SNVS449O June   2007  – April 2015 LM3668

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Buck Operation
      2. 8.3.2 Boost Operation
      3. 8.3.3 Internal Synchronous Rectification
      4. 8.3.4 Current Limit Protection
      5. 8.3.5 Undervoltage Protection
      6. 8.3.6 Short Circuit Protection
      7. 8.3.7 Shutdown
      8. 8.3.8 Thermal Shutdown
      9. 8.3.9 Start-Up
    4. 8.4 Device Functional Modes
      1. 8.4.1 PWM Operation
      2. 8.4.2 PFM Operation
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 MODE/SYNC Pin
      2. 9.1.2 VSEL Pin
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Maximum Current
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Inductor Selection
        2. 9.2.2.2 Input Capacitor Selection
        3. 9.2.2.3 Output Capacitor Selection
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
      2. 12.1.2 Documentation Support
        1. 12.1.2.1 Related Documentation
    2. 12.2 Trademarks
    3. 12.3 Electrostatic Discharge Caution
    4. 12.4 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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7 Specifications

7.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN MAX UNIT
PVIN, VDD, SW1, SW2 & VOUT pins: voltage to SGND & PGND –0.2 6 V
FB, EN, and MODE/SYNC pins (PGND and SGND-0.2) (PVIN + 0.2) V
PGND to SGND –0.2 0.2 V
Continuous power dissipation(3) Internally Limited
Maximum junction temperature (TJ-MAX) 125 °C
Maximum lead temperature (soldering, 10 sec) 260 °C
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) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications.
(3) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125ºC), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).

7.2 ESD Ratings

VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2500 V
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) ±1250
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

7.3 Recommended Operating Conditions

MIN MAX UNIT
Input voltage 2.5 5.5 V
Recommended load current 0 1 A
Junction temperature (TJ) −40 125 °C
Ambient temperature (TA) (1) −40 85 °C
(1) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125ºC), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).

7.4 Thermal Information

THERMAL METRIC(1) LM3668 UNIT
DQB (WSON)
12 PINS
RθJA Junction-to-ambient thermal resistance, WSON package(2) 47.3 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 43..4
RθJB Junction-to-board thermal resistance 21.6
ψJT Junction-to-top characterization parameter 0.4
ψJB Junction-to-board characterization parameter 21.7
RθJC(bot) Junction-to-case (bottom) thermal resistance 3.5
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
(2) Junction-to-ambient thermal resistance (RθJA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 101.6 mm x 76.2 mm x 1.6 mm. Thickness of the copper layers are 2oz/1oz/1oz/2oz. The middle layer of the board is 60 mm x 60 mm. Ambient temperature in simulation is 22°C, still air. Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design.

7.5 Electrical Characteristics

Unless otherwise noted, specifications apply to the LM3668. VIN = 3.6 V = EN, VOUT = 3.3 V. For VOUT = 4.5V-5 V, VIN = 4 V.(1)(2)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VFB Feedback voltage −40°C ≤ TA ≤ 85°C, see(2) –3% 3%
ILIM Switch peak current limit Open loop(3) 1.85 A
Switch peak current limit Open loop(3), −40°C ≤ TA ≤ 85°C 1.6 2.05
ISHDN Shutdown supply current EN = 0 V 0.01 µA
Shutdown supply current EN = 0 V, −40°C ≤ TA ≤ 85°C 1
IQ_PFM DC bias current in PFM No load, device is not switching (FB forced higher than programmed output voltage) 45 µA
DC bias current in PFM No load, device is not switching (FB forced higher than programmed output voltage)
−40°C ≤ TA ≤ 85°C		 60
IQ_PWM DC bias current in PWM PWM mode, no switching 600 µA
DC bias current in PWM PWM mode, no switching
−40°C ≤ TA ≤ 85°C		 750
RDSON(P) Pin-pin resistance for PFET Switches P1 and P2 130 180 mΩ
RDSON(N) Pin-pin resistance for NFET Switches N1 and N2 100 150 mΩ
FOSC Internal oscillator frequency PWM mode 2.2 MHz
PWM mode, −40°C ≤ TA ≤ 85°C 1.9 2.5
FSYNC Sync frequency range VIN = 3.6 V 1.6 2.7 MHz
VIH Logic high input for EN, MODE/SYNC pins −40°C ≤ TA ≤ 85°C 1.1 V
VIL Logic low input for EN, MODE/SYNC pins −40°C ≤ TA ≤ 85°C 0.4 V
IEN, MODE, SYNC EN, MODE/SYNC pins input current 0.3 µA
−40°C ≤ TA ≤ 85°C 1
(1) All voltages with respect to SGND.
(2) Minimum and Maximum limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely norm.
(3) Electrical Characteristics table reflects open loop data (FB = 0 V and current drawn from SW pin ramped up until cycle-by-cycle current limits is activated). Closed loop current limit is the peak inductor current measured in the application circuit by increasing output current until output voltage drops by 10%.
(4) CIN and COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics. COUT_MIN should not exceed −40% of suggested value. The preferable choice would be a type and make MLCC that issues –30% over the operating temperature and voltage range.

