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LTC4278IDKD#PBF [Linear]

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LTC4278IDKD#PBF
型号： LTC4278IDKD#PBF
厂家： Linear    Linear
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LTC4266A/LTC4266C  
++  
+
Quad PoE/PoE /LTPoE  
PSE Controller  
FEATURES  
DESCRIPTION  
n
Four Independent PSE Channels  
TheLTC®4266Aisaquadpowersourcingequipment(PSE)  
++  
n
Compliant with IEEE 802.3at Type 1 and 2  
controller capable of delivering up to 90W of LTPoE  
n
++  
Low Power Dissipation  
power to a compatible LTPoE powered device (PD). A  
0.25Ω Sense Resistance Per Channel  
Very High Reliability 4-Point PD Detection  
proprietarydetection/classificationschemeallowsmutual  
n
++  
++  
identification between a LTPoE PSE and LTPoE PD  
whileremainingcompatibleandinteroperablewithexisting  
Type 1 (13W) and Type 2 (25.5W) PDs. The LTC4266A  
feature set is a superset of the popular LTC4266. These  
2-Point Forced Voltage  
2-Point Forced Current  
n
High Capacitance Legacy Device Detection  
2
n
1MHz I C Compatible Serial Control Interface  
PSE controllers feature low R external MOSFETs and  
ON  
n
Midspan Backoff Timer  
0.25Ω sense resistors which are especially important at  
n
++  
Supports 2-Pair and 4-Pair Output Power  
theLTPoE currentlevelstomaintainthelowestpossible  
n
Available in Multiple Power Grades  
heat dissipation.  
++  
LTC4266A-1: LTPoE ™ 38.7W  
TheLTC4266CtargetsfullyautomaticPSEsystemspower-  
ing Type 1 (up to 13W) PDs.  
++  
LTC4266A-2: LTPoE 52.7W  
++  
++  
LTC4266A-3: LTPoE 70W  
Advanced power management features include: 14-bit  
current monitoring ADCs, DAC-programmable current  
limit, and versatile quick shutdown of preselected ports.  
Advanced power management host software is available  
under a no-cost license. PD discovery uses a proprietary  
dual-mode4-pointdetectionmechanismensuringexcellent  
immunity from false PD detection. The LTC4266 includes  
LTC4266A-4: LTPoE 90W  
LTC4266C: PoE 13W  
n
Available in 38-Lead 5mm × 7mm QFN Package  
APPLICATIONS  
n
++  
LTPoE PSE Switches/Routers  
2
n
n
n
++  
LTPoE PSE Midspans  
an I C serial interface operable up to 1MHz.  
IEEE 802.3at Type 1 PSE Switches/Routers  
The LTC4266 is available in multiple power grades al-  
lowing delivered PD power of 13W, 25W, 38.7W, 52.7W,  
70W and 90W. These controllers are available in a 38-lead  
5mm × 7mm QFN package.  
IEEE 802.3at Type 1 PSE Midspans  
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and  
++  
LTPoE and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks  
are the property of their respective owners.  
TYPICAL APPLICATION  
Complete 4-Port Ethernet High Power Source  
3.3V  
0.1μF  
SCL  
INT SHDN1 SHDN2 SHDN3 SHDN4  
V
AUTO MSD RESET MID  
DD  
SDAIN  
SDAOUT  
AD0  
0.22μF 100V  
S1B  
=4  
S1B  
=4  
LTC4266  
=4  
AD1  
–50V  
AD2  
AD3  
DGND AGND V SENSE1 GATE1 OUT1 SENSE2 GATE2 OUT2 SENSE3 GATE3 OUT3 SENSE4 GATE4 OUT4  
EE  
PORT1  
PORT2  
PORT3  
PORT4  
–50V  
SMAJ58A  
1μF  
4266 TA01  
4266acfc  
1
LTC4266A/LTC4266C  
ABSOLUTE MAXIMUM RATINGS  
PIN CONFIGURATION  
Supply Voltages (Note 1)  
TOP VIEW  
AGND – V ........................................... –0.3V to 80V  
EE  
DGND – V ........................................... –0.3V to 80V  
EE  
V
– DGND ......................................... –0.3V to 5.5V  
DD  
38 37 36 35 34 33 32  
Digital Pins  
SDAOUT  
NC  
1
2
3
4
5
6
7
8
9
31 GATE1  
SCL, SDAIN, SDAOUT, INT, SHDNn, MSD, ADn,  
RESET, AUTO, MID........... DGND –0.3V to V + 0.3V  
30 SENSE1  
SDAIN  
AD3  
OUT2  
29  
28  
DD  
GATE2  
Analog Pins  
AD2  
27 SENSE2  
GATEn, SENSEn, OUTn .......... V –0.3V to V + 80V  
EE  
EE  
AD1  
V
V
26  
25  
EE  
EE  
Operating Temperature Range  
V
EE  
AD0  
39  
LTC4266I .............................................–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  
DNC  
NC  
24 OUT3  
23 GATE3  
22 SENSE3  
21 OUT4  
DGND 10  
NC 11  
20  
NC 12  
GATE4  
13 14 15 16 17 18 19  
UHF PACKAGE  
38-LEAD (5mm = 7mm) PLASTIC QFN  
EXPOSED PAD IS V (PIN 39) MUST BE SOLDERED TO PCB  
EE  
JMAX  
T
= 125°C, e = 34°C/W  
JA  
ORDER INFORMATION  
LEAD FREE FINISH  
TAPE AND REEL  
PART MARKING* PACKAGE DESCRIPTION  
MAX PWR TEMPERATURE RANGE  
LTC4266CIUHF#PBF  
LTC4266AIUHF-1#PBF  
LTC4266AIUHF-2#PBF  
LTC4266AIUHF-3#PBF  
LTC4266AIUHF-4#PBF  
LTC4266CIUHF#TRPBF  
LTC4266AIUHF-1#TRPBF  
LTC4266AIUHF-2#TRPBF  
LTC4266AIUHF-3#TRPBF  
LTC4266AIUHF-4#TRPBF  
4266C  
38-Lead (5mm × 7mm) Plastic QFN  
38-Lead (5mm × 7mm) Plastic QFN  
38-Lead (5mm × 7mm) Plastic QFN  
38-Lead (5mm × 7mm) Plastic QFN  
38-Lead (5mm × 7mm) Plastic QFN  
13W  
–40°C to 85°C  
–40°C to 85°C  
–40°C to 85°C  
–40°C to 85°C  
–40°C to 85°C  
4266A1  
4266A2  
4266A3  
4266A4  
38.7W  
52.7W  
70W  
90W  
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.  
Consult LTC Marketing for information on non-standard lead based finish parts.  
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/  
4266acfc  
2
LTC4266A/LTC4266C  
ELECTRICAL CHARACTERISTICS  
The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V  
unless otherwise noted. (Notes 3, 4)  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
V
Main PoE Supply Voltage  
AGND – V  
EE  
EE  
l
l
l
For IEEE Type 1 Compliant Output  
For IEEE Type 2 Compliant Output  
45  
51  
54.75  
57  
57  
57  
V
V
V
++  
For LTPoE Compliant Output  
l
l
l
l
l
l
Undervoltage Lockout  
AGND – V  
20  
25  
3.3  
2.2  
30  
V
V
EE  
V
V
Supply Voltage  
V – DGND  
DD  
3.0  
4.3  
DD  
DD  
Undervoltage Lockout  
V
Allowable Digital Ground Offset  
DGND – V  
25  
57  
–5  
3
V
EE  
I
I
V
V
Supply Current  
Supply Current  
(AGND – V ) = 55V  
–2.4  
1.1  
mA  
mA  
EE  
DD  
EE  
EE  
(V – DGND) = 3.3V  
DD  
DD  
Detection  
l
l
Detection Current – Force Current  
Detection Voltage – Force Voltage  
First Point, AGND – V  
= 9V  
OUTn  
220  
140  
240  
160  
260  
180  
μA  
μA  
OUTn  
Second Point, AGND – V  
= 3.5V  
AGND – V , 5μA ≤ I  
OUTn  
≤ 500μA  
OUTn  
l
l
First Point  
Second Point  
7
3
8
4
9
5
V
V
l
l
l
l
l
Detection Current Compliance  
Detection Voltage Compliance  
Detection Voltage Slew Rate  
AGND – V  
= 0V  
0.8  
0.9  
12  
mA  
V
OUTn  
V
OC  
AGND – V  
AGND – V  
, Open Port  
, C = 0.15μF  
10.4  
OUTn  
0.01  
18.5  
32  
V/μs  
kΩ  
kΩ  
OUTn PORT  
Minimum Valid Signature Resistance  
Maximum Valid Signature Resistance  
15.5  
27.5  
17  
29.7  
Classification  
l
l
V
Classification Voltage  
AGND – V  
, 0mA ≤ I ≤ 50mA  
CLASS  
16.0  
53  
20.5  
67  
V
CLASS  
OUTn  
Classification Current Compliance  
Classification Threshold Current  
V
OUTn  
= AGND  
61  
mA  
l
l
l
l
l
Class 0 – 1  
Class 1 – 2  
Class 2 – 3  
Class 3 – 4  
5.5  
6.5  
14.5  
23  
33  
48  
7.5  
mA  
mA  
mA  
mA  
mA  
13.5  
21.5  
31.5  
45.2  
15.5  
24.5  
34.9  
50.8  
Class 4 – Overcurrent  
AGND – V , 0.1mA ≤ I ≤ 10mA  
CLASS  
l
l
V
Classification Mark State Voltage  
Mark State Current Compliance  
7.5  
53  
9
10  
67  
V
MARK  
OUTn  
V
OUTn  
= AGND  
61  
mA  
Gate Driver  
l
l
GATE Pin Pull-Down Current  
