General Description
The MAX5942A/MAX5942B integrate a complete power
IC for powered devices (PD) in a power-over-ethernet
(PoE) system. The MAX5942A/MAX5942B provide a PD
interface and a compact DC-DC PWM controller suitable
for flyback and forward converters in either isolated or
nonisolated designs.
The MAX5942A/MAX5942B PD interface complies with
the IEEE 802.3af standard, providing the PD with a detec-
tion signature, a classification signature, and an integrat-
ed isolation switch with programmable inrush current
control. These devices also feature power-mode under-
voltage lockout (UVLO) with wide hysteresis and power-
good status outputs.
The MAX5942A/MAX5942B also integrate all the build-
ing blocks necessary for implementing DC-DC fixed-
frequency isolated power supplies. This device is a
current-mode controller with an integrated high startup
circuit suitable for isolated telecom/industrial voltage
range power supplies. A high-voltage startup circuit
allows the PWM controller to draw power directly from the
18V to 67V input supply during startup. The switching
frequency is internally trimmed to 275kHz ±10%, thus
reducing magnetics and filter components. The
MAX59412A allows an 85% operating duty cycle and can
be used to implement flyback converters. The MAX5942B
limits the operating duty cycle to less than 50% and can
be used in single-ended forward converters. The
MAX5942A/MAX5942B are designed to work with or with-
out an external diode bridge in front of the PD.
The MAX5942A/MAX5942B are available in 16-pin SO
packages.
Applications
IP Phones
Wireless Access Nodes
Internet Appliances
Computer Telephony
Security Cameras
Power Devices in Power-Over-Ethernet/
Power-Over-MDI
Features
o Powered Device Interface
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
Gate Output Allows External Control of the
Internal Isolation FET
Programmable Inrush Current Control/ULVO
PGOOD/PGOOD Outputs Enable PWM
Controller
o PWM Controller
Wide Input Range: 18V to 67V
Isolated (Without Optocoupler) or Nonisolated
Power Supply
Current-Mode Control
Leading-Edge Blanking
Internally Trimmed 275kHz ±10% Oscillator
Soft-Start
MAX5942A/MAX5942B
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
________________________________________________________________ Maxim Integrated Products
1
Ordering Information
19-3024; Rev 0; 10/03
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.
PART
TEMP RANGE
PIN-
PACKAGE
M A X D U T Y
C YC L E ( % )
MAX5942AESE*
-40°C to +85°C
16 SO
85
MAX5942ACSE
0°C to +70°C
16 SO
85
MAX5942BESE*
-40°C to +85°C
16 SO
50
MAX5942BCSE
0°C to +70°C
16 SO
50
Typical Operating Circuit appears at end of data sheet.
*Future product--contact factory for availability.
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
V+
V
CC
NDRV
V-
CS
GND
PGOOD
PGOOD
OUT
TOP VIEW
MAX5942A
MAX5942B
SO
V
DD
FB
RCL
SS_SHDN
ULVO
GATE
V
EE
Pin Configuration
MAX5942A/MAX5942B
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
IN
= (GND - V
EE
) = 48V, GATE = PGOOD = PGOOD = OPEN, V- tied to OUT, V+ tied to GND, UVLO = V
EE
, T
A
= T
MIN
to T
MAX
,
unless otherwise noted. Typical values are at T
A
= +25
°C. All voltages are referenced to V
EE
, unless otherwise noted.) (Note 1)
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.
(All voltages are referenced to V
EE
, unless otherwise noted.)
GND........................................................................-0.3V to +80V
OUT, PGOOD ...........................................-0.3V to (GND + 0.3V)
RCL, GATE .............................................................-0.3V to +12V
UVLO ........................................................................-0.3V to +8V
PGOOD to OUT.........................................-0.3V to (GND + 0.3V)
V+ to V-...................................................................-0.3V to +80V
V
DD
to V-.................................................................-0.3V to +40V
V
CC
to V-..............................................................-0.3V to +12.5V
FB, NDRV, SS_SHDN, CS to V- ..................-0.3V to (V
CC
+ 0.3V)
Maximum Input/Output Current (continuous)
OUT to V
EE
...................................................................500mA
GND, RCL to V
