TI1 LM5071MTX-50 Lm5071 power over ethernet pd controller with auxiliary power interface Datasheet

LM5071
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LM5071 Power Over Ethernet PD Controller with Auxiliary Power Interface
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Compatible with 12V AC Adapters
Fully Compliant 802.3af Power Interface Port
80V, 1Ω, 400 mA Internal MOSFET
Detection Resistor Disconnect Function
Programmable Classification Current
Programmable Under-voltage Lockout with
Programmable Hysteresis
Thermal Shutdown Protection
Auxiliary Power Enable Pin
Current Mode Pulse Width Modulator
Supports both Isolated and Non-Isolated
Applications
Error Amplifier and Reference for Non-Isolated
Applications
Programmable Oscillator Frequency
Programmable Soft-Start
80% Maximum Duty Cycle Limiter, Slope
Compensation (-80 device)
50% Maximum Duty Cycle Limiter, No Slope
Compensation (-50 device)
TSSOP-16
DESCRIPTION
The LM5071 power interface port and pulse width
modulation (PWM) controller provides a complete
integrated solution for Powered Devices (PD) that
connect into Power over Ethernet (PoE) systems.
The LM5071 is specifically designed for the PD
that must accept power from auxiliary sources
such as AC adapters. The auxiliary power interface
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 interface and
switch mode power supply (SMPS) are integrated into
the IC.
Block Diagram
PoE (+)
VOUT
IEEE 802.3 af Interface
LM5071
UVLO
Signature Detection
Classification
AC
Adapter
Jack
+
_
Hot Swap
AUX
Auxiliary
Power
Enable
In-rush and Fault
Current Limiting
DC - DC
Converter
PWM Controller
Feedback
Current Mode
PoE (-)
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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LM5071
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VIN
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+3.3V
LM5071
VIN
RSIG
VIN < 10V
Switch
RCLASS
Bandgap
Regulator
VCC
Internal
High Voltage
Regulator
5V
-
+
UVLO
SMPS
Controller
UVLORTN
OUT
CS
AUX
VEE
Inrush /DC
Current Limit
VEE
RTN
COMP
RT
SS
ARTN
FB
Figure 1. Simplified Block Diagram
Connection Diagram
VIN
1
16
ARTN
RSIG
2
15
SS
RCLASS
3
14
RT
AUX
4
13
CS
UVLO
5
12
COMP
UVLORTN
6
11
FB
VEE
7
10
VCC
RTN
8
9
OUT
Figure 2. 16 Lead TSSOP
2
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PIN DESCRIPTIONS
Pin
Name
1
VIN
2
RSIG
3
RCLASS
4
AUX
5
UVLO
6
UVLORTN
7
Description
Application Information
System high potential input.
The diode “OR” of several lines entering the PD, it is the more positive
input potential.
Signature resistor pin.
Connect a resistor from VIN to this pin for signature detection. The
resistor is in parallel with the UVLO resistors and should be valued
accordingly.
Classification resistor pin.
Connect the classification programming resistor from this pin to VEE.
Auxiliary input power startup pin.
A resistor divider between the AUX voltage input to VEE programs the
startup levels with a 2.5V threshold. A high value (>300kΩ) internal pull
down resistor is present to pull the pin low if it is left open. In practice,
the divider voltage should be set well above 2.5V by the programming
resistors.
Line under-voltage lockout.
An external resistor divider from VIN to UVLORTN programs the
shutdown levels with a 2.00V threshold at the UVLO pin. Hysteresis is
set by a switched internal 10uA current source that forces additional
current into the resistor divider.
Return for the external UVLO resistors.
Connect the bottom resistor of the resistor divider between the UVLO pin
and this pin.
VEE
System low potential input.
Diode “OR’d” to the RJ45 connector and PSE’s –48V supply, it is the
more negative input potential.
8
RTN
System return for the PWM converter.
The drain of the internal current limiting power MOSFET which connects
VEE to the return path of the dc-dc converter.
9
OUT
Output of the PWM controller.