Port Off, V  
Port Off, V  
= V + 5V  
0.4  
mA  
mA  
GATEn  
GATEn  
EE  
= V + 1V  
0.08  
0.12  
30  
EE  
GATE Pin Fast Pull-Down Current  
GATE Pin On Voltage  
V
GATEn  
GATEn  
= V + 5V  
mA  
V
EE  
l
V
– V , I  
= 1μA  
8
12  
14  
EE GATEn  
Output Voltage Sense  
l
l
V
Power Good Threshold Voltage  
V
– V  
EE  
2
2.4  
2.8  
V
PG  
OUTn  
OUT Pin Pull-Up Resistance to AGND  
0V ≤ (AGND – V  
) ≤ 5V  
OUTn  
300  
500  
700  
kΩ  
4266acfc  
3
LTC4266A/LTC4266C  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V  
unless otherwise noted. (Notes 3, 4)  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
Current Sense  
V
Overcurrent Sense Voltage  
V
– V  
CUT  
SENSEn EE  
hpen = 0Fh, cutn[5:0] ≥ 4 (Note 12)  
cutrng = 0  
l
l
9
4.5  
9.38  
4.69  
9.75  
4.88  
mV/LSB  
mV/LSB  
cutrng = 1  
l
l
l
l
Overcurrent Sense in AUTO Pin Mode  
Class 0, Class 3  
Class 1  
90  
26  
94  
28  
98  
30  
mV  
mV  
mV  
mV  
Class 2  
49  
52  
55  
Class 4  
152  
159  
166  
V
V
V
Active Current Limit in 802.3af Compliant  
Mode  
V
EE  
– V , hpen = 0Fh, limn = 80h,  
SENSEn EE  
LIM  
LIM  
LIM  
V
= 55V (Note 12)  
l
l
V
< V  
< AGND – 29V  
OUT  
OUT  
102  
20  
106  
110  
50  
mV  
mV  
EE  
AGND – V  
= 0V  
Active Current Limit in High Power Mode  
Active Current Limit in AUTO Pin Mode  
hpen = 0Fh, limn = C0h, V = 55V  
EE  
l
l
l
V
V
– V = 0V to 10V  
204  
100  
20  
212  
106  
221  
113  
50  
mV  
mV  
mV  
OUT  
EE  
EE  
+ 23V < V  
< AGND – 29V  
OUT  
AGND – V  
= 0V  
OUT  
V
OUT  
– V = 0V to 10V, V = 55V  
EE EE  
Class 0 to Class 3  
Class 4  
l
l
102  
204  
106  
212  
110  
221  
mV  
mV  
l
l
V
V
DC Disconnect Sense Voltage  
Short-Circuit Sense  
V
V
– V , rdis = 0  
2.6  
1.3  
3.8  
1.9  
4.8  
mV  
mV  
MIN  
SENSEn  
SENSEn  
EE  
– V , rdis = 1  
2.41  
EE  
l
l
V
V
– V – V , rdis = 0  
160  
75  
200  
100  
255  
135  
mV  
mV  
SC  
SENSEn  
SENSEn  
EE  
LIM  
– V – V , rdis = 1  
EE  
LIM  
Port Current ReadBack  
Resolution  
No Missing Codes, fast_iv = 0  
V – V  
SENSEn  
14  
30.5  
30  
Bits  
μV/LSB  
dB  
LSB Weight  
EE  
50Hz to 60Hz Noise Rejection  
(Note 7)  
Port Voltage ReadBack  
Resolution  
No Missing Codes, fast_iv = 0  
14  
5.835  
30  
bits  
mV/LSB  
dB  
LSB Weight  
AGND – V  
(Note 7)  
OUTn  
50Hz to 60Hz Noise Rejection  
Digital Interface  
l
V
Digital Input Low Voltage  
ADn, RESET, MSD, SHDNn, AUTO, MID  
0.8  
0.8  
V
ILD  
(Note 6)  
2
l
l
I C Input Low Voltage  
SCL, SDAIN (Note 6)  
(Note 6)  
V
V
V
IHD  
Digital Input High Voltage  
Digital Output Low Voltage  
2.2  
l
l
I
I
= 3mA, I = 3mA  
0.4  
0.7  
V
V
SDAOUT  
SDAOUT  
INT  
= 5mA, I = 5mA  
INT  
Internal Pull-Up to V  
ADn, SHDNn, RESET, MSD  
50  
50  
kΩ  
kΩ  
DD  
Internal Pull-Down to DGND  
AUTO, MID  
4266acfc  
4
LTC4266A/LTC4266C  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V  
unless otherwise noted. (Notes 3, 4)  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
Timing Characteristics  
l
l
t
t
Detection Time  
Detection Delay  
Beginning to End of Detection (Note 7)  
270  
300  
290  
310  
470  
ms  
ms  
DET  
From PD Connected to Port to Detection  
Complete (Note 7)  
DETDLY  
l
l
l
l
l
t
t
t
t
t
Class Event Duration  
(Note 7)  
12  
ms  
ms  
ms  
ms  
ms  
CLE  
Class Event Turn-On Duration  
Mark Event Duration  
C
PORT  
= 0.6μF (Note 7)  
0.1  
60  
CLEON  
ME  
(Notes 7, 11)  
(Notes 7, 11)  
8.6  
22  
Last Mark Event Duration  
Power On Delay in AUTO Pin Mode  
16  
15  
MEL  
PON  
From End of Valid Detect to Application of  
Power to Port (Note 7)  
l
Turn On Rise Time  
(AGND – V ): 10% to 90% of (AGND – V ),  
24  
μs  
OUT  
EE  
C
PORT  
= 0.15μF (Note 7)  
l
l
l
l
Turn On Ramp Rate  
C
= 0.15μF (Note 7)  
10  
V/μs  
PORT  
Fault Delay  
From I  
Fault to Next Detect  
1.0  
2.3  
1.0  
1.1  
2.5  
1.3  
s
s
s
CUT  
Midspan Mode Detection Backoff  
Power Removal Detection Delay  
Rport = 15.5kꢀ (Note 7)  
2.7  
2.5  
From Power Removal After t to Next  
Detect (Note 7)  
DIS  
l
l
l
t
t
t
Maximum Current Limit Duration During Port (Note 7)  
Start-Up  
52  
62.5  
11.9  
62.5  
6.3  
66  
ms  
ms  
ms  
START  
Maximum Current Limit Duration After Port  
Start-Up  
t
Enable = 1 (Notes 7, 12)  
LIM  
LIM  
Maximum Overcurrent Duration After Port  
Start-Up  
(Note 7)  
(Note 7)  
52  
66  
CUT  
l
l
Maximum Overcurrent Duty Cycle  
5.8  
1.6  
6.7  
3.6  
%
t
Maintain Power Signature (MPS) Pulse Width Current Pulse Width to Reset Disconnect  
Sensitivity Timer (Notes 7, 8)  
ms  
MPS  
l
l
l
l
l
l
l
t
t
t
Maintain Power Signature (MPS) Dropout Time (Note 7)  
320  
350  
2
380  
6.5  
6.5  
3
ms  
μs  
μs  
s
DIS  
Masked Shut Down Delay  
Port Shut Down Delay  
(Note 7)  
(Note 7)  
MSD  
SHDN  
2
I C Watchdog Timer Duration  
1.5  
3
Minimum Pulse Width for Masked Shut Down (Note 7)  
μs  
μs  
μs  
Minimum Pulse Width for SHDN  
Minimum Pulse Width for RESET  
(Note 7)  
(Note 7)  
3
4.5  
4266acfc  
5
LTC4266A/LTC4266C  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating  
temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless  
otherwise noted. (Notes 3, 4)  
SYMBOL  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
2
I C Timing  
l
l
l
l
l
Clock Frequency  
Bus Free Time  
Start Hold Time  
SCL Low Time  
SCL High Time  
Data Hold Time  
(Note 7)  
1
MHz  
ns  
t
1
t
2
t
3
t
4
t
5
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
480  
240  
480  
240  
60  
ns  
ns  
ns  
l
l
Figure 5 (Notes 7, 9) Data into Chip  
Data Out of Chip  
ns  
ns  
120  
l
l
l
l
l
l
l
l
l
t
t
t
t
t
Data Set-Up Time  
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
Figure 5 (Notes 7, 9)  
(Notes 7, 9, 10)  
80  
ns  
ns  
ns  
ns  
ns  
ns  
μs  
μs  
ns  
6
7
8
r
Start Set-Up Time  
240  
240  
Stop Set-Up Time  
SCL, SDAIN Rise Time  
SCL, SDAIN Fall Time  
Fault Present to INT Pin Low  
Stop Condition to INT Pin Low  
ARA to INT Pin High Time  
SCL Fall to ACK Low  
120  
60  
f
150  
1.5  
1.5  
120  
(Notes 7, 9, 10)  
(Notes 7, 9)  
(Notes 7, 9)  
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 LTC4266A/LTC4266C operates with a negative supply voltage  
(with respect to ground). To avoid confusion, voltages in this data sheet  
are referred to in terms of absolute magnitude.  
Note 6: The LTC4266A/LTC4266C digital interface operates with respect to  
DGND. All logic levels are measured with respect to DGND.  
Note 7: Guaranteed by design, not subject to test.  
Note 8: The IEEE 802.3af 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
within any t  
time window.  
MPS  
MPDO  
Note 9: Values measured at V  
Note 10: If fault condition occurs during an I C transaction, the INT pin  
will not be pulled down until a stop condition is present on the I C bus.  
and V  
.
ILD(MAX)  
IHD(MIN)  
2
2
Note 11: Load Characteristic of the LTC4266A/LTC4266C during Mark:  
7V < (AGND – V  
) < 10V or I  
OUTn  
< 50μA  
OUT  
Note 12: See the LTC4266A/LTC4266C Software Programming  
documentation for information on serial bus usage and device  
configuration and status registers.  
Note 5: t is the same as t  
defined by IEEE 802.3at.  
