LTC4267
1
4267f
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
Class 2 PD with 3.3V Isolated Power Supply
802 is a registered trademark of Institute of Electrical and Electronics Engineers, Inc.
P
VCC
PWRGD
NGATE
SENSE
I
TH
/RUN
V
FB
PGND
P
OUT
V
PORTP
R
CLASS
SIGDISA
V
PORTN
LTC4267
+
+
R
CLASS
68.1
1%
5F
MIN
10k
470
100k
60.4k
P
VCC
P
VCC
4.7F
320F
22nF
PA1133
PS2911
BA5516
TLV431
SBM1040
SMAJ58A
3.3V
1.5A
CHASSIS
HD01
+
+
HD01
48V
FROM
DATA PAIR
48V
FROM
SPARE PAIR
4267 TA01
Si3440
0.1
6.8k
10k
0.1F
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Power over Ethernet
IEEE 802.3af PD Interface with
Integrated Switching Regulator
The LTC
4267 combines an IEEE 802.3af compliant Pow-
ered Device (PD) interface with a current mode switching
regulator, providing a complete power solution for PD
applications. The LTC4267 integrates the 25k signature
resistor, classifi cation current source, thermal overload pro-
tection, signature disable and power good signal along with
an undervoltage lockout optimized for use with the IEEE-
required diode bridge. The precision dual level input current
limit allows the LTC4267 to charge large load capacitors
and interface with legacy PoE systems.
The current mode switching regulator is designed for
driving a 6V rated N-channel MOSFET and features pro-
grammable slope compensation, soft-start, and constant
frequency operation, minimizing noise even with light
loads. The LTC4267 includes an onboard error amplifi er
and voltage reference allowing use in both isolated and
nonisolated confi gurations.
The LTC4267 is available in space saving, low profi le
16-pin SSOP or DFN packages.
IP Phone Power Management
Wireless Access Points
Security Cameras
Power over Ethernet
Complete Power Interface Port for IEEE 802
.3af
Powered Device (PD)
Onboard 100V, 400mA UVLO Switch
Precision Dual Level Inrush Current Limit
Integrated Current Mode Switching Regulator
Onboard 25k Signature Resistor with Disable
Programmable Classifi cation Current (Class 0-4)
Thermal Overload Protection
Power Good Signal
Integrated Error Amplifi er and Voltage Reference
Low Profi le 16-Pin SSOP and 3mm 5mm DFN
Packages
LTC4267
2
4267f
ABSOLUTE
AXI U
RATI GS
W
W
W
U
FOR ATIO
PACKAGE/ORDER I
U
U
W
ELECTRICAL CHARACTERISTICS
V
PORTN
with Respect to V
PORTP
Voltage ... 0.3V to 100V
P
OUT
, SIGDISA, PWRGD
Voltage ..................... V
PORTN
+ 100V to V
PORTN
0.3V
P
VCC
to PGND Voltage (Note 2)
Low Impedance Source ........................... 0.3V to 8V
Current Fed .......................................... 5mA into P
VCC
R
CLASS
Voltage .................V
PORTN
+ 7V to V
PORTN
0.3V
PWRGD Current .....................................................10mA
R
CLASS
Current .....................................................100mA
NGATE to PGND Voltage ........................... 0.3V to P
VCC
V
FB
, I
TH
/RUN to PGND Voltages ................ 0.3V to 3.5V
ORDER PART
NUMBER
DFN PART*
MARKING
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grades are identifi ed by a label on the shipping container.
