19-3024; Rev 0; 10/03
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
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.
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
Ordering Information
PART
MAX5942AESE*
MAX5942ACSE
MAX5942BESE*
MAX5942BCSE
TEMP RANGE
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
PIN-
PACKAGE
16 SO
16 SO
16 SO
16 SO
MAX DUTY
CYCLE (%)
85
85
50
50
Applications
IP Phones
Wireless Access Nodes
Internet Appliances
Computer Telephony
Security Cameras
Power Devices in Power-Over-Ethernet/
Power-Over-MDI
*Future
product—contact factory for availability.
Pin Configuration
TOP VIEW
V+ 1
V
DD
2
FB 3
SS_SHDN 4
ULVO 5
16 V
CC
15 NDRV
14 V-
MAX5942A
MAX5942B
13 CS
12 GND
11 PGOOD
10 PGOOD
9
OUT
Typical Operating Circuit appears at end of data sheet.
RCL 6
GATE 7
V
EE
8
SO
________________________________________________________________
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 Power-Over-Ethernet
Interface/PWM Controller for Power Devices
MAX5942A/MAX5942B
ABSOLUTE MAXIMUM RATINGS
(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
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 = 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)
PARAMETER
PD INTERFACE
DETECTION MODE
Input Offset Current
Effective Differential Input
Resistance
CLASSIFICATION MODE
Classification Current Turn-Off
Threshold
V
TH,CLSS
V
IN
rising (Note 4)
Class 0, R
CL
= 10kΩ
V
IN
= 12.6V
Class 1, R
CL
= 732Ω
to 20V, R
DISC
Class 2, R
CL
= 392Ω
= 25.5kΩ
Class 3, R
CL
= 255Ω
(Notes 5, 6)
Class 4, R
CL
= 178Ω
V
IN
= (GND - V
EE
)
Measure at GND, not including R
DISC
VIN increasing, UVLO = V
EE
37.4
30
7.4
Set UVLO externally (Note 7)
V
UVLO
increasing
Ratio to V
REF,UVLO
12
2.400
19.2
2.460
20
67
2.522
20.9
0.4
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
40.1
V
mA
V
V
V
V
V
%
mA
V
I
OFFSET
dR
V
IN
= 1.4V to 10.1V (Note 2)
V
IN
= 1.4V up to 10.1V with 1V step,
OUT =
PGOOD
= GND (Note 3)
550
10
µA
kΩ
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Classification Current
I
CLASS
POWER MODE
Operating Supply Voltage
Operating Supply Current
Default Power Turn-On Voltage
Default Power Turn-Off Voltage
Default Power Turn-On/Off
Hysteresis
External UVLO Programming
Range
UVLO External Reference Voltage
UVLO External Reference
Voltage Hysteresis
V
IN
I
IN
V
UVLO,ON
V
UVLO,OFF
VIN decreasing, UVLO = V
EE
V
HYST,UVLO
V
IN,EX
V
REF,UVLO
HYST
2
_______________________________________________________________________________________
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
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)
PARAMETER
UVLO Bias Current
UVLO Input Ground Sense
Threshold
UVLO Input Ground Sense Glitch
Rejection
Power Turn-Off Voltage,
Undervoltage Lockout Deglitch
Time
t
OFF_DLY
SYMBOL
I
UVLO
CONDITIONS
UVLO = 2.460V
MIN
-1.5
50
7
TYP
MAX
+1.5
440
UNITS
µA
mV
µs
MAX5942A/MAX5942B
V
TH,G,UVLO
(Note 8)
UVLO = V
EE
V
IN
, V
UVLO
falling (Note 9)
T
A
= +25°C
Output current =
300mA, V
GATE
= 5.6V, (Note 11)
measured between
T
A
= +85°C
OUT and V
EE
OUT = GND, V
GATE
- V
EE
, output current
< 1µA
Power-off mode, V
IN
= 12V, UVLO = V
EE
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 (Note 10)
I
SINK
= 2mA, OUT
≤
(GND - 5V) (Note 10)
GATE = high, GND - V
OUT
= 67V (Note 10)
GATE = V
EE
, PGOOD - V
EE
= 67V (Note 10)
0.32
ms
0.6
0.8
0.5
38
5
5.58
1.15
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