DIS  
MPDO  
4266acfc  
6
LTC4266A/LTC4266C  
TYPICAL PERFORMANCE CHARACTERISTICS  
Power-On Sequence in  
802.3af Classification in  
AUTO Pin Mode  
AUTO Pin Mode  
Powering Up into a 180μF Load  
10  
0
GND  
GND  
FORCED CURRENT DETECTION  
GND  
V
DD  
V
EE  
= 3.3V  
= –54V  
PORT  
VOLTAGE  
20V/DIV  
LOAD  
FULLY  
–10  
–20  
–30  
CHARGED  
–18.4  
FORCED VOLTAGE  
DETECTION  
V
EE  
PORT  
CURRENT  
802.3af  
PORT 1  
PORT 1  
FOLDBACK  
PORT  
VOLTAGE  
10V/DIV  
425mA  
CURRENT LIMIT  
CLASSIFICATION  
V
DD  
V
EE  
= 3.3V  
= –54V  
200 mA/DIV  
V
DD  
V
EE  
= 3.3V  
= –55V  
–40  
–50  
–60  
–70  
POWER ON  
0mA  
PD IS CLASS 1  
FET ON  
GATE  
VOLTAGE  
10V/DIV  
V
EE  
V
V
EE  
EE  
4266AC G02  
4266AC G03  
5ms/DIV  
5ms/DIV  
100ms/DIV  
4266AC G01  
2-Event Classification in  
AUTO Pin Mode  
Classification Transient Response  
to 40mA Load Step  
Classification Current Compliance  
0
V
DD  
V
EE  
= 3.3V  
= –54V  
GND  
V
DD  
V
EE  
= 3.3V  
= –54V  
–2  
–4  
40mA  
0mA  
PORT  
CURRENT  
20mA/DIV  
T
A
= 25°C  
–6  
–17.6  
1ST CLASS EVENT  
–8  
2ND CLASS EVENT  
–10  
–12  
–14  
–16  
–18  
–20  
PORT  
VOLTAGE  
10V/DIV  
PORT 1  
V
DD  
V
EE  
= 3.3V  
= –55V  
PORT  
VOLTAGE  
1V/DIV  
PD IS CLASS 4  
–20V  
V
EE  
4266AC G05  
4266AC G04  
0
10  
20  
30  
40  
50  
60  
70  
50μs/DIV  
10ms/DIV  
CLASSIFICATION CURRENT (mA)  
4266AC G06  
802.3at ILIM Threshold  
vs Temperature  
V
DD Supply Current vs Voltage  
VEE Supply Current vs Voltage  
1.8  
1.7  
1.6  
1.5  
1.4  
1.3  
1.2  
1.1  
1.0  
0.9  
0.8  
215  
214  
213  
212  
211  
210  
860  
856  
852  
848  
844  
840  
2.4  
2.3  
2.2  
2.1  
V
V
= 3.3V  
= –54V  
SENSE  
DD  
EE  
R
= 0.25Ω  
REG 48h = C0h  
25°C  
85°C  
–40°C  
25°C  
85°C  
–40°C  
2.0  
–40  
0
40  
–80  
120  
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3  
SUPPLY VOLTAGE (V)  
–60 –55 –50 –45 –40 –35 –30 –25 –20  
SUPPLY VOLTAGE (V)  
TEMPERATURE (°C)  
V
V
DD  
EE  
4266AC G09  
4266AC G07  
4266 G08  
4266acfc  
7
LTC4266A/LTC4266C  
TYPICAL PERFORMANCE CHARACTERISTICS  
802.3af ILIM Threshold  
vs Temperature  
802.3at ICUT Threshold  
vs Temperature  
108.00  
107.25  
106.50  
432  
429  
163  
162  
652  
648  
644  
640  
V
V
= 3.3V  
= –54V  
SENSE  
V
V
= 3.3V  
= –54V  
SENSE  
DD  
EE  
DD  
EE  
R
= 0.25Ω  
R
= 0.25Ω  
REG 48h = 80h  
PORT 1  
REG 47h = E2h  
PORT 1  
161  
160  
159  
158  
426  
423  
420  
105.75  
105.00  
636  
630  
–40  
0
40  
80  
120  
–40  
0
40  
80  
120  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
4266AC G10  
4266AC G11  
802.3af ICUT Threshold  
vs Temperature  
DC Disconnect Threshold  
vs Temperature  
8.00  
7.75  
7.50  
7.25  
7.00  
96.00  
95.25  
94.50  
93.75  
93.00  
384  
381  
2.0000  
1.9375  
V
V
= 3.3V  
= –54V  
SENSE  
V
V
= 3.3V  
= –54V  
SENSE  
DD  
EE  
DD  
EE  
R
= 0.25Ω  
R
= 0.25Ω  
REG 47h = D4h  
PORT 1  
REG 47h = E2h  
PORT 1  
378  
375  
372  
1.8750  
1.8125  
1.7500  
–40  
0
40  
80  
120  
–40  
0
40  
80  
120  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
4266AC G12  
4266AC G13  
ADC Noise Histogram  
Current Readback in Fast Mode  
ADC Integral Nonlinearity  
Current Limit Foldback  
Current Readback in Fast Mode  
1.0  
0.5  
900  
800  
700  
600  
500  
400  
300  
200  
100  
0
225  
400  
350  
300  
250  
200  
V
– V = 110.4mV  
EE  
V
= 3.3V  
SENSEn  
DD  
EE  
SENSE  
V
= –54V  
200  
175  
150  
125  
100  
75  
R
= 0.25Ω  
REG 48h = C0h  
0
150  
100  
50  
–0.5  
–1.0  
50  
25  
0
0
0
50 100 150 200 250 300 350 400 450 500  
CURRENT SENSE RESISTOR INPUT VOLTAGE (mV)  
4266AC G16  
–54  
–45  
–36  
–9  
0
191  
192  
193  
ADC OUTPUT  
196  
–27  
–18  
194  
195  
V
(V)  
OUTn  
4266AC G14  
4266AC G15  
4266acfc  
8
LTC4266A/LTC4266C  
TYPICAL PERFORMANCE CHARACTERISTICS  
ADC Noise Histogram  
ADC Integral Nonlinearity  
ADC Noise Histogram Port  
Voltage Readback in Fast Mode  
600  
Current Readback in Slow Mode  
Current Readback in Slow Mode  
300  
250  
200  
150  
100  
50  
1.0  
0.5  
V
– V = 110.4mV  
EE  
AGND – V  
= 48.3V  
OUTn  
SENSEn  
500  
400  
300  
200  
100  
0
0
–0.5  
–1.0  
0
6139  
0
50 100 150 200 250 300 350 400 450 500  
CURRENT SENSE RESISTOR INPUT VOLTAGE (mV)  
4266AC G18  
260  
261  
262  
ADC OUTPUT  
6141  
6143  
6145  
6147  
263  
264  
265  
ADC OUTPUT  
4266AC G17  
4266AC G19  
ADC Integral Nonlinearity  
Voltage Readback in Fast Mode  
ADC Noise Histogram Port  
ADC Integral Nonlinearity  
Voltage Readback in Slow Mode  
Voltage Readback in Slow Mode  
1.0  
0.5  
600  
500  
400  
300  
200  
100  
0
1.0  
0.5  
AGND – V  
= 48.3V  
OUTn  
0
0
–0.5  
–1.0  
–0.5  
–1.0  
0
10  
20  
30  
40  
50  
60  
0
10  
20  
30  
40  
50  
60  
8532  
8533  
8534  
ADC OUTPUT  
8535  
8536  
PORT VOLTAGE (V)  
PORT VOLTAGE (V)  
4266AC G20  
4266AC G22  
4266AC G21  
INTandSDAOUTPull-DownVoltage  
vs Load Current  
MOSFET Gate Drive with Fast  
Pull-Down  
3
2.5  
2
GND  
V
V
= 3.3V  
DD  
EE  
= –54V  
PORT  
VOLTAGE  
20V/DIV  
V
V
EE  
EE  
FAST PULL-DOWN  
1.5  
1
GATE  
VOLTAGE  
10V/DIV  
CURRENT LIMIT  
50Ω  
FAULT  
APPLIED  
PORT  
CURRENT  
500mA/DIV  
0.5  
0
50Ω FAULT REMOVED  
0mA  
4266AC G24  
0
5
10  
LOAD CURRENT (mA)  
15 20 25 30 35 40  
100μs/DIV  
4266AC G23  
4266acfc  
9
LTC4266A/LTC4266C  
TEST TIMING DIAGRAMS  
t
CLASSIFICATION  
DET  
FORCED-  
VOLTAGE  
FORCED-CURRENT  
0V  
t
ME  
V
t
PORTn  
MEL  
V
OC  
V
MARK  
15.5V  
20.5V  
V
CLASS  
t
CLE  
t
CLE  
PD  
CONNECTED  
t
CLEON  
t
PON  
V
EE  
INT  
4266AC F01  
Figure 1. Detect, Class and Turn-On Timing in AUTO Pin or Semi-auto Modes  
V
LIM  
0V  
V
CUT  
V
SENSEn  
V
V
TO V  
EE  
MIN  
SENSEn  
TO V  
EE  
t
, t  
START ICUT  
INT  
INT  
t
t
DIS  
MPS  
4266AC F02  
4266AC F03  
Figure 2. Current Limit Timing  
Figure 3. DC Disconnect Timing  
t
t
r
3
t
4
t
f
V
GATEn  
SCL  
SDA  
t
MSD  
V
EE  
t
SHDN  
t
t
t
t
8
t
2
5
6
7
MSD or  
SHDNn  
4266AC F04  
t
1
4266AC F05  
Figure 4. Shut Down Delay Timing  
Figure 5. I2C Interface Timing  
4266acfc  
10  
LTC4266A/LTC4266C  
I2C TIMING DIAGRAMS  
4266acfc  
11  
LTC4266A/LTC4266C  
I2C TIMING DIAGRAMS  
SCL  
SDA  
0
1
0
AD3 AD2 AD1 AD0 R/W  
FRAME 1  
ACK  
D7 D6 D5 D4 D3 D2 D1 D0  
ACK  
STOP BY  
MASTER  
START BY  
MASTER  
ACK BY  
SLAVE  
NO ACK BY  
MASTER  
FRAME 2  
DATA BYTE  
SERIAL BUS ADDRESS BYTE  
4266AC F08  
Figure 8. Reading the Interrupt Register (Short Form)  
SCL  
SDA  
0
0
0
1
1
0
0
R/W  
ACK  
0
1
0
AD3 AD2 AD1 AD0  
1
ACK  
STOP BY  
MASTER  
START BY  
MASTER  
ACK BY  
SLAVE  
NO ACK BY  
MASTER  
FRAME 1  
ALERT RESPONSE ADDRESS BYTE  
FRAME 2  
SERIAL BUS ADDRESS BYTE  
4266AC F09  
Figure 9. Reading from Alert Response Address  
4266acfc  
12  
LTC4266A/LTC4266C  
PIN FUNCTIONS  
RESET: Chip Reset, Active Low. When the RESET pin is  
low, theLTC4266A/LTC4266Cisheldinactivewithallports  
off and all internal registers reset to their power-up states.  
When RESET is pulled high, the LTC4266A/LTC4266C  
begins normal operation. RESET can be connected to  
an external capacitor or RC network to provide a power  
turn-on delay. Internal filtering of the RESET pin prevents  
glitches less than 1μs wide from resetting the LTC4266A/  
AD3: Address Bit 3. Tie the address pins high or low to set  
2
the I C serial address to which the LTC4266A/LTC4266C  
responds. This address will be 010A A A A b. Internally  
3 2 1 0  
pulled up to V .  
DD  
AD2: Address Bit 2. See AD3.  
AD1: Address Bit 1. See AD3.  
AD0: Address Bit 0. See AD3.  
LTC4266C. Internally pulled up to V .  
DD  
NC, DNC: All pins identified with “NC” or “DNC” must be  
left unconnected.  
MID: Midspan Mode Input. When high, the LTC4266A/  
LTC4266C acts as a midspan device. Internally pulled  
down to DGND.  
DGND: Digital Ground. DGND is the return for the V  
supply.  
DD  
INT: Interrupt Output, Open Drain. INT will pull low when  
anyoneofseveraleventsoccurintheLTC4266A/LTC4266C.  
It will return to a high impedance state when bits 6 or 7  
are set in the Reset PB register (1Ah). The INT signal can  
be used to generate an interrupt to the host processor,  
eliminating the need for continuous software polling.  
Individual INT events can be disabled using the Int Mask  
register (01h). See the LTC4266A/LTC4266C Software  
Programming documentation for more information. The  
V : Logic Power Supply. Connect to a 3.3V power supply  
DD  
relative to DGND. V must be bypassed to DGND near  
DD  
the LTC4266A/LTC4266C with at least a 0.1μF capacitor.  
SHDN1: Shutdown Port 1, Active Low. When pulled low,  
SHDN1 shuts down port 1, regardless of the state of the  
internal registers. Pulling SHDN1 low is equivalent to set-  
ting the Reset Port 1 bit in the Reset Pushbutton register  
(1Ah).InternalfilteringoftheSHDN1pinpreventsglitches  
lessthan1μswidefromresettingtheport.Internallypulled  
2
INT pin is only updated between I C transactions.  
up to V .  
