LT4276 Datasheet PDF - Linear

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LT4276
Linear

Part Number LT4276
Description PD Forward/Flyback Controller
Page 26 Pages


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LT4276
LTPoE++/PoE+/PoE
PD Forward/Flyback Controller
Features
n IEEE802.3af/at and LTPoE++90W Powered Device
(PD) with Forward/Flyback Controller
n LT4276A Supports All of the Following Standards:
n LTPoE++ 38.7W, 52.7W, 70W and 90W
n IEEE 802.3at 25.5W Compliant
n IEEE 802.3af up to 13W Compliant
n LT4276B is IEEE 802.3at/af Compliant
n LT4276C is IEEE 802.3af Compliant
n Superior Surge Protection (100V Absolute Maximum)
n Wide Junction Temperature Range (–40°C to 125°C)
n Auxiliary Power Support as Low as 9V
n No Opto-Isolator Required for Flyback Operation
n External Hot SwapN-Channel MOSFET for Lowest
Power Dissipation and Highest System Efficiency
n >94% End-to-End Efficiency with LT4321 Ideal Bridge
n Available in a 28-Lead 4mm × 5mm QFN Package
Applications
n High Power Wireless Data Systems
n Outdoor Security Camera Equipment
n Commercial and Public Information Displays
n High Temperature Applications
Description
The LT®4276 is a pin-for-pin compatible family of IEEE
802.3 and LTPoE++ Powered Device (PD) controllers. It
includes an isolated switching regulator controller capable
of synchronous operation in both forward and flyback
topologies with auxiliary power support.
The LT4276A employs the LTPoE++ classification scheme,
receiving 38.7W, 52.7W, 70W or 90W of power at the PD
RJ45 connector, and is backwards compatible with IEEE
802.3. The LT4276B is a fully 802.3at compliant, 25.5W
Type 2 (PoE+) PD. The LT4276C is a fully 802.3af compli-
ant, 13W Type 1 (PoE) PD.
The LT4276 supports both forward and flyback power
supply topologies, configurable for a wide range of PoE
applications. The flyback topology supports No-Opto
feedback. Auxiliary input voltage can be accurately sensed
with just a resistor divider connected to the AUX pin.
The LT4276 utilizes an external, low RDS(ON) N-channel
MOSFET for the Hot Swap function, maximizing power
delivery and efficiency, reducing heat dissipation, and
easing the thermal design.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
LTPoE++, and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Typical Application
+
AUX
37V-57V
LTPoE++ 70W Power Supply in a Forward Mode
+
VPORT
0.1µF
3.3k
10nF
FMMT723
100µH
10µF
22µF • •
VPORT HS VIN HS SW
GATE
AUX
SRC VCC
LT4276A
RCLASS
RCLASS++
GND FB31 SS ROSC
VCC FFS
PG
DLY ISEN+
ISEN–
20mΩ
SG
0.1µF
10k 100pF
T2P ITHB
4276 TA01
100k
OPTO
TO MICROPROCESSOR
VCC
For more information www.linear.com/LT4276
+
+ 5V
13A
LT4276 Family
MAX DELIVERED
POWER
LTPoE++ 90W
LTPoE++ 70W
LTPoE++ 52.7W
LTPoE++ 38.7W
25.5W
13W
LT4276
GRADE
ABC
l
l
l
l
ll
lll
4276f
1