DC-DC converter gate driver output with 800mA peak sink current
capability.
10
VCC
Output of the internal high voltage series
pass regulator. Regulated output voltage
is nominally 7.8V.
When the auxiliary transformer winding (if used) raises the voltage on
this pin above the regulation set point, the internal series pass regulator
will shutdown, reducing the controller power dissipation.
11
FB
Feedback signal.
Inverting input of the internal error amplifier. The non-inverting input is
internally connected to a 1.25V reference.
12
COMP
13
CS
14
RT / SYNC
15
SS
16
ARTN
The output of the error amplifier and input COMP pull-up is provided by an internal 5K resistor which may be used
to the Pulse Width Modulator.
to bias an opto-coupler transistor.
Current sense input.
Current sense input for current mode control and over-current protection.
Current limiting is accomplished using a dedicated current sense
comparator. If the CS pin voltage exceeds 0.5V the OUT pin switches
low for cycle-by-cycle current limiting. CS is held low for 50ns after OUT
switches high to blank leading edge current spikes.
Oscillator timing resistor pin and
synchronization input.
An external resistor connected from RT to ARTN sets the oscillator
frequency. This pin will also accept narrow ac-coupled synchronization
pulses from an external clock.
Soft-start input.
An external capacitor and an internal 10uA current source set the softstart ramp rate.
Analog PWM supply return.
RTN for sensitive analog circuitry including the SMPS current limit
amplifier.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings (1) (2)
VIN ,RTN to VEE
-0.3V to 80V
RSIG to VIN
-12V to 0V
AUX to VEE
-0.3V to 57V
UVLO to VEE
-0.3V to 13V
RCLASS to VEE
-0.3V to 7V
ARTN to RTN
-0.3V to 0.3V
VCC, OUT to ARTN
-0.3V to 16V
All other inputs to ARTN
-0.3V to 7V
ESD Rating
Human Body Model
2000V
Lead Temperature (3)
Wave (4 seconds)
260°C
Infrared (10 seconds)
240°C
Vapor Phase (75 seconds)
219°C
(1)
(2)
(3)
Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is intended to be functional. For specifications and test conditions, see Electrical Characteristics. The absolute
maximum rating of VIN, RTN to VEE is derated to (-0.3V to 76V) at -40°C.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
For detailed information on soldering the plastic TSSOP package, refer to the Packaging Databook available from Texas Instruments.
Operating Ratings
VIN voltage
1.8V to 60V
External voltage applied to VCC
8.1V to 15V
Operating Junction Temperature
-40°C to 125°C
4
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Electrical Characteristics (1)
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, VCC = 10V, RT = 30.3kΩ.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Powered Interface
IOS
Offset Current
VIN < 10.0V
10
uA
VCLSS(ON)
Signature Resistor Disable /
Classification Current Turn On
VIN with respect to VEE
10.0
11.5
12.5
V
VCLSS(OFF)
Classification Current Turn Off
VIN with respect to VEE
23.5
25.0
26.5
V
1.43
1.5
1.57
V
0.5
1.0
mA
1
1.9
mA
Classification Voltage
With respect to VEE
ICLASS
Supply Current During
Classification
VIN =17V
IDC
Supply Current During Normal
Operation
OUT floating
UVLO Pin Reference Voltage
VIN > 27V
1.95
2.00
2.05
V
UVLO Hysteresis Current
VIN > UVLO
8.0
10
11.5
uA
Softstart Release
RTN falling with respect to VEE
1.2
1.45
1.7
V
Softstart Release Hysteresis
RTN rising with respect to VEE
