SNVS846G June   2012  – November 2017 LM34925

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 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 Application Circuit: 20-V to 95-V Input and 10-V, 100-mA Output Isolated Fly-Buck Converter
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Transformer Turns Ratio
          2. 8.2.1.2.2  Total IOUT
          3. 8.2.1.2.3  RFB1, RFB2
          4. 8.2.1.2.4  Frequency Selection
          5. 8.2.1.2.5  Transformer Selection
          6. 8.2.1.2.6  Primary Output Capacitor
          7. 8.2.1.2.7  Secondary Output Capacitor
          8. 8.2.1.2.8  Type III Feedback Ripple Circuit
          9. 8.2.1.2.9  Secondary Diode
          10. 8.2.1.2.10 VCC and Bootstrap Capacitor
          11. 8.2.1.2.11 Input Capacitor
          12. 8.2.1.2.12 UVLO Resistors
          13. 8.2.1.2.13 VCC Diode
      2. 8.2.2 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 Documentation Support
      1. 11.1.1 Related Documentation
    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)

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(2) 150 °C
Storage temperature Tstg –55 150 °C
(1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Recommended Operating Conditions are conditions under which operation of the device is intended to be functional. For verified specifications and test conditions, see the Electrical Characteristics. The RTN pin is the GND reference electrically connected to the substrate.
(2) High junction temperatures degrade operating lifetimes. Operating lifetime is de-rated for junction temperatures greater than 125°C.

6.2 ESD Ratings

MIN MAX UNIT
V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins(1) 2 kV
Charged device model (CDM), per JEDEC specification JESD22-C101, all pins(2) 750 V
(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

over operating free-air temperature range (unless otherwise noted)(1)
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 de-rated for junction temperatures greater than 125°C.

6.4 Thermal Information

THERMAL METRICS(1) LM34925 UNIT
NGU DDA
8 PINS
RθJA Junction-to-ambient thermal resistance 41.3 41.1 °C/W
RθJCbot 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
RθJCtop 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 otherwise stated. (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)		 –40°C ≤ TJ ≤ 125°C 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 Non-switching, FB = 3 V 1.75 mA
IIN Shutdown Current UVLO = 0 V 50 225 µA
SWITCH CHARACTERISTICS
Buck Switch RDS(ON) ITEST = 100 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
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
CURRENT LIMIT
Current Limit Threshold 150 270 370 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 V, VIN = 48 V 2.5 µs
THERMAL SHUTDOWN
Tsd Thermal Shutdown Temperature 165 °C
Thermal Shutdown Hysteresis 20 °C
(1) All limits are verified by design. All electrical characteristics having room temperature limits are tested during production at TA = 25°C. All hot and cold limits are verified 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.
PARAMETER TEST CONDITIONS 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

LM34925 30198145.gif Figure 1. Efficiency at 750 kHz, VOUT1 = 10 V
LM34925 vcc_vs_vin.png Figure 2. VCC vs VIN
LM34925 vcc_vs_icc.png Figure 3. VCC vs ICC
LM34925 Graph - On-time vs Vin.png Figure 5. TON vs VIN and RON
LM34925 30198110.png Figure 7. IIN vs VIN (Operating, Non-Switching)
LM34925 30198107.png Figure 4. ICC vs External VCC
LM34925 30198109.png Figure 6. TOFF (ILIM) vs VFB and VIN
LM34925 30198111.png Figure 8. IIN vs VIN (Shutdown)