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PDF 5071MT Data sheet ( Hoja de datos )
| Número de pieza | 5071MT | |
| Descripción | LM5071MT | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de 5071MT (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
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November 2005
www.DataSheet4U.com
LM5071
Power Over Ethernet PD Controller with Auxiliary Power
Interface
General Description
The LM5071 power interface port and pulse width modula-
tion (PWM) controller provides a complete integrated solu-
tion for Powered Devices (PD) that connect into Power over
Ethernet (PoE) systems. The LM5071 is specifically de-
signed for the PD that must accept power from auxiliary
sources such as ac adapters. The auxiliary power inter-
face of the LM5071 activates the PWM controller when the
ac adapter is connected to power the PD when PoE network
power is unavailable. The LM5071 integrates an 80V,
400mA line connection switch and associated control for a
fully IEEE 802.3af compliant interface with a full featured
current mode pulse width modulator dc-dc converter. All
power sequencing requirements between the controller in-
terface and switch mode power supply (SMPS) are inte-
grated into the IC.
Features
n Compatible with 12V ac adapters
n Fully Compliant 802.3af Power Interface Port
n 80V, 1Ω, 400 mA Internal MOSFET
n Detection Resistor Disconnect Function
n Programmable Classification Current
n Programmable Under-voltage Lockout with
Programmable Hysteresis
n Thermal Shutdown Protection
n Auxiliary Power Enable Pin
n Current Mode Pulse Width Modulator
n Supports both Isolated and Non-Isolated Applications
n Error Amplifier and Reference for Non-Isolated
Applications
n Programmable Oscillator Frequency
n Programmable Soft-start
n 80% Maximum Duty Cycle Limiter, Slope Compensation
(-80 device)
n 50% Maximum Duty Cycle Limiter, No Slope
Compensation (-50 device)
Packages
n TSSOP-16
Block Diagram
© 2005 National Semiconductor Corporation DS201684
20168401
www.national.com
1 page  
Electrical Characteristics (Note 3) (Continued)
Specifications in standard type face are for TJ= +25˚C and those in boldface type apply over the full operatinwg wjuwnc.DtioantatSehme-et4U.com
perature range. Unless otherwise specified: VIN = 48V, VCC = 10V, RT = 30.3kΩ.
Symbol
Parameter
Conditions
Min Typ Max Units
VCC Supply
VCC UVLO (Rising)
VccReg VccReg –
– 100mV
300mV
VCC UVLO (Falling)
Supply Current (Icc)
Cload = 0
5.9 6.25 6.6 V
1.5 3 mA
Error Amplifier
GBW
Gain Bandwidth
4 MHz
DC Gain
75 dB
Input Voltage
FB = COMP
1.219
1.281
V
1.212
1.288
COMP Sink Capability
FB=1.5V COMP=1V
5 20
mA
Current Limit
ILIM Delay to Output
CS step from 0 to 0.6V, time to
20
ns
onset of OUT transition (90%)
Cycle by Cycle Current Limit
0.44
0.5
0.56
V
Threshold Voltage
Leading Edge Blanking Time
55 ns
CS Sink Impedance (clocked)
25 55 Ω
Softstart
Softstart Current Source
7 10 13 uA
Oscillator(Note 5)
Frequency1
175 200 225 KHz
(RT = 30.3K)
Frequency2
505 580 665 KHz
(RT = 10.5K)
Sync threshold
3.1 3.8 V
PWM Comparator
Delay to Output
COMP set to 2V
25 ns
CS stepped 0 to 0.4V, time to
onset of OUT transition low
Min Duty Cycle
COMP=0V
0%
Max Duty Cycle (-80 Device)
80 %
Max Duty Cycle (-50 Device)
50 %
COMP to PWM Comparator
0.33
Gain
COMP Open Circuit Voltage
4.5 5.4 6.3 V
COMP Short Circuit Current COMP= 0V
0.6 1.1 1.5 mA
Slope Compensation
Slope Comp Amplitude
Delta increase at PWM
105 mV
(LM5071-80 Device Only)
Comparator to CS
Output Section
Output High Saturation
Output Low Saturation
Rise time
Iout = 50mA,
VCC - VOUT
Iout = 100mA
Cload = 1nF
0.25
0.25
15
0.75
0.75
V
V
ns
Fall time
Cload = 1nF
15 ns
5 www.national.com
5 Page 
Classification (Continued)
TABLE 2. Classification Levels and Required External
Resistors
Class
0
1
2
3
4
PMIN
0.44W
0.44W
3.84W
6.49W
Reserved
PMAX ICLASS ICLASS RCLASS
(MIN) (MAX)
12.95W 0mA 4mA Open
3.84W 9mA 12mA 150Ω
6.49W 17mA 20mA 82.5Ω
12.95W 26mA 30mA 54.9Ω
Reserved 36mA 44mA 38.3Ω
Undervoltage Lockout (UVLO)
The IEEE 802.3af specification states that the PSE will
supply power to the PD within 400ms after completion of
detection. The LM5071 contains a programmable line Under
Voltage Lock Out (UVLO) circuit. The first resistor should be
connected between the VIN to UVLO pins; the bottom resis-
tor in the divider should be connected between the UVLO
and UVLORTN pins.
The divider must be designed such that the voltage at the
UVLO pin equals 2.0V when VIN reaches the desired mini-
mum operating level. If the UVLO threshold is not met, the
interface control and SMPS control will remain in standby.
UVLO hysteresis is accomplished with an internal 10uA
current source that is switched on and off into the impedance
of the UVLO set point divider. When the UVLO threshold is
exceeded, the current source is activated twowinws.tDanattlaySrhaeiseet4U.com
the voltage at the UVLO pin. When the UVLO pin voltage
falls below the 2.00V threshold, the current source is turned
off, causing the voltage at the UVLO pin to fall. The LM5071
UVLO thresholds cannot be programmed lower than 25V,
the AUX pin should be used to force UVLO release below
25V.
There are many additional uses for the UVLO pin. The UVLO
function can also be used to implement a remote enable /
disable function. Pulling the UVLO pin down below the
UVLO threshold disables the interface and SMPS controller
unless forced on via AUX pin operation.
AUX Pin Operation
The AUX pin can be used to force operation (UVLO release)
of the interface and switching regulator at any input voltage
above 9.5V. This is especially useful for auxiliary input (wall
transformer) input voltages. The pin has a 2.5V threshold
(0.5V hysteresis) and an input impedance of approximately
350kΩ. The input resistor provides a defined pull down
impedance if the pin is left open by the user. An external pull
down resistor should be used to provide additional noise
immunity. The resultant pin voltage from the external resistor
divider should be well above the 2.5V threshold to ensure
proper auxiliary operation. See Figure 4 for an example of a
simple yet robust auxiliary configuration.
FIGURE 4. Simplified Schematic Showing Auxiliary Implementation
20168422
11 www.national.com
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| PDF Descargar | [ Datasheet 5071MT.PDF ] | |
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