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LTC4267-3

42673fa

Power over Ethernet

IEEE 802.3af PD Interface with

Integrated Switching Regulator

The LTC

4267-3 combines an IEEE 802.3af compliant

Powered Device (PD) interface with a 300kHz current mode

switching regulator, providing a complete power solution

for PD applications. The LTC4267-3 integrates the 25k

signature resistor, classiﬁcation current source, thermal

overload protection, signature disable and power good

signal along with an undervoltage lockout optimized for

use with the IEEE-required diode bridge. The LTC4267-3

provides an increased operational current limit, maximizing

power available for class 3 applications.

The 300kHz current mode switching regulator provides

higher output power or smaller external size compared

to its lower frequency counterparts. The LTC4267-3 is

designed for driving a 6V rated N-channel MOSFET and

features programmable slope compensation, soft-start,

and constant-frequency operation, minimizing noise even

with light loads. The LTC4267-3 includes an onboard er-

ror ampliﬁer and voltage reference allowing use in both

isolated and nonisolated conﬁgurations.

The LTC4267-3 is available in a space saving, low proﬁle

16-pin SSOP or DFN packages.

IP Phone Power Management

Wireless Access Points

Security Cameras

Power over Ethernet

Complete Power Interface Port for IEEE 802

.3af

Powered Device (PD)

Onboard 100V, UVLO Switch

Constant-Frequency 300kHz Operation

Precision Dual Level Inrush Current Limit

Integrated Current Mode Switching Regulator

Onboard 25k Signature Resistor with Disable

Programmable Classiﬁcation Current (Class 0-4)

Thermal Overload Protection

Power Good Signal

Integrated Error Ampliﬁer and Voltage Reference

Low Proﬁle 16-Pin SSOP or DFN Packages

Class 2 PD with 3.3V Isolated Power Supply

VCC

PWRGD

NGATE

SENSE

/RUN

PGND

OUT

PORTP

CLASS

SIGDISA

PORTN

LTC4267-3

CLASS

68.1Ω

5µF

MIN

10k

470Ω

100k

60.4k

VCC

4.7µF

320µF

MIN

22nF

•

PA1133

PS2911

BAS516

TLV431

SBM1040

SMAJ58A

3.3V

1.5A

CHASSIS

HD01

–

HD01

–48V

FROM

DATA PAIR

–48V

FROM

SPARE PAIR

42671 TA01

Si3440

0.1Ω

6.8k

10k

0.1µF

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

LTPoE

is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

TYPICAL APPLICATION

FEATURES DESCRIPTION

APPLICATIONS

Summary of content (34 pages)

