19-2991; Rev 2; 2/06
IT
TION K
VALUA
E
BLE
AVAILA
IEEE 802.3af PD Interface Controller
For Power-Over-Ethernet
General Description
Features
♦
Fully Integrated IEEE 802.3af-Compliant PD
Interface
♦
PD Detection and Programmable Classification
Signatures
♦
Less than 10µA Leakage Current Offset During
Detection
♦
Integrated MOSFET For Isolation and Inrush
Current Limiting
♦
90V Absolute Maximum Rating
(MAX5940C/MAX5940D)
♦
Gate Output Allows External Control of the
Internal Isolation MOSFET
♦
Programmable Inrush Current Control
♦
Programmable Undervoltage Lockout
(MAX5940B/MAX5940D Only)
♦
Wide UVLO Hysteresis Accommodates Twisted-
Pair Cable Voltage Drop
♦
PGOOD/PGOOD Outputs to Enable Downstream
DC-DC Converters
♦
-40°C to +85°C Operating Temperature Range
MAX5940A/MAX5940B/MAX5940C/MAX5940D
The MAX5940A/MAX5940B/MAX5940C/MAX5940D pro-
vide complete interface function for a powered device
(PD) to comply with the IEEE 802.3af standard in a
power-over-ethernet system. MAX5940A/MAX5940B/
MAX5940C/MAX5940D provide the PD with a detection
signature, a classification signature, and an integrated
isolation switch with programmable inrush current control.
These devices also feature power-mode undervoltage
lockout (UVLO) with wide hysteresis and power-
good outputs. The MAX5940A/MAX5940B are available
with an absolute maximum rating of 80V and the
MAX5940C/MAX5940D are rated for an absolute maxi-
mum rating of 90V.
An integrated MOSFET provides PD isolation during
detection and classification. All devices guarantee a leak-
age current offset of less than 10µA during the detection
phase. A programmable current limit prevents high inrush
current during power-on. The device features power-
mode UVLO with wide hysteresis and long deglitch time
to compensate for twisted-pair cable resistive drop and to
assure glitch-free transition between detection, classifica-
tion, and power-on/-off phases.
The MAX5940A/MAX5940C provide an active-high
(PGOOD) open-drain output and a fixed UVLO threshold.
The MAX5940B/MAX5940D provide both active-high
(PGOOD) and active-low (PGOOD) outputs and have an
adjustable UVLO threshold with the default value compli-
ant to the 802.3af standard. All devices are designed to
work with or without an external diode bridge.
The MAX5940A/MAX5940B/MAX5940C/MAX5940D are
available in 8-pin SO packages and are rated over the
extended temperature range of -40°C to +85°C.
Ordering Information
PART
MAX5940AESA
MAX5940BESA
MAX5940CESA
MAX5940DESA
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
8 SO
8 SO
8 SO
8 SO
UVLO
Fixed
Adjustable
Fixed
Adjustable
Applications
IP Phones
Wireless Access Nodes
Computer Telephony
Security Cameras
IEEE 802.3af Power Devices
Pin Configurations appear at end of data sheet.
Typical Operating Circuits
D1*
GND
DC-DC CONVERTER
V+
GND
60V
68nF
R
DISC
25.5kΩ
8
C
OUT
MAX5014
GND
V
REG
2
RCLASS
R
CL
D2*
-48V
*OPTIONAL.
3
GATE
MAX5940A
MAX5940C
PGOOD 6
5
C
GATE
SS_SHDN
LOAD
4
V
EE
OUT
Typical Operating Circuits continued at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
IEEE 802.3af PD Interface Controller
For Power-Over-Ethernet
MAX5940A/MAX5940B/MAX5940C/MAX5940D
ABSOLUTE MAXIMUM RATINGS
(All voltages are referenced to V
EE
, unless otherwise noted.)