DD  
SCL:SerialClockInput.Highimpedanceclockinputforthe  
2
I C serial interface bus. SCL must be tied high if not used.  
SHDN2: Shutdown Port 2, Active Low. See SHDN1.  
SHDN3: Shutdown Port 3, Active Low. See SHDN1.  
SHDN4: Shutdown Port 4, Active Low. See SHDN1.  
SDAOUT: Serial Data Output, Open Drain Data Output for  
2
the I C Serial Interface Bus. The LTC4266A/LTC4266C  
uses two pins to implement the bidirectional SDA function  
2
to simplify optoisolation of the I C bus. To implement a  
AGND: Analog Ground. AGND is the return for the V  
EE  
standard bidirectional SDA pin, tie SDAOUT and SDAIN  
together. SDAOUT should be grounded or left floating if  
not used. See the Applications Information section for  
more information.  
supply.  
SENSE4: Port 4 Current Sense Input. SENSE4 monitors  
the external MOSFET current via a 0.5ꢀ or 0.25Ω sense  
resistor between SENSE4 and V . Whenever the voltage  
EE  
SDAIN: Serial Data Input. High impedance data input for  
acrossthesenseresistorexceedstheovercurrentdetection  
2
the I C serial interface bus. The LTC4266A/LTC4266C  
threshold V , the current limit fault timer counts up. If  
CUT  
uses two pins to implement the bidirectional SDA function  
the voltage across the sense resistor reaches the current  
2
to simplify optoisolation of the I C bus. To implement a  
limit threshold V , the GATE4 pin voltage is lowered to  
LIM  
standard bidirectional SDA pin, tie SDAOUT and SDAIN  
together. SDAIN must be tied high if not used. See the  
Applications Information section for more information.  
maintain constant current in the external MOSFET. See  
the Applications Information section for further details.  
If the port is unused, the SENSE4 pin must be tied to V .  
EE  
4266acfc  
13  
LTC4266A/LTC4266C  
PIN FUNCTIONS  
GATE4: Port 4 Gate Drive. GATE4 should be connected  
to the gate of the external MOSFET for port 4. When the  
MOSFET is turned on, the gate voltage is driven to 12V  
SENSE2: Port 2 Current Sense Input. See SENSE4.  
GATE2: Port 2 Gate Drive. See GATE4.  
OUT2: Port 2 Output Voltage Monitor. See OUT4.  
SENSE1: Port 1 Current Sense Input. See SENSE4.  
GATE1: Port 1 Gate Drive. See GATE 4.  
(typ) above V . During a current limit condition, the  
EE  
voltage at GATE4 will be reduced to maintain constant  
current through the external MOSFET. If the fault timer  
expires, GATE4 is pulled down, turning the MOSFET off  
and recording a t  
or t  
event. If the port is unused,  
OUT1: Port 1 Output Voltage Monitor. See OUT4.  
CUT  
START  
float the GATE4 pin.  
AUTO: AUTO Pin Mode Input. AUTO pin mode allows the  
OUT4: Port 4 Output Voltage Monitor. OUT4 should be  
connected to the output port. A current limit foldback  
circuitlimitsthepowerdissipationintheexternalMOSFET  
by reducing the current limit threshold when the drain-to-  
source voltage exceeds 10V. The port 4 Power Good bit is  
LTC4266A/LTC4266C to detect and power up a PD even  
2
if there is no host controller present on the I C bus. The  
voltageoftheAUTOpindeterminesthestateoftheinternal  
registerswhentheLTC4266A/LTC4266Cisresetorcomes  
out of V UVLO (see the LTC4266A/LTC4266C Software  
DD  
set when the voltage from OUT4 to V drops below 2.4V  
Programmingdocumentation).Thestatesoftheseregister  
EE  
2
(typ). A 500k resistor is connected internally from OUT4  
to AGND when the port is idle. If the port is unused, OUT4  
pin must be floated.  
bits can subsequently be changed via the I C interface.  
The real-time state of the AUTO pin is read at bit 0 in the  
Pin Status register (11h). Internally pulled down to DGND.  
Must be tied locally to either V or DGND.  
DD  
SENSE3: Port 3 Current Sense Input. See SENSE4.  
GATE3: Port 3 Gate Drive. See GATE4.  
MSD: Maskable Shutdown Input. Active low. When pulled  
low, all ports that have their corresponding mask bit set  
in the Misc Config register (17h) will be reset, equivalent  
to pulling the SHDN pin low. Internal filtering of the MSD  
pin prevents glitches less than 1μs wide from resetting  
OUT3: Port 3 Output Voltage Monitor. See OUT4.  
V : Main Supply Input. Connect to a –45V to –57V  
EE  
supply, relative to AGND.  
ports. Internally pulled up to V .  
DD  
4266acfc  
14  
LTC4266A/LTC4266C  
OPERATION  
++  
Overview  
between a LTPoE PD and all other types of IEEE compli-  
++  
ant PDs allowing LTPoE PSEs to remain compliant and  
interoperable with existing equipment.  
Power over Ethernet, or PoE, is a standard protocol for  
sending DC power over copper Ethernet data wiring.  
The IEEE group that administers the 802.3 Ethernet data  
standards added PoE powering capability in 2003. This  
original PoE spec, known as 802.3af, allowed for 48V DC  
power at up to 13W. This initial spec was widely popular,  
but 13W was not adequate for some requirements. In  
2009, the IEEE released a new standard, known as 802.3at  
LTC4266 Product Family  
The LTC4266 is a third-generation quad PSE controller  
that implements four PSE ports in either an end-point or  
midspandesign.Virtuallyallnecessarycircuitryisincluded  
to implement an IEEE 802.3at compliant PSE design,  
requiringonlyanexternalpowerMOSFETandsenseresis-  
tor per channel; these minimize power loss compared to  
alternative designs with on-board MOSFETs and increase  
system reliability in the event a single channel fails.  
+
or PoE , increasing the voltage and current requirements  
to provide 25W of power.  
The IEEE standard also defines PoE terminology. A device  
that provides power to the network is known as a PSE, or  
powersourcingequipment,whileadevicethatdrawspower  
from the network is known as a PD, or powered device.  
PSEs come in two types: Endpoints (typically network  
switches or routers), which provide data and power; and  
Midspans, which provide power but pass through data.  
MidspansaretypicallyusedtoaddPoEcapabilitytoexisting  
non-PoE networks. PDs are typically IP phones, wireless  
access points, security cameras, and similar devices.  
The LTC4266 comes in three grades which support dif-  
ferent PD power levels.  
TheA-gradeLTC4266extendsPoEpowerdeliverycapabili-  
ties to LTPoE levels. LTPoE is a Linear Technology  
proprietary specification allowing for the delivery of up to  
90WtoLTPoE compliantPDs.TheLTPoE architecture  
extends the IEEE physical power negotiation to include  
38.7W, 52.7W, 70W and 90W power levels. The A-grade  
LTC4266 also incorporates all B- and C-grade features.  
++  
++  
++  
++  
++  
PoE Evolution  
The B-grade LTC4266 is a fully IEEE-compliant Type 2  
PSE supporting autonomous detection, classification  
and powering of Type 1 and Type 2 PDs. The B-grade  
LTC4266 also incorporates all C-grade features. The  
B-grade LTC4266 is marketed and numbered without the  
B suffix for legacy reasons; the absence of power grade  
suffix infers a B-grade part.  
+
Even during the process of creating the IEEE PoE 25.5W  
specification, it became clear that there was a significant  
and increasing need for more than 25.5W of delivered  
power. The LTC4266A family responds to this market by  
allowing a reliable means of providing up to 90W of deliv-  
++  
++  
ered power to a LTPoE PD. The LTPoE specification  
providesreliabledetectionandclassificationextensionsto  
the existing IEEE PoE technique that are backward com-  
patible and interoperable with existing Type 1 and Type 2  
TheC-gradeLTC4266isafullyautonomous802.3atType1  
PSE solution. Intended for use only in AUTO pin mode,  
the C-grade chipset autonomously supports detection,  
classification and powering of Type 1 PDs. As a Type 1  
PSE, 2-event classification is prohibited and Class 4 PDs  
are automatically treated as Class 0 PDs.  
++  
PDs. Unlike other proprietary PoE solutions, Linear’s  
++  
LTPoE solution provides mutual identification between  
++  
the PSE and PD. This ensures that the LTPoE PD knows  
it may use the requested power at start-up because it has  
++  
++  
detected a LTPoE PSE. LTPoE PSEs can differentiate  
4266acfc  
15  
LTC4266A/LTC4266C  
OPERATION  
PoE Basics  
New in 802.3at  
Common Ethernet data connections consist of two or four  
twisted pairs of copper wire (commonly known as CAT-5  
cable), transformer-coupled at each end to avoid ground  
loops. PoE systems take advantage of this coupling ar-  
rangement by applying voltage between the center-taps  
of the data transformers to transmit power from the PSE  
to the PD without affecting data transmission. Figure 10  
shows a high-level PoE system schematic.  
Thenewer802.3atstandardsupersedes802.3afandbrings  
several new features:  
• A PD may draw as much as 25.5W. Such PDs (and the  
PSEs that support them) are known as Type 2. Older  
13W 802.3af equipment is classified as Type 1. Type 1  
PDs will work with all PSEs; Type 2 PDs may require  
Type2PSEstoworkproperly.TheLTC4266A/LTC4266C  
is designed to work in both Type 1 and Type 2 PSE de-  
signs, and also supports non-standard configurations  
at higher power levels.  
To avoid damaging legacy data equipment that does not  
expect to see DC voltage, the PoE spec defines a protocol  
that determines when the PSE may apply and remove  
power. Valid PDs are required to have a specific 25k  
common-mode resistance at their input. When such a PD  
is connected to the cable, the PSE detects this signature  
resistance and turns on the power. When the PD is later  
disconnected, the PSE senses the open circuit and turns  
power off. The PSE also turns off power in the event of a  
current fault or short-circuit.  
• The Classification protocol is expanded to allow Type 2  
PSEs to detect Type 2 PDs, and to allow Type 2 PDs to  
determine if they are connected to a Type 2 PSE. Two  
versions of the new Classification protocol are avail-  
able: an expanded version of the 802.3af Class Pulse  
protocol, and an alternate method integrated with the  
existing LLDP protocol (using the Ethernet data path).  
The LTC4266A/LTC4266C fully supports the new Class  
Pulse protocol and is also compatible with the LLDP  
protocol(whichisimplementedinthedatacommunica-  
tions layer, not in the PoE circuitry).  
When a PD is detected, the PSE optionally looks for a  
classification signature that tells the PSE the maximum  
power the PD will draw. The PSE can use this information  
to allocate power among several ports, police the current  
consumption of the PD, or to reject a PD that will draw  
more power that the PSE has available. For a 802.3af PSE,  
the classification step is optional; if a PSE chooses not to  
classify a PD, it must assume that the PD is a 13W (full  
802.3af power) device.  