4267
LTC4267CDHC
LTC4267IDHC
(Note 1)
The
denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25C. (Note 3)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
PORTN
Supply Voltage
Voltage with Respect to V
PORTP
Pin
Maximum Operating Voltage
(Notes 4, 5, 6)
57
V
Signature
Range
1.5 9.5 V
Classifi cation Range
12.5
21
V
UVLO Turn-On Voltage
34.8 36.0 37.2
V
UVLO Turn-Off Voltage
29.3 30.5 31.5
V
V
TURNON
P
VCC
Turn-On Voltage
Voltage with Respect to PGND
7.8
8.7
9.2
V
V
TURNOFF
P
VCC
Turn-Off Voltage
Voltage with Respect to PGND
4.6 5.7 6.8
V
V
HYST
P
VCC
Hysteresis
V
TURNON
V
TURNOFF
1.5
3.0
V
V
CLAMP1mA
P
VCC
Shunt Regulator Voltage
I
PVCC
= 1mA, V
ITH
/RUN = 0V, Voltage
8.3
9.4 10.3
V
with Respect to PGND
SENSE to PGND Voltage .............................. 0.3V to 1V
NGATE Peak Output Current (<10s) ..........................1A
Operating Ambient Temperature Range
LTC4267C ................................................ 0C to 70C
LTC4267I ............................................. 40C to 85C
Junction Temperature
GN
Package
...................................................... 150C
DHC
Package
.................................................... 125C
Storage Temperature Range ................... 65C to 150C
Lead Temperature (Soldering, 10 sec) .................. 300C
ORDER PART
NUMBER
GN PART
MARKING
4267
4267I
LTC4267CGN
LTC4267IGN
T
JMAX
= 125C,
JA
= 43.5C/W
EXPOSED PAD (PIN 17)
MUST BE SOLDERED TO ELECTRICALLY
ISOLATED PCB HEAT SINK
T
JMAX
= 150C,
JA
= 90C/W
16
15
14
13
12
11
10
9
17
1
2
3
4
5
6
7
8
TOP VIEW
DHC16 PACKAGE
16-LEAD (3mm
5mm) PLASTIC DFN
I
TH
/RUN
PGND
NGATE
P
VCC
R
CLASS
NC
V
PORTN
NC
V
FB
PGND
SENSE
V
PORTP
SIGDISA
PWRGD
P
OUT
NC
TOP VIEW
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PGND
I
TH
/RUN
NGATE
P
VCC
R
CLASS
NC
V
PORTN
PGND
PGND
V
FB
SENSE
V
PORTP
SIGDISA
PWRGD
P
OUT
PGND
LTC4267
3
4267f
ELECTRICAL CHARACTERISTICS
The
denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25C. (Note 3)
SYMBOL PARAMETER
CONDITIONS
MIN TYP
MAX
UNITS
V
MARGIN
V
CLAMP1mA
V
TURNON
Margin
0.05
0.6
V
I
VPORTN_ON
V
PORTN
Supply Current when ON
V
PORTN
= 48V, P
OUT
, PWRGD, SIGDISA Floating
3
mA
I
PVCC_ON
P
VCC
Supply Current
(Note 7)
Normal Operation
V
ITH
/RUN PGND = 1.3V
240 350
A
Start-Up
P
VCC
PGND = V
TURNON
100mV
40 90
A
I
VPORTN_CLASS
V
PORTN
Supply Current
V
PORTN
= 17.5V, P
OUT
Tied to V
PORTP
, R
CLASS
,
0.35 0.5 0.65 mA
During Classifi cation
SIGDISA Floating (Note 8)
I
CLASS
Current Accuracy
10mA < I
CLASS
< 40mA, 12.5V V
PORTN
21V
3.5
%
During Classifi cation
(Notes 9, 10)
R
SIGNATURE
Signature Resistance
1.5V V
PORTN
9.5V, P
OUT
Tied to V
PORTP
,
23.25 26.00 k
IEEE 802.3af 2-Point Measurement (Notes 4, 5)
R
INVALID
Invalid Signature Resistance
1.5V V
PORTN
9.5V, SIGDISA and P
OUT
Tied to
9 11.8 k
V
PORTP
, IEEE 802.3af 2-Point Measurement
(Notes 4, 5)
V
IH
Signature Disable
With Respect to V
PORTN
3
57
V
High Level Input Voltage
High Level Invalidates Signature (Note 11)
V
IL
Signature Disable
With Respect to V
PORTN
0.45
V
Low Level Input Voltage
Low Level Enables Signature
R
INPUT
Signature Disable, Input Resistance
With Respect to V
PORTN
100
k
V
PG_OUT
Power Good Output Low Voltage
I = 1mA V
PORTN
= 48V,
0.5
V
PWRGD Referenced to V
PORTN
Power Good Trip Point
V
PORTN
= 48V, Voltage between V
PORTN
and P
OUT
V
PG _FALL
P
OUT
Falling
1.3 1.5 1.7
V
V
PG_RISE
P
OUT
Rising
2.7
3.0
3.3
V
I
PG_LEAK
Power Good Leakage Current
V
PORTN
= 0V, PWRGD FET Off, V
PWRGD
= 57V
1
A
R
ON
On-Resistance
I = 350mA, V
PORTN
= 48V, Measured from
1.0
1.6
V
PORTN
to P
OUT
(Note 10)
2
V
ITHSHDN
Shutdown Threshold (at I
TH
/RUN) P
VCC
PGND = V
TURNON
+ 100mV
0.15 0.28 0.45
V
I
THSTART
Start-Up Current Source at I
TH
/RUN V
ITH
/RUN PGND = 0V, P
VCC
P
GND
= 8V
0.2
0.3
0.4
A
V
FB
Regulated Feedback Voltage