GND (MAX5940A/MAX5940B) ...............................-0.3V to +80V
GND (MAX5940C/MAX5940D)...............................-0.3V to +90V
OUT,
PGOOD
...........................................-0.3V to (GND + 0.3V)
RCLASS, GATE ......................................................-0.3V to +12V
UVLO ........................................................................-0.3V to +8V
PGOOD to OUT.........................................-0.3V to (GND + 0.3V)
Maximum Input/Output Current (continuous)
OUT to V
EE
...................................................................500mA
GND, RCLASS to V
EE
.....................................................70mA
UVLO,
PGOOD,
PGOOD to V
EE
.....................................20mA
GATE to V
EE
....................................................................80mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin SO (derate 5.9mW/°C above +70°C)..................470mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) ................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
IN
= (GND - V
EE
) = 48V, GATE =
PGOOD
= PGOOD = OUT = OPEN, UVLO = V
EE
, T
A
= -40°C
to +85°C, unless otherwise noted.
Typical values are at T
A
= +25°C. All voltages are referenced to V
EE
, unless otherwise noted.) (Note 1)
PARAMETER
DETECTION MODE
Input Offset Current (Note 2)
Effective Differential Input
Resistance (Note 3)
CLASSIFICATION MODE
Classification Current Turn-Off
Threshold (Note 4)
V
TH,CLSS
V
IN
rising
Class 0, R
CL
= 10kΩ
Classification Current (Notes 5, 6)
I
CLASS
V
IN
= 12.6V to Class 1, R
CL
= 732Ω
20V, R
DISC
= Class 2, R
CL
= 392Ω
25.5kΩ
Class 3, R
CL
= 255Ω
Class 4, R
CL
= 178Ω
V
IN
= (GND - V
EE
)
Measure at GND, not including R
DISC
MAX5940A/MAX5940C
Default Power Turn-On Voltage
V
UVLO, ON
V
IN
increasing
MAX5940B/MAX5940D,
UVLO = V
EE
34.3
37.4
30
4.2
7.4
12
2.400
Ratio to V
REF,UVLO
UVLO = 2.460V
19.2
-1.5
2.460
20
67
2.522
20.9
+1.5
0.4
35.4
38.6
20.8
0
9.17
17.29
26.45
36.6
21.8
22.5
2
11.83
19.71
29.55
41.4
67
1
36.6
39.9
V
V
mA
mA
V
I
OFFSET
dR
V
IN
= 1.4V to 10.1V
V
IN
= 1.4V up to 10.1V with 1V step,
OUT =
PGOOD
= GND
550
10
µA
kΩ
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER MODE
Operating Supply Voltage
Operating Supply Current
V
IN
I
IN
Default Power Turn-Off Voltage
Default Power Turn-On/Off
Hysteresis
External UVLO Programming
Range
UVLO External Reference Voltage
UVLO External Reference Voltage
Hysteresis
UVLO Bias Current
V
UVLO, OFF
V
HYST,
UVLO
V
IN
decreasing, UVLO = V
EE for
MAX5940B/MAX5940D
MAX5940A/MAX5940C
MAX5940B/MAX5940D, UVLO = V
EE
Set UVLO externally (MAX5940B/
MAX5940D only) (Note 7)
V
V
V
V
%
µA
V
IN,EX
V
REF, UVLO
HYST
I
UVLO
2
_______________________________________________________________________________________
IEEE 802.3af PD Interface Controller
For Power-Over-Ethernet
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= (GND - V
EE
) = 48V, GATE =
PGOOD
= PGOOD = OUT = OPEN, UVLO = V
EE
, T
A
= -40°C to +85°C, unless otherwise noted.
