LTC4279
Single Port PoE/PoE+/
LTPoE++ PSE Controller
FEATURES
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DESCRIPTION
The
LTC
®
4279
is an autonomous single port power sourc-
ing equipment (PSE) controller designed for use in IEEE
802.3at Type 1, Type 2 and LTPoE++ compliant Power
over Ethernet (PoE) systems. The LTC4279 provides fully
autonomous IEEE 802.3 and LTPoE++ compliant operation
without a microcontroller. The LTC4279 simplifies PSE
implementation, requiring only a single supply and a small
number of passive support components.
The LTC4279 delivers lowest-in-industry heat dissipation
by utilizing a low-R
DS(ON)
external MOSFET and a 0.1Ω
sense resistor, eliminating the need for expensive heat
sinks and increasing efficiency.
PD discovery uses a proprietary dual-mode 4-point detec-
tion mechanism ensuring excellent immunity from false
PD detection. Midspan PSEs are supported with physical
layer classification and a 2.5 second backoff timer.
Legacy and custom PDs are supported with pin-selectable
LEGACY and UltraPWR modes. LEGACY mode detects
and powers pre-IEEE specification PDs. UltraPWR mode
aggressively turns on and powers custom PDs requiring
high inrush and/or operational currents.
L,
LT, LTC, LTM, Linear Technology, the Linear logo and LTPoE++ are registered trademarks of
Analog Devices, Inc. All other trademarks are the property of their respective owners.
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Compliant with IEEE 802.3at Type 1 and 2
Supports LTPoE++
®
Up to 90W
Supports Dual-Signature PDs
Fully Autonomous Operation without Microcontroller
Very Low Power Dissipation
– 0.1Ω Sense Resistance
– Low R
DS(ON)
External MOSFET
Very High Reliability 4-Point PD Detection
– 2-Point Forced Voltage and Forced Current
Robust Short-Circuit Protection
Cable Surge Protected ±80V OUT Pin
Classification Dependent I
CUT
and I
LIM
Current
Thresholds
Supports 2-Pair and 4-Pair Output Power
UltraPWR Mode Supports Custom PDs Up to 123W
Pin-Selectable Detection Backoff Timer for Midspans
Pin Programmable Legacy PD Detection
Pin Programmable Maximum Power Mode
Status LED Pin
Available in 20-Pin QFN and 16-Pin SO Packages
APPLICATIONS
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PoE PSE Endpoints (Switch/Router)
PoE Midspan Power Injectors
Power Forwarders
Femto Cells
Security Systems
TYPICAL APPLICATION
10
TVS
BULK
1µF
100V
X7R
SMAJ58A
V
EE
R
PM
AGND
LTC4279
OUT
GATE
SENSE
0.1
V
EE
VSSK
4279 TA01
LED
RESET
MID
LEGACY
DUALPD
0.22µF
100V S1B
X7R
R
GATE
+
PORT
–
MAXIMUM PD INPUT POWER
Type 1 (13W)
Type 2 (25.5W)
LTPoE++ 38.7W
LTPoE++ 52.7W
LTPoE++ 70W
LTPoE++ 90W
UltraPWR – (Up to 123W*)
*Depending on V
PSE
R
PM
(±1%)
2.37k
3.32k
4.64k
5.90k
7.87k
10.0k
13.0k
PWRMODE
C
BULK
4279fa
For more information
www.linear.com/LTC4279
1
LTC4279
ABSOLUTE MAXIMUM RATINGS
(Notes 1 and 4)
Supply Voltages
AGND – V
EE
........................................... –0.3V to 80V
VSSK ................................... V
EE
– 0.3V to V
EE
+ 0.3V
LEGACY, MID, DUALPD, LED,
RESET,
GATE, PWRMODE ......... V
EE
– 0.3V to V
EE
+ 80V
OUT............................................ V
EE
– 80V to V
EE
+ 80V
SENSE ........................................ V
EE
– 20V to V
EE
+ 80V
Operating Ambient Temperature Range
LTC4279I .............................................–40°C to 85°C
Junction Temperature (Note 2) ............................ 125°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
PIN CONFIGURATION
TOP VIEW
RESET
DNC
TOP VIEW
MID 1
DNC 2
DNC 3
VSSK 4
SENSE 5
GATE 6
OUT 7
AGND 8
16
RESET
15 DNC
14 DUALPD
13 LEGACY
12 PWRMODE
11 DNC
10 V
EE
9
LED
DNC 1
DNC 2
DNC 3
V
EE
4
VSSK 5
SENSE 6
7
GATE
8
OUT
9 10
AGND
LED
21
V
EE
DNC
16 DUALPD
15 LEGACY
14 DNC
13 PWRMODE
12
DNC
11
DNC
MID
20 19 18 17
S PACKAGE
