SNVS682D November   2010  – December 2015 LM3444

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
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Theory of Operation
      2. 7.3.2 Valley-Fill Circuit
      3. 7.3.3 Valley-Fill Operation
      4. 7.3.4 Buck Converter
      5. 7.3.5 Overview Of Constant Off-Time Control
      6. 7.3.6 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Determining Duty-Cycle (D)
      2. 8.1.2  Calculating Off-Time
      3. 8.1.3  Setting the Switching Frequency
      4. 8.1.4  Inductor Selection
      5. 8.1.5  Setting the LED Current
      6. 8.1.6  Valley Fill Capacitors
      7. 8.1.7  Determining the Capacitance Value of the Valley-Fill Capacitors
      8. 8.1.8  Determining Maximum Number of Series Connected LEDs Allowed
      9. 8.1.9  Output Capacitor
      10. 8.1.10 Switching MOSFET
      11. 8.1.11 Recirculating Diode
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  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

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN MAX UNIT
VCC and GATE to GND –0.3 14 V
ISNS to GND –0.3 2.5 V
FILTER and COFF to GND –0.3 7 V
COFF input current 60 mA
Continuous power dissipation(3) Internally limited
TJ Junction temperature 150 °C
Maximum lead temperature (soldering) 260 °C
Tstg Storage temperature –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, contact the Texas Instruments Sales Office/Distributors for availability and specifications.
(3) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 165°C (typical) and disengages at TJ = 145°C (typical).

6.2 ESD Ratings

VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 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.

6.3 Recommended Operating Conditions

MIN MAX UNIT
VCC 8 13 V
TJ Junction temperature –40 125 °C

6.4 Thermal Information

THERMAL METRIC(1) LM3444 UNIT
DGS (VSSOP) D (SOIC)
10 PINS 8 PINS
RθJA Junction-to-ambient thermal resistance 163.8 111.3 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 58.4 58.0 °C/W
RθJB Junction-to-board thermal resistance 83.6 51.1 °C/W
ψJT Junction-to-top characterization parameter 6.1 11.9 °C/W
ψJB Junction-to-board characterization parameter 82.3 51.0 °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

All typical limits are for TJ = 25°C and all maximum and minimum limits apply over the full operating temperature range
(TJ = −40°C to 125°C). Minimum and maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VCC = 12 V.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VCC SUPPLY
IVCC Operating supply current 1.58 2.25 mA
VCC-UVLO Rising threshold 7.4 7.7 V
Falling threshold 6 6.4
Hysterisis 1
COFF
VCOFF Time-out threshold 1.225 1.276 1.327 V
RCOFF Off timer sinking impedance 33 60 Ω
tCOFF Restart timer 180 µs
CURRENT LIMIT
VISNS ISNS limit threshold 1.174 1.269 1.364 V
tISNS Leading edge blanking time 125 ns
Current limit reset delay 180 µs
ISNS limit to GATE delay ISNS = 0 to 1.75-V step 33 ns
CURRENT SENSE COMPARATOR
VFILTER FILTER open circuit voltage 720 750 780 mV
RFILTER FILTER impedance 1.12 MΩ
VOS Current sense comparator offset voltage –4 0.1 4 mV
GATE DRIVE OUTPUT
VDRVH GATE high saturation IGATE = 50 mA 0.24 0.5 V
VDRVL GATE low saturation IGATE = 100 mA 0.22 0.5
IDRV Peak souce current GATE = VCC/2 –0.77 A
Peak sink current GATE = VCC/2 0.88
tDV Rise time Cload = 1 nF 15 ns
Fall time Cload = 1 nF 15
THERMAL SHUTDOWN
TSD Thermal shutdown temperature  See (1) 165 °C
Thermal shutdown hysteresis 20
(1) 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. 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 = 125°C), 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).

6.6 Typical Characteristics

LM3444 30127504.gif Figure 1. fSW vs Input Line Voltage
LM3444 30127507.gif Figure 3. VCC UVLO vs Temperature
LM3444 30127574.gif Figure 5. Off Threshold (C11) vs Temperature
LM3444 30127572.gif Figure 7. Leading Edge Blanking Variation Over Temperature
LM3444 30127505.gif Figure 2. Efficiency vs Input Line Voltage
LM3444 30127508.gif Figure 4. Minimum On-Time (tON) vs Temperature
LM3444 30127510.gif
Figure 6. Normalized Variation in fSW Over VBUCK Voltage