Referenced to PGND, P
VCC
P
GND
= 8V (Note 12)
0.780 0.800 0.812
V
I
FB
V
FB
Input Current
P
VCC
P
GND
= 8V (Note 12)
10
50
nA
g
m
Error Amplifi er Transconductance
I
TH
/RUN Pin Load = 5A (Note 12)
200
333
500
A/V
V
O(LINE)
Output Voltage Line Regulation
V
TURNOFF
< P
VCC
< V
CLAMP
(Note
12)
0.05 mV/V
V
O(LOAD)
Output Voltage Load Regulation
I
TH
/RUN Sinking 5A, P
VCC
P
GND
= 8V (Note 12)
3
mV/A
I
TH
/RUN Sourcing 5A, P
VCC
P
GND
= 8V (Note 12)
3
mV/A
I
POUT_LEAK
P
OUT
Leakage
V
PORTN
= 0V, Power MOSFET Off,
150
A
P
OUT
= 57V (Note 13)
I
LIM_HI
Input Current Limit, High Level
V
PORTN
= 48V, P
OUT
= 43V (Note 14, 15)
0C T
A
70C
325
375
400
mA
40C T
A
85C
300
375
400
mA
I
LIM_LO
Input Current Limit, Low Level
V
PORTN
= 48V, P
OUT
= 43V (Note 14, 15)
80
140 180
mA
f
OSC
Oscillator
Frequency
V
ITH
/RUN PGND = 1.3V, P
VCC
P
GND
= 8V
180
200
240
kHz
DC
ON(MIN)
Minimum Switch On Duty Cycle
V
ITH
/RUN PGND = 1.3V, V
FB
PGND = 0.8V,
6
8
%
P
VCC
P
GND
= 8V
DC
ON(MAX)
Maximum Switch On Duty Cycle
V
ITH
/RUN PGND = 1.3V, V
FB
PGND = 0.8V,
70
80
90
%
P
VCC
P
GND
= 8V
LTC4267
4
4267f
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: P
VCC
internal clamp circuit self regulates to 9.4V with respect to
PGND.
Note 3: The LTC4267 operates with a negative supply voltage in the range
of 1.5V to 57V. To avoid confusion, voltages for the PD interface
are always referred to in terms of absolute magnitude. Terms such as
"maximum negative voltage" refer to the largest negative voltage and
a "rising negative voltage" refers to a voltage that is becoming more
negative.
Note 4: The LTC4267 is designed to work with two polarity protection
diode drops between the PSE and PD. Parameter ranges specifi ed in the
Electrical Characteristics section are with respect to this product pins and
are designed to meet IEEE 802.3af specifi cations when these diode drops
are included. See the Application Information section.
Note 5: Signature resistance is measured via the two-point V/I method
as defi ned by IEEE 802.3af. The PD signature resistance is offset from the
25k to account for diode resistance. With two series diodes, the total PD
resistance will be between 23.75k and 26.25k and meet IEEE 802.3af
specifi cations. The minimum probe voltages measured at the LTC4267
pins are 1.5V and 2.5V. The maximum probe voltages are 8.5V and
9.5V.
Note 6: The PD interface includes hysteresis in the UVLO voltages to
preclude any start-up oscillation. Per IEEE 802.3af requirements, the PD
will power up from a voltage source with 20 series resistance on the fi rst
trial.
Note 7: Dynamic Supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 8: I
VPORTN_CLASS
does not include classifi cation current
programmed at the R
CLASS
pin. Total current in classifi cation mode will be
I
VPORTN_CLASS
+ I
CLASS
(See note 9).
Note 9: I
CLASS
is the measured current fl owing through R
CLASS
. I
CLASS
accuracy is with respect to the ideal current defi ned as I
CLASS
= 1.237/
R
CLASS
. The current accuracy does not include variations in R
CLASS
resistance. The total classifi cation current for a PD also includes the IC
quiescent current (I
VPORTN_CLASS
). See Applications Information.
Note 10: For the DHC package, this parameter is assured by design and
wafer level testing.
Note 11: To disable the 25k signature, tie SIGDISA to V
PORTP
or hold
SIGDISA high with respect to V
PORTN
. See Applications Information.
Note 12: The switching regulator is tested in a feedback loop that servos
V
FB
to the output of the error amplifi er while maintaining I
TH
/RUN at the
midpoint of the current limit range.
Note 13: I
POUT_LEAK
includes current drawn through P
OUT
by the power
good status circuit. This current is compensated for in the 25k signature
resistance and does not affect PD operation.
