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LTC4264

4264f

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

High Power PD Interface

Controller with 750mA

Current Limit

The LTC

4264 is an integrated Powered Device (PD) in-

terface controller intended for IEEE 802.3af Power over

Ethernet (PoE) and high power PoE applications up to 35W.

By including a precision dual current limit, the LTC4264

keeps inrush below the IEEE802.3af current limit levels

to ensure interoperability success while allowing for high

power PD operation. The LTC4264 includes a ﬁ eld-proven

power MOSFET delivering up to 750mA to the PD load while

maintaining compliance with the IEEE802.3af standard.

Complementary power good outputs allow the LTC4264 to

interface directly with a host of DC/DC converter products.

The LTC4264 provides a complete signature and power

interface solution for PD designs by incorporating the 25k

signature resistor, classiﬁ cation circuitry, input current

limit, undervoltage lockout, thermal overload protection,

signature disable and power good signaling.

The LTC4264 PD interface controller can be used along with

a variety of Linear Technology DC/DC converter products

to provide a complete, cost effective power solution for

high power PD applications.

The LTC4264 is available in the space-saving low proﬁ le

(4mm × 3mm) DFN package.

■

Complete High Power PD Interface Controller

■

IEEE 802.3af

Compliant

■

Onboard 750mA Power MOSFET

■

Complementary Power Good Outputs

■

Flexible Auxiliary Power Options

■

Precision Dual Current Limit with Disable

■

Programmable Classiﬁ cation Current to 75mA

■

Onboard 25k Signature Resistor with Disable

■

Undervoltage Lockout

■

Complete Thermal Overload Protection

■

Available in Low Proﬁ le (4mm × 3mm) DFN Package

■

802.11n Access Points

■

High Power VoIP Video Phones

■

RFID Reader Systems

■

PTZ Security Cameras and Surveillance Equipment

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

GND

CLASS

LIM_EN

SHDN

CLASS

SMAJ58A

–54V FROM

DATA PAIR

–54V FROM

SPARE PAIR

0.1µF

PWRGD

LTC4264

RUN

5µF

MIN

3.3V

TO LOGIC

RTN

SWITCHING

POWER

SUPPLY

OUT

4264 TA01a

–

DF1501S

50V/DIV

OUT

50V/DIV

PWRGD – V

OUT

50V/DIV

200mA/DIV

TIME (5ms/DIV)

4264 TA01b

LOAD

= 100µF

Turn On vs Time

Summary of content (24 pages)