PAGE 1
LTC4267-3 Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator DESCRIPTION FEATURES n n n n n n n n n n n Complete Power Interface Port for IEEE 802®.
PAGE 2
LTC4267-3 ABSOLUTE MAXIMUM RATINGS (Note 1) VPORTN with Respect to VPORTP Voltage.... 0.3V to –100V POUT, SIGDISA, PWRGD Voltage...................... VPORTN + 100V to VPORTN –0.3V PVCC to PGND Voltage (Note 2) Low Impedance Source............................ –0.3V to 8V Current Fed........................................... 5mA into PVCC RCLASS Voltage..................VPORTN + 7V to VPORTN – 0.3V PWRGD Current......................................................10mA RCLASS Current......................
PAGE 3
LTC4267-3 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 3) SYMBOL PARAMETER CONDITIONS VPORTN Supply Voltage Maximum Operating Voltage Signature Range Classification Range UVLO Turn-On Voltage UVLO Turn-Off Voltage Voltage with Respect to VPORTP Pin (Notes 4, 5, 6) VTURNON PVCC Turn-On Voltage VTURNOFF VHYST MIN TYP MAX UNITS V V V V V V ● ● ● ● ● –1.5 –12.5 –34.8 –29.
PAGE 4
LTC4267-3 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 3) SYMBOL PARAMETER CONDITIONS ILIM_HI Input Current Limit, High Level ILIM_LO Input Current Limit, Low Level MIN TYP MAX UNITS VPORTN = –48V, POUT = –43V (Note 14, 15) ● 350 450 mA VPORTN = –48V, POUT = –43V (Note 14, 15) ● 90 205 mA 300 330 kHz 8 9.
PAGE 5
LTC4267-3 TYPICAL PERFORMANCE CHARACTERISTICS 0.5 Input Current vs Input Voltage Classification Range 50 TA = 25°C 0.3 0.2 0.
PAGE 6
LTC4267-3 TYPICAL PERFORMANCE CHARACTERISTICS 812 801.0 PVCC = 8V 330 TA = 25°C PVCC ≤ VCLAMP1mA 800.8 808 800.6 VFB VOLTAGE (mV) VFB VOLTAGE (mV) Oscillator Frequency vs Temperature Reference Voltage vs Supply Voltage OSCILLATOR FREQUENCY (kHz) Reference Voltage vs Temperature 804 800 796 800.4 800.2 800.0 799.8 799.6 799.4 792 799.2 788 –50 –30 –10 10 30 50 70 90 110 799.0 6 6.5 TEMPERATURE (°C) 42673 G10 330 310 300 290 280 270 6 6.5 7 7.5 8 8.
PAGE 7
LTC4267-3 TYPICAL PERFORMANCE CHARACTERISTICS 450 PVCC = VTURNON – 0.1V SHUTDOWN THRESHOLD (mV) 50 40 30 20 10 0 –50 –30 –10 10 30 50 70 TEMPERATURE (°C) 90 110 ITH/RUN Start-Up Current Source vs Temperature 600 400 350 300 250 200 150 100 –50 –30 –10 10 30 50 70 90 400 300 200 100 0 –50 –30 –10 10 30 50 70 TEMPERATURE (°C) 90 110 42673 G19 Soft-Start Time vs Temperature 4.0 PVCC = 8V 3.5 110 3.
PAGE 8
LTC4267-3 PIN FUNCTIONS (DFN/SSOP) PGND (Pins 2, 15/Pins 1, 8, 9, 16): Switching Regulator Negative Supply. This pin is the negative supply rail for the switching regulator controller and must be tied to POUT. ITH/RUN (Pin 1/Pin 2): Current Threshold/Run Input. This pin performs two functions. It serves as the switching regulator error amplifier compensation point as well as the run/shutdown control input. Nominal voltage range is 0.7V to 1.9V. Forcing the pin below 0.
PAGE 9
LTC4267-3 BLOCK DIAGRAM VPORTP 1.237V + – RCLASS PVCC SIGDISA CLASSIFICATION CURRENT LOAD 0.3µA 0.28V 25k SIGNATURE RESISTOR EN 9k 800mV REFERENCE VCC SHUNT REGULATOR PWRGD + EN – PVCC < VTURNON UNDERVOLTAGE LOCKOUT VFB INPUT CURRENT LIMIT SHUTDOWN SOFTSTART CLAMP CONTROL CIRCUITS + SHUTDOWN COMPARATOR 16k POWER GOOD 375mA + ERROR AMPLIFIER – + CURRENT COMPARATOR R S – PVCC Q SWITCHING LOGIC AND BLANKING CIRCUIT NGATE GATE DRIVER ITH/RUN 140mA 20mV – 1.
