enables a Power over Ethernet (PoE) powered device
(PD) to receive power in either voltage polarity from
RJ-45 data pairs, spare pairs, or both. The LT4321 and
eight N-channel MOSFETs replace the eight diodes in a
passive PoE rectifier bridge. The LT4321 eases thermal
design and increases delivered power.
An internal charge pump allows an all-NMOS bridge
eliminating larger and more costly PMOS switches. The
LT4321 works with 2-pair and 4-pair applications. High
impedance input sense pins prevent reverse current on
unused pairs. If the power source fails or is shorted, a
fast turn-off minimizes reverse current transients. Unlike
discrete ideal bridge solutions, the LT4321 will operate
through transients without enabling the MOSFETs on
unpowered pairs.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PowerPath and LTPoE++ are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
n
n
n
n
n
n
Reduces Heat, Eliminates Thermal Design Problems
Maximizes Power Efficiency
Less than 800µA Quiescent Operating Current
Fully Compatible with IEEE 802.3 Detection and
Classification
IEEE 802.3 Compliant When Paired with a Powered
Device (PD) Controller
Works with 2-Pair and 4-Pair PoE Applications
Compatible with PoE, PoE+, and LTPoE++™
100V Absolute Maximum Voltage
H-Grade Version Operates Up to 125°C
16-Lead 4mm × 4mm QFN Package
applicaTions
n
n
PoE/PoE+/ LTPoE++ Powered Devices
DC Polarity Correction and Ideal Diode-ORing of
Telecom Supplies
Typical applicaTion
Powered Device for PoE (to 13W), PoE+ (to 25.5W), or Linear LTPoE++ (to 90W) Systems
1
0.1µF
DATA
PAIRS
2
3
IN12
6
IN36
IN45
4
IN78
5
7
BG45 TG45
TG78 BG78
OUTN
LT4321
EN
PWRGD
GND
TG12 BG12
BG36 TG36
OUTP
EN
LT4275
SMAJ60A
VPORT
HSGATE
HSSRC
+
10µF
V
IN
ISOLATED
POWER
SUPPLY
RUN
GND
+
–
V
OUT
SPARE
PAIRS
4321 TA01
8
4321f
For more information
www.linear.com/LT4321
1
LT4321
absoluTe MaxiMuM raTings
(Notes 1, 2)
pin conFiguraTion
TOP VIEW
BG12
BG36
12 OUTP
17
OUTN
11 EN
10
EN
9
5
TG78
6
IN78
7
BG78
8
BG45
OUTN
TG12
TG36 1
IN36 2
IN45 3
TG45 4
IN12
OUTP-OUTN............................................. –0.3V to 100V
IN12, IN36, IN45, IN78 ....................... –2V to OUTP + 2V
BG12, BG36, BG45, BG78 Voltages .......... –0.3V to 100V
TG12, TG36, TG45, TG78
Voltages ....................................... –0.3V to OUTP + 12V
TG12-IN12 Voltage ......................................–0.3V to 12V
TG36-IN36 Voltage .....................................–0.3V to 12V
TG45-IN45 Voltage .....................................–0.3V to 12V
TG78-IN78 Voltage......................................–0.3V to 12V
EN,
EN,
..................................................... –0.3V to 100V
Operating Ambient Temperature Range
LT4321I ................................................–40°C to 85°C
LT4321H............................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
16 15 14 13
UF PACKAGE
16-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JC
= 4.5°C/W
EXPOSED PAD (PIN 17) IS OUTN, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT4321IUF#PBF
LT4321HUF#PBF
TAPE AND REEL
LT4321IUF#TRPBF
LT4321HUF#TRPBF
PART MARKING*
4321
4321
PACKAGE DESCRIPTION
16-Lead 4mm × 4mm Plastic QFN
16-Lead 4mm × 4mm Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–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/
4321f
2
For more information
www.linear.com/LT4321
LT4321
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, OUTP = 20V to 80V unless otherwise noted.
SYMBOL
V
UVLO
I
S
(DET)
I
S
(OFF)
I
S
(ON)
PARAMETER
Operating Supply Range
Undervoltage Lockout
Total Supply Current in Detect Region
Total Supply Current in Shutdown
Total Operating Supply Current
Top Gate Drive
V
BG
Bottom Gate Drive
Top Gate Pull-Up Current
Top Gate Pull-Down Current
Bottom Gate Pull-Up Current
Bottom Gate Pull-Down Current
EN
Pull-Up Resistance (Active Low)
EN Pull-Down Resistance (Active High)
V
IH
V
IL
V
ENOC
∆V
SD
Digital Input High
Digital Input Low
EN
Open Circuit Voltage
Topside Forward Regulation Voltage
Bottom Comparator Turn-On Threshold
Bottom Comparator Turn-Off Threshold
CONDITIONS
|IN12-IN36|, |IN45-IN78|, OUTP
OUTP-OUTN
OUTP < 10V
OUTP > 12V, EN < V
IL
and
EN
> V
IH
EN > V
IH
or
EN
< V
IL
, OUTP > 20V
INn = OUTP + ∆V
SD(MAX)
+ 5mV, 10µA Out of
TGn (Note 3)
10µA Out of BGn (Note 3)
TGn = INn (Note 3)
INn = OUTP – 0.25V; TGn – INn = 5V
BGn < V
BG
(Note 3)
BGn = 5V
OUTP = 55V
OUTP = 55V
EN,
EN
EN,
EN
OUTP = 55V
INn - OUTP
INn - OUTN
INn - OUTN
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
MIN
20
15
TYP
17
0.8
32
0.5
MAX
80
18
5
60
0.8
11
13
250
45
310
310
2.6
UNITS
V
V
µA
µA
mA
V
V
µA
mA
µA
mA
kΩ
kΩ
V
V
V
mV
mV
mV
7.7
10
50
1.25
15
3
160
160
0.5
2
2
–30
2
9.5
11.5
120
30
250
250
2.5
10
–15
15
3
18
0
30
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:
Referenced with respect to OUTN unless otherwise specified.