PAGE 1
LTC4264 High Power PD Interface Controller with 750mA Current Limit DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Complete High Power PD Interface Controller IEEE 802.
PAGE 2
LTC4264 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Notes 1, 2) TOP VIEW VIN Voltage ................................................. 0.3V to –90V VOUT Voltage ......... VIN + 90V (and ≤ GND) to VIN – 0.3V SHDN Voltage ............................ VIN + 90V to VIN – 0.3V RCLASS, ILIM_EN Voltage ............... VIN + 7V to VIN – 0.3V PWRGD Voltage (Note 3) Low Impedance Source ....VOUT + 11V to VOUT – 0.3V Current Fed ..........................................................5mA PWRGD Voltage ...
PAGE 3
LTC4264 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. (Note 4) SYMBOL PARAMETER CONDITIONS VIL_ILIM ILIM_EN Low Level Input Voltage With Respect to VIN (Note 13) ● 1 V VPWRGD_OUT Active Low Power Good Output Low Voltage IPWRGD = 1mA, VIN = –54V, ⎯P⎯W⎯R⎯G⎯D Referenced to VIN ● 0.
PAGE 4
LTC4264 TYPICAL PERFORMANCE CHARACTERISTICS Input Current vs Input Voltage 25k Detection Range Input Current vs Input Voltage 100 0.5 TA = 25°C TA = 25°C 0.2 CLASS 5* 60 CLASS 4 40 CLASS 3 CLASS 2 CLASS 1 20 0.1 INPUT CURRENT (mA) INPUT CURRENT (mA) 0.3 CLASS 1 OPERATION 11.5 80 0.4 INPUT CURRENT (mA) Input Current vs Input Voltage 12.0 11.0 85°C 10.5 –40°C 10.0 9.
PAGE 5
LTC4264 PIN FUNCTIONS SHDN (Pin 1): Shutdown Input. Used to command the LTC4264 to present an invalid signature. Connecting SHDN to GND lowers the signature resistance to an invalid value and disables other LTC4264 operations. If unused, tie SHDN to VIN. NC (Pin 2): No Internal Connection. RCLASS (Pin 3): Class Select Input. Used to set the current the LTC4264 maintains during classiﬁcation. Connect a resistor between RCLASS and VIN. (See Table 2.) ILIM_EN (Pin 4): Input Current Limit Enable.
PAGE 6
LTC4264 BLOCK DIAGRAM CLASSIFICATION CURRENT LOAD SHDN 1 1.
PAGE 7
LTC4264 APPLICATIONS INFORMATION OVERVIEW 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 is becoming established in the marketplace, Powered Device (PD) equipment vendors are running into the 12.95W power limit established by the IEEE 802.3af standard.
PAGE 8
LTC4264 APPLICATIONS INFORMATION PSE RJ45 PD GND RJ45 0.1µF 0.1µF DGND BYP 3.3V VDD AUTO 1 AGND DETECT CMPD3003 1/4 LTC4259A CAT5 1 Tx1 1k 0.47µF Rx1 2 2 3 3 6 6 Rx1 VEE SENSE GATE OUT 10k S1B 0.25Ω 0.1µF DF1501S 5µF MIN SMAJ58A GND RCLASS PWRGD DC/DC CONVERTER LTC4264 Tx1 VIN VOUT SMAJ58A – + + + – – VOUT –54V IRLR3410 0.1µF GND 0.1µF AGND DETECT CMPD3003 1/4 LTC4259A 4 Rx2 5 1k 7 7 8 8 Rx2 SENSE GATE OUT 10k S1B 0.25Ω DC/DC CONVERTER LTC4264 5 VIN 0.
PAGE 9
LTC4264 APPLICATIONS INFORMATION DETECTION V1 –10 VIN (V) SERIES DIODES TIME DETECTION V2 CLASSIFICATION –20 UVLO TURN-ON –30 The IEEE 802.3af-deﬁned operating modes for a PD reference the input voltage at the RJ45 connector on the PD. The PD must be able to handle power received in either polarity. For this reason, it is common to install diode bridges BR1 and BR2 between the RJ45 connector and the LTC4264 (Figure 4).
PAGE 10
LTC4264 APPLICATIONS INFORMATION RJ45 1 2 3 POWERED DEVICE (PD) INTERFACE AS DEFINED BY IEEE 802.3af 6 TX + T1 BR1 TX – RX + TO PHY RX – GND 4 SPARE + BR2 5 7 8 LTC4264 0.1µF 100V D3 VIN SPARE – 4264 F04 Figure 4. PD Front End Using Diode Bridges on Main and Spare Inputs LTC4264 TO PSE GND 16k 25k SIGNATURE RESISTOR SHDN VIN 4264 F05 SIGNATURE DISABLE Figure 5.
PAGE 11
LTC4264 APPLICATIONS INFORMATION During classiﬁcation, the PSE presents a ﬁxed voltage between –15.5V and –20.5V to the PD (Figure 6). With the input voltage in this range, the LTC4264 asserts a load current from the GND pin through the RCLASS resistor. The magnitude of the load current is set with the selection of the RCLASS resistor. The resistor value associated with each class is shown in Table 2. Table 2. Summary of IEEE 802.
PAGE 12
LTC4264 APPLICATIONS INFORMATION UNDERVOLTAGE LOCKOUT INPUT CURRENT LIMIT The IEEE 802.3af speciﬁcation dictates a maximum turnon voltage of 42V and a minimum turn-off voltage of 30V for the PD. In addition, the PD must maintain large on-off hysteresis to prevent current-resistance (I-R) drops in the wiring between the PSE and the PD from causing start-up oscillation.
PAGE 13
LTC4264 APPLICATIONS INFORMATION During the inrush event as C1 is being charged, a large amount of power is dissipated in the MOSFET. The LTC4264 is designed to accept this load and is thermally protected to avoid damage to the onboard power MOSFET. If a thermal overload does occur, the power MOSFET turns off, allowing the die to cool. Once the die has returned to a safe temperature, the LTC4264 automatically switches to ILIMIT_LOW, and load capacitor C1 charging resumes.
PAGE 14