PAGE 10
LTC4267-3 APPLICATIONS INFORMATION DETECTION V1 Table 1. LTC4267-3 Operational Mode as a Function of Input Voltage INPUT VOLTAGE (VPORTN with RESPECT to VPORTP) LTC4267-3 MODE OF OPERATION 0V to – 1.4V Inactive –1.5V to –9.5V** 25k Signature Resistor Detection –9.8V to –12.4V Classification Load Current Ramps up from 0% to 100% –12.
PAGE 11
LTC4267-3 APPLICATIONS INFORMATION Series Diodes 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 accept power of either polarity at each of its inputs, so it is common to install diode bridges (Figure 2). The LTC4267-3 takes this into account by compensating for these diode drops in the threshold points for each range of operation. A similar adjustment is made for the UVLO voltages.
PAGE 12
LTC4267-3 APPLICATIONS INFORMATION CURRENT PATH LTC4267-3 TO PSE VPORTP 25k SIGNATURE RESISTOR 9k 16k PSE PROBING VOLTAGE SOURCE –15.5V TO –20.5V SIGNATURE DISABLE SIGDISA LTC4267-3 RCLASS RCLASS VPORTN VPORTN 42673 F03 PSE 42673 F04 PD Figure 4. IEEE 802.3af Classification Probing Classification Once the PSE has detected a PD, the PSE may optionally classify the PD.
PAGE 13
LTC4267-3 APPLICATIONS INFORMATION the classification current is reenabled. C1 will discharge through the PD circuitry and the POUT pin will go to a high impedance state. LTC4267-3 TO PSE UNDERVOLTAGE LOCKOUT CIRCUIT VPORTN VPORTP C1 5µF MIN + PGND POUT INPUT LTC4267-3 VOLTAGE POWER MOSFET 0V TO UVLO* OFF >UVLO* ON *UVLO INCLUDES HYSTERESIS RISING INPUT THRESHOLD ≅ –36V FALLING INPUT THRESHOLD ≅ –30.5V 42673 F05 CURRENT-LIMITED TURN ON Figure 5.
PAGE 14
LTC4267-3 APPLICATIONS INFORMATION LTC4267-3 PWRGD R9 100k THERMAL SHUTDOWN UVLO – TO PSE + PGND + – C1 5µF MIN –48V C1 R18 5µF 10k 100V POUT C15 0.047µF D6 MMBD4148 OPTIONAL AUXILIARY SWITCHING REGULATOR ACTIVE-HIGH ENABLE FOR RUN PIN WITH INTERNAL PULL-UP 300k PGND RSTART 42673 F06 Figure 6. LTC4267-3 Power Good the LTC4267-3 will attempt to quickly charge capacitor C1 using an internal secondary current limit circuit.
PAGE 15
LTC4267-3 APPLICATIONS INFORMATION temperature exceeds the overtemperature trip point, the current is reduced to zero and very little power is dissipated in the part until it cools below the overtemperature set point. Once the LTC4267-3 has charged up the load capacitor and the PD is powered and running, there will be minor residual heating due to the DC load current of the PD flowing through the internal MOSFET.
PAGE 16
LTC4267-3 APPLICATIONS INFORMATION Adjustable Slope Compensation LTC4267-3 PWM SHUTDOWN PVCC < VTURNOFF ALL VOLTAGES WITH RESPECT TO PGND VITH/RUN < VITHSHDN (NOMINALLY 0.28V) VITH/RUN > VITHSHDN AND PVCC > VTURNON (NOMINALLY 8.7V) LTC4267-3 PWM ENABLED 42673 F08 Figure 8.
PAGE 17
LTC4267-3 APPLICATIONS INFORMATION Diode Bridge IEEE 802.3af allows power wiring in either of two configurations: on the TX/RX wires or via the spare wire pairs in the RJ45 connector. The PD is required to accept power in either polarity on either the main or 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 these diode bridges. The IEEE 802.
PAGE 18
LTC4267-3 APPLICATIONS INFORMATION D11 B1100 D9 B1100 R2 75Ω C3 0.01µF 200V R1 75Ω C7 0.01µF 200V D10 B1100 10Ω D12 B1100 D6 SMAJ58A C2 1000pF 2kV J2 1 2 IN FROM PSE 3 6 TX+ 16 T1 1 15 2 TX– 14 3 RX+ 11 6 10 7 9 8 RX– 4 5 7 8 C11 0.1µF 100V OUT TO PHY TXOUT+ TXOUT– D13 MMSD4148 RXOUT+ C25 0.01µF 200V C24 0.01µF 200V RXOUT– R31 75Ω R30 75Ω D14 B1100 SPARE+ SPARE– D15 B1100 RJ45 NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTORS ARE 5% 2.
