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  • LM3645 Synchronous Boost Quad LED Flash Driverwith 2-A High-Side Current Sources

    • SNVSCV4 September   2024 LM3645

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  • LM3645 Synchronous Boost Quad LED Flash Driverwith 2-A High-Side Current Sources
  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
    7. 5.7 Switching Characteristics
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Power Amplifier Synchronization (TORCH/TX)
      2. 6.3.2 Input Voltage Flash Monitor (IVFM)
      3. 6.3.3 Fault/Protections
        1. 6.3.3.1  Fault Operation
        2. 6.3.3.2  Flash Time-Out
        3. 6.3.3.3  Overvoltage Protection (OVP)
        4. 6.3.3.4  Current Limit
        5. 6.3.3.5  NTC Thermistor Input/Outputs (TEMP1, TEMP2)
        6. 6.3.3.6  Thermal Scale Back
        7. 6.3.3.7  Thermal Shutdown (TSD)
        8. 6.3.3.8  Undervoltage Lockout (UVLO)
        9. 6.3.3.9  LED and/or VOUT Short Fault
        10. 6.3.3.10 Fault Behavior Table
    4. 6.4 Device Functioning Modes
      1. 6.4.1 Flash Mode
      2. 6.4.2 Torch Mode
      3. 6.4.3 IR Mode
      4. 6.4.4 Voltage Mode
      5. 6.4.5 Mode Transitions
      6. 6.4.6 Boost Operation
        1. 6.4.6.1 Start-Up (Enabling The Device)
        2. 6.4.6.2 Pass Mode
        3. 6.4.6.3 Output Voltage Regulation
    5. 6.5 Programming and Control
      1. 6.5.1 Dx_EN Bits
      2. 6.5.2 STR1 and STR2 Usage
      3. 6.5.3 TOR/TX Usage
      4. 6.5.4 Control State Diagram
      5. 6.5.5 I2C-Compatible Interface
        1. 6.5.5.1 Data Validity
        2. 6.5.5.2 Start and Stop Conditions
        3. 6.5.5.3 Transferring Data
        4. 6.5.5.4 I2C-Compatible Chip Address
    6. 6.6 Register Descriptions
      1. 6.6.1 MainReg Registers
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Output Control Examples
        1. 7.2.2.1 Four Channel Flash with Strobe1 Trigger Starting in Standby
        2. 7.2.2.2 Four Channel Flash with Strobe1 Trigger Starting in I2C Torch
        3. 7.2.2.3 Mixed Mode Functionality
        4. 7.2.2.4 Voltage Mode Only
        5. 7.2.2.5 Voltage Mode With Advanced IR
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1 Snubber Requirement
        2. 7.2.3.2 Output Capacitor Selection
        3. 7.2.3.3 Input Capacitor Selection
        4. 7.2.3.4 Inductor Selection
      4. 7.2.4 Application Curves
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Third-Party Products Disclaimer
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information
  14. IMPORTANT NOTICE

Package Options

Mechanical Data (Package|Pins)
  • YCG|25
    • MXBG410
Thermal pad, mechanical data (Package|Pins)
Orderable Information
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Data Sheet

LM3645 Synchronous Boost Quad LED Flash Driver
with 2-A High-Side Current Sources

1 Features

  • Quad independent led current source programmability
  • Accurate and programmable LED current range from 0.525 mA to 2 A
  • Optimized flash LED current during low battery conditions (IVFM)
  • > 85% efficiency in torch mode (at 100 mA) and flash mode (at 1 A to 2 A)
  • Grounded cathode LED operation for improved thermal management
  • Dual hardware strobe enable (STR1, STR2)
  • Synchronization input for RF power amplifier pulse events (TORCH/TX)
  • Hardware torch enable (TORCH/Tx)
  • Dual remote NTC monitoring (TEMP1, TEMP2)
  • Fixed output voltage mode
  • 1-MHz I2C-compatible interface
    • (I2C Address = 0x65)

2 Applications

  • Camera phone white LED flash
  • Digital still cameras
  • Barcode scanners
  • Handheld data terminals

3 Description

The LM3645 is a quad LED flash driver that provides a high level of adjustability within a small solution size. The LM3645 utilizes a synchronous boost converter to provide power to the quad 2A constant current LED sources. The quad 256 level current sources provide the flexibility to adjust the current ratios between LED1, LED2, LED3 and LED4 with each driver capable of delivering a maximum of 2A. An adaptive regulation method ensures the current sources remain in regulation and maximizes efficiency.

Features of the LM3645 are controlled via an I2C-compatible interface. These features include: dual hardware flash pins and a hardware torch or Tx interrupt pin (STR1, STR2 and TORCH/TX), and dual NTC thermistor monitors. The device offers independently programmable currents in each output leg to drive the LEDs in a flash or movie mode (Torch) condition as well as a fast turn-on and turn-off IR Mode.

Two switching frequency options, overvoltage protection (OVP), and adjustable current limit allow for the use of tiny, low-profile inductors and 10µF ceramic capacitors. The device operates over a –40°C to +85°C ambient temperature range.

Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LM3645 DSBGA (25) 2.192mm × 1.927mm
(1) For all available packages, see the orderable addendum at the end of the data sheet.
LM3645 Simplified Application Simplified Application

4 Pin Configuration and Functions

LM3645 YCG Package, 25-Pin DSBGAFigure 4-1 YCG Package, 25-Pin DSBGA
Table 4-1 Pin Functions
PINTYPEDESCRIPTION
NO.NAME
A3INPInput voltage connection. Connect this pin to the input supply and bypass to GND with a 10-µF or larger ceramic capacitor
B1SWPDrain connection for internal N-channel MOSFET and synchronous P-channel MOSFET switches
B2
C1OUTPStep-up DC-DC converter output. Connect 2 × 10-µF ceramic capacitors between this terminal and GND
C2
C3
C4
A1GNDGGround
A2
E1D1PHigh-side current source outputs for flash LEDs
E2
D1D2P
D2
D4D3P
D5
E4D4P
E5
A4ENIActive high hardware enable. Drive EN pin high to turn on the device. An internal pulldown resistor of 300 kΩ is between EN and GND.
A5SDAI/OI2C serial data input/output
B5SCLII2C serial clock input
B3STR1IActive high hardware flash enable. Drive STR1 high to turn on flash or IR pulse. An internal pulldown resistor of 300 kΩ is between STR1 and GND.
B4STR2IActive high hardware flash enable. Drive STR2 high to turn on flash or IR pulse. An internal pulldown resistor of 300 kΩ is between STR2 and GND.
C5TORCH/TXIActive high hardware torch enable or power amplifier synchronization input. Internal pulldown resistor of 300 kΩ between TORCH/TX and GND.
E3TEMP1I/OThreshold detector for NTC temperature sensing and current scale back
D3TEMP2I/O

 
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