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LM2585
SNVS120G – APRIL 2000 – REVISED MAY 2019
LM2585 4-V to 40-V, 3-A Step-Up Wide VIN Flyback Converter
1 Features
3 Description
•
•
•
•
•
The LM2585 series of regulators are monolithic
integrated circuits specifically designed for flyback,
step-up (boost), and forward converter applications.
The device is available in 4 different output voltage
versions: 3.3 V, 5 V, 12 V, and adjustable.
1
•
•
•
•
•
Requires Few External Components
Family of Standard Inductors and Transformers
NPN Output Switches 3 A, Can Stand Off 65 V
Wide Input Voltage Range: 4 V to 40 V
Current-mode Operation for Improved Transient
Response, Line Regulation, and Current Limit
100-kHz Switching Frequency
Internal Soft-Start Function Reduces In-rush
Current During Start-up
Output Transistor Protected by Current Limit,
Undervoltage Lockout, and Thermal Shutdown
System Output Voltage Tolerance of ±4%
Maximum Over Line and Load Conditions
Create a Custom Design Using the LM2585 With
the WEBENCH® Power Designer
2 Applications
•
•
•
•
Flyback Regulator
Multiple-output Regulator
Simple Boost Regulator
Forward Converter
Requiring a minimum number of external
components, these regulators are cost effective and
simple to use. Included in the datasheet are typical
circuits of boost and flyback regulators. Also listed
are selector guides for diodes and capacitors and a
family of standard inductors and flyback transformers
designed to work with these switching regulators.
The power switch is a 3-A NPN device that can stand
off 65 V. Protecting the power switch are current and
thermal limiting circuits, and an undervoltage lockout
circuit. This IC contains a 100-kHz fixed-frequency
internal oscillator that permits the use of small
magnetics. Other features include soft start mode to
reduce in-rush current during start-up, current mode
control for improved rejection of input voltage and
output load transients and cycle-by-cycle current
limiting. An output voltage tolerance of ±4%, within
specified input voltages and output load conditions, is
specified for the power supply system.
Device Information(1)
PART NUMBER PACKAGE
LM2585
BODY SIZE (NOM)
DDPAK/ TO-263 (5) 10.16 mm × 8.42 mm
TO-220 (5)
14.986 mm × 10.16 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
12-V Flyback Regulator Design Example
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM2585
SNVS120G – APRIL 2000 – REVISED MAY 2019
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configurations.................................................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
4
4
4
5
5
6
6
7
8
9
Absolute Maximum Ratings .....................................
ESD Ratings..............................................................
Recommended Operating Ratings............................
Thermal Information ..................................................
Electrical Characteristics: 3.3 V ...............................
Electrical Characteristics: 5 V ..................................
Electrical Characteristics: 12-V ................................
Electrical Characteristics: Adjustable ........................
Electrical Characteristics: All Versions .....................
Typical Characteristics ............................................
Detailed Description ............................................ 11
7.1 Overview ................................................................. 11
7.2 Functional Block Diagram ....................................... 13
7.3 Feature Description................................................. 13
8
Application and Implementation ........................ 15
8.1 Application Information............................................ 15
8.2 Typical Applications ................................................ 15
8.3 Additional Application Examples............................. 27
9
Layout ................................................................... 29
9.1 Layout Guidelines ................................................... 29
9.2 Heat Sink/Thermal Considerations ......................... 29
10 Device and Documentation Support ................. 31
10.1
10.2
10.3
10.4
10.5
10.6
Device Support......................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
31
31
31
31
31
32
11 Mechanical, Packaging, and Orderable
Information ........................................................... 32
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision F (April 2013) to Revision G
•
Editorial changes only, no technical revisions; add links for WEBENCH .............................................................................. 1
Changes from Revision E (April 2013) to Revision F
•
2
Page
Page
Changed layout of National Semiconductor data sheet to TI format.................................................................................... 30
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5 Pin Configurations
NDH Package
5-Pin TO-220
Top View
KTT Package
5-Pin DDPAK/TO-263
Top View
NDH Package
5-Pin TO-220
Side View
KTT Package
5-Pin DDPAK/TO-263
Side View
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2)
−0.4 V ≤ VIN ≤ 45 V
Input Voltage
−0.4 V ≤ VSW ≤ 65 V
Switch Voltage
Switch Current
(3)
Internally Limited
−0.4 V ≤ VCOMP ≤ 2.4 V
Compensation Pin Voltage
−0.4 V ≤ VFB ≤ 2 V
Feedback Pin Voltage
−65°C to +150°C
Storage Temperature Range
Lead Temperature
(Soldering, 10 sec.)
260°C
Maximum Junction Temperature (4)
Power Dissipation
(1)
(2)
(3)
(4)
150°C
(4)
Internally Limited
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions the
device is intended to be functional, but device parameter specifications may not be specified under these conditions. For specifications
and test conditions see Electrical Characteristics: All Versions .
