TIDUCL3 February   2017

 

  1. 1 Overview
  2. 2 Resources
  3. 3 Features
  4. 4 Applications
  5. 5 Design Images
  6. 6 System Overview
    1. 6.1 System Description
    2. 6.2 Key System Specifications
    3. 6.3 Block Diagram
    4. 6.4 Highlighted Products
      1. 6.4.1 LMT87-Q1
      2. 6.4.2 TLC555-Q1
      3. 6.4.3 OPA2377-Q1
      4. 6.4.4 TL431-Q1
      5. 6.4.5 TPS92691-Q1
  7. 7 System Design Theory
    1. 7.1  PCB and Form Factor
    2. 7.2  Optimizing Board Performance Based on LED String Voltage and Current
    3. 7.3  Switching Frequency
    4. 7.4  Output Overvoltage Protection (OVP)
    5. 7.5  Current Monitoring (IMON)
    6. 7.6  Thermal Foldback
      1. 7.6.1 Changing Thermal Foldback Response
        1. 7.6.1.1 Changing Starting Point for Thermal Foldback
        2. 7.6.1.2 Changing Slope of Thermal Foldback
        3. 7.6.1.3 Constant Current at High Temperatures
      2. 7.6.2 Thermal Foldback Without PWM Dimming
    7. 7.7  Clock Generation (PWM)
    8. 7.8  Onboard Supply and Setting Duty Cycle
    9. 7.9  Buffering, Averaging, and Filtering
    10. 7.10 Boost Converter
  8. 8 Getting Started Hardware
    1. 8.1 Hardware
    2. 8.2 LED Selection
    3. 8.3 J3, LED+, LED– (Boost)
    4. 8.4 J1, POS(+), NEG(–)
    5. 8.5 J4, Temperature Sensor Connection
    6. 8.6 Duty Cycle Adjust
  9. 9 Testing and Results
    1. 9.1 Duty Cycle Accuracy
    2. 9.2 Thermal Foldback Testing
    3. 9.3 EMI Testing
    4. 9.4 Accuracy Calculation
  10. 10Design Files
    1. 10.1 Schematics
    2. 10.2 Bill of Materials
    3. 10.3 PCB Layout Recommendations
      1. 10.3.1 Layout Prints
    4. 10.4 Altium Project
    5. 10.5 Gerber Files
    6. 10.6 Assembly Drawings
  11. 11Related Documentation
    1. 11.1 Trademarks
  12. 12About the Author

6.2 Key System Specifications

Table 1. Electrical Characteristics

PARAMETER COMMENTS MIN TYP MAX UNIT
SYSTEM INPUT AND OUTPUT
VIN Operating input voltage Battery-voltage range; outputs are functional 5 14 18 V
VUVLO Input UVLO setting Undervoltage lockout (UVLO) — 4.5 — —
VSWMax Vmax switch Maximum switch node voltage — — 100 V
VOUT Output voltage LED+ to LED– (Boost) 21 — 60 V
VOUT Output voltage LED + to VIN (Boost-to-Battery) 3 — 36 —
VTR Transient immunity Load dump (ISO7637-2) — — 60 V
VIN_MIN Minimum input voltage Cold crank (ISO 7637-2) 5 — — V
IIN Input current Output at full load — 2 — A
IOUT Output current Maximum current per string — 350 365 mA
Maximum output power — — — — 25 W
PWM dimming range 240-Hz PWM frequency — — 20:1 — —
LEDOpen and short detect LED open and short detection — — Yes — —
LED Single short detect LED single-short detection — — No — —
ONBOARD VOLTAGES
V 5V5 Auxiliary supply, shunt regulator TLC555, LMT87-Q1, op amp supply, and reference generation — 5 — V
VCC Bias Supply shunt regulator
(TLE431-Q1)		 — 5 — V
VPREC_PWM TLC555 out Amplitude TLC555 clock at output — 5 — V
CLOCKS
fPREC_PWM Square wave frequency Frequency at TLC555-Q1 out, U1 240 — — Hz
DOUT Square wave duty cycle Duty cycle of fPREC_PWM 5 — 50 %
DACC Duty cycle accuracy Accuracy of DOUT 2% — — —
fOSCL Oscillator frequency LED driver, TPS92691-Q1 — 390 — kHz
THERMAL
TA Temperature range Operating and ambient temperature –40 — 125 °C
PULSE TOLERANCE
Cold crank Operational
Jump start Operational
Jump start Operational
BASEBOARD
Number of layers Two layers, single-side populated
Form factor 71 mm × 51 mm