• Fault protection current levels and timing are adjusted  
to reduce peak power in the MOSFET during a fault;  
this allows the new 25.5W power levels to be reached  
using the same MOSFETs as older 13W designs.  
CAT 5  
20Ω MAX  
ROUNDTRIP  
0.05μF MAX  
PSE  
PD  
RJ45  
4
RJ45  
4
5
5
GND  
1N4002  
SPARE PAIR  
=4  
0.22μF  
100V  
X7R  
1
1
DGND  
AGND  
5μF ≤ C  
IN  
≤ 300μF  
SMAJ58A  
58V  
Tx  
Rx  
Tx  
3.3V  
V
DD  
INT  
SCL  
SDAIN  
SDAOUT  
2
3
2
3
INTERRUPT  
DATA PAIR  
DATA PAIR  
SMAJ58A  
1/4  
2
LTC4266  
I C  
0.1μF  
1N4002  
=4  
Rx  
V
SENSE GATE OUT  
EE  
1μF  
GND  
6
6
100V  
X7R  
DC/DC  
CONVERTER  
R
PWRGD  
+
OUT  
CLASS  
S1B  
V
0.25Ω  
LTC4265  
–48V  
7
8
7
–48V  
–48V  
OUT  
–
IN  
8
S1B  
SPARE PAIR  
4266AC F10  
Figure 10. Power over Ethernet System Diagram  
4266acfc  
16  
LTC4266A/LTC4266C  
OPERATION  
++  
Extended Power LTPoE  
allows the AUTO pin mode LTC4266A to autonomously  
power up to supported power levels. If the AUTO pin is  
high, internal circuitry determines the maximum deliver-  
able power. PDs requesting more than the available power  
limits are not powered.  
TheLTC4266Aaddsthecapabilitytoautonomouslydeliver  
++  
up to 90W of power to the PD. LTPoE PDs may forgo  
++  
++  
802.3LLDPsupportandrelysolelyontheLTPoE Physi-  
cal Classification to negotiate power with LTPoE PSEs;  
this greatly simplifies high-power PD implementations.  
++  
Table 1. LTPoE Auto Pin Mode Maximum Delivered  
Power Capabilities  
++  
LTPoE classification may be optionally enabled for the  
PART  
PAIRS  
PD POWER  
38.7W  
52.7W  
70W  
LTC4266A by setting both the High Power Enable and  
LTC4266A-1  
LTC4266A-2  
LTC4266A-3  
LTC4266A-4  
4
4
4
4
++  
LTPoE Enable bits.  
++  
The higher levels of LTPoE delivery impose additional  
layoutandcomponentselectionconstraints.TheLTC4266A  
is offered in 4 power levels (-1, -2, -3, and -4) which  
90W  
4266acfc  
17  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
Operating Modes  
disconnect detection is enabled. The host controller may  
also command the port to remove power at any time.  
The LTC4266A/LTC4266C include four independent ports,  
each of which can operate in one of four modes: manual,  
semi-auto, AUTO pin, or shutdown.  
Reset and the AUTO/MID Pins  
TheinitialLTC4266A/LTC4266Cconfigurationdependsonthe  
state of the AUTO and MID pins during reset. Reset occurs  
at power-up, or whenever the RESET pin is pulled low or  
the global Reset All bit is set. Changing the state of AUTO  
or MID after power-up will not properly change the port  
behavior of the LTC4266A/LTC4266C until a reset occurs.  
Table 2. Operating Modes  
AUTOMATIC  
AUTO  
DETECT/  
CLASS  
I
/I  
CUT LIM  
POWER-UP ASSIGNMENT  
MODE  
PIN OPMD  
AUTO Pin  
1
11b  
Enabled at Automatically  
Reset  
Yes  
Reserved  
Semi-auto  
0
0
11b  
10b  
N/A  
N/A  
N/A  
No  
Although typically used with a host controller, the  
LTC4266A/LTC4266C can also be used in a standalone  
mode with no connection to the serial interface. If there is  
no host present, the AUTO pin must be tied high so that, at  
reset, all ports will be configured to operate automatically.  
Each port will detect and classify repeatedly until a PD is  
Host  
Enabled  
Upon  
Request  
Manual  
0
0
01b Once Upon  
Request  
Upon  
No  
No  
Request  
Shutdown  
00b  
Disabled  
Disabled  
• Inmanualmode,theportwaitsforinstructionsfromthe  
host system before taking any action. It runs a single  
detection or classification cycle when commanded to  
by the host, and reports the result in its Port Status  
register. The host system can command the port to turn  
on or off the power at any time. This mode should only  
be used for diagnostic and test purposes.  
discovered, set I  
and I according to the classifica-  
CUT  
LIM  
tion results, apply power after successful detection, and  
remove power when a PD is disconnected.  
Table 3 shows the I  
and I  
values that will be auto-  
LIM  
CUT  
matically set in standalone (AUTO pin) mode, based on  
the discovered class.  
• In semi-auto mode, the port repeatedly attempts to  
detect and classify any PD attached to it. It reports the  
status of these attempts back to the host, and waits for  
a command from the host before turning on power to  
theport.Thehostmustenabledetection(andoptionally  
classification) for the port before detection will start.  
Table 3. ICUT and ILIM Values in Standalone AUTO Pin Mode  
CLASS  
I
I
LIM  
CUT  
Class 1  
112mA  
206mA  
375mA  
638mA  
425mA  
425mA  
425mA  
850mA  
Class 2  
Class 3 or Class 0  
Class 4  
• AUTO pin mode operates the same as semi-auto mode  
except that it will automatically turn on the power to the  
The automatic setting of the I  
and I  
values only  
LIM  
CUT  
occurs if the LTC4266A/LTC4266C is reset with the AUTO  
port if detection is successful. In AUTO pin mode, I  
CUT  
pin high.  
and I values are set automatically by the LTC4266A/  
LIM  
LTC4266C. This operational mode is only valid if the  
AUTO pin is high at reset or power-up and remains high  
during operation.  
Ifthestandaloneapplicationisamidspan, theMIDpinmust  
be tied high to enable correct midspan detection timing.  
DETECTION  
• In shutdown mode, the port is disabled and will not  
detect or power a PD.  
Detection Overview  
Regardlessofwhichmodeitisin,theLTC4266A/LTC4266C  
will remove power automatically from any port that gener-  
ates a current limit fault. It will also automatically remove  
power from any port that generates a disconnect event if  
Toavoiddamagingnetworkdevicesthatwerenotdesigned  
to tolerate DC voltage, a PSE must determine whether  
the connected device is a real PD before applying power.  
4266acfc  
18  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
The IEEE specification requires that a valid PD have a  
common-mode resistance of 25k 5% at any port volt-  
age below 10V. The PSE must accept resistances that fall  
between 19k and 26.5k, and it must reject resistances  
above 33k or below 15k (shaded regions in Figure 11).  
The PSE may choose to accept or reject resistances in the  
undefinedareasbetweenthemust-acceptandmust-reject  
ranges.Inparticular,thePSEmustrejectstandardcomputer  
network ports, many of which have 150Ω common-mode  
termination resistors that will be damaged if power is ap-  
plied to them (the black region at the left of Figure 11).  
PD signature resistances between 17k and 29k (typically)  
are detected as valid and reported as Detect Good in the  
corresponding Port Status register. Values outside this  
range,includingopenandshort-circuits,arealsoreported.  
Iftheportmeasureslessthan1Vatthefirstforced-current  
test, the detection cycle will abort and Short Circuit will  
be reported. Table 4 shows the possible detection results.  
Table 4. Detection Status  
MEASURED PD SIGNATURE  
Incomplete or Not Yet Tested  
<2.4k  
DETECTION RESULT  
Detect Status Unknown  
Short Circuit  
RESISTANCE 0Ω  
10k  
20k  
30k  
Capacitance > 2.7μF  
C
Too High  
Too Low  
PD  
2.4k < R < 17k  
R
SIG  
PD  
150Ω (NIC)  
23.75k  
26.25k  
26.5k  
PD  
17k < R < 29k  
Detect Good  
R Too High  
SIG  
PSE  
PD  
15k 19k  
33k  
4266AC F11  
>29k  
>50k  
Open Circuit  
Figure 11. IEEE 802.3af Signature Resistance Ranges  
Voltage > 10V  
Port Voltage Outside Detect Range  
4-Point Detection  
More On Operating Modes  
TheLTC4266A/LTC4266Cusesa4-pointdetectionmethod  
todiscoverPDs.False-positivedetectionsareminimizedby  
checkingforsignatureresistancewithbothforced-current  
and forced-voltage measurements. Initially, two test cur-  
rents are forced onto the port (via the OUTn pin) and the  
resulting voltages are measured. The detection circuitry  
subtractsthetwoV-Ipointstodeterminetheresistiveslope  
while removing offset caused by series diodes or leakage  
at the port (see Figure 12). If the forced-current detection  
yields a valid signature resistance, two test voltages are  
then forced onto the port and the resulting currents are  
measured and subtracted. Both methods must report  
valid resistances for the port to report a valid detection.  
Theport’soperatingmodedetermineswhentheLTC4266A/  
LTC4266C runs a detection cycle. In manual mode, the  
port will idle until the host orders a detect cycle. It will  
then run detection, report the results, and return to idle  
to wait for another command.  
In semi-auto mode, the LTC4266A/LTC4266C autono-  
mously polls a port for PDs, but it will not apply power  
until commanded to do so by the host. The Port Status  
register is updated at the end of each detection cycle. If a  
valid signature resistance is detected and classification is  
enabled, the port will classify the PD and report that result  
as well. The port will then wait for at least 100ms (or 2  
seconds if midspan mode is enabled), and will repeat the  
detection cycle to ensure that the data in the Port Status  
register is up-to-date.  
275  
FIRST  
DETECTION  
POINT  
25kΩ SLOPE  
If the port is in semi-auto mode and high power opera-  
tion is enabled, the port will not turn on in response to  
a power-on command unless the current detect result is  
165  
SECOND  
DETECTION  
POINT  
Detect Good. Any other detect result will generate a t  
VALID PD  
START  
fault if a power-on command is received. If the port is not  
in high power mode, it will ignore the detection result and  
apply power when commanded, maintaining backwards  
compatibility with the LTC4259A.  
0V-2V  
OFFSET  
VOLTAGE  
4266AC F12  
Figure 12. PD Detection  
4266acfc  
19  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
60  
50  
40  
30  
20  
10  
0
BehaviorinAUTOpinmodeissimilartosemi-auto;however,  
after Detect Good is reported and the port is classified (if  
classification is enabled), it is automatically powered on  
without further intervention. In standalone (AUTO pin)  
PSE LOAD LINE  
48mA  
OVER  
CURRENT  
CLASS 4  
CLASS 3  
mode, the I  
and I thresholds are automatically set;  
CUT  
LIM  
33mA  
23mA  
see the Reset and the AUTO/MID Pin section for more  
information.  