If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Note that switch current and output current are not identical in a step-up regulator. Output current cannot be internally limited when the
LM2585 is used as a step-up regulator. To prevent damage to the switch, the output current must be externally limited to 3 A. However,
output current is internally limited when the LM2585 is used as a flyback regulator (see Typical Flyback Regulator Applications for more
information).
The junction temperature of the device (TJ) is a function of the ambient temperature (TA), the junction-to-ambient thermal resistance
(θJA), and the power dissipation of the device (PD). A thermal shutdown will occur if the temperature exceeds the maximum junction
temperature of the device: PD × θJA + TA(MAX) ≥ TJ(MAX). For a safe thermal design, check that the maximum power dissipated by the
device is less than: PD ≤ [TJ(MAX) − TA(MAX))]/θJA. When calculating the maximum allowable power dissipation, derate the maximum
junction temperature—this ensures a margin of safety in the thermal design.
6.2 ESD Ratings
V(ESD)
(1)
Electrostatic discharge
(minimum)
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
(C = 100 pF, R = 1.5 kΩ)
VALUE
UNIT
2000
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Ratings
4 V ≤ VIN ≤ 40 V
Supply Voltage
Output Switch Voltage
0 V ≤ VSW ≤ 60 V
Output Switch Current
ISW ≤ 3 A
−40°C ≤ TJ ≤ +125°C
Junction Temperature Range
4
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6.4 Thermal Information
LM2585
THERMAL METRIC (1)
RθJA
RθJC
(1)
(2)
(3)
(4)
(5)
(6)
KTT (DDPAK/TO-263
NDH (TO-220)
5 PINS
5 PINS
56 (2)
65 (3)
35
(4)
45 (5)
26
(6)
—
Junction-to-ambient thermal resistance
Junction-to-case thermal resistance
2
2
UNIT
°C/W
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC package thermal metrics application
report.
Junction-to-ambient thermal resistance for the 5-lead TO-263 mounted horizontally against a PC board area of 0.136 square inches (the
same size as the DDPAK/TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Junction-to-ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with ½ inch leads in a
socket, or on a PC board with minimum copper area.
Junction-to-ambient thermal resistance for the 5-lead TO-263 mounted horizontally against a PC board area of 0.4896 square inches
(3.6 times the area of the DDPAK/TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Junction-to-ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with ½ inch leads
soldered to a PC board containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.
Junction-to-ambient thermal resistance for the 5-lead TO-263 mounted horizontally against a PC board copper area of 1.0064 square
inches (7.4 times the area of the DDPAK/TO-2633 package) of 1 oz. (0.0014 in. thick) copper. Additional copper area reduces thermal
resistance further.
6.5 Electrical Characteristics: 3.3 V
Specifications with standard type face are for TJ = 25°C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, VIN = 5V.
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS Test Circuit of Figure 47
VOUT
Output Voltage
TYP
MIN
MAX
UNIT
3.3
3.17/3.14
3.43/3.46
V
20
50/100
mV
20
50/100
mV
3.358/3.366
V
(1)
VIN = 4V to 12V
ILOAD = 0.3A to 1.2A
ΔVOUT/
Line Regulation
VIN = 4V to 12V
ILOAD = 0.3A
ΔVIN
ΔVOUT/
Load Regulation
VIN = 12V
ILOAD = 0.3A to 1.2A
ΔILOAD
Efficiency
η
UNIQUE DEVICE PARAMETERS
VREF
ΔVREF
VIN = 5V, ILOAD = 0.3A
76%
(2)
Output Reference
Measured at Feedback Pin
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
3.3
3.242/3.234
2.0
mV
Line Regulation
GM
AVOL
(1)
(2)
(3)
Error Amp
ICOMP = −30 μA to +30 μA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ
1.193
0.678
260
151/75
2.259
mmho
V/V
(3)
External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the
LM2585 is used as shown in Figure 47 and Figure 48, system performance will be as specified by the system parameters.
All room temperature limits are 100% production tested, and all limits at temperature extremes are specified via correlation using
standard Statistical Quality Control (SQC) methods.
A 1-MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuring AVOL.