EE
............................................................70mA
UVLO, PGOOD, PGOOD to V
EE
.....................................20mA
GATE to V
EE
....................................................................80mA
V
DD
, V
CC
.........................................................................20mA
NDRV Continuous ...........................................................25mA
NDRV (pulsed for less than 1µs) .......................................±1A
Continuous Power Dissipation (T
A
= +70°C)
16-Pin SO (derate 9.1mW/°C above +70°C)................727mW
Operating Temperature Ranges
MAX5942_CSE...................................................0°C to +70°C
MAX5942_ESE ................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) ................................+300°C
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PD INTERFACE
DETECTION MODE
Input Offset Current
I
OFFSET
V
IN
= 1.4V to 10.1V (Note 2)
10
µA
Effective Differential Input
Resistance
dR
V
IN
= 1.4V up to 10.1V with 1V step,
OUT = PGOOD = GND (Note 3)
550
k
CLASSIFICATION MODE
Classification Current Turn-Off
Threshold
V
TH,CLSS
V
IN
rising (Note 4)
20.8
21.8
22.5
V
Class 0, R
CL
= 10k
0
2
Class 1, R
CL
= 732
9.17
11.83
Class 2, R
CL
= 392
17.29
19.71
Class 3, R
CL
= 255
26.45
29.55
Classification Current
I
CLASS
V
IN
= 12.6V
to 20V, R
DISC
= 25.5k
(Notes 5, 6)
Class 4, R
CL
= 178
36.6
41.4
mA
POWER MODE
Operating Supply Voltage
V
IN
V
IN
= (GND - V
EE
)
67
V
Operating Supply Current
I
IN
Measure at GND, not including R
DISC
0.4
1
mA
Default Power Turn-On Voltage
V
UVLO,ON
VIN increasing, UVLO = V
EE
37.4
38.6
40.1
V
Default Power Turn-Off Voltage
V
UVLO,OFF
VIN decreasing, UVLO = V
EE
30
V
Default Power Turn-On/Off
Hysteresis
V
HYST,UVLO
7.4
V
External UVLO Programming
Range
V
IN,EX
Set UVLO externally (Note 7)
12
67
V
UVLO External Reference Voltage
V
REF,UVLO
V
UVLO
increasing
2.400
2.460
2.522
V
UVLO External Reference
Voltage Hysteresis
HYST
Ratio to V
REF,UVLO
19.2
20
20.9
%
MAX5942A/MAX5942B
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
_______________________________________________________________________________________
3
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
UVLO Bias Current
I
UVLO
UVLO = 2.460V
-1.5
+1.5
µA
UVLO Input Ground Sense
Threshold
V
TH,G,UVLO
(Note 8)
50
440
mV
UVLO Input Ground Sense Glitch
Rejection
UVLO = V
EE
7
µs
Power Turn-Off Voltage,
Undervoltage Lockout Deglitch
Time
t
OFF_DLY
V
IN
, V
UVLO
falling (Note 9)
0.32
ms
T
A
= +25°C
(Note 11)
0.6
1.1
Isolation Switch N-Channel
MOSFET On-Resistance
R
ON
Output current =
300mA, V
GATE
= 5.6V,
measured between
OUT and V
EE
T
A
= +85°C
0.8
1.5
Isolation Switch N-Channel
MOSFET Off-Threshold Voltage
V
GSTH
OUT = GND, V
GATE
- V
EE
, output current
< 1µA
0.5
V
GATE Pulldown Switch Resistance
R
G
Power-off mode, V
IN
= 12V, UVLO = V
EE
38
80
GATE Charging Current
I
G
V
GATE
= 2V
5
10
15
µA
GATE High Voltage
V
GATE
I
GATE
= 1µA
5.58
5.76
5.93
V
V
OUT
- V
EE
, |V
OUT
- V
EE
| decreasing,
V
GATE
= 5.75V
1.15
1.23
1.31
V
PGOOD, PGOOD Assertion
V
OUT
Threshold
V
OUTEN
Hysteresis
70
mV
(GATE - V
EE
) increasing, OUT = V
EE
4.62
4.76
4.91
V
PGOOD, PGOOD Assertion
V
GATE
Threshold
V
GSEN
Hysteresis
80
mV
PGOOD Output Low Voltage
V
OLDCDC
I
SINK
= 2mA (Note 10)
0.4
V
PGOOD Output Low Voltage
I
SINK
= 2mA, OUT
(GND - 5V) (Note 10)
0.2
V
PGOOD Leakag e C ur r ent
GATE = hi g h, GN D - V
OU T
= 67V ( N ote 10)
1
µA
PGOOD Leakag e C ur r ent
GATE = V
E E
, P GOOD - V
E E
= 67V ( N ote 10)
1
µA
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= (GND - V
EE
) = 48V, GATE = PGOOD = PGOOD = OPEN, V- tied to OUT, V+ tied to GND, UVLO = V
EE
, T
A
= T
MIN
to T
MAX
,
unless otherwise noted. Typical values are at T
A
= +25
°C. All voltages are referenced to V
EE
, unless otherwise noted.) (Note 1)
ELECTRICAL CHARACTERISTICS (PWM Controller)
(All voltages referenced to V-. V
DD
= 13V, a 10µF capacitor connects V
CC
to V-, V
CS
= V-, V+ = 48V, 0.1µF capacitor connected to
SS_SHDN, NDRV = open circuit, V
FB
= 3V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SUPPLY CURRENT
I
V+(NS)
V
DD
= 0V, V+ = 67V, driver not switching
0.8
1.6
V+ Supply Current
I
V+(S)
V+ = 67V, V
DD
= 0V, V
FB
= 4V, driver