CLASS 2  
TYPICAL  
CLASS 3  
PD LOAD  
LINE  
14.5mA  
6.5mA  
The signature detection circuitry is disabled when the port  
is initially powered up with the AUTO pin low, in shutdown  
mode, or when the corresponding Detect Enable bit is  
cleared.  
CLASS 1  
CLASS 0  
0
5
10  
15  
20  
25  
VOLTAGE (V  
)
CLASS  
4266AC F13  
Detection of Legacy PDs  
Figure 13. PD Classification  
Table 5. Classification Values  
Proprietary PDs that predate the original IEEE 802.3af  
standard are commonly referred to today as legacy de-  
vices. One type of legacy PD uses a large common mode  
capacitance (>10ꢁF) as the detection signature. Note that  
PDs in this range of capacitance are defined as invalid, so  
a PSE that detects legacy PDs is technically noncompliant  
with the IEEE spec.  
CLASS  
Class 0  
Class 1  
Class 2  
Class 3  
Class 4  
RESULT  
No Class Signature Present; Treat Like Class 3  
3W  
7W  
13W  
25.5W (Type 2)  
The LTC4266A/LTC4266C can be configured to detect  
this type of legacy PD. Legacy detection is disabled by  
default, but can be manually enabled on a per-port basis.  
When enabled, the port will report Detect Good when it  
sees either a valid IEEE PD or a high-capacitance legacy  
PD. With legacy mode disabled, only valid IEEE PDs will  
be recognized.  
If classification is enabled, the port will classify the PD  
immediatelyafterasuccessfuldetectioncycleinsemi-auto  
or AUTO pin modes, or when commanded to in manual  
mode. It measures the PD classification signature by ap-  
plying 18V for 12ms (both values typical) to the port via  
the OUTn pin and measuring the resulting current; it then  
reports the discovered class in the Port Status register.  
If the LTC4266A/LTC4266C is in AUTO pin mode, it will  
CLASSIFICATION  
additionally use the classification result to set the I  
CUT  
802.3af Classification  
and I thresholds. See the Reset and the AUTO/MID Pin  
LIM  
section for more information.  
A PD can optionally present a classification signature to  
the PSE to indicate the maximum power it will draw while  
operating. The IEEE specification defines this signature as  
aconstantcurrentdrawwhenthePSEportvoltageisinthe  
The classification circuitry is disabled when the port is  
initially powered up with the AUTO pin low, in shutdown  
mode, or when the corresponding Class Enable bit is  
cleared.  
V
range(between15.5Vand20.5V), withthecurrent  
CLASS  
level indicating one of 5 possible PD classes. Figure 13  
shows a typical PD load line, starting with the slope of the  
25kꢀ signature resistor below 10V, then transitioning to  
the classification signature current (in this case, Class 3)  
in the V  
range. Table 5 shows the possible clas-  
CLASS  
sification values.  
4266acfc  
20  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
802.3at 2-Event Classification  
Class 0 to 3), the LTC4266A will not provide power and  
will restart the detection process. To aid in diagnosis, the  
Port Status register will always report the results of the  
lastclasspulse,so,forexample,aninvalidClass4–Class2  
combination would report a second class pulse was run  
in the High Power Status register (which implies that the  
first cycle found Class 4), and Class 2 in the Port Status  
register.  
The802.3atspecificationdefinestwomethodsofclassify-  
ing a Type 2 PD. The LTC4266A supports 802.3at 2-event  
classification. The LTC4266C does not support 2-event  
classification.  
One method adds extra fields to the Ethernet LLDP data  
protocol;althoughtheLTC4266A/LTC4266Ciscompatible  
with this classification method, it cannot perform clas-  
sification directly since it doesn’t have access to the data  
path. LLDP classification requires the PSE to power the  
PD as a standard 802.3af (Type 1) device. It then waits  
for the host to perform LLDP communication with the PD  
and update the PSE port data. The LTC4266A/LTC4266C  
POWER CONTROL  
External MOSFET, Sense Resistor Summary  
The primary function of the LTC4266A/LTC4266C is to  
control the delivery of power to the PSE port. It does this  
by controlling the gate drive voltage of an external power  
MOSFET while monitoring the current via an external  
sense resistor and the output voltage at the OUT pin. This  
supports changing the I  
and I  
levels on the fly, al-  
LIM  
CUT  
lowing the host to complete LLDP classification.  
The second 802.3at classification method, known as  
2-event classification or ping-pong, is supported by the  
LTC4266A. A Type 2 PD that is requesting more than 13W  
will indicate Class 4 during normal 802.3af classification.  
If the LTC4266A sees Class 4, it forces the port to a speci-  
fied lower voltage (called the mark voltage, typically 9V),  
pauses briefly, and then re-runs classification to verify the  
Class 4 reading (Figure 1). It also sets a bit in the High  
Power Status register to indicate that it ran the second  
classification cycle. The second cycle alerts the PD that  
it is connected to a Type 2 PSE which can supply Type 2  
power levels.  
input supply to the  
circuitry serves to couple the raw V  
EE  
port in a controlled manner that satisfies the PD’s power  
needs while minimizing power dissipation in the MOSFET  
and disturbances on the V backplane.  
EE  
The LTC4266A/LTC4266C is designed to use 0.25ꢀ sense  
resistors to minimize power dissipation. It also supports  
0.5ꢀsenseresistors,whicharethedefaultwhenLTC4258/  
LTC4259A compatibility is desired.  
Inrush Control  
Once the command has been given to turn on a port, the  
LTC4266A/LTC4266C ramps up the GATE pin of that port’s  
external MOSFET in a controlled manner. Under normal  
power-up circumstances, the MOSFET gate will rise until  
the port current reaches the inrush current limit level  
(typically 450mA), at which point the GATE pin will be  
2-event ping-pong classification is enabled by setting a bit  
in the port’s High Power Mode register. Note that a ping-  
pongenabledportonlyrunsthesecondclassificationcycle  
when it detects a Class 4 device; if the first cycle returns  
Class 0 to 3, the port assumes it is connected to a Type 1  
PD and does not run the second classification cycle.  
servoed to maintain the specified I  
current. During  
INRUSH  
this inrush period, a timer (t  
) runs. When output  
START  
Invalid Type 2 Class Combinations  
chargingiscomplete,theportcurrentwillfallandtheGATE  
pin will be allowed to continue rising to fully enhance the  
The 802.3at specification defines a Type 2 PD class sig-  
nature as two consecutive Class 4 results; a Class 4 fol-  
lowed by a Class 0-3 is not a valid signature. In AUTO pin  
mode, the LTC4266A will power a detected PD regardless  
of the classification results, with one exception: if the PD  
presents an invalid Type 2 signature (Class 4 followed by  
MOSFET and minimize its on-resistance. The final V is  
GS  
nominally 12V. The inrush period is maintained until the  
t
timer expires. At this time if the inrush current limit  
START  
level is still exceeded the port will be turned back off and  
a t fault reported.  
START  
4266acfc  
21  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
Current Limit  
TomaintainIEEEcompliance,I shouldbekeptat425mA  
LIM  
for all Type 1 PDs, and 850mA if a Type 2 PD is detected.  
EachLTC4266A/LTC4266Cportincludestwocurrentlimit-  
I
is automatically reset to 425mA when a port turns off.  
LIM  
Table 6. Example Current Limit Settings  
INTERNAL REGISTER SETTING (hex)  
= 0.5Ω = 0.25Ω  
ing thresholds (I  
and I ), each with a corresponding  
CUT  
LIM  
timer (t  
and t ). Setting the I  
and I thresholds  
CUT  
LIM  
CUT LIM  
depends on several factors: the class of the PD, the volt-  
age of the main supply (V ), the type of PSE (Type 1 or  
I
(mA)  
R
SENSE  
R
SENSE  
EE  
LIM  
Type 2), the sense resistor (0.5Ω or 0.25Ω), the SOA of  
the MOSFET, and whether or not the system is required  
to implement class enforcement.  
53  
88  
106  
159  
213  
266  
319  
372  
08  
89  
80  
8A  
09  
8B  
88  
08  
89  
Per the IEEE specification, the LTC4266A/LTC4266C will  
allow the port current to exceed I  
for a limited period  
CUT  
of time before removing power from the port, whereas it  
willactivelycontroltheMOSFETgatedrivetokeeptheport  
current below I . The port does not take any action to  
425  
478  
00  
8E  
92  
CB  
10  
D2  
40  
4A  
50  
5A  
60  
52  
80  
LIM  
limit the current when only the I threshold is exceeded,  
CUT  
but does start the t  
timer. If the current drops below  
CUT  
531  
8A  
the I  
current threshold before its timer expires, the  
CUT  
584  
t
timer counts back down, but at 1/16 the rate that it  
CUT  
638  
90  
9A  
C0  
CA  
D0  
DA  
E0  
49  
40  
4A  
50  
5A  
60  
52  
counts up. If the t  
timer reaches 60ms (typical) the  
CUT  
744  
port is turned off and the port t  
fault is set. This allows  
CUT  
850  
the current limit circuitry to tolerate intermittent overload  
signalswithdutycyclesbelowabout6%;longerdutycycle  
overloads will turn the port off.  
956  
1063  
1169  
1275  
1488  
1700  
1913  
2125  
2338  
2550  
2975  
The I  
current limiting circuit is always enabled and  
LIM  
actively limiting port current. The t  
timer is enabled  
LIM  
only when the programmable t  
allows t to be set to a shorter value than t  
field is non-zero. This  
LIMn  
to provide  
LIM  
CUT  
more aggressive MOSFET protection and turn off a port  
before MOSFET damage can occur. The t timer starts  
LIM  
when the I threshold is exceeded. When the t timer  
LIM  
LIM  
reaches1.7ms(typ)timestheprogrammablet  
fieldthe  
LIMn  
port is turned off and the port t  
fault is set. When the  
LIM  
t
field is zero, t  
behaviors are tracked by the t  
LIMn  
LIM CUT  
I
Foldback  
LIM  
timer, which counts up during both I and I  
events.  
LIM  
CUT  
The LTC4266A/LTC4266C features a two-stage foldback  
circuit that reduces the port current if the port voltage falls  
below the normal operating voltage. This keeps MOSFET  
power dissipation at safe levels for typical 802.3af MOS-  
FETs, even at extended 802.3at power levels. Current  
limit and foldback behavior are programmable on a per-  
I
is typically set to a lower value than I to allow the  
LIM  
CUT  
port to tolerate minor faults without current limiting.  
Per the IEEE specification, the LTC4266A/LTC4266C will  
automatically set I to 425mA (shown in bold in Table 6)  
LIM  
during inrush at port turn-on, and then switch to the  
programmed I  
setting once inrush has completed.  
port basis. Table 6 gives examples of recommended I  
LIM  
LIM  
register settings.  
4266acfc  
22  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
The LTC4266A/LTC4266C will support current levels well  
beyond the maximum values in the 802.3at specification.  
