SNVS847F June   2012  – November 2017 LM34926

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 Ratings
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 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  Control Overview
      2. 7.3.2  VCC Regulator
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Overvoltage Comparator
      5. 7.3.5  On-Time Generator
      6. 7.3.6  Current Limit
      7. 7.3.7  N-Channel Buck Switch and Driver
      8. 7.3.8  Synchronous Rectifier
      9. 7.3.9  Undervoltage Detector
      10. 7.3.10 Thermal Protection
      11. 7.3.11 Ripple Configuration
      12. 7.3.12 Soft Start
    4. 7.4 Device Functional Modes
  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  Custom Design With WEBENCH® Tools
        2. 8.2.2.2  Transformer Turns Ratio
        3. 8.2.2.3  Total IOUT
        4. 8.2.2.4  RFB1, RFB2
        5. 8.2.2.5  Frequency Selection
        6. 8.2.2.6  Transformer Selection
        7. 8.2.2.7  Primary Output Capacitor
        8. 8.2.2.8  Secondary Output Capacitor
        9. 8.2.2.9  Type III Feedback Ripple Circuit
        10. 8.2.2.10 Secondary Diode
        11. 8.2.2.11 VCC and Bootstrap Capacitor
        12. 8.2.2.12 Input Capacitor
        13. 8.2.2.13 UVLO Resistors
        14. 8.2.2.14 VCC Diode
      3. 8.2.3 Application Curves
  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 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

6 Specifications

6.1 Absolute Maximum Ratings(1)(2)

MIN MAX UNIT
VIN, UVLO to RTN –0.3 100 V
SW to RTN –1.5 VIN + 0.3 V
SW to RTN (100-ns transient) –5 VIN + 0.3 V
BST to VCC 100 V
BST to SW 13 V
RON to RTN –0.3 100 V
VCC to RTN –0.3 13 V
FB to RTN –0.3 5 V
Maximum junction temperature(3) 150 °C
Storage temperature, Tstg –55 150 °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 RTN pin is the GND reference electrically connected to the substrate.
(3) High junction temperatures degrade operating lifetimes. Operating lifetime is derated for junction temperatures greater than 125°C.

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) ±750
(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 Ratings

MIN MAX UNIT
VIN voltage 7.5 100 V
Operating junction temperature(1) –40 125 °C
(1) High junction temperatures degrade operating lifetimes. Operating lifetime is derated for junction temperatures greater than 125°C.

6.4 Thermal Information

THERMAL METRICS(1) LM34926 UNIT
NGU (WSON) DDA (SO PowerPAD)
8 PINS 8 PINS
RθJA Junction-to-ambient thermal resistance 41.3 41.1 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance 3.2 2.4 °C/W
ΨJB Junction-to-board thermal characteristic parameter 19.2 24.4 °C/W
RθJB Junction-to-board thermal resistance 19.1 30.6 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 34.7 37.3 °C/W
ΨJT Junction-to-top thermal characteristic parameter 0.3 6.7 °C/W
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report (SPRA953).

6.5 Electrical Characteristics

Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over –40°C to 125°C junction temperature range unless otherwise stated. VIN = 48 V unless stated otherwise. See(1).
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VCC SUPPLY
VCC Reg VCC Regulator Output VIN = 48 V, ICC = 20 mA 6.25 7.6 8.55 V
VCC Current Limit VIN = 48 V(2) 26 mA
VCC UVLO Threshold (VCC increasing) 4.15 4.5 4.9 V
VCC UVLO Hysteresis 300 mV
VCC Drop Out Voltage VIN = 8 V, ICC = 20 mA 2.3 V
IIN Operating Current Nonswitching, FB = 3 V 1.75 mA
IIN Shutdown Current UVLO = 0 V 50 225 µA
UNDERVOLTAGE SENSING FUNCTION
UV Threshold UV Rising 1.19 1.225 1.26 V
UV Hysteresis Input Current UV = 2.5 V –10 –20 -29 µA
Remote Shutdown Threshold Voltage at UVLO Falling 0.32 0.66 V
Remote Shutdown Hysteresis 110 mV
REGULATION AND OVERVOLTAGE COMPARATORS
FB Regulation Level Internal Reference Trip Point for Switch ON 1.2 1.225 1.25 V
FB Overvoltage Threshold Trip Point for Switch OFF 1.62 V
FB Bias Current 60 nA
SWITCH CHARACTERISTICS
Buck Switch RDS(ON) ITEST = 200 mA, BST-SW = 7 V 0.8 1.8 Ω
Synchronous RDS(ON) ITEST = 200 mA 0.45 1 Ω
Gate Drive UVLO VBST − VSW Rising 2.4 3 3.6 V
Gate Drive UVLO Hysteresis 260 mV
CURRENT LIMIT
Current Limit Threshold 390 575 750 mA
Current Limit Response Time Time to Switch Off 150 ns
OFF-Time Generator (Test 1) FB = 0.1 V, VIN = 48 V 12 µs
OFF-Time Generator (Test 2) FB = 1.0 V, VIN = 48 V 2.5 µs
THERMAL SHUTDOWN
Tsd Thermal Shutdown Temperature 165 °C
Thermal Shutdown Hysteresis 20 °C
(1) All limits are specified by design. All electrical characteristics having room temperature limits are tested during production at TA = 25°C. All hot and cold limits are ensured by correlating the electrical characteristics to process and temperature variations and applying statistical process control.
(2) VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.

6.6 Switching Characteristics

Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over –40°C to 125°C junction temperature range unless otherwise stated. VIN = 48 V unless otherwise stated.
MIN TYP MAX UNIT
ON-TIME GENERATOR
TON Test 1 VIN = 32 V, RON = 100 kΩ 270 350 460 ns
TON Test 2 VIN = 48 V, RON = 100 kΩ 188 250 336 ns
TON Test 3 VIN = 75 V, RON = 250 kΩ 250 370 500 ns
TON Test 4 VIN = 10 V, RON = 250 kΩ 1880 3200 4425 ns
MINIMUM OFF-TIME
Minimum Off-Timer FB = 0 V 144 ns

6.7 Typical Characteristics

LM34926 30198243.gif Figure 1. Efficiency at 750 kHz, VOUT1 = 10 V
LM34926 30198206.png Figure 3. VCC vs ICC
LM34926 Graph - On-time vs Vin.png Figure 5. TON vs VIN and RON
LM34926 30198210.png Figure 7. IIN vs VIN (Operating, Non-Switching)
LM34926 30198205.png Figure 2. VCC vs VIN
LM34926 30198207.png Figure 4. ICC vs External VCC
LM34926 30198209.png Figure 6. TOFF (ILIM) vs VFB and VIN
LM34926 30198211.png Figure 8. IIN vs VIN (Shutdown)