0.8
1.1
1.3
V
RDS(ON)
PowerFET Resistance
I = 350mA, VIN = 48V
1
2.2
Ω
ILEAK
SMPS Bias Current
VEE = 0V, VIN = RTN = 57V
100
uA
AUX Pin Threshold
AUX pin rising with respect to VEE
2.4
2.5
2.65
V
AUX Pin Threshold Hysteresis
AUX pin falling with respect to VEE
0.4
0.5
0.6
V
ZAUX
AUX Pin Input Impedance
AUX = 0.5V
IINRUSH
Inrush Current Limit
VEE = 0V, RTN = 3.0V
70
100
130
mA
ILIM
DC Current Limit
VEE = 0V, RTN = 3.0V,
Temp = 0°C to 85°C
350
390
420
mA
ILIM
DC Current Limit
VEE = 0V, RTN = 3.0V, Temp = 40°C to 125°C
325
390
420
mA
VinMin
Operational VIN Input Voltage
AUX = 5V, Vcc = Vin (2)
9.5
VccReg
VCC Regulation
Open ckt
7.5
7.8
8.1
VCC Current Limit
See (3)
15
20
VCC UVLO (Rising)
VccReg
– 300mV
VccReg –
100mV
VCC UVLO (Falling)
5.9
6.25
6.6
V
1.5
3
mA
350
kΩ
Startup Regulator
V
V
mA
VCC Supply
Supply Current (Icc)
Cload = 0
Error Amplifier
GBW
Gain Bandwidth
4
MHz
DC Gain
75
dB
Input Voltage
FB = COMP
COMP Sink Capability
FB=1.5V COMP=1V
ILIM Delay to Output
CS step from 0 to 0.6V, time to
onset of OUT transition (90%)
1.219
1.212
5
1.281
1.288
V
20
mA
20
ns
Current Limit
Cycle by Cycle Current Limit
Threshold Voltage
(1)
(2)
(3)
0.44
0.5
0.56
V
Min and Max limits are 100% production tested at 25 °C. Limits over the operating temperature range are specified through correlation
using Statistical Quality Control (SQC) methods. Limits are used to calculate Texas Instruments’ Average Outgoing Quality Level
(AOQL).
The Vcc regulator requires an external source whenever the Vin pin is below 13V with respect to RTN. An external load on Vcc
increases this startup voltage requirement.
Device thermal limitations may limit usable range.
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Electrical Characteristics(1) (continued)
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, VCC = 10V, RT = 30.3kΩ.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Leading Edge Blanking Time
55
ns
CS Sink Impedance (clocked)
25
55
Ω
7
10
13
uA
Frequency1
(RT = 30.3K)
175
200
225
KHz
Frequency2
(RT = 10.5K)
505
580
665
KHz
3.1
3.8
V
Soft-Start
Softstart Current Source
Oscillator (4)
Sync threshold
PWM Comparator
Delay to Output
COMP set to 2V
CS stepped 0 to 0.4V, time to onset
of OUT transition low
Min Duty Cycle
COMP=0V
25
ns
0
%
Max Duty Cycle (-80 Device)
80
%
Max Duty Cycle (-50 Device)
50
%
COMP to PWM Comparator Gain
0.33
COMP Open Circuit Voltage
4.5
5.4
6.3
V
0.6
1.1
1.5
mA
COMP Short Circuit Current
COMP= 0V
Slope Comp Amplitude
(LM5071-80 Device Only)
Delta increase at PWM Comparator
to CS
105
Output High Saturation
Iout = 50mA,
VCC - VOUT
0.25
0.75
Output Low Saturation
Iout = 100mA
0.25
0.75
Rise time
Cload = 1nF
15
ns
Fall time
Cload = 1nF
15
ns
165
°C
25
°C
125
°C/W
Slope Compensation
mV
Output Section
V
V
Thermal Shutdown
Tsd
Thermal Shutdown Temp.
Thermal Shutdown
Hysteresis
Thermal Resistance
θJA
(4)
6
Junction to Ambient
PW Package
Specification applies to the oscillator frequency. The operational frequency of the LM5071-50 devices is divided by two.
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Typical Performance Characteristics
Default Current Limit vs Temperature
Oscillator Frequency vs RT Resistance
OSCILLATOR FREQUENCY (kHz)
400
DEFAULT CURRENT LIMIT (mA)
395
390
385
380
375
370
365
1000
800
600
400
200
0
360
-40
-20
0
20
40
60
80
0
100 120
5
10 15 20 25 30 35 40 45 50
RT RESISTANCE (k:)
TEMPERATURE (oC)
Figure 3.
