LM5070
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SNVS308G – OCTOBER 2004 – REVISED APRIL 2013
LM5070 Integrated Power Over Ethernet PD Interface and PWM Controller
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FEATURES
DESCRIPTION
•
•
•
•
•
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The LM5070 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
LM5070 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. Two options are available
providing either an 80% maximum duty cycle limit
with slope compensation (on the –80 suffix) device or
a 50% maximum duty cycle limit and no slope
compensation on the (–50 suffix) device.
1
2
•
•
•
•
•
•
•
•
•
Fully Compliant 802.3af Power Interface Port
80V, 1Ω, 400 mA Internal MOSFET
Programmable Inrush Current Limit
Detection Resistor Disconnect Function
Programmable Classification Current
Programmable Under-voltage Lockout with
Programmable Hysteresis
Thermal Shutdown Protection
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)
800 mA Peak Gate Driver
PACKAGES
•
•
TSSOP-16
WSON-16 (5 mm x 5 mm)
Block Diagrams
RJ45
Connector
VDC
TX+ (1)
To PHY
TX- (2)
IEEE 802.3af
Interface
LM5070
UVLO
Signature Detection
Classification
RX+ (3)
To PHY
RX- (6)
(4)
(5)
Hot Plug Controller
In-rush and Fault
Current Limiting
DC-DC
Converter
Controller
Current Mode
(7)
(8)
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.
Copyright © 2004–2013, Texas Instruments Incorporated
LM5070
SNVS308G – OCTOBER 2004 – REVISED APRIL 2013
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+3.3V
LM5070
VIN
VIN
RSIG
VIN < 10V
Switch
RCLASS Bandgap
Regulator
OUT
RCLP Programmable
Inrush Current
VEE
VCC
Internal
High Voltage
Regulator
5V
SMPS
Controller
VEE
CS
RTN
C OMP
SS
RT
ARTN
FB
Figure 1. Simplified Block Diagram and Application
Connection Diagram
VIN
1
16
ARTN
RSIG
2
15
SS
RCLASS
3
14
RT
UVLO
4
13
CS
UVLORTN
5
12
COMP
RCLP
6
11
FB
VEE
7
10
VCC
RTN
8
9
OUT
Figure 2. 16 Lead TSSOP/WSON
See Package Number PW or NHQ0016A
2
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PIN DESCRIPTIONS
Pin
Name
1
VIN
2
RSIG
3
RCLASS
4
UVLO
5
UVLORTN
6
RCLP
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 25kΩ signature resistor from VIN to this pin for signature
detection.
Classification resistor pin.
Connect the classification programming resistor from this pin to VEE.
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.
Current limit programming pin.
Programs the inrush current limit for the device. If left open, the inrush
current limit will default to 400mA max.
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
The output of the error amplifier and input
to the Pulse Width Modulator.
COMP pull-up is provided by an internal 5K resistor which may be used
to bias an opto-coupler transistor.
13
CS
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.
14
RT / SYNC
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.
15
SS
Soft-start input.
An external capacitor and an internal 10uA current source set the softstart ramp rate.
16
ARTN
Analog PWM supply return.
RTN for sensitive analog circuitry including the SMPS current limit
amplifier.
—
EP
Exposed PAD, underside of the WSON
package option.
Internally bonded to the die substrate. Connect to VEE potential for low
thermal impedance.
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
UVLO to VEE
-0.3V to 57V
UVLORTN
-0.3V to 13V
RCLASS, RCLP 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
Storage Temperature
-65°C to +150°C
Junction Temperature
150°C
Lead Temperature (3)
Wave (4 seconds)
260°C
Infrared (10 seconds)
240°C
Vapor Phase (75 seconds)
(1)
219°C
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 the 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 plastic TSSOP and WSON packages, see the Packaging Databook available from TI.
(2)
(3)
Operating Ratings
VIN voltage
1.8V to 75V
External voltage applied to VCC
8.1V to 15V
Operating Junction Temperature
-40°C to +125°C
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
10
uA
Powered Interface
IOS
Offset Current
VIN < 10.0V
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
20.5
22.0
23.0
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 > 12V
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
ILIM
Default Current Limit
VEE = 0V, RTN = 3.0V,
Temp = 0°C to 85°C
420
mA
(1)
4
350
390
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 Average Outgoing Quality Level (AOQL).
