

2.ISL6844EVAL2.pdf (12 pages)

Specifications of ISL6844EVAL2

Main Purpose

Special Purpose DC/DC, Power Over Ethernet

Outputs And Type

1, Isolated

Power - Output

11W

Voltage - Output

3.3V

Current - Output

3.35A

Voltage - Input

36 ~ 57V

Regulator Topology

Flyback

Board Type

Fully Populated

Utilized Ic / Part

ISL6844

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Frequency - Switching

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Introduction

With advancements being made at a furious pace in the field

of networking, applications have started focusing on

achieving the most out of the existing infrastructure. Power

over Ethernet (PoE) is one such classic example that

integrates power and data lines. PoE consists of two power

entities: Power Sourcing Equipment (PSE) and Powered

Devices (PDs), for use with the physical layers. These utilize

the same LAN cabling (CAT-5 cables), that are used for

transmission of data, over spare twisted pair cables. Typical

applications include IP phones, WLAN access points,

security cameras and RFID tag readers, to name a few.

Scope

This document focuses on Intersil’s solution for the Powered

Device portion of the circuit, which complies with IEEE

802.3af, the standard for PoE. An inexpensive approach with

discrete circuitry has been adopted instead of an integrated

solution. With PoE soon turning into a commodity market,

low cost will be key, as compared to utilization of

sophisticated integrated solutions. The following solution has

been optimized for performance per the IEEE 802.3af

standard, with low cost and optimal performance as the

prime objectives. The evaluation board is currently available.

Powered Device (PD)

The PD needs to be able to operate with a maximum

average input power of 12.95W, and should be operational

between 36V and 57V DC. Class 0 (default) was selected for

this design, to provide the end user with maximum flexibility

with their output power requirements. Discrete classification

circuit may be added, as required, at a very low additional

cost. Other specifications selected are in line with the

requirements as specified in Table 33-12 of IEEE802.3af,

and are listed below:

Specifications Chosen for the PD Design

Operating Input Voltage range: 36V-57V DC

Max. Input Operating Current: 350mA

Max. Input Inrush Current: 400mA

Output Voltage: 3.3V

Output Current: 3.35A

Ripple: 50mV

Typical Efficiency: 87%

Isolation: 1500V DC

P-P

Application Note

1-888-INTERSIL or 1-888-468-3774

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

Selection of the Power Topology

While selecting the topology for this application, the emphasis

was placed on two key features: optimized performance and

low cost. A simple low-power design requirement, combined

with low cost target dictated the use of a flyback converter for

this application. Given that the input power available is limited

by the PSE, high efficiency becomes an essential

requirement. The converter is being operated in the

continuous current mode to achieve this goal.

IC Selection

Intersil’s superior industry-standard ISL684x family of PWM

controllers would best serve the needs of this design. Some

key features of this family of parts include:

• Tight internal voltage reference of 1% over temperature.

• 40ns peak current sensing.

• 1A MOSFET driver

ISL6844 was selected for its large UVLO hysteresis, UVLO

start threshold, and the fact that the converter has been

designed for a maximum operational duty cycle of 50%, thus

protecting the IC by limiting the duty cycle in case of extreme

fault conditions.

Transformer Design

The design of the flyback transformer is an iterative process,

and involves the following steps:

• Calculate the energy storage needed.

• Select core geometry and material.

• Select the maximum desired flux density of operation.

• Select core size.

• Calculate the maximum flux density.

• Calculate the turns ratio.

• Select the wire gauge, number of strands, winding order

• Estimate the losses.

• Verify the design.

While the details of the design are not discussed in this

document, as a summary, it was decided to proceed with an

EP-13 core, in order to achieve a balance of good

performance and low cost. The evaluation board provides

the end users with the option of using two other low-profile

cores for their transformer design, and can be tailored to

meet the customers’ specific requirements.

Intersil PoE Evaluation Board

and insulation requirements.