Figure 4.
UVLO Hysteresis Current vs Temperature
Softstart Current vs Temperature
12
11.5
11.5
SOFTSTART CURRENT (PA)
UVLO HYSTERESIS CURRENT (PA)
12
11
10.5
10
9.5
9
8.5
8
-40
11
10.5
10
9.5
9
8.5
-20
0
20
40
60
80
8
-40
100 120
-20
o
0
20
40
60
80
100 120
o
TEMPERATURE ( C)
TEMPERATURE ( C)
Figure 5.
Figure 6.
Error Amp Input Voltage vs temperature
Oscillator Frequency vs Temperature
RT = 15.2 kΩ
1.275
406
1.270
404
1.265
402
FREQUENCY (kHz)
SMPS BG (V)
1.260
1.255
1.250
1.245
1.240
400
398
396
394
1.235
392
1.230
1.225
-60 -40 -20
0
20 40 60 80 100 120 140
390
-40
-20
0
20
40
60
80
100 120
o
o
TEMPERATURE ( C)
TEMPERATURE ( C)
Figure 7.
Figure 8.
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Typical Performance Characteristics (continued)
VCC vs ICC
Input Current vs Input Voltage
9
3
8
INPUT CURRENT (mA)
2.5
VCC (V)
7
6
5
4
3
2
1.5
1
0.5
2
1
0
0
5
10
15
20
25
0
10
20
30
40
50
60
70
80
INPUT VOLTAGE (V)
ICC (mA)
Figure 9.
Figure 10.
UVLO Threshold vs Temperature
2.05
2.04
2.03
UVLO VTH (V)
2.02
2.01
2.00
1.99
1.98
1.97
1.96
1.95
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (oC)
Figure 11.
8
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Specialized Block Diagrams
VIN 5
+
EN
_
VBG
+
2V -
VCC
10 PA
UVLO
+
+
_
+
_
2.5V
VEE
VCC
FB
COMP
RTN
ARTN
FB
_
350 k:
OUT
1V
Hysteresis
COMP
+
AUX
Gate
Control
CS
force_enable
_
OUT
CS
Thermal
Limit
SS
10V
VIN
See Figure 4
1.5V +
RSIG
Power OK
_
RCLASS
SMPS
Controller
RT
1.5V
SS
+
EN
LOCAL_EN
VIN
RT
UVLORTN
LT25V
2V
-
60V
Figure 12. Top Level Block Diagram
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RT
Slope
Compensation
Generator
45 PA
0
OSC
VCC
CLK
-50 Device Has
No Slope
Compensation
80% MAX
DUTY LIMIT (-80)
50% MAX
DUTY LIMIT (-50)
5V
5k
1.25V
FB
Q
R
Q
DRIVER
OUT
PWM
100k
+
-
S
1.4V
+
LOGIC
50k
SS
10 PA
SS
SS
COMP
2k
0.5V
+
-
CURRENT
LIMIT
CS
CLK +LEB
Figure 13. PWM Controller Block Diagram
10
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DETAILED OPERATING DESCRIPTION
The LM5071 power interface port and pulse width modulation (PWM) controller provides a complete integrated
solution for Powered Devices (PD) that connect into Power over Ethernet (PoE) systems. Major features of the
PD interface portion of the IC include detection, classification, thermal limit, programmable undervoltage lockout,
and current limit monitoring. The device also includes a high-voltage start-up bias regulator that operates over a
wide input range up to 60V. The switch mode power supply (SMPS) control portion of the IC includes power
good sensing, VCC regulator under-voltage lockout, cycle-by-cycle current limit, error amplifier, slope
compensation, soft-start, and oscillator sync capability. This high speed BiCMOS IC has total propagation delays
less than 100ns and a 1MHz capable oscillator programmed by a single external resistor. The LM5071 PWM
controller provides current-mode control for dc-dc converter topologies requiring a single drive output, such as
Flyback and Forward topologies. The LM5071 PWM enables all of the advantages of current-mode control
including line feed-forward, cycle-by-cycle current limit and simplified loop compensation. The oscillator ramp is
internally buffered and added to the PWM comparator input ramp to provide slope compensation necessary for
current mode control at duty cycles greater than 50% (-80 suffix only).
