SNVS217G May   2004  – September 2015 LM2731

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
      1. 7.1.1 Theory of Operation
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Pin Operation
      2. 7.4.2 Thermal Shutdown
      3. 7.4.3 Current Limit
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Selecting the External Capacitors
        2. 8.2.2.2  Selecting the Output Capacitor
        3. 8.2.2.3  Selecting the Input Capacitor
        4. 8.2.2.4  Feedforward Compensation
        5. 8.2.2.5  Selecting Diodes
        6. 8.2.2.6  Setting the Output Voltage
        7. 8.2.2.7  Switching Frequency
        8. 8.2.2.8  Duty Cycle
        9. 8.2.2.9  Inductance Value
        10. 8.2.2.10 Maximum Switch Current
        11. 8.2.2.11 Calculating Load Current
        12. 8.2.2.12 Design Parameters VSW and ISW
        13. 8.2.2.13 Inductor Suppliers
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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6 Specifications

6.1 Absolute Maximum Ratings(1)

MIN MAX UNIT
Operating Junction Temperature –40 125 °C
Lead Temperature (Soldering, 5 sec.) 300 °C
Power Dissipation(2) Internally Limited
FB Pin Voltage –0.4 6 V
SW Pin Voltage –0.4 22 V
Input Supply Voltage –0.4 14.5 V
SHDN Pin Voltage –0.4 VIN + 0.3 V
Storage Temperature, Tstg –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) The maximum power dissipation which can be safely dissipated for any application is a function of the maximum junction temperature, TJ(MAX) = 125°C, the junction-to-ambient thermal resistance for the SOT-23 package, RθJA = 265°C/W, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature for designs using this device can be calculated using the formula: LM2731 20059123.gif. If power dissipation exceeds the maximum specified above, the internal thermal protection circuitry will protect the device by reducing the output voltage as required to maintain a safe junction temperature.

6.2 ESD Ratings

VALUE UNIT
V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(2) ±2000 V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) The human body model is a 100-pF capacitor discharged through a 1.5-kΩ resistor into each pin.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)
MIN NOM MAX UNIT
VIN Input Supply Voltage 2.7 14 V
Vsw SW Pin Voltage 3 20 V
Vshdn Shutdown Supply Voltage(1) 0 VIN V
TJ Junction Temperature Range –40 125 ºC
(1) This pin should not be allowed to float or be greater than VIN + 0.3 V.

6.4 Thermal Information

THERMAL METRIC(1) LM2731 UNIT
DBV (SOT-23)
5 PINS
RθJA Junction-to-ambient thermal resistance 209.9 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 122 °C/W
RθJB Junction-to-board thermal resistance 38.4 °C/W
ψJT Junction-to-top characterization parameter 12.8 °C/W
ψJB Junction-to-board characterization parameter 37.5 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance N/A °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report, SPRA953.