March 12, 2007

All other trademarks mentioned are the property of their respective owners.

Intersil (and design) is a registered trademark of Intersil Americas Inc.

AN1192.3

Related parts for ISL6844EVAL2

ISL6844EVAL2 Summary of contents

Page 1

... CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. | 1-888-INTERSIL or 1-888-468-3774 Intersil (and design registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2005-2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners. AN1192.3 ...

Page 2

... ISL6844EVAL1Z. For this implementation, a discrete gate drive circuit was designed, using a gate drive transformer to meet isolation requirements. • A conventionally rectified version, ISL6844EVAL2Z, is also available for end users to whom tight regulation is not critical, but emphasis is on cost saving at the expense of slightly reduced efficiency. Since the feedback is tapped ...

Page 3

The ripple current handling capacity of the output capacitor needs least 2.85A at full load, the ripple being the difference between the peak current and the maximum DC load seen. To bring the voltage ripple down to ...

Page 4

FIGURE 3. SECONDARY GATE DRIVE - Vgs OF Q3 CONDITION 48V OUT NOTE: Channel 1: Vgs of Primary MOSFET Channel 2: Vgs of Secondary MOSFET FIGURE 4. GATE DRIVE TRANSITION - CONDITION: V ...

Page 5

... Fixed Control (Bias, Gate Drive) - 300mW giving a total loss of about 1.6W (or 12.3%). This allows the solution to hit the 87% efficiency target. In the case of a diode-rectified circuit (ISL6844EVAL2Z), the VI loss across the diode would be about 1W, resulting in an additional 7% power consumption. The advantage of this version is the cost savings achieved by not having to use the relatively expensive gate drive circuitry ...

Page 6

... BOM for both the versions are listed below. Other output voltage versions are available upon request. Please contact our Technical Support Center for custom output voltage requirements. They can be reached through Intersil’s website at http://www.intersil.com or via phone at 1-888- INTERSIL. COMPLETE SOLUTION 4 ...

Page 7

... Input Connector for Power and Data - J1 Output Connector for Power and Data - J2 Input Rectifier Diodes - CR8, CR9 Ethernet Transformer (10/100 Base Ethernet Transformer (Gigabit Network Transient Voltage Suppressor - VR3 Schottky Rectifier (used in ISL6844EVAL2Z) - CR6 Safety Capacitor - C20 7 Application Note 1192 AN1192.3 March 12, 2007 ...

Page 8

... Front End Circuit - Identical for both ISL6844EVAL1Z and ISL6844EVAL2Z ...

Page 9

Schematic - ISL6844EVAL1Z Z ...

Page 10

... Resistor, 2.49kΩ, 1%, 1/16W Resistor, 31.6kΩ, 1%, 1/16W Resistor, 29.4kΩ, 1%, 1/16W Resistor, 17.8kΩ, 1%, 1/16W Resistor, 100kΩ, 1%, 1/16W Resistor, 249kΩ, 1%, 1/16W Resistor, 100Ω, 1%, 1/10W PACKAGE VENDOR MSOP-8 Intersil SOP-8 Renesas SOP-8 Renesas LFPAK Renesas SOT-23 Philips SOT-23 ...

Page 11

... Schematic - ISL6844EVAL2Z Z ...

Page 12

... ISL6844EVAL2Z BOM REF DES QTY PART NUMBER U1 1 ISL6844IUZ Q1 1 HAT2038R-EL HAT2088R-EL-E VR1 1 MMBZ5255B-7-F VR2 1 MMBZ5240B-7-F VR3 1 SMAJ58A CR1 1 BAS21 CR6 1 PDS1040-13 CR7 1 BAT54 CR8, CR9 2 DF02S T1 1 PA1267NL Alternate source T3 1 HX2260NL C1 C2012X7R2A104K C2 1 UPW2A180MED C5, C10, C15 3 C1608X7R1E104K C6 1 EEF-SD0G151R ...

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