Typical values are at T
A
= +25°C. All voltages are referenced to V
EE
, unless otherwise noted.) (Note 1)
PARAMETER
UVLO Input Ground Sense
Threshold (Note 8)
UVLO Input Ground Sense Glitch
Rejection
Power Turn-Off Voltage,
Undervoltage Lockout Deglitch
Time (Note 9)
t
OFF_DLY
SYMBOL
V
TH,G,UVLO
UVLO = V
EE
CONDITIONS
MIN
50
7
TYP
MAX
440
UNITS
mV
µs
MAX5940A/MAX5940B/MAX5940C/MAX5940D
V
IN
, V
UVLO
falling
T
A
= +25°C
(Note 10)
T
A
= +85°C
0.32
ms
Isolation Switch N-Channel
MOSFET On-Resistance
R
ON
Output current =
300mA, V
GATE
= 6V,
measured between
OUT and V
EE
0.6
0.8
0.5
38
5
5.59
1.16
10
5.76
1.23
70
4.62
4.76
80
1.1
Ω
1.5
V
80
15
5.93
1.31
Ω
µA
V
V
mV
4.91
V
mV
0.4
1
1
V
µA
µA
Isolation Switch N-Channel
MOSFET Off-Threshold Voltage
GATE Pulldown Switch Resistance
GATE Charging Current
GATE High Voltage
PGOOD,
PGOOD
Assertion V
OUT
Threshold
PGOOD,
PGOOD
Assertion V
GATE
Threshold
PGOOD,
PGOOD
Output Low
Voltage (Note 11)
PGOOD Leakage Current (Note 11)
PGOOD
Leakage Current (Note 11)
V
GSTH
R
G
I
G
V
GATE
V
OUTEN
OUT = GND, V
GATE
- V
EE,
output current
< 1µA
Power-off mode, V
IN
= 12V,
UVLO = V
EE
for MAX5940B
V
GATE
= 2V
I
GATE
= 1µA
V
OUT
- V
EE
, |V
OUT
- V
EE
| decreasing,
V
GATE
= 5.75V
Hysteresis
(GATE - V
EE
) increasing, OUT = V
EE
Hysteresis
I
SINK
= 2mA; for PGOOD, OUT
≤
(GND - 5V)
GATE = high, GND - V
OUT
= 67V
GATE = V
EE
,
PGOOD
- V
EE
= 67V
V
GSEN
V
OLDCDC
Note 1:
All min/max limits are production tested at +85°C. Limits at +25°C and -40°C are guaranteed by design.
Note 2:
The input offset current is illustrated in Figure 1.
Note 3:
Effective differential input resistance is defined as the differential resistance between GND and V
EE
without any external
resistance. See Figure 1.
Note 4:
Classification current is turned off whenever the IC is in power mode.
Note 5:
See Table 2 in the
PD Classification Mode
section. R
DISC
and R
CL
must be ±1%, 100ppm or better. I
CLASS
includes the IC
bias current and the current drawn by R
DISC
.
Note 6:
See the
Thermal Dissipation
section for details.
Note 7:
When UVLO is connected to the midpoint of an external resistor-divider with a series resistance of 25.5kΩ (±1%), the turn-
on threshold set-point for the power mode is defined by the external resistor-divider. Make sure the voltage on the UVLO
pin does not exceed its maximum rating of 8V when V
IN
is at the maximum voltage (MAX5940B only).
Note 8:
When the UVLO input voltage is below V
TH,G,UVLO,
the MAX5940B sets the UVLO threshold internally.
Note 9:
An input voltage or V
UVLO
glitch below their respective thresholds shorter than or equal to t
OFF_DLY
does not cause the
MAX5940A/MAX5940B/MAX5940C/MAX5940D to exit power-on mode (as long as the input voltage remains above an opera-
ble voltage level of 12V).
Note 10:
Guaranteed by design.
Note 11:
PGOOD references to OUT while
PGOOD
references to V
EE
.
_______________________________________________________________________________________
3
IEEE 802.3af PD Interface Controller
For Power-Over-Ethernet
MAX5940A/MAX5940B/MAX5940C/MAX5940D
I
IN
dR
i
≅
1V
(V
INi + 1
- V
INi
)
=
(I
INi + 1
- I
INi
) (I
INi + 1
- I
INi
)
V
INi
dR
i
I
OFFSET
≅
I
INi
-
I
INi + 1
I
INi
dR
i
I
OFFSET
V
INi
1V
V
INi + 1
V
IN
Figure1. Effective Differential Input Resistance/Offset Current
Typical Operating Characteristics
(V
IN
= (GND - V
EE
) = 48V, GATE =
PGOOD
= PGOOD = OUT = OPEN, UVLO = V
EE
(MAX5940B), T
A
= -40°C to +85°C. Typical values
are at T
A
= +25°C. All voltages are referenced to V
EE
, unless otherwise noted.)