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6.6 Electrical Characteristics: 5 V
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS Test Circuit of Figure 47
VOUT
Output Voltage
TYP
MIN
MAX
UNIT
5.0
4.80/4.75
5.20/5.25
V
20
50/100
mV
20
50/100
mV
(1)
VIN = 4V to 12V
ILOAD = 0.3A to 1.1A
ΔVOUT/
Line Regulation
VIN = 4V to 12V
ILOAD = 0.3A
ΔVIN
ΔVOUT/
Load Regulation
VIN = 12V
ILOAD = 0.3A to 1.1A
ΔILOAD
Efficiency
η
VIN = 12V, ILOAD = 0.6A
80
Output Reference
Measured at Feedback Pin
5.0
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
UNIQUE DEVICE PARAMETERS
VREF
ΔVREF
%
(2)
4.913/4.900
5.088/5.100
3.3
V
mV
Line Regulation
GM
AVOL
Error Amp
ICOMP = −30 μA to +30 μA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
(1)
(2)
(3)
RCOMP = 1.0 MΩ
0.750
0.447
165
99/49
1.491
mmho
V/V
(3)
External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the
LM2585 is used as shown in Figure 47 and Figure 48, system performance will be as specified by the system parameters.
All room temperature limits are 100% production tested, and all limits at temperature extremes are specified via correlation using
standard Statistical Quality Control (SQC) methods.
A 1-MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuring AVOL.
6.7 Electrical Characteristics: 12-V
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS Test Circuit of Figure 48
VOUT
Output Voltage
ΔVOUT/
Line Regulation
TYP
MIN
MAX
UNIT
12.0
11.52/11.40
12.48/12.60
V
20
100/200
mV
20
100/200
mV
12.21/12.24
V
(1)
VIN = 4V to 10V
ILOAD = 0.2A to 0.8A
VIN = 4V to 10V
ILOAD = 0.2A
ΔVIN
ΔVOUT/
Load Regulation
VIN = 10V
ILOAD = 0.2A to 0.8A
ΔILOAD
Efficiency
η
VIN = 10V, ILOAD = 0.6A
93%
Output Reference
Measured at Feedback Pin
12.0
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
UNIQUE DEVICE PARAMETERS
VREF
ΔVREF
(2)
11.79/11.76
7.8
mV
Line Regulation
GM
AVOL
(1)
(2)
(3)
6
Error Amp
ICOMP = −30 μA to +30 μA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ
0.328
0.186
70
41/21
0.621
mmho
V/V
(3)
External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the
LM2585 is used as shown in Figure 47 and Figure 48, system performance will be as specified by the system parameters.
All room temperature limits are 100% production tested, and all limits at temperature extremes are specified via correlation using
standard Statistical Quality Control (SQC) methods.
A 1-MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuring AVOL.
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6.8 Electrical Characteristics: Adjustable
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS Test Circuit of Figure 48
VOUT
Output Voltage
TYP
MIN
MAX
UNIT
12.0
11.52/11.40
12.48/12.60
V
20
100/200
mV
20
100/200
mV
1.252/1.255
V
(1)
VIN = 4V to 10V
ILOAD = 0.2A to 0.8A
ΔVOUT/
Line Regulation
VIN = 4V to 10V
ILOAD = 0.2A
ΔVIN
ΔVOUT/
Load Regulation
VIN = 10V
ILOAD = 0.2A to 0.8A
ΔILOAD
Efficiency
η
VIN = 10V, ILOAD = 0.6A
93%
Output Reference
Measured at Feedback Pin
1.230
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
UNIQUE DEVICE PARAMETERS
VREF
ΔVREF
(2)
1.208/1.205
1.5
mV
Line Regulation
GM
AVOL
IB
Error Amp
ICOMP = −30 μA to +30 μA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ
Error Amp
VCOMP = 1.0V
3.200
1.800
670
400/200
6.000
mmho
V/V
(3)
125
425/600
nA
Input Bias Current
(1)
(2)
(3)
External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the
LM2585 is used as shown in Figure 47 and Figure 48, system performance will be as specified by the system parameters.
All room temperature limits are 100% production tested, and all limits at temperature extremes are specified via correlation using
standard Statistical Quality Control (SQC) methods.
A 1-MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuring AVOL.
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6.9 Electrical Characteristics: All Versions
PARAMETER
TEST CONDITIONS
COMMON DEVICE PARAMETERS for all versions
IS
Input Supply Current
TYP
MIN
MAX
UNIT
(1)
(Switch Off) (2)
11
15.5/16.5
mA
ISWITCH = 1.8A
50
100/115
mA
3.30
3.05
3.75
V
100
85/75
115/125
kHz
VUV
Input Supply
Undervoltage Lockout
RLOAD = 100Ω
fO
Oscillator Frequency
Measured at Switch Pin
RLOAD = 100Ω
VCOMP = 1.0V
fSC
Short-Circuit
Frequency
Measured at Switch Pin
RLOAD = 100Ω
25
kHz
VFEEDBACK = 1.15V
VEAO
Error Amplifier
Output Swing
Upper Limit (3)
2.8
Lower Limit (2)
0.25
(4)
IEAO
Error Amp
Output Current
(Source or Sink)
See
ISS
Soft Start Current
VFEEDBACK = 0.92V
2.6/2.4
V
0.40/0.55
V
165
110/70
260/320
μA
11.0
8.0/7.0
17.0/19.0
μA
93/90
VCOMP = 1.0V
D
Maximum Duty
Cycle
RLOAD = 100Ω (3)
98
IL
Switch Leakage
Current
Switch Off
15
VSUS
Switch Sustaining
Voltage
dV/dT = 1.5V/ns
VSAT
Switch Saturation
Voltage
ISWITCH = 3.0A
ICL
NPN Switch
Current Limit
(1)
(2)
(3)
(4)
8
%
300/600
μA
VSWITCH = 60V
65
0.45
4
3
V
0.65/0.9
V
7.0
A
All room temperature limits are 100% production tested, and all limits at temperature extremes are specified via correlation using
standard Statistical Quality Control (SQC) methods.