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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
ILIM
Min
Typ
Max
Units
Default Current Limit
Parameter
VEE = 0V, RTN = 3.0V,
Temp = -40°C to 125°C
Conditions
325
390
420
mA
Current Limit Programming
Accuracy
VEE = 0V, RTN = 3.0V,
RCLP = 80.6kΩ
-20
+20
%
VCC Regulation
Open ckt
7.5
7.8
VCC Current Limit
See (2)
15
20
VccReg –
300mV
VccReg –
100mV
5.9
6.25
6.6
V
1.5
3
mA
Startup Regulator
VccReg
8.1
V
mA
VCC Supply
VCC UVLO (Rising)
VCC UVLO (Falling)
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
0.44
0.5
0.56
V
Leading Edge Blanking Time
55
CS Sink Impedance (clocked)
25
55
ns
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
Softstart
Softstart Current Source
Oscillator (3)
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
COMP Short Circuit Current
COMP= 0V
4.5
5.4
6.3
V
0.6
1.1
1.5
mA
Slope Compensation
Slope Comp Amplitude
(LM5070-80 Device Only)
(2)
(3)
Delta increase at PWM
Comparator to CS
105
mV
Device thermal limitations may limit usable range.
Specification applies to the oscillator frequency. The operational frequency of the LM5070-50 devices is divided by two.
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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
V
Output Section
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
PW Package
125
°C/W
NHQ0016A Package
32
°C/W
V
Thermal Shutdown
Tsd
Thermal Shutdown Temp.
Thermal
Shutdown
Hysteresis
Thermal Resistance
θJA
6
Junction to Ambient
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Typical Performance Characteristics
Inrush Current Limit
vs
RCLP Resistor
400
450
395
400
INRUSH CURRENT LIMIT (mA)
DEFAULT CURRENT LIMIT (mA)
Default Current Limit
vs
Temperature
390
385
380
375
370
365
350
300
250
200
150
100
50
0
30
360
-40
-20
0
20
40
60
80
100 120
40
TEMPERATURE (oC)
50 60 70 80 90
RCLP RESISTOR (k:)
100 110
Figure 3.
Figure 4.
Oscillator Frequency
vs
RT Resistance
UVLO Hysteresis Current
vs
Temperature
UVLO HYSTERESIS CURRENT (PA)
OSCILLATOR FREQUENCY (kHz)
12
1000
800
600
400
200
0
0
5
11.5
11
10.5
10
9.5
9
8.5
8
-40
10 15 20 25 30 35 40 45 50
-20
0
20
40
60
80
100 120
RT RESISTANCE (k:)
Figure 5.
Figure 6.
Softstart Current
vs
Temperature
Error Amp Input Voltage
vs
temperature
12
1.275
11.5
1.270
1.265
11
1.260
10.5
SMPS BG (V)
SOFTSTART CURRENT (PA)
TEMPERATURE (oC)
10
9.5
1.255
1.250
1.245
1.240
9
1.235
8.5
8
-40
1.230
-20
0
20
40
60
80
1.225
-60 -40 -20
100 120
0
20 40 60 80 100 120 140
TEMPERATURE (oC)
TEMPERATURE (oC)
Figure 7.
Figure 8.
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Typical Performance Characteristics (continued)
VCC
vs
ICC
406
9
404
8
402
7
400
6
VCC (V)
FREQUENCY (kHz)
Oscillator Frequency
vs
Temperature
RT = 15.2 kΩ
398
5
396
4
394
3
392
2
390
-40
1
-20
0
20
40
60
80
0
100 120
5
10
15
20
25
ICC (mA)
TEMPERATURE (oC)
Figure 9.
Figure 10.
Input Current
vs
Input Voltage
UVLO Threshold
vs
Temperature
3
2.05
2.04
2.03
2.02
2
UVLO VTH (V)
INPUT CURRENT (mA)
2.5
1.5
1
2.01
2.00
1.99
1.98
1.97
0.5
1.96
0
0
10
20
30
40
50
60
70
1.95
-60 -40 -20
80
INPUT VOLTAGE (V)
Figure 11.
8
0
20 40 60 80 100 120 140
TEMPERATURE (oC)
Figure 12.
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BLOCK DIAGRAMS
VIN
10 PA
+
VBG
VCC
EN
-
LT20V
1.5V
+
-
UVLO
2V
60V
+
+
-
2V
Power OK
LOCKOUT
LOCAL_EN
OUT
Switch Mode
Power Supply
Controller
UVLORTN
5V
VIN
RT
See
Figure 3
for Detail
+
1.5V
EN
SS
CS
-
COMP
RCLASS
Thermal Limit
RSIG
+
-
10V
+
-
1.5V
FB
ARTN
VIN
+
-
RCLP
Gate
Control
VEE
RTN
Figure 13. Top Level Block Diagram
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
SS
10 PA
SS
COMP
2k
0.5V
+
-
CURRENT
LIMIT
CS
CLK +LEB
Figure 14. PWM Controller Block Diagram
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Detailed Operating Description
The LM5070 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, programmable inrush current limit, thermal limit,
programmable undervoltage lockout, and current limit monitoring. The device also includes a high-voltage startup bias regulator that operates over a wide input range up to 75V. 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, softstart, 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 LM5070 PWM controller provides current-mode control for dc-dc converter topologies requiring a
single drive output, such as Flyback and Forward topologies. The LM5070 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 LM5070 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 shows the LM5070 operating modes and associated input voltage range.