7.6 Typical Characteristics

Typical Application Circuit (see Figure 46): VIN = 3.6 V, L = 2.2 µH, CIN = 10 µF, COUT = 22 µF(4), TA = 25°C , unless otherwise stated.
LM3668 20191484.gifFigure 1. Supply Current vs Temperature (Not Switching)
(VOUT = 3.4 V)
LM3668 20191481.gifFigure 3. NFET_RDS (on) vs. Temperature (VOUT = 3.4 V)
LM3668 20191480.gifFigure 5. ILIMIT vs. Temperature (VOUT = 3.4 V)
LM3668 20191428.gifFigure 7. Efficiency at VOUT = 2.8 V (Auto Mode)
LM3668 20191417.pngFigure 9. Efficiency at VOUT = 3 V (Auto Mode)
LM3668 20191476.gifFigure 11. Efficiency at VOUT = 3.3 V (Auto Mode)
LM3668 20191478.gifFigure 13. Efficiency at VOUT = 3.4 V (Auto Mode)
LM3668 20191474.gifFigure 15. Efficiency at VOUT = 4.5 V (Auto Mode)
LM3668 20191470.gifFigure 17. Efficiency at VOUT = 5 V (Auto Mode)
LM3668 20191451.gifFigure 19. Line Transient in Boost Mode (VOUT = 3.4 V, Load = 500 mA)
LM3668 20191453.gifFigure 21. Load Transient in Buck Mode (Forced PWM Mode) VIN = 4.2 V, VOUT = 3.4 V, Load = 0 to 500 mA
LM3668 20191455.pngFigure 23. Load Transient in Buck-Boost Operation (Forced PWM Mode) VIN = 3.44 V, VOUT = 3.4 V, Load = 0 to 500 mA
LM3668 20191457.pngFigure 25. Load Transient in Boost Mode (Forced PWM Mode) VIN = 2.7 V, VOUT = 3 V, Load = 0 to 500 mA
LM3668 20191436.pngFigure 27. Load Transient in Buck Mode (Auto Mode) VIN = 4.2 V, VOUT = 3.3 V, Load = 50 to 150 mA
LM3668 20191435.pngFigure 29. Load Transient in Buck-Boost Mode (Auto Mode) VIN = 3.6 V, VOUT = 3.3 V, Load = 50-150 mA
LM3668 20191460.pngFigure 31. Load Transient in Boost Mode (Forced PWM Mode) VIN = 3.5 V, VOUT = 5 V, Load = 0 to 500 mA
LM3668 20191462.pngFigure 33. Typical Switching Waveform in Buck Mode (PWM Mode) VIN = 3.6 V, VOUT = 3 V, Load = 500 mA
LM3668 20191464.gifFigure 35. Typical Switching Waveform in Buck Mode (PFM Mode) VIN = 3.6 V, VOUT = 3 V, Load = 50mA
LM3668 20191466.pngFigure 37. Typical Switching Waveform in Buck Mode (PWM Mode) VIN = 4 V, VOUT = 3.4 V, Load = 500 mA
LM3668 20191468.gifFigure 39. Typical Switching Waveform in Buck Mode (PFM Mode) VIN = 4 V, VOUT = 3.4 V, Load = 50 mA
LM3668 20191482.gifFigure 2. Switching Frequency vs. Temperature
(VOUT = 3.4 V)
LM3668 20191483.gifFigure 4. PFET_RDS (on) vs. Temperature (VOUT = 3.4 V)
LM3668 20191427.gifFigure 6. Efficiency at VOUT = 2.8 V (Forced PWM Mode)
LM3668 20191473.gifFigure 8. Efficiency at VOUT = 3 V (Forced PWM Mode)
LM3668 20191477.gifFigure 10. Efficiency at VOUT = 3.3 V (Forced PWM Mode)
LM3668 20191479.gifFigure 12. Efficiency at VOUT = 3.4 V (Forced PWM Mode)
LM3668 20191475.gifFigure 14. Efficiency at VOUT = 4.5 V (Forced PWM Mode)
LM3668 20191471.gifFigure 16. Efficiency at VOUT = 5 V (Forced PWM Mode)
LM3668 20191431.gifFigure 18. Line Transient in Buck Mode (VOUT = 3.4 V, Load = 500 mA)
LM3668 20191452.gifFigure 20. Line Transient in Buck-Boost Mode (VOUT = 3.4 V, Load = 500 mA)
LM3668 20191454.gifFigure 22. Load Transient in Boost Operation (Forced PWM Mode) VIN = 2.7 V, VOUT = 3.4 V, Load = 0 to 500 mA
LM3668 20191456.pngFigure 24. Load Transient in Buck Mode (Forced PWM Mode) VIN = 4.2 V, VOUT = 3 V, Load = 0 to 500 mA
LM3668 20191458.pngFigure 26. Load Transient in Buck-Boost Mode (Forced PWM Mode) VIN = 3.05 V, VOUT = 3 V, Load = 0 to 500 mA
LM3668 20191434.pngFigure 28. Load Transient in Boost Mode (Auto Mode) VIN = 2.7 V, VOUT = 3.3 V, Load = 50 to 150 mA
LM3668 20191459.pngFigure 30. Load Transient in Buck Mode (Forced PWM Mode) VIN = 5.5 V, VOUT = 5 V, Load = 0 to 500 mA
LM3668 20191461.pngFigure 32. Typical Switching Waveform in Boost Mode (PWM Mode) VIN = 2.7 V, VOUT = 3 V, Load = 500 mA
LM3668 20191463.gifFigure 34. Typical Switching Waveformt in Boost Mode (PFM Mode) VIN = 2.7 V, VOUT = 3 V, Load = 50 mA
LM3668 20191465.gifFigure 36. Typical Switching Waveform in Boost Mode (PWM Mode) VIN = 3 V, VOUT = 3.4 V, Load = 500 mA
LM3668 20191467.gifFigure 38. Typical Switching Waveform in Boost Mode (PFM Mode) VIN = 3 V, VOUT = 3.4 V, Load = 50 mA