Modes of Operation
The LM5071 PD interface is designed to provide a fully compliant IEEE 802.3af system. As such, the modes of
operation take into account the barrel rectifiers often utilized to correctly polarize the dc input from the Ethernet
cable.
Table 1. Operating Modes With Respect to Input Voltage
Input Voltage VIN wrt VEE
Mode of Operation
1.8V to 10.0V
Detection (Signature)
12.5V to 25.0V
Classification
25.0V to UVLO Rising Vth
Awaiting Full Power
60V to UVLO Falling Vth
Normal Powered Operation
An external signature resistor is connected to VEE when VIN exceeds 1.8V, initiating detection mode. During
detection mode, quiescent current drawn by the LM5071 is less than 10uA. Between 10.0V and 12.5V, the
device enters classification mode and the signature resistor is disabled. The nominal range for classification
mode is 11.5V to 25.0V. The classification current is turned off once the classification range voltage is exceeded,
to reduce power dissipation. Between 25.0V and UVLO release, the device is in a standby state, awaiting the
input voltage to reach the operational range to complete the power up sequence. Once the VIN voltage increases
above the upper UVLO threshold voltage, the internal power MOSFET is enabled to deliver a constant current to
charge the input capacitor of the dc-dc converter. When the MOSFET Vds voltage falls below 1.5V, the internal
Power Good signal enables the SMPS controller. The LM5071 is specified to operate with an input voltage as
high as 60.0V. The SMPS controller and internal MOSFET are disabled when VIN falls to the lower UVLO
threshold.
Detection Signature
To detect a potential powered device candidate, the PSE (Power Sourcing Equipment) will apply a voltage from
2.8V to 10V across the input terminals of the PD. The voltage can be of either polarity so a diode barrel network
is required on both lines to ensure this capability. The PSE will take two measurements, separated by at least 1V
and 2ms of time. The voltage ramp between measurement points will not exceed 0.1V/us. The delta voltage /
delta current calculation is then performed; if the detected impedance is above 23.75kΩ and below 26.25kΩ, the
PSE will consider a PD to be present. If the impedance is less than 15kΩ or greater than 33kΩ a PD will be
considered not present and will not receive power. Impedances between these values may or may not indicate
the presence of a valid PD. The LM5071 will enable the signature resistor at a controller input voltage of 1.5V to
take into account the diode voltage drops. An external signature resistor should be placed between the VIN and
RSIG pins. The signature resistor is in parallel with the external UVLO resistor divider, and its value should be
calculated accordingly. Targeting 24.5kΩ increases margin in the signature design as the input bridge rectifier
diodes contribute to the series resistance measured at the PD input terminals. The PSE will tolerate no more
than 1.9V of offset voltage (caused by the external diodes) or more than 10uA of offset current (bias current).
The input capacitance must be greater than 0.05uF and less than 0.12uF. To increase efficiency, the signature
resistor is disabled by the LM5071 controller once the input voltage is above the detection range (> 11V).
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Classification
To classify the PD, the PSE will present a voltage between 14.5V and 20.5V to the PD. The LM5071 enables
classification mode at a nominal input voltage of 11.5V. An internal 1.5V linear regulator and an external resistor
connected to the RCLASS pin provide classification programming current. Table 1 shows the external
classification resistor required for a particular class.
The classification current flows through the IC into the classification resistor. The suggested resistor values take
into account the bias current flowing into the IC. A different desired RCLASS can be calculated by dividing 1.5V
by the desired classification current.