The shaded areas in Table 6 indicate settings that may  
require a larger external MOSFET, additional heat sinking,  
Disconnect  
The LTC4266A/LTC4266C monitors the port to make sure  
that the PD continues to draw the minimum specified  
current. A disconnect timer counts up whenever port  
current is below 7.5mA (typ), indicating that the PD has  
or enabling t  
.
LIM  
been disconnected. If the t timer expires, the port will  
DIS  
MOSFET Fault Detection  
be turned off and the disconnect bit in the fault event reg-  
LTC4266A/LTC4266C PSE ports are designed to tolerate  
significant levels of abuse, but in extreme cases it is pos-  
sible for the external MOSFET to be damaged. A failed  
MOSFET may short source to drain, which will make the  
port appear to be on when it should be off; this condition  
may also cause the sense resistor to fuse open, turning  
off the port but causing the LTC4266A/LTC4266C SENSE  
pin to rise to an abnormally high voltage. A failed MOSFET  
may also short from gate to drain, causing the LTC4266A/  
LTC4266C GATE pin to rise to an abnormally high voltage.  
The LTC4266A/LTC4266C OUT, SENSE and GATE pins are  
designed to tolerate up to 80V faults without damage.  
ister will be set. If the current returns before the t timer  
DIS  
runs out, the timer resets and will start counting from the  
beginning if the undercurrent condition returns. As long  
as the PD exceeds the minimum current level more often  
than t , it will stay powered.  
DIS  
Althoughnotrecommended,theDCdisconnectfeaturecan  
be disabled by clearing the corresponding DC Disconnect  
Enable bits. Note that this defeats the protection mecha-  
nisms built into the IEEE spec, since a powered port will  
stay powered after the PD is removed. If the still-powered  
port is subsequently connected to a non-PoE data device,  
the device may be damaged.  
IftheLTC4266A/LTC4266Cseesanyoftheseconditionsfor  
more than 180ꢁs, it disables all port functionality, reduces  
the gate drive pull-down current for the port and reports  
a FET Bad fault. This is typically a permanent fault, but  
the host can attempt to recover by resetting the port, or  
by resetting the entire chip if a port reset fails to clear the  
fault. If the MOSFET is in fact bad, the fault will quickly  
return, and the port will disable itself again. The remaining  
ports of the LTC4266A/LTC4266C are unaffected.  
The LTC4266A/LTC4266C does not include AC disconnect  
circuitry, but includes AC Disconnect Enable bits to main-  
tain compatibility with the LTC4259A. If the AC Disconnect  
Enable bits are set, DC disconnect will be used.  
Shutdown Pins  
The LTC4266A/LTC4266C includes a hardware SHDN pin  
for each port. When a SHDN pin is pulled to DGND, the  
corresponding port will be shut off immediately. The port  
An open or missing MOSFET will not trigger a FET Bad  
2
remains shut down until re-enabled via I C or a device  
fault,butwillcauseat  
faultiftheLTC4266A/LTC4266C  
START  
reset in AUTO pin mode.  
attempts to turn on the port.  
Masked Shutdown  
Voltage and Current Readback  
The LTC4266A/LTC4266C provides a low latency port  
shedding feature to quickly reduce the system load when  
required. By allowing a pre-determined set of ports to  
be turned off, the current on an overloaded main power  
supply can be reduced rapidly while keeping high priority  
devices powered. Each port can be configured to high or  
low priority; all low-priority ports will shut down within  
6.5ꢁs after the MSD pin is pulled low. If multiple ports in  
a LTC4266A/LTC4266C device are shut down via MSD,  
The LTC4266A/LTC4266C measures the output voltage  
and current at each port with an internal A/D converter.  
Port data is only valid when the port power is on. The  
converter has two modes:  
• Slow mode: 14 samples per second, 14.5 bits resolution  
• Fast mode: 440 samples per second, 9.5 bits resolution  
In fast mode, the least significant 5 bits of the lower byte  
are zeroes so that bit scaling is the same in both modes.  
4266acfc  
23  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
they are staggered by at least 0.55ꢁs to help reduce volt-  
age transients on the main supply. If a port is turned off  
via MSD, the corresponding Detection and Classification  
Enable bits are cleared, so the port will remain off until  
the host explicitly re-enables detection.  
Register Description  
For information on serial bus usage and device configura-  
tionandstatus,refertotheLTC4266A/LTC4266CSoftware  
Programming documentation.  
EXTERNAL COMPONENT SELECTION  
SERIAL DIGITAL INTERFACE  
Power Supplies and Bypassing  
Overview  
The LTC4266A/LTC4266C requires two supply voltages to  
TheLTC4266A/LTC4266Ccommunicateswiththehostus-  
ingastandardSMBus/I C2-wireinterface.TheLTC4266A/  
operate. V requires 3.3V (nominally) relative to DGND.  
DD  
2
V requires a negative voltage of between –45V and –57V  
EE  
LTC4266C is a slave-only device, and communicates with  
the host master using the standard SMBus protocols.  
Interrupts are signaled to the host via the INT pin. The  
Timing Diagrams (Figures 5 through 9) show typical  
communicationwaveformsandtheirtimingrelationships.  
More information about the SMBus data protocols can be  
found at www.smbus.org.  
for Type 1 PSEs, –51V to –57V for Type 2 PSEs or –54.75V  
++  
to –57V for LTPoE PSEs, relative to AGND. The relation-  
ship between the two grounds is not fixed; AGND can be  
referenced to any level from V to DGND, although it  
DD  
should typically be tied to either V or DGND.  
DD  
V
provides power for most of the internal LTC4266A/  
DD  
LTC4266C circuitry, and draws a maximum of 3mA. A  
The LTC4266A/LTC4266C requires both the V and V  
supplyrailstobepresentfortheserialinterfacetofunction.  
DD  
EE  
ceramic decoupling cap of at least 0.1ꢁF should be placed  
fromV toDGND,ascloseaspracticaltoeachLTC4266A/  
DD  
LTC4266C chip.  
Bus Addressing  
Figure 14 shows a three component low dropout regula-  
tor for a negative supply to DGND generated from the  
The LTC4266A/LTC4266C’s primary serial bus address is  
010xxxxb, with the lower four bits set by the AD3-AD0  
pins; this allows up to 16 LTC4266A/LTC4266Cs on a  
single bus. All LTC4266A/LTC4266Cs also respond to  
the address 0110000b, allowing the host to write the  
same command (typically configuration commands) to  
multiple LTC4266A/LTC4266Cs in a single transaction. If  
the LTC4266A/LTC4266C is asserting the INT pin, it will  
also respond to the alert response address (0001100b)  
per the SMBus spec.  
negative V supply. V is tied to AGND and DGND is  
EE  
DD  
negativereferencedtoAGND.Thisregulatordrivesasingle  
LTC4266A/LTC4266C device. In Figure 15, DGND is tied  
to AGND in this boost converter circuit for a positive V  
DD  
supply of 3.3V above AGND. This circuit can drive multiple  
LTC4266A/LTC4266C devices and opto couplers.  
AGND  
AGND  
V
DD  
D1  
Interrupts and SMBAlert  
C1  
0.1μF  
CMHZ4687-4.3V  
LTC4266  
DGND  
Most LTC4266A/LTC4266C port events can be configured  
to trigger an interrupt, asserting the INT pin and alerting  
the host to the event. This removes the need for the host  
to poll the LTC4266A/LTC4266C, minimizing serial bus  
trafficandconservinghostCPUcycles.MultipleLTC4266A/  
LTC4266Cs can share a common INT line, with the host  
using the SMBAlert protocol (ARA) to determine which  
LTC4266A/LTC4266C caused an interrupt.  
Q2  
CMPTA92  
V
R5  
750k  
EE  
V
EE  
4266AC F14  
Figure 14. Negative LDO to DGND  
4266acfc  
24  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
L3  
L4  
10μH  
D28  
B1100  
100μH  
SUMIDA CDRH5D28-101NC  
SUMIDA CDRH4D28-100NC  
3.3V AT 400mA  
C74  
100μF  
6.3V  
C73  
10μF  
6.3V  
C75  
R51  
4.7k  
1%  
R53  
R52  
3.32k  
1%  
10μF  
4.7k  
16V  
1%  
C76  
10μF  
63V  
C78  
0.22μF  
100V  
+
5
Q13  
Q14  
FMMT723  
C77  
0.22μF  
100V  
V
FMMT723  
CC  
1
3
6
Q15  
ITH/RUN  
NGATE  
SENSE  
FDC2512  
R58  
10Ω  
LTC3803  
R54  
56k  
4
R55  
806Ω  
1%  
R56  
47.5k  
1%  
V
FB  
R57  
1k  
R59  
0.100Ω  
1%, 1W  
C79  
2200pF  
GND  
2
R60  
10Ω  
V
EE  
4266AC F15  
Figure 15. Positive VDD Boost Converter  
V
is the main supply that provides power to the PDs.  
IEEE 802.3 Ethernet specifications require that network  
segments (including PoE circuitry) be electrically isolated  
from the chassis ground of each network interface device.  
However,networksegmentsarenotrequiredtobeisolated  
fromeachother,providedthatthesegmentsareconnected  
to devices residing within a single building on a single  
power distribution system.  
EE  
Because it supplies a relatively large amount of power and  
issubjecttosignificantcurrenttransients,itrequiresmore  
design care than a simple logic supply. For minimum IR  
loss and best system efficiency, set V near maximum  
EE  
amplitude (57V), leaving enough margin to account for  
transient over- or undershoot, temperature drift, and the  
line regulation specs of the particular power supply used.  
For simple devices such as small PoE switches, the isola-  
tion requirement can be met by using an isolated main  
power supply for the entire device. This strategy can be  
used if the device has no electrically conducting ports  
other than twisted-pair Ethernet. In this case, the SDAIN  
and SDAOUT pins can be tied together and will act as a  
Bypass capacitance between AGND and V is very im-  
EE  
portant for reliable operation. If a short-circuit occurs  
at one of the output ports it can take as long as 1ꢁs for  
the LTC4266A/LTC4266C to begin regulating the current.  
During this time the current is limited only by the small  
impedancesinthecircuitandahighcurrentspiketypically  
2
standard I C/SMBus SDA pin.  
occurs, causing a voltage transient on the V supply and  
EE  
If the device is part of a larger system, contains additional  
external non-Ethernet ports, or must be referenced to  
protective ground for some other reason, the Power over  
Ethernet subsystem (including all LTC4266A/LTC4266Cs)  
must be electrically isolated from the rest of the system.  
Figure 16 shows a typical isolated serial interface. The  
SDAOUT pin of the LTC4266A/LTC4266C is designed to  
possibly causing the LTC4266A/LTC4266C to reset due to  
a UVLO fault. A 1ꢁF, 100V X7R capacitor placed near the  
V
pin is recommended to minimize spurious resets.  
EE  
Isolating the Serial Bus  
The LTC4266A/LTC4266C includes a split SDA pin (SDAIN  
and SDAOUT) to ease opto-isolation of the bidirectional  
SDA line.  