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LT4276
Absolute Maximum Ratings
(Notes 1, 2)
VPORT, HSSRC, VIN Voltages......................–0.3 to 100V
HSGATE Current.................................................. ±20mA
VRCCCLAVoSlSta,gReC...L..A..S..S..+...+....................................... –0.3 to 8V
Voltages..................................–0.3 to 8V (and ≤ VPORT)
SISFESNT+, ,FIFSSEDNL–Y,VIoTlHtaBg,eTs2...P...V..o..l.t..a.g..e..s................–..0....3...t.o...V..C..C.+±00..33VV
FB31 Voltage...................................................+12V/–30V
RCLASS/RCLASS++ Current............................... –50mA
AUX Current......................................................... ±1.4mA
ROSC Current...................................................... ±100µA
RLDCMP Current....................................................±500µA
T2P Current..........................................................–2.5mA
Operating Junction Temperature Range (Note 3)
LT4276AI/LT4276BI/LT4276CI...............–40°C to 85°C
LT4276AH/LT4276BH/LT4276CH........ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Pin Configuration
TOP VIEW
28 27 26 25 24 23
GND 1
22 DNC
AUX 2
RCLASS++/NC* 3
RCLASS 4
T2P/NC** 5
VCC 6
VCC 7
VCC 8
9
21 VCC
20 PG
29
GND
19 GND
18 SG
17 ISEN+
16 ISEN–
15 RLDCMP
10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 150°C, θJC = 3.4°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
*RCLASS++ is not connected in the LT4276B and LT4276C
**T2P is not connected in the LT4276C
Order Information
LEAD FREE FINISH TAPE AND REEL
PART MARKING* MAX PD POWER PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT4276AIUFD#PBF LT4276AIUFD#TRPBF 4276A
90W
28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C
LT4276AHUFD#PBF LT4276AHUFD#TRPBF 4276A
90W
28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C
LT4276BIUFD#PBF LT4276BIUFD#TRPBF 4276B
25.5W
28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C
LT4276BHUFD#PBF LT4276BHUFD#TRPBF 4276B
25.5W
28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C
LT4276CIUFD#PBF LT4276CIUFD#TRPBF 4276C
13W
28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C
LT4276CHUFD#PBF LT4276CHUFD#TRPBF 4276C
13W
28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C
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 nonstandard 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/
4276f
2 For more information www.linear.com/LT4276



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LT4276
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications
RFFSDLY = 5.23kΩ to GND. AUX connected to
GarNeDaut nTlJe=ss25o°thCe.rVwViPsOeRsTp=ecViHfiSeSdR.C(=NoVtVeIN2)=
40V,
VVCC
=
VCCREG,
ROSC,
PG,
and
SG
Open,
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
VSIG
VCLASS
VMARK
VPORT, HSSRC, VIN Operating Voltage
VPORT Signature Range
VPORT Classification Range
VPORT Mark Range
VPORT AUX Range
Signature/Class Hysteresis Window
At VPORT Pin
At VPORT Pin
At VPORT Pin
At VPORT Pin, After 1st Classification Event
At VPORT Pin, VAUX ≥ 6.45V
l
l 1.5
l 12.5
l 5.6
l8
l 1.0
60 V
10 V
21 V
10 V
60 V
V
Reset Threshold
l 2.6
5.6 V
VHSON
VHSOFF
Hot Swap Turn-On Voltage
Hot Swap Turn-Off Voltage
Hot Swap On/Off Hysteresis Window
l 35 37
l 30
31
l3
V
V
V
Supply Current
VPORT, HSSRC & VIN Supply Current
VVPORT = VHSSRC = VVIN = 60V
l
2
VPORT Supply Current During Classification VVPORT = 17.5V, RCLASS, RCLASS++ Open l 0.7 1.0 1.3
VPORT Supply Current During Mark Event VVPORT = VMARK after 1st Classification Event l 0.4
2.2
Signature and Classification
mA
mA
mA
Signature Resistance
Signature Resistance During Mark Event
RCLASS/RCLASS++ Voltage
Classification Stability Time
Digital Interface
VSIG (Note 4)
VMARK (Note 4)
–10mA ≥ IRCLASS ≥ –36mA
VVPORT Step to 17.5V, RCLS = 35.7Ω
l 23.6 24.4 25.5
l 5.2
8.3 11.4
l 1.36 1.40 1.43
l2
V
ms
VAUXT
IAUXH
AUX Threshold
AUX Pin Current
T2P Output High
T2P Leakage
Hot Swap Control
VAUX = 6.05V
VVCC - VT2P, –1mA Load
VT2P = 0V
l 6.05 6.25 6.45
l 3.3 5.3 7.3
l 0.3
l –1
1
V
µA
V
µA
IGPU HSGATE Pull Up Current
HSGATE Voltage
VHSGATE - VHSSRC = 5V (Note 5)
–10µA Load, with respect to HSSRC
l –27 –22 –18
l 10
14
µA
V
HSGATE Pull Down Current
VCC Supply
VCCREG VCC Regulation Voltage
Feedback Amplifier
VHSGATE - VHSSRC = 5V
l 400
l 7.2 7.6 8.0
µA
V
VFB FB31 Regulation Voltage
FB31 Pin Bias Current
gm Feedback Amplifier Average Trans-
Conductance
RLDCMP Open
Time Average, –2µA < IITHB < 2µA
l 3.11 3.17 3.23
-0.1
l –52 –40 –26
V
µA
µA/V
ISINK ITHB Average Sink Current
Soft-Start
Time Average, VFB31 = 0V
l 4.4
8.0 13.4
µA
ISFST Charging Current
VSFST = 0.5V, 3.0V
l –49 –42 –36
µA
For more information www.linear.com/LT4276
4276f
3