Note 3:
All conditions for external MOSFET turn on must be met. See
Table 1 and Table 2.
4321f
For more information
www.linear.com/LT4321
3
LT4321
Typical perForMance characTerisTics
Total Supply Current in Shutdown
40
35
30
CURRENT (µA)
CURRENT (µA)
25
20
15
10
5
0
0
10
20
30
40 50
V
IN
(V)
60
–40°C
25°C
100°C
125°C
70
80
IN12 = IN45 = V
IN
IN36 = IN78 = 0V
700
Total Supply Current in Ideal
Bridge Mode, 2-Pair
IN12 = V
IN
IN36 = 0
600 FLOAT IN45, IN78
EN =
EN
= 0
500
400
300
200
100
0
40 50
V
IN
(V)
–40°C
25°C
100°C
125°C
0
10
20
30
60
70
80
CURRENT (µA)
700
Total Supply Current in Ideal
Bridge Mode, 4-Pair
IN12 = IN45 = V
IN
IN36 = IN78 = 0
600 EN =
EN
= 0
500
400
300
200
100
0
40 50
V
IN
(V)
–40°C
25°C
100°C
125°C
0
10
20
30
60
70
80
4321 G01
4321 G02
4321 G03
Input Pin Current
1.0
OUTP = 80V
3.0
2.5
0.5
CURRENT (µA)
2.0
V
ENOC
(V)
EN
Open Circuit Voltage
18
16
14
12
I
BGn
(mA)
–40°C
25°C
100°C
125°C
0
10
20
30 40 50
OUTP (V)
60
70
80
10
8
6
4
2
0
BGn Pull-Down Strength
0.0
1.5
1.0
–0.5
–40°C
25°C
100°C
125°C
0
20
40
INn (V)
60
80
4321 G04
0.5
0
–1.0
0
2
4
6
V
BGn
(V)
8
10
12
4321 G06
4321 G05
BGn Pull-Up Strength
35
30
25
I
TG12
(mA)
I
BGn
(mA)
20
15
10
5
0
0
2
4
6
V
BGn
(V)
4321 G07
TG Pull-Down Strength
3.5
3.0
2.5
2.0
1.5
1.0
0.5
8
10
12
0
0
2
I
TG12
(µA)
OUTP = 20V
OUTP = 80V
180
160
140
120
100
80
60
IN45 = IN78 = FLOAT
EN = OUTP
IN12 = OUTP –250mV
IN36 = OUTN –50mV
4
6
∆V
TGATE
(V)
8
10
4321 G08
TG Pull-Up Strength
IN12 – IN36 = 20V
IN12 – IN36 = 30V
IN12 – IN36 = 80V
40
20
0
0
IN45 = IN78 = FLOAT
EN = OUTP
2
4
6
∆V
TGATE
(V)
8
10
4321 G09
4321f
4
For more information
www.linear.com/LT4321
LT4321
pin FuncTions
IN12:
Data Pair Input 1. In a PoE system, IN12 connects
to the center tap of the transformer connected to pins 1
and 2 on an RJ45 connector.
IN36:
Data Pair Input 2. In a PoE system, IN36 connects
to the center tap of the transformer connected to pins 3
and 6 on an RJ45 connector.
IN45:
Spare Pair Input 1. In a PoE system, IN45 connects
to the center tap of the transformer connected to pins 4
and 5 on an RJ45 connector.
IN78:
Spare Pair Input 2. In a PoE system, IN78 connects
to the center tap of the transformer connected to pins 7
and 8 on an RJ45 connector.
TG12:
Top-Side Gate Driver Output. TG12 pin pulls high
with respect to IN12 when IN12 is greater than OUTP and
IN36 is less than OUTN.
TG36:
Top-Side Gate Driver Output. TG36 pin pulls high
with respect to IN36 when IN36 is greater than OUTP and
IN12 is less than OUTN.
TG45:
Top-Side Gate Driver Output. TG45 pin pulls high
with respect to IN45 when IN45 is greater than OUTP and
IN78 is less than OUTN.
TG78:
Top-Side Gate Driver Output. TG78 pin pulls high
with respect to IN78 when IN78 is greater than OUTP and
IN45 is less than OUTN.
BG12:
Bottom-Side Gate Driver Output. BG12 pin pulls
high with respect to OUTN when IN36 is greater than OUTP
and IN12 is less than OUTN.
BG36:
Bottom-Side Gate Driver Output. BG36 pin pulls
high with respect to OUTN when IN12 is greater than OUTP
and IN36 is less than OUTN.
BG45:
Bottom-Side Gate Driver Output. BG45 pin pulls
high with respect to OUTN when IN78 is greater than OUTP
and IN45 is less than OUTN.
BG78:
Bottom-Side Gate Driver Output. BG78 pin pulls
high with respect to OUTN when IN45 is greater than OUTP
and IN78 is less than OUTN.
EN:
Enable, Active Low. Pull down to OUTN to enable ideal
diode bridge mode. EN is internally pulled up to V
ENOC
.
Tie to OUTP if the application circuit uses the EN pin to
enable ideal bridge mode.
EN:
Enable, Active High. Pull up to enable ideal diode
bridge mode. EN is internally pulled down to OUTN. Tie
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