6.5 Electrical Characteristics

Limits are for TJ = 25°C. Unless otherwise specified: VIN = 5 V, VSHDN = 5 V, IL = 0 A.
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
VIN Input Voltage −40°C ≤ TJ ≤ 125°C 2.7 14 V
VOUT (MIN) Minimum Output Voltage Under Load RL = 43 Ω
X Option(5)		 VIN = 2.7 V 7 V
−40°C ≤ TJ ≤ 125°C 5.4
VIN = 3.3 V 10
−40°C ≤ TJ ≤ 125°C 8
VIN = 5 V 16
RL = 43 Ω
Y Option(5)		 VIN = 2.7 V 7.5
−40°C ≤ TJ ≤ 125°C 6
VIN = 3.3 V 11
−40°C ≤ TJ ≤ 125°C 8.75
VIN = 5 V 15
RL = 15 Ω
X Option(5)		 VIN = 2.7 V 5
−40°C ≤ TJ ≤ 125°C 3.75
VIN = 3.3 V 6.5
−40°C ≤ TJ ≤ 125°C 5
VIN = 5 V 10
RL = 15 Ω
Y Option(5)		 VIN = 2.7 V 5
−40°C ≤ TJ ≤ 125°C 4
VIN = 3.3 V 7
−40°C ≤ TJ ≤ 125°C 5.5
VIN = 5 V 10
ISW Switch Current Limit See(3) TJ = 25°C 1.8 2 A
−40°C ≤ TJ ≤ 125°C 1.4
RDS(ON) Switch ON-Resistance ISW = 100 mA
Vin = 5 V		 TJ = 25°C 260 400 mΩ
−40°C ≤ TJ ≤ 125°C 500
ISW = 100 mA
Vin = 3.3 V		 TJ = 25°C 300 450
−40°C ≤ TJ ≤ 125°C 550
SHDNTH Shutdown Threshold Device ON −40°C ≤ TJ ≤ 125°C 1.5 V
Device OFF −40°C ≤ TJ ≤ 125°C 0.5
ISHDN Shutdown Pin Bias Current VSHDN = 0 0 µA
VSHDN = 5 V TJ = 25°C 0
−40°C ≤ TJ ≤ 125°C 2
VFB Feedback Pin Reference Voltage VIN = 3 V TJ = 25°C 1.230 V
−40°C ≤ TJ ≤ 125°C 1.205 1.255
IFB Feedback Pin Bias Current VFB = 1.23 V TJ = 25°C 60 nA
−40°C ≤ TJ ≤ 125°C 500
IQ Quiescent Current VSHDN = 5 V, Switching "X" TJ = 25°C 2 mA
−40°C ≤ TJ ≤ 125°C 3
VSHDN = 5 V, Switching "Y" TJ = 25°C 1
−40°C ≤ TJ ≤ 125°C 2
VSHDN = 5 V, Not Switching TJ = 25°C 400 µA
−40°C ≤ TJ ≤ 125°C 500
VSHDN = 0 0.024 1
ΔVFB/ΔVIN FB Voltage Line Regulation 2.7 V ≤ VIN ≤ 14 V 0.02 %/V
FSW Switching Frequency(4) “X” Option TJ = 25°C 1.6 MHz
−40°C ≤ TJ ≤ 125°C 1 1.85
“Y” Option TJ = 25°C 0.6
−40°C ≤ TJ ≤ 125°C 0.4 0.8
DMAX Maximum Duty Cycle(4) “X” Option TJ = 25°C 86%
−40°C ≤ TJ ≤ 125°C 78%
“Y” Option TJ = 25°C 93%
−40°C ≤ TJ ≤ 125°C 88%
IL Switch Leakage Not Switching VSW = 5 V 1 µA
(1) Limits are ensured by testing, statistical correlation, or design.
(2) Typical values are derived from the mean value of a large quantity of samples tested during characterization and represent the most likely expected value of the parameter at room temperature.
(3) Switch current limit is dependent on duty cycle (see Typical Characteristics).
(4) Specified limits are the same for Vin = 3.3 V input.
(5) L = 10 µH, COUT = 4.7 µF, duty cycle = maximum

6.6 Typical Characteristics

Unless otherwise specified: VIN = 5 V, SHDN pin tied to VIN.
LM2731 20059102.gif Figure 1. Iq VIN (Active) vs Temperature - X Option
LM2731 20059105.gif Figure 3. Oscillator Frequency vs Temperature - X Option
LM2731 20059101.gif Figure 5. Maximum Duty Cycle vs Temperature - X Option
LM2731 20059125.gif Figure 7. Iq VIN (Idle) vs Temperature
LM2731 20059127.gif Figure 9. Feedback Voltage vs Temperature
LM2731 20059129.gif Figure 11. Current Limit vs Temperature
LM2731 20059135.gif
VIN = 2.7 V VOUT = 5 V
Figure 13. Efficiency vs Load Current - X Option
LM2731 20059138.gif
VIN = 2.7 V VOUT = 12 V
Figure 15. Efficiency vs Load Current - X Option
LM2731 20059141.gif
VIN = 5 V VOUT = 18 V
Figure 17. Efficiency vs Load Current - X Option
LM2731 20059143.gif
VIN = 3.3 V VOUT = 5 V
Figure 19. Efficiency vs Load Current - Y Option
LM2731 20059145.gif
VIN = 2.7 V VOUT = 12 V
Figure 21. Efficiency vs Load Current - Y Option
LM2731 20059147.gif
VIN = 5 V VOUT = 12 V
Figure 23. Efficiency vs Load Current - Y Option
LM2731 20059104.gif
Figure 2. Iq VIN (Active) vs Temperature - Y Option
LM2731 20059101.gif Figure 4. Oscillator Frequency vs Temperature - Y Option
LM2731 20059106.gif Figure 6. Maximum Duty Cycle vs Temperature - Y Option
LM2731 20059126.gif Figure 8. Feedback Bias Current vs Temperature
LM2731 20059128.gif Figure 10. RDS(ON) vs Temperature
LM2731 20059152.gif Figure 12. RDS(ON) vs VIN
LM2731 20059137.gif
VIN = 4.2 V VOUT = 5 V
Figure 14. Efficiency vs Load Current - X Option
LM2731 20059140.gif
VIN = 5 V VOUT = 12 V
Figure 16. Efficiency vs Load Current - X Option
LM2731 20059142.gif
VIN = 2.7 V VOUT = 5 V
Figure 18. Efficiency vs Load Current - Y Option
LM2731 20059144.gif
VIN = 4.2 V VOUT = 5 V
Figure 20. Efficiency vs Load Current - Y Option
LM2731 20059146.gif
VIN = 3.3 V VOUT = 12 V
Figure 22. Efficiency vs Load Current - Y Option