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PDF LM5072 Data sheet ( Hoja de datos )
| Número de pieza | LM5072 | |
| Descripción | Integrated 100V Power Over Ethernet PD Interface and PWM Controller | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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March 2006
LM5072
Integrated 100V Power Over Ethernet PD Interface and
PWM Controller with Aux Support
General Description
The LM5072 Powered Device (PD) interface and Pulse-
Width-Modulation (PWM) controller provides a complete
power solution, fully compliant to IEEE 802.3af, for the PD
connecting into Power over Ethernet (PoE) networks. This
controller integrates all functions necessary to implement
both a PD powered interface and DC-DC converter with a
minimum number of external components. The LM5072 pro-
vides the flexibility for the PD to also accept power from
auxiliary sources such as AC adapters in a variety of con-
figurations. The low RDS(ON) PD interface hot swap MOS-
FET and programmable DC current limit extend the range of
LM5072 applications up to twice the power level of 802.3af
compliant PD devices. The 100V maximum voltage rating
simplifies selection of the transient voltage suppressor that
protects the PD from network transients. The LM5072 in-
cludes an easy-to-use PWM controller that facilitates the
various single-ended power supply topologies including the
flyback, forward and buck. The PWM control scheme is
based on peak current mode control, which provides inher-
ent advantages including line feed-forward, cycle-by-cycle
current limit, and simplified feedback loop compensation.
Two versions of the LM5072 provide either an 80% maxi-
mum duty cycle (-80 suffix), or a 50% maximum duty cycle
(-50 suffix).
Features
PD Interface
n Fully Compliant IEEE 802.3af PD Interface
n Versatile Auxiliary Power Options
n 9V Minimum Auxiliary Power Operating Range
n 100V Maximum Input Voltage Rating
n Programmable DC Current Limit Up To 800mA
n 100V, 0.7Ω Hot Swap MOSFET
n Integrated PD Signature Resistor
n Integrated PoE Input UVLO
n Programmable Inrush Current Limit
n PD Classification Capability
n Power Good Indicator
n Thermal Shutdown Protection
PWM Controller
n Current Mode PWM Controller
n 100V Start-up Regulator
n Error Amplifier with 2% Voltage Reference
n Supports Isolated and Non-Isolated Applications
n Programmable Oscillator Frequency
n Programmable Soft-Start
n 800 mA Peak Gate Driver
n 80% Maximum Duty Cycle with Built-in Slope
Compensation (-80 device)
n 50% Maximum Duty Cycle, No Slope Compensation
(-50 device)
Applications
n IEEE 802.3af Compliant PoE Powered Devices
n Non-Compliant, Application Specific Devices
n Higher Power Ethernet Powered Devices
Packages
n TSSOP-16 EP (Exposed Pad)
Simplified Application Diagram
© 2006 National Semiconductor Corporation DS201846
20184601
www.national.com
1 page  
Electrical Characteristics (Note 4) Specifications in standard type face are for TJ = +25˚C and those in
boldface type apply over the full operating junction temperature range. Unless otherwise specified: VIN = 48V, FOSC =
250kHz. (Continued)
SYMBOL
PARAMETER
Auxiliary Power Option
ICL_FAUX Threshold
ICL_FAUX Pull Down Current
RAUX Lower Threshold (I = 22 µA)
RAUX Upper Threshold (I = 250 µA)
RAUX Lower Threshold Hysteresis
RAUX Lower Threshold Current
RAUX Upper Threshold Current
VCC Regulator
VccReg VCC Regulation (VccReg)
VCC Current Limit
VCC UVLO (Rising)
CONDITIONS
ICL_FAUX Pin Rising
RAUX Pin Rising
RAUX Pin Falling
VCC UVLO (Falling)
VIN Supply Current
Supply Current (Icc)
VCC Regulator Dropout
Error Amplifier
Gain Bandwidth
DC Gain
Input Voltage
COMP Sink Capability
Current Limit
ILIM Delay to Output
Cycle by Cycle Current Limit Threshold
Voltage
Leading Edge Blanking Time
CS Sink Impedance (clocked)
Soft-start
Soft-start Current Source
Oscillator
Frequency1 (RT = 26.1 kΩ)
Frequency2 (RT = 8.7 kΩ)
Sync threshold
PWM Comparator
Delay to Output
Min Duty Cycle
Max Duty Cycle (-80 Device)
Max Duty Cycle (-50 Device)
COMP to PWM Comparator Gain
COMP Open Circuit Voltage
COMP Short Circuit Current
Slope Compensation (LM5072-80 Device Only)
Slope Comp Amplitude
Output Section
Output High Saturation
VCC = 10V
VCC = 10V
VIN – VCC (Note 6)
MIN TYP MAX UNITS
8.1 8.7 9.3 V
50 µA
2.3 2.5 3.0 V
5.4 6.0 6.9 V
0.8 V
16 22 28 µA
187 250 313 µA
7.4
15
VccReg
– 210
mV
5.9
7.7
VccReg
– 100
mV
6.2
8
6.5
2.0
3
6.5
V
mA
V
V
mA
mA
V
1.225
5
3 MHz
67 dB
1.275
V
10 mA
0.45
30 ns
0.5 0.55 V
65 ns
35 55 Ω
8 10 12 µA
175 200 225 KHz
515 580 645 KHz
2.6 3.2 3.8 V
25 ns
0%
75 80 85 %
47 50 53 %
0.33
4.3 5.2 6.1 V
0.6 1.0 1.4 mA
70 90 110 mV
0.25 0.75
V
5 www.national.com
5 Page 
Modes of Operation
Per the IEEE 802.3af specification, when a PD is connected
to a PoE system it transitions through several operating
modes in sequence including detection, classification (op-
tional), turn on, normal operation, and power removal. Each
operating mode corresponds to a specific PoE voltage range
fed through the Ethernet cable. Figure 3 shows the IEEE
802.3af specified sequence of operating modes and the
corresponding PD input voltages.
Current steering diode-bridges are required for the PD inter-
face to accept all allowable connections and polarities of
PoE voltage from the RJ-45 connector (see the example
application circuits in Figures 18, 19, 20 and 21). The bridge
will cause some reduction of the input voltage sensed by the
LM5072. To guarantee full compliance to the specification in
all operating modes, the LM5072 takes into account the
voltage drop across the bridge diodes and responds appro-
priately to the voltage received from the PoE cable. Table 1
presents the response in each operating mode to voltages
across the VIN and VEE pins.
FIGURE 3. Sequence of PoE Operating Modes
20184617
Mode of Operation
Detection (Signature)
Classification
Startup
Normal Operation
TABLE 1. Operating Modes With Respect To Input Voltage
Voltage from PoE Cable per
IEEE 802.3af
2.7V to 10.0V
14.5V to 20.5V
42V max
57V to 36V
LM5072 Input Voltage
(VIN pin to VEE pin)
1.5V to 10.0V
12V to 23.5V
38V (UVLO Release, VIN Rising)
75V to 32V (UVLO, VIN Falling)
11 www.national.com
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LM5072.PDF ] | |
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