16-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 80°C/W,
θ
JC
= 30°C/W
UFD PACKAGE
20-LEAD (4mm × 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3.4°C/W
EXPOSED PAD (PIN 21) IS V
EE
ORDER INFORMATION
LEAD FREE FINISH
LTC4279IUFD#PBF
LTC4279IS#PBF
TAPE AND REEL
LTC4279IUFD#TRPBF
LTC4279IS#TRPBF
http://www.linear.com/product/LTC4279#orderinfo
PART MARKING
4279
LTC4279S
PACKAGE DESCRIPTION
20-Lead (4mm × 5mm) Plastic QFN
16-Lead Plastic SO
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
4279fa
For more information
www.linear.com/LTC4279
LTC4279
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3 and 4)
SYMBOL
V
EE
PARAMETER
Main PoE Supply Voltage
CONDITIONS
AGND – V
EE
For IEEE Type 1 Compliant Output
For IEEE Type 2, DUALPD, LTPoE++ 38.7W and
LTPoE++ 52.7W Compliant Output
For LTPoE++ 70W and LTPoE++ 90W Compliant
Output
For UltraPWR Output
AGND – V
EE
AGND – V
EE
= 55V
V
EE
< V
UVLO_VEE
First Point, AGND – V
OUT
= 10V
Second Point, AGND – V
OUT
= 3.5V
AGND – V
OUT
, 5µA ≤ I
OUT
≤ 500µA
First Point
Second Point
AGND – V
OUT
= 0V
AGND – V
OUT
, Open Port
AGND – V
OUT
, C
PORT
= 0.15µF (Note 6)
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ELECTRICAL CHARACTERISTICS
MIN
45
51
54.75
51
20
TYP
MAX
57
57
57
65
UNITS
V
V
V
V
V
mA
kΩ
µA
µA
V
V
mA
V
V/µs
kΩ
kΩ
V
mV
V
mV
mV
mV
mV
mV
mV
mA
mA
mA
V
UVLO_VEE
Undervoltage Lockout
I
EE
R
EE
Detection
Detection Current – Forced Current
Detection Voltage – Forced Voltage
V
EE
Supply Current
V
EE
Supply Resistance
25
–1.7
30
12
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220
143
7
3
240
160
8
4
0.8
10.4
260
180
9
5
0.9
12
0.01
18.5
32
20.5
Detection Current Compliance
V
OC
Detection Voltage Compliance
Detection Voltage Slew Rate
Min. Valid Signature Resistance
Max. Valid Signature Resistance
Classification
V
CLASS
V
MARK
Classification Voltage
Classification Current Compliance
Mark State Voltage
Mark State Current Compliance
Classification Threshold Voltage
15.5
27.5
16
8.8
7.5
8.8
0.5
1.3
2.1
3.1
4.5
0.4
0.08
8
2
300
17
29.7
AGND – V
OUT
, 0mV ≤ V
SENSE
≤ 8.8mV
SENSE – VSSK, V
OUT
= AGND
AGND – V
OUT
, 0.1mV ≤ V
SENSE
≤ 0.5mV
SENSE – VSSK, V
OUT
= AGND
SENSE – VSSK
Class 0 to 1
Class 1 to 2
Class 2 to 3
Class 3 to 4
Class 4 to Overcurrent
Port Off, V
GATE
= V
EE
+ 5V
Port Off, V
GATE
= V
EE
+ 1V
V
GATE
= V
EE
+ 5V
V
GATE
– V
EE
, I
GATE
= 1µA
V
OUT
– V
EE
0V ≤ (AGND – V
OUT
) ≤ 5V
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9.4
9.4
0.65
1.45
2.3
3.3
4.8
10
10
10
0.8
1.6
2.5
3.5
5.1
Gate Driver
GATE Pin Pull-Down Current
GATE Pin Fast Pull-Down Current
GATE Pin On Voltage
Output Voltage Sense
Power Good Threshold Voltage
OUT Pin Pull-Up Resistance to AGND
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0.12
30
14
2.4
500
2.8
700
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V
V
kΩ
4279fa
For more information
www.linear.com/LTC4279
3
LTC4279
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3 and 4)
SYMBOL
V
CUT
PARAMETER
Overcurrent Sense
CONDITIONS
SENSE – VSSK
Class 0, Class 3
Class 1
Class 2
Class 4
LTPoE++ 38.7W
LTPoE++ 52.7W, Dual-Signature PD
LTPoE++ 70W
LTPoE++ 90W
SENSE – VSSK, V
EE
≤ OUT ≤ V
EE
+ 10V
Class 0 to 3
Class 4
LTPoE++ 38.7W
LTPoE++ 52.7W, Dual-Signature PD
LTPoE++ 70W
LTPoE++ 90W
UltraPWR
SENSE – VSSK, V
EE
≤ OUT ≤ AGND – 29V,
Class 0 to 4, LTPoE++
Dual-Signature PD
UltraPWR
SENSE – VSSK (Note 10)
SENSE – VSSK – V
LIM
MID, LEGACY, DUALPD,
RESET
(Note 9)
MID, LEGACY, DUALPD,
RESET
(Note 9)
MID, LEGACY, DUALPD
RESET
RESET
(Note 9)
V
LED
– V
EE
, I
LED
= 1mA
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ELECTRICAL CHARACTERISTICS
MIN
TYP
MAX
UNITS
Current Sense
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35.6
10.0
19.6
60.8
89.0
130
160
225
40.8
81.6
120
140
180
240
280
40.8
81.6
140
0.5
30
37.5
11.2
20.8
63.6
91.9
135
165
232