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LT4276
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications
RFFSDLY = 5.23kΩ to GND. AUX connected to
GarNeDaut nTlJe=ss25o°thCe.rVwViPsOeRsTp=ecViHfiSeSdR.C(=NoVtVeIN2)=
40V,
VVCC
=
VCCREG,
ROSC,
PG,
and
SG
Open,
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Gate Outputs
PG, SG Output High Level
PG, SG Output Low Level
I = –1mA
I = 1mA
l VCC –0.1
l
V
1V
PG Rise Time, Fall Time
PG = 1000pF
15 ns
SG Rise Time, Fall Time
SG = 400pF
15 ns
Current Sense/Overcurrent
VFAULT
ΔVSENSE/
ΔVITHB
VITHB(OS)
Timing
Overcurrent Fault Threshold
Current Sense Comparator Threshold with
Respect to VITHB
VITHB Offset
VISEN+ - VISEN
l 125
l –130
140
–111
155
–98
l 3.03 3.17 3.33
mV
mV/V
V
fOSC
fT2P
tMIN
DMAX
tPGDELAY
tFBDLY
tFB
tPGSG
tSTART
tFAULT
IMPS
Default Switching Frequency
Switching Frequency
LTPoE++ Signal Frequency
Minimum PG On Time
Maximum PG Duty Cycle
PG Turn-On Delay-Flyback
PG Turn-On Delay-Forward
Feedback Amp Enable Delay Time
Feedback Amp Sense Interval
PG Falling to SG Rising Delay Time-Flyback
PG Falling to SG Falling Delay Time-
Forward
Start Timer (Note 6)
Fault Timer (Note 6)
MPS Current
ROSC Pin Open
ROSC = 45.3kΩ to GND
5.23kΩ from FFSDLY to GND
52.3kΩ from FFSDLY to GND
10.5kΩ from FFSDLY to VCC
52.3kΩ from FFSDLY to VCC
Resistor from FFSDLY to GND
10.5kΩ from FFSDLY to VCC
52.3kΩ from FFSDLY to VCC
Delay After Power Good
Delay After Overcurrent Fault
l 200 214 223
l 280 300 320
fSW/256
l 175 250 330
l 63 66 70
45
171
92
391
350
550
20
67
301
l 80 86 93
l 80 86 93
l 10 12 14
kHz
kHz
ns
%
ns
ns
ns
ns
ns
ns
ns
ns
ns
ms
ms
mA
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. All voltages with respect to GND unless otherwise noted. Positive
currents are into pins; negative currents are out of pins unless otherwise
noted.
Note 3. This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature can exceed 150°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 4. Signature resistance specifications do not include resistance
added by the external diode bridge which can add as much as 1.1kΩ to the
port resistance.
Note 5. IGPU available in PoE powered operation. That is, available after
V(VPORT) > VHSON and V(AUX) < VAUXT, over the range where V(VPORT)
is between VHSOFF and 60V.
Note 6. Guaranteed by design, not subject to test.
4276f
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