To measure this parameter, the feedback voltage is set to a high value, depending on the output version of the device, to force the error
amplifier output low. Adj: VFB = 1.41 V; 3.3 V: VFB = 3.8 V; 5 V: VFB = 5.75 V; 12 V: VFB = 13.8 V.
To measure this parameter, the feedback voltage is set to a low value, depending on the output version of the device, to force the error
amplifier output high. Adj: VFB = 1.05 V; 3.3 V: VFB = 2.81 V; 5 V: VFB = 4.25 V; 12 V: VFB = 10.2 V.
To measure the worst-case error amplifier output current, the LM2585 is tested with the feedback voltage set to its low value (specified
in Tablenote 3) and at its high value (specified in Tablenote 2).
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6.10 Typical Characteristics
Figure 1. Supply Current vs Temperature
Figure 2. Reference Voltage vs Temperature
Figure 3. ΔReference Voltage vs Supply Voltage
Figure 4. Current Limit vs Temperature
Figure 5. Feedback Pin Bias Current vs Temperature
Figure 6. Switch Saturation Voltage vs Temperature
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Typical Characteristics (continued)
Figure 7. Switch Transconductance vs Temperature
Figure 8. Oscillator Frequency vs Temperature
Figure 9. Error Amp Transconductance vs Temperature
Figure 10. Error Amp Voltage Gain vs Temperature
Figure 11. Short Circuit Frequency vs Temperature
10
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7 Detailed Description
7.1 Overview
The LM2585 is ideally suited for use in the flyback regulator topology. The flyback regulator can produce a single
output voltage, such as the one shown in Figure 12, or multiple output voltages. In Figure 12, the flyback
regulator generates an output voltage that is inside the range of the input voltage. This feature is unique to
flyback regulators and cannot be duplicated with buck or boost regulators.
The operation of a flyback regulator is as follows (refer to Figure 12): when the switch is on, current flows
through the primary winding of the transformer, T1, storing energy in the magnetic field of the transformer. Note
that the primary and secondary windings are out of phase, so no current flows through the secondary when
current flows through the primary. When the switch turns off, the magnetic field collapses, reversing the voltage
polarity of the primary and secondary windings. Now rectifier D1 is forward biased and current flows through it,
releasing the energy stored in the transformer. This produces voltage at the output.
The output voltage is controlled by modulating the peak switch current. This is done by feeding back a portion of
the output voltage to the error amp, which amplifies the difference between the feedback voltage and a 1.23-V
reference. The error amp output voltage is compared to a ramp voltage proportional to the switch current (in
other words, inductor current during the switch on time). The comparator terminates the switch on time when the
two voltages are equal, thereby controlling the peak switch current to maintain a constant output voltage.
Figure 12. 12-V Flyback Regulator Design Example
As shown in Figure 12, the LM2585 can be used as a flyback regulator by using a minimum number of external
components. The switching waveforms of this regulator are shown in Figure 13. Typical characteristics observed
during
the
operation
of
this
circuit
are
shown
in
Figure
14.
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Overview (continued)
A: Switch Voltage, 20 V/div
B: Switch Current, 2 A/div
C: Output Rectifier Current, 2 A/div
D: Output Ripple Voltage, 50 mV/div
AC-Coupled
Horizontal: 2 μs/div
Figure 13. Switching Waveforms
Figure 14. VOUT Load Current Step Response
12
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7.2 Functional Block Diagram
For Fixed Versions
3.3V, R1 = 3.4k, R2 = 2k
5V, R1 = 6.15k, R2 = 2k
12V, R1 = 8.73k, R2 = 1k
For Adj. Version
R1 = Short (0Ω), R2 = Open
7.3 Feature Description
7.3.1 Step-Up (Boost) Regulator Operation
Figure 15 shows the LM2585 used as a step-up (boost) regulator. This is a switching regulator that produces an
output voltage greater than the input supply voltage.