Per the IEEE 802.3af specification, classification is optional, and the PSE will default to class 0 if a valid
classification current is not detected. If PD classification is not desired (i.e., Class 0), simply leave the RCLASS
pin open. The classification time period may not last longer than 75ms as per IEEE 802.3af. The LM5071 will
remain in classification mode until VIN is greater than 25V.
Table 2. Classification Levels and Required External Resistors
Class
PMIN
PMAX
ICLASS
(MIN)
ICLASS
(MAX)
RCLASS
0
0.44W
12.95W
1
0.44W
3.84W
0mA
4mA
Open
9mA
12mA
150Ω
2
3.84W
3
6.49W
6.49W
17mA
20mA
82.5Ω
12.95W
26mA
30mA
4
Reserved
Reserved
54.9Ω
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 resistor 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
minimum 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
to instantly raise 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 14 for an example of a simple yet
robust auxiliary configuration.
12
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+AUX
+PoE
VCC
VIN
+V OUT
LM 5071
RCLASS
SS
UVLO
RT
COMP
UVLORTN
CS
100 k:
FB
AUX
ARTN
RTN
100 k:
-PoE
OUT
VEE
- AUX
0.1 PF
Figure 14. Simplified Schematic Showing Auxiliary Implementation
Power Supply Operation
Once the UVLO threshold has been satisfied, the interface controller of the LM5071 will charge up the SMPS
input capacitor through the internal power MOSFET. This load capacitance provides input filtering for the power
converter section and must be at least 5uF per the IEEE 802.3af specification. To accomplish the charging in a
controlled manner, the power MOSFET is current limited to 100mA.
The SMPS controller will not initiate operation until the load capacitor is completely charged. The power
sequencing between the interface circuitry and the SMPS controller occurs automatically within the LM5071.
Detection circuitry monitors the RTN pin to detect interface startup completion. When the RTN pin potential drops
below 1.5V with respect to VEE, the VCC regulator of the SMPS controller is enabled. The soft-start function is
enabled once the VCC regulator achieves minimum operating voltage. The inrush current limit only applies to the
initial charging phase. The interface power MOSFET current limit will revert to the default protection current limit
of 390mA once the SMPS is powered up and the soft-start pin sequence begins.
High Voltage Start-up Regulator
The LM5071 contains an internal high voltage startup regulator that allows the input pin (VIN) to be connected
directly to line voltages as high as 60V. The regulator output is internally current limited to 15mA. The
recommended capacitance range for the VCC regulator output is 0.1uF to 10uF. When the voltage on the VCC pin
reaches the regulation point of 7.8V, the controller output is enabled. The controller will remain enabled until VCC
falls below 6.25V.
In typical applications, a transformer auxiliary winding is diode connected to the VCC pin. This winding should
raise the VCC voltage above 8.1V to shut off the internal startup regulator. Though not required, powering VCC
from an auxiliary winding improves conversion efficiency while reducing the power dissipated in the controller.
The external VCC capacitor must be selected such that the capacitor maintains the VCC voltage greater than the
VCC UVLO falling threshold (6.25V) during the initial start-up. During a fault condition when the converter auxiliary
winding is inactive, external current draw on the VCC line should be limited such that the power dissipated in the
start-up regulator does not exceed the maximum power dissipation capability of the LM5071 package.
If the VCC auxiliary winding is used with a low voltage auxiliary supply (wall transformer), the VCC pin could back
feed through the LM5071 to the VIN pin. A diode from VCC to VIN should be used to clamp the VCC pin and
prevent this internal back feed. The winding voltage will remain the same and extra power will be dissipated in
the series resistor. Also, note that when using a very low voltage auxiliary supply (<14V), a diode from the AUX
supply to the VCC pin should be used to ensure VCC startup.