Note 14: The LTC4267 PD Interface includes thermal protection. In the
event of an overtemperature condition, the PD interface will turn off
the switching regulator until the part cools below the overtemperature
limit. The LTC4267 is also protected against thermal damage from
incorrect classifi cation probing by the PSE. If the LTC4267 exceeds the
overtemperature threshold, the classifi cation load current is disabled.
Note 15: The PD interface includes dual level input current limit. At turn-
on, before the P
OUT
load capacitor is charged, the PD current level is set
to a low level. After the load capacitor is charged and the P
OUT
V
PORTN
voltage difference is below the power good threshold, the PD switches to
high level current limit. The PD stays in high level current limit until the
input voltage drops below the UVLO turn-off threshold.
Note 16: Peak current sense voltage is reduced dependent on duty cycle
and an optional external resistor in series with the SENSE pin (R
SL
). For
details, refer to the programmable slope compensation feature in the
Applications Information section.
Note 17: Guaranteed by design.
Note 18: The PD interface includes overtemperature protection that is
intended to protect the device from momentary overload conditions.
Junction temperature will exceed 125C when overtemperature protection
is active. Continuous operation above the specifi ed maximum operating
junction temperature may impair device reliability.
ELECTRICAL CHARACTERISTICS
The
denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25C. (Note 3)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t
RISE
NGATE
Drive
Rise
Time
C
LOAD
= 3000pF, P
VCC
P
GND
=
8V
40 ns
t
FALL
NGATE
Drive
Fall
Time
C
LOAD
= 3000pF, P
VCC
P
GND
=
8V
40 ns
V
IMAX
Peak
Current
Sense
Voltage
R
SL
= 0, P
VCC
P
GND
= 8V (Note 16)
90
100 115
mV
I
SLMAX
Peak Slope Compensation Output Current
P
VCC
P
GND
= 8V (Note 17)
5
A
t
SFST
Soft-Start
Time
P
VCC
P
GND
= 8V
1.4
ms
T
SHUTDOWN
Thermal Shutdown Trip Temperature
(Notes 14, 18)
140
C
LTC4267
5
4267f
TYPICAL PERFOR
U
W
CE CHARACTERISTICS
A
Input Current vs Input Voltage
25k Detection Range
Input Current vs Input Voltage
Input Current vs Input Voltage
Input Current vs Input Voltage
Signature Resistance vs
Input Voltage
Normalized UVLO Threshold vs
Temperature
Power Good Output Low Voltage
vs Current
P
OUT
Leakage Current
Current Limit vs Input Voltage
V
PORTN
VOLTAGE (V)
0
0
INPUT CURRENT (mA)
0.1
0.2
0.3
0.4
0.5
2
4
6
8
4267 G01
10
T
A
= 25C
V
PORTN
VOLTAGE (V)
12
9.0
INPUT CURRENT (mA)
9.5
10.5
11.0
11.5
14
16
4267 G03
10.0
18
20
22
12.0
85C
40C
CLASS 1 OPERATION
V
PORTN
VOLTAGE (V)
0
0
INPUT CURRENT (mA)
10
20
30
40
50
10
20
30
40
4267 G02
50
60
CLASS 4
CLASS 3
CLASS 2
CLASS 1
CLASS 0
T
A
= 25C
V
PORTN
VOLTAGE (V)
0
INPUT CURRENT (mA)
1
2
3
45
55
4267 G04
60
40
50
EXCLUDES ANY LOAD CURRENT
T
A
= 25C
V
PORTN
VOLTAGE (V)
1
22
V1:
V2:
SIGNATURE RESISTANCE (k
)
23
25
26
27
3
5
4267 G05
24
7
9
6
10
2
4
8
28
RESISTANCE =
DIODES: S1B
T
A
= 25C
=
V
I
V2 V1
I
2
I
1
IEEE UPPER LIMIT
IEEE LOWER LIMIT
LTC4267 + 2 DIODES
LTC4267 ONLY
CURRENT (mA)
0
V
PG_OUT
(V)
2
3
8
4267 G07
1
0
2
4
6
10
4
T
A
= 25C
P
OUT
PIN VOLTAGE (V)
0
0
V
OUT
CURRENT (A)
30
60
120
90
20
40
4267 G08
60
V
IN
= 0V
T
A
= 25C
V
PORTN
VOLTAGE (V)
40
CURRENT LIMIT (mA)
200
60
4267 G09
100
45
50
55
400
300
85C
85C
40C
40C
HIGH CURRENT MODE
LOW CURRENT MODE
TEMPERATURE (C)
40
2
NORMALIZED UVLO THRESHOLD (%)
1
0
1
2
20
0
20
40
4267 G06
60
80
APPLICABLE TO TURN-ON
AND TURN-0FF THRESHOLDS
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