PAGE 19
LTC4267-3 APPLICATIONS INFORMATION where IIN_CLASS is the LTC4267-3 IC supply current during classification and is 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 50mW maximum and is transient so heating is typically not a concern. In order to maintain loop stability, the layout should minimize capacitance at the RCLASS node.
PAGE 20
LTC4267-3 APPLICATIONS INFORMATION The load capacitor can store significant energy when fully charged. The design of a PD must ensure that this energy is not inadvertently dissipated in the LTC4267-3. The polarity-protection diode(s) prevent an accidental short on the cable from causing damage. However, if the VPORTN pin is shorted to VPORTP inside the PD while the capacitor is charged, current will flow through the parasitic body diode of the internal MOSFET and may cause permanent damage to the LTC4267-3.
PAGE 21
LTC4267-3 APPLICATIONS INFORMATION Output Transformer Design Considerations Since the external feedback resistor divider sets the output voltage, the PD designer has relative freedom in selecting the transformer turns ratio. The PD designer can use simple ratios of small integers (i.e. 1:1, 2:1, 3:2) which yields more freedom in setting the total turns and mutual inductance and may allow the use of an off the shelf transformer.
PAGE 22
LTC4267-3 APPLICATIONS INFORMATION ISOLATED DESIGN EXAMPLE –48V FROM DATA PAIR + C1 RSTART – LPRI PGND PVCC VPORTP –48V FROM SPARE PAIR – VPORTN NGATE VPORTN Q1 RLIM RSENSE PGND VPORTP VFB ITH/RUN COUT LSEC RSL SENSE LTC4267-3 SIGDISA POUT • PGND RCLASS RCLASS + VOUT • CPVCC PVCC 0.1µF 100V D1 T1 VPORTP OPTOISOLATOR PGND PVCC PGND ERROR AMPLIFIER RC CC R2 R1 PGND CISO NONISOLATED DESIGN EXAMPLE T1 LBIAS D2 –48V FROM DATA PAIR R3 RSTART – 0.
PAGE 23
LTC4267-3 APPLICATIONS INFORMATION RSTART is connected to VPORTP and supplies a current, typically 100µA, to charge CPVCC. After some time, the voltage on CPVCC reaches the PVCC turn-on threshold. The LTC4267-3 switching regulator then turns on abruptly and draws its normal supply current. The NGATE pin begins switching and the external MOSFET (Q1) begins to deliver power.
PAGE 24
LTC4267-3 APPLICATIONS INFORMATION External Preregulator Compensating the Main Loop The circuit in Figure 13 shows a third way to power the LTC4267-3 switching regulator circuit. An external series preregulator consists of a series pass transistor Q1, zener diode D1, and a bias resistor RB. The preregulator holds PVCC at 7.6V nominal, well above the maximum rated PVCC turn-off threshold of 6.8V.
PAGE 25
LTC4267-3 APPLICATIONS INFORMATION Selecting the Switching Transistor With the N-channel power MOSFET driving the primary of the transformer, the inductance will cause the drain of the MOSFET to traverse twice the voltage across VPORTP and PGND. The LTC4267-3 operates with a maximum supply of – 57V; thus the MOSFET must be rated to handle 114V or more with sufficient design margin.
PAGE 26