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+AUX
+PoE
VCC
VIN
+V OUT
LM 5071
RCLASS
SS
UVLO
RT
COMP
UVLORTN
CS
100 k:
FB
AUX
ARTN
RTN
100 k:
-PoE
OUT
VEE
- AUX
0.1 PF
Figure 15. Simplified Schematic Showing Low Voltage Auxiliary Supply
Error Amplifier
An internal high gain error amplifier is provided within the LM5071. The amplifier’s non-inverting reference is set
to a fixed reference voltage of 1.25V. The inverting input is connected to the FB pin. In non-isolated applications,
the power converter output is connected to the FB pin via voltage scaling resistors. Loop compensation
components are connected between the COMP and FB pins. For most isolated applications the error amplifier
function is implemented on the secondary side of the converter and the internal error amplifier is not used. The
internal error amplifier is configured as an open drain output and can be disabled by connecting the FB pin to
ARTN. An internal 5K pull-up resistor between a 5V reference and COMP can be used as the pull-up for an
optocoupler in isolated applications.
Current Limit / Current Sense
The LM5071 provides a cycle-by-cycle over current protection function. Current limit is accomplished by an
internal current sense comparator. If the voltage at the current sense comparator input CS exceeds 0.5V with
respect to RTN/ARTN, the output pulse will be immediately terminated. A small RC filter, located near the CS pin
of the controller, is recommended to filter noise from the current sense signal. The CS input has an internal
MOSFET which discharges the CS pin capacitance at the conclusion of every cycle. The discharge device
remains on an additional 50ns after the beginning of the new cycle to attenuate the leading edge spike on the
current sense signal.
The LM5071 current sense and PWM comparators are very fast, and may respond to short duration noise
pulses. Layout considerations are critical for the current sense filter and sense resistor. The capacitor associated
with the CS filter must be located very close to the device and connected directly to the pins of the controller (CS
and ARTN). If a current sense transformer is used, both leads of the transformer secondary should be routed to
the sense resistor and the current sense filter network. A sense resistor located in the source of the primary
power MOSFET may be used for current sensing, but a low inductance resistor is required. When designing with
a current sense resistor, all of the noise sensitive low power ground connections should be connected together
local to the controller and a single connection should be made to the high current power return (sense resistor
ground point).
14
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Oscillator, Shutdown and Sync Capability
A single external resistor connected between the RT and ARTN pins sets the LM5071 oscillator frequency.
Internal to the LM5071–50 device (50% duty cycle limited option) is an oscillator divide by two circuit. This divide
by two circuit creates an exact 50% duty cycle clock which is used internally to create a precise 50% duty cycle
limit function. Because of this divide by two, the internal oscillator actually operates at twice the frequency of the
output (OUT). For the LM5071–80 device the oscillator frequency and the operational output frequency are the
same. To set a desired output operational frequency (F), the RT resistor can be calculated from:
LM5071-80:
RT =
1
F x 165 x 10-12
(1)
LM5071-50:
RT =
1
F x 330 x 10-12
(2)
The LM5071 can also be synchronized to an external clock. The external clock must have a higher frequency
than the free running oscillator frequency set by the RT resistor. The clock signal should be capacitively coupled
into the RT pin with a 100pF capacitor. A peak voltage level greater than 3.7 volts at the RT pin is required for
detection of the sync pulse. The sync pulse width should be set between 15 to 150ns by the external
components. The RT resistor is always required, whether the oscillator is free running or externally synchronized.
The voltage at the RT pin is internally regulated to a 2 volts. The RT resistor should be located very close to the
device and connected directly to the pins of the controller (RT and ARTN).
PWM Comparator / Slope Compensation
The PWM comparator compares the current ramp signal with the loop error voltage derived from the error
amplifier output. The error amplifier output voltage at the COMP pin is offset by 1.4V and then further attenuated
by a 3:1 resistor divider. The PWM comparator polarity is such that 0 Volts on the COMP pin will result in zero
duty cycle at the controller output. For duty cycles greater than 50 percent, current mode control circuits are
subject to sub-harmonic oscillation. By adding an additional fixed slope voltage ramp signal (slope compensation)
to the current sense signal, this oscillation can be avoided. The LM5071-80 integrates this slope compensation
by summing a current ramp generated by the oscillator with the current sense signal. Additional slope
compensation may be added by increasing the source impedance of the current sense signal (with an external
resistor between the CS pin and current sense resistor). Since the LM5071-50 is not capable of duty cycles
greater than 50%, there is no slope compensation feature in this device.
