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LTC4265

4265fa

TYPICAL APPLICATION

DESCRIPTION

IEEE 802.3at High Power PD

Interface Controller with

2-Event Classiﬁ cation Recognition

The LTC

4265 is a 3rd generation Powered Device (PD)

Interface controller intended for IEEE 802.3at high power

Power-over-Ethernet (PoE) applications up to 25.5W. By

supporting 1-event and 2-event classiﬁ cation signaling as

deﬁ ned by IEEE 802.3, the LTC4265 can be used in a wide

range of product conﬁ gurations. A 100V MOSFET isolates

the DC/DC converter during detection and classiﬁ cation,

and provides 100mA inrush current for a smooth power-

up transition. The LTC4265 also includes complementary

power good outputs, an on-board signature resistor,

undervoltage/overvoltage lockout and comprehensive

thermal protection. All Linear Technology PD solutions

include a shutdown pin with signature corrupt to provide

ﬂ exible auxiliary power options.

The LTC4265 PD interface controller can be used along

with a variety of DC/DC converter products to provide a

complete, cost effective power solution for high power

PD applications.

The LTC4265 is available in the space-saving low proﬁ le

(4mm × 3mm) DFN package and is drop-in compatible

with the LTC4264.

Turn-On vs Time

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

FEATURES

APPLICATIONS

IEEE 802.3af/at Powered Device (PD) Controller

IEEE 802.3at 2-event Classiﬁ cation Signaling

Programmable Classiﬁ cation Current

Flexible Auxiliary Power Support Using SHDN Pin

Rugged 100V Onboard MOSFET with 100mA Inrush

Current Limit.

Complementary Power Good Outputs

Onboard Signature Resistor

Comprehensive Thermal Protection

Undervoltage and Overvoltage Lockout

12-Lead, 4mm × 3mm DFN Package

802.11n Access Points

High Power VoIP Video Phones

RFID Reader Systems

PTZ Security Cameras and Surveillance Equipment

GND

CLASS

SHDN

CLASS

54V FROM

DATA PAIR

54V FROM

SPARE PAIR

0.1µF

PWRGD

LTC4265

T2PSE

RUN

5µF

MIN

3.3V

TO LOGIC

RTN

SWITCHING

POWER

SUPPLY

OUT

4265 TA01a

–

TO LOGICTO AUX

GND – V

50V/DIV

GND – V

OUT

50V/DIV

PWRGD – V

OUT

50V/DIV

100mA/DIV

TIME

25ms/DIV

4265 TA01b

LOAD

= 100µF

Summary of content (20 pages)