A brief explanation of how the LM2585 boost regulator works is as follows (refer to Figure 15). When the NPN
switch turns on, the inductor current ramps up at the rate of VIN/L, storing energy in the inductor. When the
switch turns off, the lower end of the inductor flies above VIN, discharging its current through diode (D) into the
output capacitor (COUT) at a rate of (VOUT − VIN)/L. Thus, energy stored in the inductor during the switch on time
is transferred to the output during the switch off time. The output voltage is controlled by adjusting the peak
switch current, as described in .
Figure 15. 12-V Boost Regulator
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Feature Description (continued)
By adding a small number of external components (as shown in Figure 15), the LM2585 can be used to produce
a regulated output voltage that is greater than the applied input voltage. The switching waveforms observed
during the operation of this circuit are shown in Figure 16. Typical performance of this regulator is shown in
Figure 17.
A: Switch Voltage, 10 V/div
B: Switch Current, 2 A/div
C: Inductor Current, 2 A/div
D: Output Ripple Voltage,
100 mV/div, AC-Coupled
Horizontal: 2 μs/div
Figure 16. Switching Waveforms
Figure 17. VOUT Response To Load Current Step
14
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8 Application and Implementation
8.1 Application Information
The LM2585 series of regulators are monolithic integrated circuits specifically designed for flyback, step-up
(boost), and forward converter applications. Requiring a minimum number of external components, these
regulators are cost effective and simple to use.
8.2 Typical Applications
8.2.1 Typical Boost Regulator Applications
Figure 18 through Figure 21 show four typical boost applications)—one fixed and three using the adjustable
version of the LM2585. Each drawing contains the part number(s) and manufacturer(s) for every component. For
the fixed 12-V output application, the part numbers and manufacturers' names for the inductor are listed in
Table 3. For applications with different output voltages, refer to the Switchers Made Simple software.
Figure 18. 5-V to 12-V Boost Regulator
Figure 19. 12-V to 24-V Boost Regulator
Figure 20. 24-V to 36-V Boost Regulator
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Typical Applications (continued)
*The LM2585 will require a heat sink in these applications. The size of the heat sink will depend on the maximum
ambient temperature. To calculate the thermal resistance of the IC and the size of the heat sink needed, see Heat
Sink/Thermal Considerations
Figure 21. 24-V to 48-V Boost Regulator
8.2.2 Typical Flyback Regulator Applications
Figure 22 through Figure 27 show six typical flyback applications, varying from single output to triple output. Each
drawing contains the part number(s) and manufacturer(s) for every component except the transformer. For the
transformer part numbers and manufacturers names, the table in Table 1.
Figure 22. Single-Output Flyback Regulator
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Typical Applications (continued)
Figure 23. Single-Output Flyback Regulator
Figure 24. Single-Output Flyback Regulator
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Typical Applications (continued)
Figure 25. Dual-Output Flyback Regulator
Figure 26. Dual-Output Flyback Regulator
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Typical Applications (continued)
Figure 27. Triple-Output Flyback Regulator
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Typical Applications (continued)
8.2.2.1 Transformer Selection (T)
Table 1 lists the standard transformers available for flyback regulator applications. Included in the table are the
turns ratio(s) for each transformer, as well as the output voltages, input voltage ranges, and the maximum load
currents for each circuit.
Table 1. Transformer Selection Table
Applications
Figure 22
Figure 23
Figure 24
Figure 25
Figure 26
Transformers
T7
T7
T7
T6
T6
T5
4V–6V
4V–6V
8V–16V
4V–6V
18V–36V
18V–36V
VOUT1
3.3V
5V
12V
12V
12V
5V
IOUT1 (Max)
1.4A
1A
0.8A
0.15A
0.6A
1.8A
1
1
1
1.2
1.2
0.5
VOUT2
−12V
−12V
12V
IOUT2 (Max)
0.15A
0.6A
0.25A
1.2
1.2
1.15
VIN
N1
N2
Figure 27
VOUT3
−12V
IOUT3 (Max)
0.25A
N3
1.15
Table 2. Transformer Manufacturer Guide
Manufacturers' Part Numbers
Transform
er Type
(1)
(2)
(3)
(4)
Coilcraft
Pulse
Surface Mount
Surface Mount
Coilcraft
(1)
(1)
(2)
Pulse
Renco
Schott
(2)
(3)
(4)
T5
Q4338-B
Q4437-B
PE-68413
—
RL-5532
67140890
T6
Q4339-B
Q4438-B
PE-68414
—
RL-5533
67140900
T7
S6000-A
S6057-A
—
PE-68482
RL-5751
26606
Coilcraft Inc. Phone: (800) 322-2645 www.coilcraft.com
Pulse Engineering Inc. Phone: (619) 674-8100 www.digikey.com
Renco Electronics Inc. Phone: (800) 645-5828 www.cdiweb.com/renco
Schott Corp. Phone: (612) 475-1173 www.schottcorp.com/
8.2.2.2 Transformer Footprints
Figure 28 through Figure 42 show the footprints of each transformer, listed in Table 1.