LTC4267-3 APPLICATIONS INFORMATION OPTION 1: AUXILIARY POWER INSERTED BEFORE LTC4267-3 PD RJ45 1 2 3 6 TX+ T1 ~ TX– RX+ BR1 HD01 TO PHY ~ RX– D3 SMAJ58A TVS + C14 0.1µF 100V RSTART – C1 VPORTP SPARE+ 4 ~ 5 7 LTC4267-3 BR2 HD01 SPARE– 8 PVCC + ~ + CPVCC PGND – VPORTN POUT PGND D8 S1B ISOLATED WALL 38V TO 57V TRANSFORMER – OPTION 2: AUXILIARY POWER INSERTED AFTER LTC4267-3 PD WITH SIGNATURE DISABLED RJ45 1 2 3 6 TX+ T1 ~ TX– RX+ + ~ 100k C14 0.
PAGE 27
LTC4267-3 APPLICATIONS INFORMATION from the PSE while the transformer will sit unused. This configuration is not a problem in a PoE system. On the other hand, if the wall transformer voltage is higher than the PSE voltage, the LTC4267-3 switching regulator will draw power from the transformer. In this situation, it is necessary to address the issue of power cycling that may occur if a PSE is present. The PSE will detect the PD and apply power.
PAGE 28
LTC4267-3 APPLICATIONS INFORMATION low impedance alternate connection should be employed between the PGND pins of the LTC4267-3 and the PGND side of RSENSE, away from the high current loop. This Kelvin sensing will ensure an accurate representation of the sense voltage is measured by the LTC4267-3.
PAGE 29
LTC4267-3 TYPICAL APPLICATIONS Class 3 PD with 5V Nonisolated Power Supply COILTRONICS CTX-02-15242 4.7µH 12µF 100V –48V FROM DATA PAIR + 2.2µF 100V 100k VPORTP HD01 9.1V PVCC 300µF* • 1µF LTC4267-3 0.1µF NGATE + HD01 – RCLASS 45.3Ω 1% 10k 150pF 200V VFB SIGDISA POUT 220Ω SENSE ITH/RUN 22nF VPORTN * THREE 100µF CERAMICS FDC2512 PWRGD SMAJ58A –48V FROM SPARE PAIR UPS840 • MMBTA42 BAS516 10Ω – 220k 5V 1.8A PGND 27k 0.04Ω 1% 42.2k 1% 42673 TA02 8.
PAGE 30
J1 T1 T2 * ** 1 2 3 4 5 6 7 8 TO PHY TO PHY SMAJ58A 10Ω 45.3Ω 0.1µF HALO HFJ11 RP28E-L12 INTEGRATED JACK COILCRAFT D1766-AL PULSE PA0184 TWO 100µF CAPACITORS IN PARALLEL 47µF AND 220µF IN PARALLEL J1 9 10 11 12 13 14 12µF 100V PVCC 2.2µF 100V PGND VFB VPORTN POUT ITH/RUN SENSE SIGDISA RCLASS PWRGD NGATE LTC4267-3 VPORTP 4.7µH 220k 4.7µF PVCC BCX5616 8.2k 10p 51Ω BAS516 6.8k PVCC 10Ω BAS516 8.2V 220k 0.1µF 2.2k 0.
PAGE 31
LTC4267-3 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DHC Package 16-Lead Plastic DFN (5mm × 3mm) (Reference LTC DWG # 05-08-1706 Rev Ø) 0.65 ±0.05 3.50 ±0.05 1.65 ±0.05 2.20 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 4.40 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 5.00 ±0.10 (2 SIDES) R = 0.20 TYP 3.00 ±0.10 (2 SIDES) 9 R = 0.115 TYP 0.40 ±0.10 16 1.65 ±0.
PAGE 32
LTC4267-3 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641 Rev B) .189 – .196* (4.801 – 4.978) .045 ±.005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ±.0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ±.004 × 45° (0.38 ±0.10) .007 – .0098 (0.178 – 0.249) .
PAGE 33
LTC4267-3 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 10/12 Changed 12.95W IEEE 802.3af reference to 13.0W 9 Updated maximum power levels for class 0 and class 3 to 13.0W 12 Added 10Ω resistor to VPORTP pin in Figure 9 and Figure 10.
PAGE 34
LTC4267-3 TYPICAL APPLICATIONS High-Efficiency Class 3 PD with 3.3V Isolated Power Supply 10Ω PULSE PA1136 4.7µH 12µF 100V 2.2µF 100V 220k 220k 330Ω 510Ω MMTBA42 9.1V –48V FROM DATA PAIR 10Ω MMSD4148 VPORTP PVCC B1100 (8 PLACES) –48V FROM SPARE PAIR ITH/RUN • 0.068Ω 1% PVCC 100k VPORTN *100µF CERAMIC + 470µF TANTALUM POUT CHASSIS Si3440 45.3Ω 1% SIGDISA 570µF* • 10k SENSE RCLASS 3.3V 2.6A • BAS516 150pF BAS516 PVCC NGATE SMAJ58A SBM1040 4.7µF LTC4267-3 0.