PAGE 1
LTC4265 IEEE 802.3at High Power PD Interface Controller with 2-Event Classification Recognition FEATURES DESCRIPTION n The LTC®4265 is a 3rd generation Powered Device (PD) Interface controller intended for IEEE 802.3at high power Power-over-Ethernet (PoE) applications up to 25.5W. By supporting 1-event and 2-event classiﬁcation signaling as deﬁned by IEEE 802.3, the LTC4265 can be used in a wide range of product conﬁgurations.
PAGE 2
LTC4265 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2, 3) GND Voltage ............................................ –0.3V to 100V VOUT Voltage ........................–0.3V to 100V (and ≤ GND) VOUT Pull-Up Current ..................................................1A SHDN ....................................................... –0.3V to 100V RCLASS, Voltage ............................................ –0.3V to 7V RCLASS Current.......................................................
PAGE 3
LTC4265 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. PARAMETER CONDITIONS Operating Input Voltage Signature Range Classiﬁcation Range Turn-On Voltage Undervoltage Lock Out Overvoltage Lock Out At GND Pin (Note 5) MIN TYP MAX UNITS 60 9.8 21 37.2 V V V V V V l l l l 1.5 12.5 ON/UVLO Hysteresis Window l 4.1 V Signature/Class Hysteresis Window l 1.
PAGE 4
LTC4265 TYPICAL PERFORMANCE CHARACTERISTICS Input Current vs Input Voltage 25k Detection Range Input Current vs Input Voltage 50 TA = 25°C INPUT CURRENT (mA) INPUT CURRENT (mA) TA = 25°C 0.3 0.2 30 CLASS 3 20 CLASS 2 CLASS 1 0.1 10 0 0 CLASS 1 OPERATION CLASS 4 40 0.4 Input Current vs Input Voltage 11.0 INPUT CURRENT (mA) 0.5 10.5 85°C –40°C 10.0 CLASS 0 0 2 4 6 GND VOLTAGE (V) 10 8 0 50 20 30 40 GND VOLTAGE (V) (RISING) 10 4265 G01 9.
PAGE 5
LTC4265 PIN FUNCTIONS SHDN (Pin 1): Shutdown Input. Use this pin for auxiliary power application. Drive SHDN high to disable LTC4265 operation and corrupt the signature resistance. If unused, tie SHDN to VIN. VOUT (Pins 7, 8): Output Voltage Negative Rail. Connects VOUT to VIN through an internal power MOSFET. Pins 7 and 8 must be electrically tied together at the package. T2PSE (Pin 2): Type-2 PSE Indicator, Open-Drain. Low impedance indicates the presence of a Type-2 PSE.
PAGE 6
LTC4265 APPLICATIONS INFORMATION OVERVIEW 50 Power over Ethernet (PoE) continues to gain popularity as more products are taking advantage of having DC power and high speed data available from a single RJ45 connector. As PoE continues to grow in the marketplace, Powered Device (PD) equipment vendors are running into the 12.95W power limit established by the IEEE 802.3af standard. GND (V) 40 30 ON UVLO 20 10 CLASSIFICATION DETECTION V2 DETECTION V1 GND – VOUT (V) 50 The IEE802.
PAGE 7
LTC4265 APPLICATIONS INFORMATION These modes satisfy the requirements deﬁned in the IEEE 802.3af/at speciﬁcation. Table 1. LTC4265 Modes of Operation as a Function of Input Voltage GND (V) LTC4265 MODES OF OPERATION 0V to 1.4V Inactive (Reset After 1st Classiﬁcation Event) 1.5V to 9.8V (5.4V to 9.8V) 25k Signature Resistor Detection Before 1st Classiﬁcation Event (Mark, 11k Signature Corrupt After 1st Classiﬁcation Event) DETECTION 12.
PAGE 8
LTC4265 APPLICATIONS INFORMATION SIGNATURE CORRUPT OPTION In some designs that include an auxiliary power option, it is necessary to prevent a PD from being detected by a PSE. The LTC4265 signature resistance can be corrupted with the SHDN pin (Figure 3). Taking the SHDN pin high will reduce the signature resistor below 11k which is an invalid signature per the IEEE 802.3af/at speciﬁcation, and alerts the PSE not to apply power.
PAGE 9
LTC4265 APPLICATIONS INFORMATION GND (V) 40 1st CLASS 2nd CLASS 30 ON UVLO 20 10 DETECTION V1 DETECTION V2 1st MARK 2nd MARK INRUSH PD CURRENT The PSE repeats this sequence, signaling the 2nd Classiﬁcation and 2nd mark event occurrence. This alerts the LTC4265 that a Type-2 PSE is present. The Type-2 PSE then applies power to the PD and the LTC4265 charges up the reservoir capacitor C1 with a controlled inrush current.
PAGE 10
LTC4265 APPLICATIONS INFORMATION PD STABILITY DURING CLASSIFICATION Classiﬁcation presents a challenging stability problem due to the wide range of possible classiﬁcation load current. The onset of the classiﬁcation load current introduces a voltage drop across the cable and increases the forward voltage of the input diode bridge. This may cause the PD to oscillate between detection and classiﬁcation with the onset and removal of the classiﬁcation load current.
PAGE 11