Figure 28. Coilcraft S6000-A (Top View)
20
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Figure 30. Coilcraft Q4437-B (Top View)
(Surface Mount)
Figure 31. Coilcraft Q4338-B
(Top View)
Figure 32. Coilcraft S6057-A (Top View)
(Surface Mount)
Figure 33. Coilcraft Q4438-B (Top View)
(Surface Mount)
Figure 34. Pulse PE-68482 (Top View)
Figure 35. Pulse Pe-68414 (Top View)
(Surface Mount)
Figure 36. Pulse PE-68413 (Top View)
(Surface Mount)
Figure 37. Renco Rl-5751 (Top View)
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Figure 38. Renco Rl-5533
(Top View)
Figure 39. Renco Rl-5532 (Top View)
Figure 40. Schott 26606 (Top View)
Figure 41. Schott 67140900 (Top View)
Figure 42. Schott 67140890
(Top View)
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8.2.3 Design Requirements
Table 3 contains a table of standard inductors, by part number and corresponding manufacturer, for the fixed
output regulator of Figure 18.
Table 3. Inductor Selection Table
(1)
(2)
(3)
(4)
Coilcraft (1)
Pulse (2)
Renco (3)
Schott (4)
Schott (Surface Mount) (4)
D03316-153
PE-53898
RL-5471-7
67146510
67146540
Coilcraft Inc. Phone: (800) 322-2645 1102 Silver Lake Road, Cary, IL 60013 Fax: (708) 639-1469
Pulse Engineering Inc. Phone: (619) 674-8100 12220 World Trade Drive, San Diego, CA 92128 Fax: (619) 674-8262
Renco Electronics Inc. Phone (800) 645-5828 60 Jeffryn Blvd. East, Deer Park, NY 11729 Fax: (516) 586-5562
Schott Corp. Phone: (612) 475-1173 1000 Parkers Lane Road, Wayzata, MN 55391 Fax: (612) 475-1786
8.2.4 Detailed Design Procedure
8.2.4.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the LM2585 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
• Run electrical simulations to see important waveforms and circuit performance
• Run thermal simulations to understand board thermal performance
• Export customized schematic and layout into popular CAD formats
• Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
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8.2.4.2 Programming Output Voltage (Selecting R1 And R2)
Referring to the adjustable regulator in Figure 50, the output voltage is programmed by the resistors R1 and R2
by the following formula:
VOUT = VREF (1 + R1/R2)
where
•
VREF = 1.23 V
(1)
Resistors R1 and R2 divide the output voltage down so that it can be compared with the 1.23-V internal
reference. With R2 between 1k and 5k, R1 is:
R1 = R2 (VOUT/VREF − 1)
where
•
VREF = 1.23V
(2)
For best temperature coefficient and stability with time, use 1% metal film resistors.
8.2.4.3 Short Circuit Condition
Due to the inherent nature of boost regulators, when the output is shorted (Figure 50), current flows directly from
the input, through the inductor and the diode, to the output, bypassing the switch. The current limit of the switch
does not limit the output current for the entire circuit. To protect the load and prevent damage to the switch, the
current must be externally limited, either by the input supply or at the output with an external current limit circuit.
The external limit should be set to the maximum switch current of the device, which is 3A.
In a flyback regulator application (Figure 43), using the standard transformers, the LM2585 will survive a short
circuit to the main output. When the output voltage drops to 80% of its nominal value, the frequency drops to 25
kHz. With a lower frequency, off times are larger. With the longer off times, the transformer can release all of its
stored energy before the switch turns back on. Hence, the switch turns on initially with zero current at its
collector. In this condition, the switch current limit will limit the peak current, saving the device.
Figure 43. Flyback Regulator
8.2.4.4 Flyback Regulator Input Capacitors
A flyback regulator draws discontinuous pulses of current from the input supply. Therefore, there are two input
capacitors needed in a flyback regulator; one for energy storage and one for filtering (Figure 43). Both are
required due to the inherent operation of a flyback regulator. To keep a stable or constant voltage supply to the
LM2585, a storage capacitor (≥100 μF) is required. If the input source is a rectified DC supply and/or the
application has a wide temperature range, the required rms current rating of the capacitor might be very large.
This means a larger value of capacitance or a higher voltage rating will be needed of the input capacitor. The
storage capacitor will also attenuate noise which may interfere with other circuits connected to the same input
supply voltage.
24
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In addition, a small bypass capacitor is required due to the noise generated by the input current pulses. To
eliminate the noise, insert a 1.0 μF ceramic capacitor between VIN and ground as close as possible to the device.