2
drive the inputs of an opto-coupler directly. Standard I C/  
SMBusdevicestypicallycannotdriveopto-couplers,soU1  
is used to buffer the signals from the host controller side.  
4266acfc  
25  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
0.1μF  
2
I C ADDRESS  
LTC4266  
V
DD  
INT  
SCL  
SDAIN  
SDAOUT  
AD0  
AD1  
AD2  
AD3  
DGND  
AGND  
0100000  
0100001  
0100010  
0.1μF  
0.1μF  
LTC4266  
V
DD  
INT  
SCL  
SDAIN  
SDAOUT  
AD0  
AD1  
AD2  
AD3  
DGND  
AGND  
2k  
2k  
U2  
200Ω  
V
CPU  
SCL  
DD  
U1  
200Ω  
SDA  
0.1μF  
LTC4266  
HCPL-063L  
V
DD  
TO  
INT  
SCL  
SDAIN  
SDAOUT  
AD0  
CONTROLLER  
U3  
200Ω  
200Ω  
AD1  
AD2  
AD3  
DGND  
AGND  
SMBALERT  
0.1μF  
t
t
t
0.1μF  
GND CPU  
HCPL-063L  
U1: FAIRCHILD NC7WZ17  
U2, U3: AGILENT HCPL-063L  
LTC4266  
V
DD  
INT  
SCL  
SDAIN  
SDAOUT  
AD0  
0101110  
AD1  
AD2  
AD3  
DGND  
AGND  
0.1μF  
LTC4266  
ISOLATED  
3.3V  
V
INT  
DD  
SCL  
SDAIN  
SDAOUT  
AD0  
+
10μF  
0101111  
AD1  
AD2  
AD3  
DGND  
AGND  
ISOLATED  
GND  
4266AC F16  
Figure 16. Opto-Isolating the I2C Bus  
4266acfc  
26  
LTC4266A/LTC4266C  
APPLICATIONS INFORMATION  
External MOSFET  
ESD/Cable Discharge Protection  
CarefulselectionofthepowerMOSFETiscriticaltosystem  
reliability. LTC recommends either Fairchild IRFM120A,  
FDT3612, FDMC3612 or Philips PHT6NQ10T for their  
proven reliability in Type 1 and Type 2 PSE applications.  
Non-standard applications that provide more current than  
the 850mA IEEE maximum may require heat sinking and  
other MOSFET design considerations. Contact LTC Ap-  
plications before using a MOSFET other than one of these  
recommended parts.  
EthernetportscanbesubjecttosignificantESDeventswhen  
long data cables, each potentially charged to thousands  
of volts, are plugged into the low impedance of the RJ45  
jack. To protect against damage, each port requires a pair  
of clamp diodes; one to AGND and one to V (Figure 10).  
EE  
An additional surge suppressor is required for each  
LTC4266A/LTC4266C chip from V to AGND. The diodes  
EE  
at the ports steer harmful surges into the supply rails,  
where they are absorbed by the surge suppressor and the  
V
bypass capacitance. The surge suppressor has the  
EE  
Sense Resistor  
additional benefit of protecting the LTC4266A/LTC4266C  
from transients on the V supply.  
EE  
TheLTC4266A/LTC4266Cisdesignedtouseeither0.5Ωor  
0.25Ω current sense resistors. For new designs 0.25Ω is  
recommended to reduce power dissipation; the 0.5Ω op-  
tion is intended for existing systems where the LTC4266A/  
LTC4266Cisusedasadrop-inreplacementfortheLTC4258  
or LTC4259A. The lower sense resistor values reduce  
heat dissipation. Four commonly available 1Ω resistors  
(0402 or larger package size) can be used in parallel in  
S1B diodes work well as port clamp diodes, and an  
SMAJ58AorequivalentisrecommendedfortheV surge  
EE  
suppressor.  
LAYOUT GUIDELINES  
Strict adherence to board layout, parts placement and  
routing guidelines is critical for optimal current read-  
ing accuracy, IEEE compliance, system robustness, and  
thermal dissipation.  
place of a single 0.25Ω resistor. In order to meet the I  
CUT  
and I accuracy required by the IEEE specification, the  
LIM  
sense resistors should have 1% tolerance or better, and  
no more than 200ppm/°C temperature coefficient.  
Power delivery above 25.5W imposes additional compo-  
nent and layout restraints. Specifically MOSFET, sense  
resistor and transformer selection is crucial to safe and  
reliable system operation.  
Port Output Cap  
Each port requires a 0.22ꢁF cap across its outputs to  
keep the LTC4266A/LTC4266C stable while in current limit  
during startup or overload. Common ceramic capacitors  
often have significant voltage coefficients; this means the  
capacitance is reduced as the applied voltage increases.  
To minimize this problem, X7R ceramic capacitors rated  
for at least 100V are recommended.  
Contact LTC Applications to obtain a full set of layout  
guidelines, example layouts and BOMs.  
4266acfc  
27  
LTC4266A/LTC4266C  
PACKAGE DESCRIPTION  
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.  
UHF Package  
38-Lead Plastic QFN (5mm × 7mm)  
(Reference LTC DWG # 05-08-1701 Rev C)  
0.70 p 0.05  
5.50 p 0.05  
5.15 0.05  
4.10 p 0.05  
3.15 0.05  
3.00 REF  
PACKAGE  
OUTLINE  
0.25 p 0.05  
0.50 BSC  
5.5 REF  
6.10 p 0.05  
7.50 p 0.05  
RECOMMENDED SOLDER PAD LAYOUT  
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED  
PIN 1 NOTCH  
R = 0.30 TYP OR  
0.35 s 45o CHAMFER  
0.75 p 0.05  
3.00 REF  
5.00 p 0.10  
37 38  
0.00 – 0.05  
0.40 p0.10  
PIN 1  
TOP MARK  
1
2
(SEE NOTE 6)  
5.15 0.10  
5.50 REF  
7.00 p 0.10  
3.15 0.10  
(UH) QFN REF C 1107  
0.200 REF 0.25 p 0.05  
R = 0.125  
TYP  
R = 0.10  
TYP  
0.50 BSC  
BOTTOM VIEW—EXPOSED PAD  
NOTE:  
1. DRAWING CONFORMS TO JEDEC PACKAGE  
OUTLINE M0-220 VARIATION WHKD  
2. DRAWING NOT TO SCALE  
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE  
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE  
5. EXPOSED PAD SHALL BE SOLDER PLATED  
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION  
ON THE TOP AND BOTTOM OF PACKAGE  
3. ALL DIMENSIONS ARE IN MILLIMETERS  
4266acfc  
28  
LTC4266A/LTC4266C  
REVISION HISTORY  
REV  
DATE  
DESCRIPTION  
PAGE NUMBER  
A
8/11  
Changed Gate Typical voltage to 12V.  
3, 14, 21  
2
Changed SCL, SDAIN V to 1.0V (I C compliance).  
4
IL  
Table 4 (Class) reference and caption changed to Table 5.  
20  
Power Supplies and Bypassing section changed to –45 for Type 1 minimum and –51 for Type 2 minimum.  
Related Parts Table CUT/LIM changed to I /I  
24  
.
30  
CUT LIM  
++  
B
C
02/12 Change LTPoE power levels from 35W, 45W to 38.7W, 52.7W respectively  
1, 2, 15, 17  
2
Revised MAX value for V I C Input Low Voltage  
4
ILD  
Clarified AUTO pin mode relationship to reset pin  
18  
17  
08/12 Table 1: Changed twisted pair requirement from 2-pair to 4-pair for 38.7W and 52.7W  
4266acfc  
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.  
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-  
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.  
29  
LTC4266A/LTC4266C  
TYPICAL APPLICATION  
ISOLATED  
3.3V  
ISOLATED  
GND  
0.1μF  
DGND AGND  
0.22μF  
2k  
2k  
100V  
X7R  
V
DD  
U2  
FB1  
FB2  
200Ω  
200Ω  
SCL  
V
CPU  
1/4  
DD  
SDAIN  
SDAOUT  
INT  
LTC4266  
U1  
SCL  
V
SENSE GATE OUT  
EE  
1μF  
100V  
X7R  
S1B  
R
S
0.25Ω  
SDA  
Q1  
HCPL-063L  
SMAJ58A  
S1B  
–48V  
ISOLATED  
U3  
RJ45  
200Ω  
200Ω  
CONNECTOR  
T1  
1
2
t
t
t
t
0.01μF  
200V  
0.01μF  
200V  
3
4
5
6
7
8
75Ω  
75Ω  
INTERRUPT  
PHY  
0.1μF  
GND CPU  
(NETWORK  
PHYSICAL  
LAYER  
HCPL-063L  
CHIP)  
t
t
t
t
0.01μF  
200V  
0.01μF  
200V  
75Ω  
75Ω  
4266AC F17  
1000pF  
2000V  
Figure 17. One Complete Isolated Powered Ethernet Port  
RELATED PARTS  
PART NUMBER  
LTC4270/LTC4271  
LTC4266  
DESCRIPTION  
COMMENTS  
Transformer Isolation, Supports Type 1, Type 2 and LTPoE PDs  
2-Event Classification, Programmable I /I  
+
++  
++  
12-Port PoE/PoE /LTPoE PSE Controller  
Quad IEEE 802.3at PoE PSE Controller  
Single IEEE 802.3at PoE PSE Controller  
Single IEEE 802.3at PoE PSE Controller  
IEEE 802.3at PD Interface Controller  
CUT LIM  
LTC4274  
2-Event Classification, Programmable I /I  
CUT LIM  
LTC4274A/LTC4274C  
LTC4265  
13W through 90W Support  
100V, 1A Internal Switch, 2-Event Classification Recognition  
LTC4267  
IEEE 802.3af PD Interface with Integrated Switching  
Regulator  
Internal 100V, 400mA Switch, Dual Inrush Current,  
Programmable Class  
LTC4269-1  
LTC4269-2  
LTC4278  
IEEE 802.3at PD Interface with Integrated Flyback  
Switching Regulator  
2-Event Classification, Programmable Classification, Synchronous  
No-Opto Flyback Controller, 50kHz to 250kHz, Auxiliary Support  
IEEE 802.3at PD Interface with Integrated Forward  
Switching Regulator  
2-Event Classification, Programmable Classification, Synchronous  
Forward Controller, 100kHz to 500kHz, Auxiliary Support  
IEEE 802.3at PD Interface with Integrated Flyback  
Switching Regulator  
2-Event Classification, Programmable Classification, Synchronous  
No-Opto Flyback Controller, 50kHz to 250kHz, 12V Auxiliary Support  
4266acfc  
LT 0812 REV C • PRINTED IN USA  
LinearTechnology Corporation  
1630 McCarthy Blvd., Milpitas, CA 95035-7417  
30  
●
●
© LINEAR TECHNOLOGY CORPORATION 2011  
(408) 432-1900 FAX: (408) 434-0507 www.linear.com  

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