LTC4265 APPLICATIONS INFORMATION Once C1 is fully charged, the LTC4265 turns on is internal MOSFET and passes power to the PD load. The LTC4265 continues to power the PD load as long as the input voltage does not fall below the UVLO threshold. When the LTC4265 input voltage falls below the UVLO threshold, the PD load is disconnected, and classiﬁcation mode resumes. C1 discharges through the LTC4265 circuitry.
PAGE 12
LTC4265 APPLICATIONS INFORMATION OVERVOLTAGE LOCKOUT The LTC4265 includes an overvoltage lockout (OVLO) feature (Figure 5) which protects the LTC4265 and its load from an overvoltage event. If the input voltage exceeds the OVLO threshold, the LTC4265 discontinues PD operation. Normal operations resume when the input voltage falls below the OVLO threshold and when C1 is charged up. The LTC4265 includes a Thermal Protection feature which protects the LTC4265 from excessive heating.
PAGE 13
LTC4265 APPLICATIONS INFORMATION Bel Fuse, Coilcraft, Halo, Pulse, and Tyco (Table 4) can assist in selecting an appropriate isolation transformer and proper termination methods. Table 4. Power-over-Ethernet Transformer Vendors VENDOR CONTACT INFORMATION Bel Fuse Inc. 206 Van Vorst Street Jersey City, NJ 07302 Tel: 201-432-0463 www.belfuse.com Coilcraft Inc. 1102 Silver Lake Road Gary, IL 60013 Tel: 847-639-6400 www.coilcraft.
PAGE 14
LTC4265 APPLICATIONS INFORMATION Input Capacitor Transient Voltage Suppressor This occurs when the PSE voltage drops quickly. The input diode bridge reverses bias, and the PD load momentarily powers off the load capacitor. If the PD does not draw power within the PSE’s 300ms disconnection delay, the PSE may remove power from the PD. Thus, it is necessary to evaluate the load current and capacitance to ensure that an inadvertent shutdown cannot occur.
PAGE 15
LTC4265 APPLICATIONS INFORMATION Figure 9 shows two interface options using the T2PSE pin and the opto-isolator. The T2PSE pin is active low and connects to an opt-isolater to communicate across the DC/DC converter isolation barrier. The pull up resistor RP is sized according to the requirements of the opto-isolator operating current, the pull-down capability of the T2PSE pin, and the choice of V+.
PAGE 16
LTC4265 APPLICATIONS INFORMATION Shutdown Interface To corrupt the signature resistance, the SHDN pin can be driven high with respect to VIN or connected to GND. If unused, connect SHDN directly to VIN. PD applications may also opt for a seamless transition — that is, without power disruption — between PoE and auxiliary power. Exposed Pad The most common auxiliary power option injects power between the LTC4265 and the DC/DC converter. Figure 10 presents an example of this application.
PAGE 17
LTC4265 APPLICATIONS INFORMATION IEEE 802.3at SYSTEM POWER-UP REQUIREMENT LAYOUT CONSIDERATION FOR THE LTC4265 Under the IEEE 802.3at standard, a PD must operate under 12.95 Watts in accordance with IEEE 802.3af standards until it recognizes a Type-2 PSE. Initializing PD operation in 12.95-Watt mode eliminates interoperability issue in case a Type-2 PD is connects to a Type-1 PSE. Once the PD recognizes a Type-2 PSE, the IEEE 802.3at standard requires the PD to wait 80ms in 12.95W operation before 25.
PAGE 18
–54V FROM SPARE PAIR –54V FROM DATA PAIR B1100 s 8 PLCS 30.9Ω 3.01k 29.4k VCC 30k 100k 4265 TA02a 11.6 11.9 12.0 12.1 12.2 12.3 12.4 77 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A) 33pF 0.1μF 11.7 38.3k 10k 51k 4.7nF 1nF SG • 1 8 • 1μF 100Ω 2.2nF 2kV • LTV357TA GND 25mΩ 47pF 150Ω • PA2467NL 4 FDS3572 2.2nF BAT54 15Ω MMBT3906 MMBT3904 PE-68386 • 5 15Ω 470pF 2kV 4265 TA02b 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.
PAGE 19
LTC4265 PACKAGE DESCRIPTION DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev C) 0.70 p0.05 3.60 p0.05 2.20 p0.05 3.30 p0.05 1.70 p 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 p0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 p 0.10 12 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) 0.200 REF 3.00 p0.10 (2 SIDES) 3.30 p0.10 1.70 p 0.10 PIN 1 NOTCH R = 0.20 OR 0.35 s 45o CHAMFER 0.
PAGE 20
LTC4265 TYPICAL APPLICATION PoE-Based Self-Driven Synchronous Forward Power Supply 1mH DO1608C-105 BAS516 PA2431NL • 18V PDZ18B GND • 10μH + 2.2μF 100V 10μF 100V B1100 s 8 PLCS • 4.7nF 250V 33k VCC –54V FROM DATA PAIR 10k BAS516 133Ω 50mΩ 237k SOUT VIN OUT LTC4265 SMAJ58A 30.9Ω 0.1μF 100V OC ISENSE GND COMP LT1952 RCLASS SHDN VIN 1nF FDS2582 FDS8880 BAS516 10.0k Efﬁciency vs Load Current 5.1Ω 2.2nF 2kV 2k 33k VCC 22k 4.7nF PS2801-1-L BC857BF SS_MAXDC PGND 1nF 5.