8.2.4.5 Switch Voltage Limits
In a flyback regulator, the maximum steady-state voltage appearing at the switch, when it is off, is set by the
transformer turns ratio, N, the output voltage, VOUT, and the maximum input voltage, VIN (maximum):
VSW(OFF) = VIN (Max) + (VOUT +VF)/N
where
•
VF is the forward biased voltage of the output diode and is 0.5 V for Schottky diodes and 0.8 V for ultra-fast
recovery diodes (typically).
(3)
In certain circuits, there exists a voltage spike, VLL, superimposed on top of the steady-state voltage (Figure 13,
waveform A). Usually, this voltage spike is caused by the transformer leakage inductance and/or the output
rectifier recovery time. To “clamp” the voltage at the switch from exceeding its maximum value, a transient
suppressor in series with a diode is inserted across the transformer primary (as shown in the circuit on the front
page and other flyback regulator circuits throughout the datasheet). The schematic in Figure 43 shows another
method of clamping the switch voltage. A single voltage transient suppressor (the SA51A) is inserted at the
switch pin. This method clamps the total voltage across the switch, not just the voltage across the primary.
If poor circuit layout techniques are used (see Layout Guidelines), negative voltage transients may appear on the
Switch pin (pin 4). Applying a negative voltage (with respect to the IC's ground) to any monolithic IC pin causes
erratic and unpredictable operation of that IC. This holds true for the LM2585 IC as well. When used in a flyback
regulator, the voltage at the Switch pin (pin 4) can go negative when the switch turns on. The “ringing” voltage at
the switch pin is caused by the output diode capacitance and the transformer leakage inductance forming a
resonant circuit at the secondary(ies). The resonant circuit generates the “ringing” voltage, which gets reflected
back through the transformer to the switch pin. There are two common methods to avoid this problem. One is to
add an RC snubber around the output rectifier(s), as in Figure 43. The values of the resistor and the capacitor
must be chosen so that the voltage at the Switch pin does not drop below −0.4 V. The resistor may range in
value between 10 Ω and 1 kΩ, and the capacitor will vary from 0.001 μF to 0.1 μF. Adding a snubber will
(slightly) reduce the efficiency of the overall circuit.
The other method to reduce or eliminate the “ringing” is to insert a Schottky diode clamp between pins 4 and 3
(ground), also shown in Figure 43. This prevents the voltage at pin 4 from dropping below −0.4 V. The reverse
voltage rating of the diode must be greater than the switch off voltage.
8.2.4.6 Output Voltage Limitations
The maximum output voltage of a boost regulator is the maximum switch voltage minus a diode drop. In a
flyback regulator, the maximum output voltage is determined by the turns ratio, N, and the duty cycle, D, by the
equation:
VOUT ≈ N × VIN × D/(1 − D)
(4)
The duty cycle of a flyback regulator is determined by the following equation:
(5)
Theoretically, the maximum output voltage can be as large as desired—just keep increasing the turns ratio of the
transformer. However, there exists some physical limitations that prevent the turns ratio, and thus the output
voltage, from increasing to infinity. The physical limitations are capacitances and inductances in the LM2585
switch, the output diode(s), and the transformer—such as reverse recovery time of the output diode (mentioned
above).
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Figure 44. Input Line Filter
8.2.4.7 Noisy Input Line Condition
A small, low-pass RC filter should be used at the input pin of the LM2585 if the input voltage has an unusual
large amount of transient noise, such as with an input switch that bounces. The circuit in Figure 44 demonstrates
the layout of the filter, with the capacitor placed from the input pin to ground and the resistor placed between the
input supply and the input pin. Note that the values of RIN and CIN shown in the schematic are good enough for
most applications, but some readjusting might be required for a particular application. If efficiency is a major
concern, replace the resistor with a small inductor (say 10 μH and rated at 100 mA).
8.2.4.8 Stability
All current-mode controlled regulators can suffer from an instability, known as subharmonic oscillation, if they
operate with a duty cycle above 50%. To eliminate subharmonic oscillations, a minimum value of inductance is
required to ensure stability for all boost and flyback regulators. The minimum inductance is given by:
where
•
VSAT is the switch saturation voltage and can be found in the Characteristic Curves.
(6)
Figure 45. Circuit Board Layout
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8.2.5 Application Curve
Figure 46. Supply Current vs Switch Current
8.3 Additional Application Examples
8.3.1 Test Circuits
CIN1—100 μF, 25V Aluminum Electrolytic
CIN2—0.1 μF Ceramic
T—22 μH, 1:1 Schott #67141450
D—1N5820
COUT—680 μF, 16V Aluminum Electrolytic
CC—0.47 μF Ceramic
RC—2k
Figure 47. Lm2585-3.3 And Lm2585-5.0
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Additional Application Examples (continued)
CIN1—100 μF, 25V Aluminum Electrolytic
CIN2—0.1 μF Ceramic
L—15 μH, Renco #RL-5472-5
D—1N5820
COUT—680 μF, 16V Aluminum Electrolytic
CC—0.47 μF Ceramic
RC—2k
For 12V Devices: R1 = Short (0Ω) and R2 = Open
For ADJ Devices: R1 = 48.75k, ±0.1% and R2 = 5.62k, ±1%
Figure 48. Lm2585-12 And Lm2585-Adj
Figure 49. Flyback Regulator
Figure 50. Boost Regulator
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9 Layout
9.1 Layout Guidelines
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring
inductance generate voltage transients which can cause problems. For minimal inductance and ground loops,
keep the length of the leads and traces as short as possible. Use single point grounding or ground plane
construction for best results. Separate the signal grounds from the power grounds (as indicated in Figure 45).