DETECTION CURRENT vs. INPUT VOLTAGE
MAX5940A/B toc01
CLASSIFICATION CURRENT
vs. INPUT VOLTAGE
MAX5940A/B toc02
EFFECTIVE DIFFERENTIAL INPUT
RESISTANCE vs. INPUT VOLTAGE
EFFECTIVE DIFFERENTIAL INPUT RESISTANCE (MΩ)
MAX5940A/B toc03
0.5
R
DISC
= 25.5kΩ
DETECTION CURRENT (mA)
0.4
50
CLASSIFICATION CURRENT (mA)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
2
4
6
8
10
40
CLASS 4
0.3
I
IN
+ I
RDISC
30
CLASS 3
CLASS 2
CLASS 1
CLASS 0
0.2
20
0.1
10
0
0
2
4
6
8
10
INPUT VOLTAGE (V)
0
0
5
10
15
20
25
30
INPUT VOLTAGE (V)
12
INPUT VOLTAGE (V)
INPUT OFFSET CURRENT
vs. INPUT VOLTAGE
MAX5940A/B toc04
NORMALIZED UVLO
vs. TEMPERATURE
1.008
1.006
NORMALIZED UVLO
1.004
V
PGOOD
(mV)
1.002
1.000
0.998
0.996
0.994
50
150
UVLO = V
EE
MAX5940A/B toc05
PGOOD OUTPUT LOW VOLTAGE
vs. CURRENT
MAX5940A/B toc06
0
-0.5
INPUT OFFSET CURRENT (μA)
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
1
3
5
7
9
1.010
250
200
100
0.992
0.990
11
-40
-15
10
35
60
85
INPUT VOLTAGE (V)
TEMPERATURE (°C)
0
0
5
10
I
SINK
(mA)
15
20
4
_______________________________________________________________________________________
IEEE 802.3af PD Interface Controller
For Power-Over-Ethernet
MAX5940A/MAX5940B/MAX5940C/MAX5940D
Typical Operating Characteristics (continued)
(V
IN
= (GND - V
EE
) = 48V, GATE =
PGOOD
= PGOOD = OUT = OPEN, UVLO = V
EE
(MAX5940B), T
A
= -40°C to +85°C. Typical values
are at T
A
= +25°C. All voltages are referenced to V
EE
, unless otherwise noted.)
PGOOD OUTPUT LOW VOLTAGE
vs. CURRENT
MAX5940A/B toc07
OUT LEAKAGE CURRENT
vs. TEMPERATURE
V
OUT
= 67V
OUT LEAKAGE CURRENT (nA)
16
MAX5940A/B toc08
INRUSH CURRENT CONTROL (V
IN
= 12V)
MAX5940A/B toc09
400
20
320
V
PGOOD
(mV)
V
GATE
5V/div
240
12
I
INRUSH
100mA/div
V
OUT TO
V
EE
10V/div
PGOOD
160
8
80
4
10V/div
0
0
5
10
I
SINK
(mA)
15
20
0
-40
-15
10
35
60
85
1ms/div
TEMPERATURE (°C)
INRUSH CURRENT CONTROL (V
IN
= 48V)
MAX5940A/B toc10
INRUSH CURRENT CONTROL (V
IN
= 67V)
MAX5940A/B toc11
V
GATE
5V/div
V
GATE
5V/div
I
INRUSH
100mA/div
V
OUT TO
V
EE
50V/div
I
INRUSH
100mA/div
V
OUT TO
V
EE
50V/div
PGOOD
PGOOD
50V/div
2ms/div
2ms/div
50V/div
_______________________________________________________________________________________
5
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