0.4
0.2
1
1
V
mV
V
V
µA
µA
Isolation Switch N-Channel
MOSFET On-Resistance
R
ON
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
Output Low Voltage
PGOOD Output Low Voltage
PGOOD Leakage Current
PGOOD
Leakage Current
V
GSTH
R
G
I
G
V
GATE
V
OUTEN
V
GSEN
V
OLDCDC
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
SUPPLY CURRENT
I
V+(NS)
V+ Supply Current
V+ Supply Current After Startup
I
V+(S)
V
DD
= 0V, V+ = 67V, driver not switching
V+ = 67V, V
DD
= 0V, V
FB
= 4V, driver
switching
V+ = 67V, V
DD
= 13V, V
FB
= 4V
0.8
1.6
14
1.6
3.2
mA
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
_______________________________________________________________________________________
3
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
MAX5942A/MAX5942B
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
V
DD
Supply Current
V+ Shutdown Current
V
DD
Shutdown Current
PREREGULATORS/STARTUP
V+ Input Voltage
V
DD
Supply Voltage
INTERNAL REGULATORS
V
CC
Output Voltage
V
CC
Undervoltage Lockout
OUTPUT DRIVER
Peak Source Current
Peak Sink Current
NDRV High-Side Driver
Resistance
NDRV Low-Side Driver
Resistance
ERROR AMPLIFIER
FB Input Resistance
FB Input Bias Current
Error Amplifier Gain (Inverting)
Closed-Loop 3dB Bandwidth
FB Input Voltage Range
SLOPE COMPENSATION
Slope Compensation
THERMAL SHUTDOWN
Thermal Shutdown Temperature
Thermal Hysteresis
CURRENT LIMIT
CS Threshold Voltage
CS Input Bias Current
Current-Limit Comparator
Propagation Delay
CS Blanking Time
OSCILLATOR
Clock Frequency Range
Max Duty Cycle
FB = V-
MAX5942A, FB = V-
MAX5942B, FB = V-
235
75
44
275
314
85
50
kHz
%
V
ILIM
FB = 4V
0V
≤
V
CS
≤
2V, FB = 4V
25mV overdrive on CS, FB = V-
FB = GND, only PWM comparator is blanked
419
-1
180
70
465
510
+1
mV
µA
ns
ns
+150
25
°C
°C
V
SCOMP
MAX5942A
26
mV/µs
2
R
IN
I
FB
A
VCL
V
FB
= V
SS_SHDN
50
±1
-20
200
3
kΩ
µA
V/V
kHz
V
R
OH
R
OL
V
CC
= 11V (externally forced)
V
CC
= 11V (externally forced)
V
CC
= 11V, externally forced, NDRV
sourcing 50mA
V
CC
= 11V, externally forced, NDRV sinking
50mA
570
1000
4
1.6
12
4
mA
mA
Ω
Ω
V
CC_UVLO
Powered from V+, I
CC
= 7.5mA, V
DD
= 0V
Powered from V
DD
, I
CC
= 7.5mA
V
CC
falling
7.5
9.0
9.8
10.0
6.6
12
11.0
V
V
18
13
67
36
V
V
SYMBOL
I
VDD(NS)
I
VDD(S)
CONDITIONS
V
DD
= 36V, driver not switching
V
DD
= 36V, driver switching, V
OPTO
= 4V
V
SS_SHDN
= 0V, V+ = 67V
V
SS_SHDN
= 0V
MIN
TYP
0.9
1.9
180
4
MAX
1.6
3.2
290
20
UNITS
mA
µA
µA
4
_______________________________________________________________________________________
IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
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
SOFT-START
SS Source Current
SS Sink Current
Peak Soft-Start Voltage Clamp
Shutdown Threshold
No external load
V
SS_SHDN
falling (Note 11)
V
SS_SHDN
rising (Note 11)
I
SSO
V
SS_SHDN
= V-
2.0
1
2.331
0.25
0.53
2.420
0.37
0.59
2.500
0.41
0.65
4.5
6.5
µA
mA
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX5942A/MAX5942B
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 25.5kΩ (±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.
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.
Note 1:
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
Figure 1. Effective Differential Input Resistance/Offset Current
_______________________________________________________________________________________
5
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