When using the Adjustable version, physically locate the programming resistors as near the regulator IC as
possible, to keep the sensitive feedback wiring short.
9.2 Heat Sink/Thermal Considerations
In many cases, no heat sink is required to keep the LM2585 junction temperature within the allowed operating
range. For each application, to determine whether or not a heat sink will be required, the following must be
identified:
1) Maximum ambient temperature (in the application).
2) Maximum regulator power dissipation (in the application).
3) Maximum allowed junction temperature (125°C for the LM2585). For a safe, conservative design, a
temperature approximately 15°C cooler than the maximum junction temperature should be selected (110°C).
4) LM2585 package thermal resistances θJA and θJC (given in Thermal Information).
Total power dissipated (PD) by the LM2585 can be estimated as follows:
where
•
•
•
•
•
VIN is the minimum input voltage
VOUT is the output voltage
N is the transformer turns ratio
D is the duty cycle
ILOAD is the maximum load current (and ∑ILOAD is the sum of the maximum load currents for multiple-output
flyback regulators)
(7)
The duty cycle is given by:
where
•
•
VF is the forward biased voltage of the diode and is typically 0.5V for Schottky diodes and 0.8V for fast
recovery diodes
VSAT is the switch saturation voltage and can be found in the Characteristic Curves
(8)
When no heat sink is used, the junction temperature rise is:
ΔTJ = PD × θJA.
(9)
Adding the junction temperature rise to the maximum ambient temperature gives the actual operating junction
temperature:
TJ = ΔTJ + TA.
(10)
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Heat Sink/Thermal Considerations (continued)
If the operating junction temperature exceeds the maximum junction temperatue in item 3 above, then a heat
sink is required. When using a heat sink, the junction temperature rise can be determined by the following:
ΔTJ = PD × (θJC + θInterface + θHeat Sink)
(11)
Again, the operating junction temperature will be:
TJ = ΔTJ + TA
(12)
As before, if the maximum junction temperature is exceeded, a larger heat sink is required (one that has a lower
thermal resistance).
Included in the Switchers Made Simple design software is a more precise (non-linear) thermal model that can
be used to determine junction temperature with different input-output parameters or different component values.
It can also calculate the heat sink thermal resistance required to maintain the regulator junction temperature
below the maximum operating temperature.
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10 Device and Documentation Support
10.1 Device Support
10.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
10.1.2 Development Support
10.1.2.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the LM2585 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
• Run electrical simulations to see important waveforms and circuit performance
• Run thermal simulations to understand board thermal performance
• Export customized schematic and layout into popular CAD formats
• Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
10.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
10.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
10.4 Trademarks
E2E is a trademark of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
10.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
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10.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
11 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
www.ti.com
7-Dec-2022
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)
Samples
(4/5)
(6)
LM2585S-12/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-12 P+
Samples
LM2585S-3.3/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-3.3 P+
Samples
LM2585S-5.0/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-5.0 P+
Samples
LM2585S-ADJ
NRND
DDPAK/
TO-263
KTT
5
45
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2585S
-ADJ P+
LM2585S-ADJ/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-ADJ P+
Samples
LM2585SX-12/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-12 P+
Samples
LM2585SX-5.0
NRND
DDPAK/
TO-263
KTT
5
500
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2585S
-5.0 P+
LM2585SX-5.0/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-5.0 P+
Samples
LM2585SX-ADJ/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2585S
-ADJ P+
Samples
LM2585T-12/NOPB
ACTIVE
TO-220
NDH
5
45
RoHS-Exempt
& Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2585T
-12 P+
Samples
LM2585T-3.3/NOPB
ACTIVE
TO-220
NDH
5
45
RoHS-Exempt
& Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2585T
-3.3 P+
Samples
LM2585T-5.0/NOPB
ACTIVE
TO-220
NDH
5
45
RoHS-Exempt
& Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2585T
-5.0 P+
Samples
LM2585T-ADJ
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2585T
-ADJ P+
LM2585T-ADJ/NOPB
ACTIVE
TO-220
NDH
5
45
RoHS-Exempt
& Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2585T
-ADJ P+
(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.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
7-Dec-2022
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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