42.5
85.0
127
148
191
255
295
42.5
85.0
148
0.75
60
39.6
12.0
22.0
67.2
95.0
140
170
240
44.2
88.4
135
160
200
270
310
44.2
88.4
160
1
90
0.8
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
V
V
µA
µA
V
V
LIM
Active Current Limit
Inrush Active Current Limit
V
MIN
V
SC
DC Disconnect Sense Voltage
Short-Circuit Sense
Digital Input Low Voltage
Digital Input High Voltage
Internal Pull-Down to V
EE
Internal Pull-Up to V
ROC
Digital Interface
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2.1
10
–10
3.6
0.4
10
380
12
9.6
6.8
16
410
15
12
8.6
20
440
18
14.4
0.1
10.8
24
82
15
24
10
V
ROC
LED Pin
Input Open Circuit Voltage
Output Low
LED Pin Current Limit
V
mA
ms
ms
ms
ms
ms
ms
ms
µs
V/µs
PSE Timing Characteristics
t
DET
t
CLE1
t
CLE
t
CLEON
t
ME
t
MEL
t
PON
Detection Time
Class Event Duration, Single Class Event
Class Event Duration
Class Event Turn-On Duration
Mark Event Duration
Last Mark Event Duration
Power-On Delay
Turn-On Rise Time
Turn-On Ramp Rate
Beginning to End of Detection (Note 6)
(Note 6)
(Note 6)
C
PORT
= 0.6µF (Note 6)
(Note 6, Note 8)
(Note 6, Note 8)
From End of Valid Detect to Application of
Power to Port (Note 6)
(AGND – V
OUT
): 10% to 90% of (AGND – V
EE
),
C
PORT
= 0.15µF (Note 6)
C
PORT
= 0.15µF (Note 6)
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4279fa
For more information
www.linear.com/LTC4279
LTC4279
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3 and 4)
SYMBOL
t
TOCL
t
ED
PARAMETER
Turn-On Class Transition
Fault Delay
LEGACY Mode Detection Backoff
Midspan Mode Detection Backoff
Power Removal Detection Delay
t
START
t
CUT
Maximum Current Limit Duration During Port
Start-Up
Maximum Overcurrent Duration after Port
Start-Up
Maximum Overcurrent Duty Cycle
t
LIM
Maximum Current Limit Duration after Port
Start-Up
CONDITIONS
C
PORT
= 0.15µF (Note 6)
From I
CUT
or I
LIM
Fault to Next Detect (Note 6)
LEGACY Enabled, R
PORT
= 150Ω (Note 6)
LEGACY Disabled, MID Enabled, R
PORT
=
15.5kΩ (Note 6)
From Power Removal after t
DIS
to Next Detect
(Note 6)
(Note 6)
(Note 6)
(Note 6)
LTPoE++ PD, Dual-Signature PD or UltraPWR
Mode Enabled (Note 6)
(Legacy or IEEE PD) and UltraPWR Mode
Disabled (Note 6)
t
MPS
t
DIS
Maintain Power Signature (MPS) Pulse Width
Sensitivity
Minimum Pulse Width for
RESET
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 140°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 3:
All currents into device pins are positive; all currents out of device
pins are negative.
Note 4:
The LTC4279 operates with a negative supply voltage (with
respect to AGND). To avoid confusion, voltages in this data sheet are
referred to in terms of absolute magnitude.
Current Pulse Width to Reset Disconnect Timer
(Notes 6 and 7)
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ELECTRICAL CHARACTERISTICS
MIN
1
2.7
2.3
1
52
52
5.8
10
52
1.6
320
4.5
TYP
1.3
3
2.5
1.3
59
59
6.3
12
59
MAX
0.1
3.3
2.7
2.5
66
66
6.7
14
66
3.6
UNITS
ms
s
s
s
s
ms
ms
%
ms
ms
ms
ms
µs
Maintain Power Signature (MPS) Dropout Time (Notes 5 and 6)
350
380
Note 5:
t
DIS
is the same as t
MPDO
defined by IEEE 802.3.
Note 6:
Guaranteed by design, not subject to test.
Note 7:
The IEEE 802.3at specification allows a PD to present its
Maintain Power Signature (MPS) on an intermittent basis without being
disconnected. In order to stay powered, the PD must present the MPS for
t
MPS
within any t
MPDO
time window.
Note 8:
Load characteristics of the LTC4279 during Mark:
7V < (AGND – V
OUT
) < 10V or I
OUT
< 50µA.
Note 9:
The LTC4279 Digital Interface operates with respect to V
EE
. All
logic levels are measured with respect to V
EE
.
Note 10:
See Main PoE Power Supply section for DC disconnect related
power supply requirements.
4279fa
For more information
www.linear.com/LTC4279
5
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