Soft-Start
The softstart feature allows the power converter to gradually reach the initial steady state operating point, thereby
reducing start-up stresses, output overshoot and current surges. At power on, after the VCC undervoltage lockout
threshold is satisfied, an internal 10μA current source charges an external capacitor connected to the SS pin.
The capacitor voltage will ramp up slowly and will limit the COMP pin voltage and the duty cycle of the output
pulses.
Gate Driver and Maximum Duty Cycle Limit
The LM5071 provides an internal gate driver (OUT), which can source and sink a peak current of 800mA. The
LM5071 is available in two duty cycle limit options. The maximum output duty cycle is typically 80% for the
LM5071-80 option and precisely equal to 50% for the LM5071-50 option. The maximum duty cycle function for
the LM5071-50 is accomplished with an internal toggle flip-flop which ensures an accurate duty cycle limit. The
internal oscillator frequency of the LM5071-50 is therefore twice the operating frequency of the PWM controller
(OUT pin).
The 80% maximum duty cycle limit of the LM5071-80 is determined by the internal oscillator and varies more
than the 50% limit of the LM5071-50. For the LM5071-80, the internal oscillator frequency and the operational
frequency of the PWM controller are equal.
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Thermal Protection
Internal thermal shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction
temperature is exceeded. This feature prevents catastrophic failures from accidental device overheating. When
activated, typically at 165 degrees Celsius, the controller is forced into a low power standby state, disabling the
output driver, bias regulator, main interface pass MOSFET, and classification regulator if enabled. After the
temperature is reduced (typical hysteresis = 25°C) the VCC regulator will be enabled and a softstart sequence
initiated.
Thermal shutdown is not enabled during auxiliary power operation as the power MOSFET is not running any
current and should not experience an over-temperature condition. If the drain of the MOSFET exceeds 2.5V with
respect to VEE (internal Power Good de-assertion), PoE UVLO becomes de-asserted (insertion of PoE or other
48V supply), or the auxiliary power is removed, thermal limit will be re-enabled immediately.
LM5071 Application Circuit Diagrams
Figure 16. Single Isolated Output with Diode Rectification and 12V Auxiliary Supply
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Figure 17. Dual Isolated Output with Diode Rectification
Figure 18. Non-Isolated Output Buck with Diode Rectification
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REVISION HISTORY
Changes from Revision D (April 2013) to Revision E
•
18
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 17
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PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Op Temp (°C)
Top-Side Markings
(3)
(4)
LM5071MT-50/NOPB
ACTIVE
TSSOP
PW
16
92
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
5071MT
-50
LM5071MT-80
ACTIVE
TSSOP
PW
16
92
TBD
Call TI
Call TI
-40 to 125
5071MT
-80
LM5071MT-80/NOPB
ACTIVE
TSSOP
PW
16
92
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
5071MT
-80
LM5071MTX-50
ACTIVE
TSSOP
PW
16
2500
TBD
Call TI
Call TI
-40 to 125
5071MT
-50
LM5071MTX-50/NOPB
ACTIVE
TSSOP
PW
16
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
5071MT
-50
LM5071MTX-80/NOPB
ACTIVE
TSSOP
PW
16
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
5071MT
-80
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a
continuation of the previous line and the two combined represent the entire Top-Side Marking for that device.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Apr-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM5071MTX-50
TSSOP
PW
16
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
LM5071MTX-50/NOPB
TSSOP
PW
16
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
LM5071MTX-80/NOPB
TSSOP
PW
16
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Apr-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM5071MTX-50
TSSOP
PW
16
2500
367.0
367.0
35.0
LM5071MTX-50/NOPB
TSSOP
PW
16
2500
367.0
367.0
35.0
LM5071MTX-80/NOPB
TSSOP
PW
16
2500
367.0
367.0
35.0
Pack Materials-Page 2
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