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 20.5V
Classification
23.0V to UVLO Rising Vth
Awaiting Full Power
75V 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 LM5070 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 21.5V. The classification current is turned off once the classification range voltage is exceeded,
to reduce power dissipation. Between 21.5V 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 LM5070 is specified to operate with an input voltage as
high as 75V. 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 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 LM5070 will enable the signature resistor at a controller input voltage of 1.5V to take into account the diode
voltage drops. 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 LM5070 controller once the input voltage
is above the detection range (> 11V).
10
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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 LM5070 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 2 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 then 75ms as per IEEE 802.3af. The LM5070 will
remain in classification mode until VIN is greater than 22V.
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
53.6Ω
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 LM5070 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 bottom resistor should not be tied to VEE because any current from
VIN to VEE will cause the system to violate the 10uA maximum offset current specification during detection mode.
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 LM5070 UVLO thresholds cannot be
programmed lower than 23V, otherwise the device would operate in classification mode with both the
classification current source and the SMPS enabled. The combined power dissipation of these two functions
could exceed the maximum power dissipation of the package.
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.
Power Supply Operation / Current Limit Programming
Once the UVLO threshold has been satisfied, the interface controller of the LM5070 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 375mA. The IEEE 802.3af specification requires that
the load capacitance be charged within 75ms.
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Some legacy PSEs may not be able to supply the IEEE maximum power of 15W to the PD, and this can be a
problem during startup. Low power PDs that are used in these legacy systems will require a lower startup current
limit. The LM5070 can be programmed for a reduced inrush current limit level with a resistor at RCLP pin. The
programmable inrush current limit range is 75mA to 390mA. If the RCLP pin is left open, the LM5070 will default
to 390mA, near the maximum allowed per the IEEE 802.3 specification. To set a desired inrush current limit
(limit), the RCLP resistor can be calculated from:
RCLP =
16000:-A
Ilimit (A)
(1)
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 LM5070.
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 RCLP programmed inrush current limit
only applies to the initial charging phase. The interface power MOSFET current limit will revert to the fixed 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 LM5070 contains an internal high voltage startup regulator that allows the input pin (VIN) to be connected
directly to line voltages as high as 75V. 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 V CC 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 LM5070 package.
Error Amplifier
An internal high gain error amplifier is provided within the LM5070. 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 LM5070 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.
12
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The LM5070 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).
Oscillator, Shutdown and Sync Capability
A single external resistor connected between the RT and ARTN pins sets the LM5070 oscillator frequency.
Internal to the LM5070–50 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 LM5070–80 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:
LM5070-80:
RT =
1
F x 165 x 10-12
(2)
LM5070-50:
RT =
1
F x 330 x 10-12
(3)
The LM5070 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 LM5070-80 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 LM5070-50 is not capable of duty cycles
greater than 50%, there is no slope compensation feature in this device.
Softstart
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.
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Gate Driver and Maximum Duty Cycle Limit
The LM5070 provides an internal gate driver (OUT), which can source and sink a peak current of 800mA. The
LM5070 is available in two duty cycle limit options. The maximum output duty cycle is typically 80% for the
LM5070-80 option and precisely equal to 50% for the LM5070-50 option. The maximum duty cycle function for
the LM5070-50 is accomplished with an internal toggle flip-flop which ensures an accurate duty cycle limit. The
internal oscillator frequency of the LM5070-50 is therefore twice the operating frequency of the PWM controller
(OUT pin).
The 80% maximum duty cycle limit of the LM5070-80 is determined by the internal oscillator and varies more
than the 50% limit of the LM5070-50. For the LM5070-80, the internal oscillator frequency and the operational
frequency of the PWM controller are equal.
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.
14
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LM5070 Application Circuit – Isolated Output with Diode Rectification
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LM5070 Application Circuit – Isolated Output with Synchronous Rectification
16
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SNVS308G – OCTOBER 2004 – REVISED APRIL 2013
REVISION HISTORY
Changes from Revision F (April 2013) to Revision G
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 16
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM5070MTC-50/NOPB
ACTIVE
TSSOP
PW
16
92
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
5070M
TC-50
LM5070MTC-80/NOPB
ACTIVE
TSSOP
PW
16
92
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
5070M
TC-80
LM5070MTCX-50/NOPB
ACTIVE
TSSOP
PW
16
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
5070M
TC-50
LM5070MTCX-80/NOPB
ACTIVE
TSSOP
PW
16
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
5070M
TC-80
LM5070SD-50/NOPB
ACTIVE
WSON
NHQ
16
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
L00051B
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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