switching
1.6
3.2
mA
V+ Supply Current After Startup
V+ = 67V, V
DD
= 13V, V
FB
= 4V
14
µA
MAX5942A/MAX5942B
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
4
_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (PWM Controller) (continued)
(All voltages referenced to V-. V
DD
= 13V, a 10µF capacitor connects V
CC
to V-, V
CS
= V-, V+ = 48V, 0.1µF capacitor connected to
SS_SHDN, NDRV = open circuit, V
FB
= 3V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
I
VDD(NS)
V
DD
= 36V, driver not switching
0.9
1.6
V
DD
Supply Current
I
VDD(S)
V
DD
= 36V, driver switching, V
OPTO
= 4V
1.9
3.2
mA
V+ Shutdown Current
V
SS_SHDN
= 0V, V+ = 67V
180
290
µA
V
DD
Shutdown Current
V
SS_SHDN
= 0V
4
20
µA
PREREGULATORS/STARTUP
V+ Input Voltage
18
67
V
V
DD
Supply Voltage
13
36
V
INTERNAL REGULATORS
Powered from V+, I
CC
= 7.5mA, V
DD
= 0V
7.5
9.8
12
V
CC
Output Voltage
Powered from V
DD
, I
CC
= 7.5mA
9.0
10.0
11.0
V
V
CC
Undervoltage Lockout
V
CC_UVLO
V
CC
falling
6.6
V
OUTPUT DRIVER
Peak Source Current
V
CC
= 11V (externally forced)
570
mA
Peak Sink Current
V
CC
= 11V (externally forced)
1000
mA
NDRV High-Side Driver
Resistance
R
OH
V
CC
= 11V, externally forced, NDRV
sourcing 50mA
4
12
NDRV Low-Side Driver
Resistance
R
OL
V
CC
= 11V, externally forced, NDRV sinking
50mA
1.6
4
ERROR AMPLIFIER
FB Input Resistance
R
IN
50
k
FB Input Bias Current
I
FB
V
FB
= V
SS_SHDN
±1
µA
Error Amplifier Gain (Inverting)
A
VCL
-20
V/V
Closed-Loop 3dB Bandwidth
200
kHz
FB Input Voltage Range
2
3
V
SLOPE COMPENSATION
Slope Compensation
V
SCOMP
MAX5942A
26
mV/µs
THERMAL SHUTDOWN
Thermal Shutdown Temperature
+150
°C
Thermal Hysteresis
25
°C
CURRENT LIMIT
CS Threshold Voltage
V
ILIM
FB = 4V
419
465
510
mV
CS Input Bias Current
0V
V
CS
2V, FB = 4V
-1
+1
µA
Current-Limit Comparator
Propagation Delay
25mV overdrive on CS, FB = V-
180
ns
CS Blanking Time
FB = GN D , onl y P W M com p ar ator i s b l anked 70
ns
OSCILLATOR
Clock Frequency Range
FB = V-
235
275
314
kHz
MAX5942A, FB = V-
75
85
Max Duty Cycle
MAX5942B, FB = V-
44
50
%
MAX5942A/MAX5942B
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
_______________________________________________________________________________________
5
I
IN
I
INi
+1
I
INi
I
OFFSET
dR
i
1V
V
INi
V
INi
+1
I
OFFSET
I
INi
-
V
INi
dR
i
dR
i
(V
INi + 1
- V
INi
)
=
1V
(I
INi + 1
- I
INi
)
(I
INi + 1
- I
INi
)
Figure 1. Effective Differential Input Resistance/Offset Current
ELECTRICAL CHARACTERISTICS (PWM Controller) (continued)
(All voltages referenced to V-. V
DD
= 13V, a 10µF capacitor connects V
CC
to V-, V
CS
= V-, V+ = 48V, 0.1µF capacitor connected to
SS_SHDN, NDRV = open circuit, V
FB
= 3V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
Note 1:
All min/max limits for the PD interface are production tested at +85°C (extended grade)/+70°C (commercial grade). Limits
at +25°C and -40°C are guaranteed by design. All PWM controller min/max limits are 100% production tested at +25°C
and +85°C (extended grade)/+70°C (commercial grade). Limits at -40°C are guaranteed by design, unless otherwise
noted.
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.
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 100ppm or better.
Note 6:
See Thermal Dissipation section for details.
Note 7:
When UVLO is connected to the midpoint of an external resistor-divider with a series resistance of 25.5k
(±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.
Note 8:
When the V
UVLO
is below V
TH, G, UVLO,
the MAX5942_ sets the turn-on voltage threshold internally (V
UVLO,ON
).
Note 9:
An input voltage or V
UVLO
glitch below their respective thresholds shorter than or equal to t
OFF_DLY
will not cause the
MAX5942A/MAX5942B to exit power-on mode (as long as the input voltage remains above an operable voltage level of 12V).
Note 10: PGOOD references to OUT while PGOOD references to V
EE
.
Note 11: Guaranteed by design.
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SOFT-START
SS Source Current
I
SSO
V
SS_SHDN
= V-
2.0
4.5
6.5
µA
SS Sink Current
1
mA
Peak Soft-Start Voltage Clamp
No external load
2.331
2.420
2.500
V
V
SS_SHDN
falling (Note 11)
0.25
0.37
0.41
Shutdown Threshold
V
SS_SHDN
rising (Note 11)
0.53
0.59
0.65
V
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