LTC4264 APPLICATIONS INFORMATION The active high PWRGD pin features an internal, opencollector output referenced to VOUT. During inrush, the active high PWRGD pin pulls low until the load capacitor is fully charged. At that point, PWRGD becomes high impedance, indicating the converter may begin running. The active high PWRGD pin can interface directly with the “Run” pin of converter products. The PWRGD pin features an internal 14V clamp to VOUT which protects the DC/DC converter from excessive voltage.
PAGE 15
LTC4264 APPLICATIONS INFORMATION thermal shutdown. For DC loads the maximum ambient temperature can be calculated as: TMAX = 125 – θJA • PWR (°C) where TMAX is the maximum ambient operating temperature, θJA is the junction-to-ambient thermal resistance (43°C/W), and PWR is the power dissipation for the LTC4264 in Watts (IPD2RON). such as Bel Fuse, Coilcraft, Halo, Pulse, and Tyco (Table 4) can provide assistance with selection of an appropriate isolation transformer and proper termination methods.
PAGE 16
LTC4264 APPLICATIONS INFORMATION Diode Bridge IEEE 802.3af allows power wiring in either of two conﬁgurations on the TX/RX wires, and power can be applied to the PD via the spare wire pair in the RJ45 connector. The PD is required to accept power in either polarity on both the data and spare inputs; therefore it is common to install diode bridges on both inputs in order to accommodate the different wiring conﬁgurations. Figure 9 demonstrates an implementation of the diode bridges. The IEEE 802.
PAGE 17
LTC4264 APPLICATIONS INFORMATION OPTION 1: AUXILIARY POWER INSERTED BEFORE LTC4264 RJ45 1 2 3 6 TX + T1 ~ TX – RX + TO PHY RX – D3 SMAJ58A TVS + BR1 ~ – ~ + C14 0.
PAGE 18
LTC4264 APPLICATIONS INFORMATION will be drawn from the PSE. On the other hand, if the adapter voltage is lower, the PSE will continue to supply power to the PD and the adapter will not be used. Proper operation will occur in either scenario. Option 2 applies power directly to the DC/DC converter. In this conﬁguration the adapter voltage does not need to exceed the LTC4264 turn-on UVLO requirement and can be selected based solely on the PD load requirements.
PAGE 19
LTC4264 APPLICATIONS INFORMATION RCLASS from Table 2. If a unique load current is required, the value of RCLASS can be calculated as: RCLASS = 1.237V/(ILOAD – IIN_CLASS) IIN_CLASS is the LTC4264 IC supply current during classiﬁcation given in the electrical speciﬁcations. The RCLASS resistor must be 1% or better to avoid degrading the overall accuracy of the classiﬁcation circuit. Resistor power dissipation will be 100mW maximum and is transient so heating is typically not a concern.
PAGE 20
LTC4264 APPLICATIONS INFORMATION Shutdown Interface To disable the 25k signature resistor, connect SHDN to the GND pin. Alternately, the SHDN pin can be driven high with respect to VIN. Examples of interface circuits that disable the signature and all LTC4264 functions are shown in Figure 10, options 2 and 4. Note that the SHDN input resistance is relatively large and the threshold voltage is fairly low.
PAGE 21
LTC4264 APPLICATIONS INFORMATION VOUT, to avoid the possibility of leakage shutting down the LTC4264. If not used, tie SHDN to VIN. The load capacitor connected between GND and VOUT of the LTC4264 can store signiﬁcant energy when fully charged. The design of a PD must ensure that this energy is not inadvertently dissipated in the LTC4264. The polarity-protection diodes prevent an accidental short on the cable from causing damage.
PAGE 22
–54V FROM SPARE PAIR –54V FROM DATA PAIR B2100 × 8 PLCS RCLASS 0.1µF 100V 3.01k 1% FB VCC 20k 1/4W 22µF 16V 100k 2.1k 1% 150k 33pF PG 0.1µF VC SENSE– SENSE+ OSC SFST CCMP GND LT3825 ENDLY SG SG 0.1µF 3300pF 0.1µF 0.015Ω 1/8W Si4488DY 10k 680pF 1000pF 100V 10Ω Figure 12. High Efﬁciency, Triple Output Power Supply 15k PGDLY tON SYNC RCMP VOUT 20k 29.4k 1% 91Ω BAS21 2.2µF 100V VIN 12µF 100V UVLO 402k + ILIM_EN PWRGD RCLASS PWRGD LTC4264 SHDN GND SMAJ58A 4.
PAGE 23
LTC4264 PACKAGE DESCRIPTION DE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev C) 0.70 ±0.05 3.60 ±0.05 1.70 ±0.05 2.20 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 3.30 ±0.05 (2 SIDES) 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ± 0.10 12 R = 0.05 TYP 3.00 ±0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) 1.70 ± 0.05 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 0.200 REF 0.75 ±0.05 0.00 – 0.05 6 0.25 ± 0.05 3.30 ±0.
PAGE 24
LTC4264 TYPICAL APPLICATION LTC4264 with Auxiliary Supply VOUT+ OUT TO DC/DC CONVERTER + AC ADAPTER 24V 30W D1 SMAJ58A – B2100 4 PLCS PD IN 36V TO 57V 14 1 2 3 6 IN FROM HIGH POWER PSE T3 ETH1-230LD 13 12 11 10 4 5 7 8 9 • • • • • • • • • • • • D3 D4 D2 D5 1 + 2 3 TO 4 PHY 5 6 D7 Q5 FMMT23 D8 R18 100k D6 R5 R6 75Ω 75Ω C14 C15 0.01µF 0.01µF 200V 200V R7 75Ω C16 0.01µF 200V C5 12µF 100V R14 100k J1 SS-6488-NF-K1 R4 75Ω C13 0.01µF 200V C8 0.