SLUSCZ1 May   2017 TPS92518-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Parameter Measurement Information
    1. 7.1 CSN Pin Falling Delay (tDEL)
    2. 7.2 Off-Timer (tOFF)
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  General Operation
        1. 8.3.1.1 Constant Off-Time vs. Constant µs×V operation
        2. 8.3.1.2 Output Equation
        3. 8.3.1.3 OFF Timer
          1. 8.3.1.3.1 Off-time and Maximum Off-time Calculations
      2. 8.3.2  Important System Considerations: Off-Timer and Maximum Peak Threshold Values
        1. 8.3.2.1 Peak Current Sense Comparator
        2. 8.3.2.2 Peak Current Threshold - LEDx _PKTH_DAC
        3. 8.3.2.3 Off-Time Thresholds - LEDx_TOFF_DAC and LEDx_MAXOFF_DAC
      3. 8.3.3  Shunt FET or Matrix dimming: Maximum Off-timer Calculation
        1. 8.3.3.1 Output Ringing and TPS92518-Q1 Protection
        2. 8.3.3.2 Live Peak and Off-Time Threshold Changes
      4. 8.3.4  VIN and the VCC Internal Regulators
      5. 8.3.5  Output Enable Control Logic
        1. 8.3.5.1 EN/UV2 - SPI Control Bypass
      6. 8.3.6  BOOT Capacitor and BOOT UVLO
      7. 8.3.7  Drop-out Operation
        1. 8.3.7.1 Early Drop-Out (Boot Capacitor Voltage >> VBOOT-UVLO)
        2. 8.3.7.2 Full Drop-Out (Boot Capacitor Voltage reaching VBOOT-UVLO)
        3. 8.3.7.3 Minimum BOOT Voltage and FET Control
        4. 8.3.7.4 BOOT Controlled internal Pull-Down
      8. 8.3.8  Analog and PWM Dimming
        1. 8.3.8.1 Dimming Methods
        2. 8.3.8.2 PWMx Pin Operation
        3. 8.3.8.3 PWM Dimming - Current Rise Performance
        4. 8.3.8.4 PWM and Analog Dimming - Linearity Limitations and Buck Converters
          1. 8.3.8.4.1 PWM:
          2. 8.3.8.4.2 ANALOG:
        5. 8.3.8.5 DCM Current Calculation
        6. 8.3.8.6 Current Sharing
      9. 8.3.9  VIN and CSPx Pin Configuration
      10. 8.3.10 Enable and Undervoltage Lock-out Configuration
      11. 8.3.11 Voltage Sampling and DAC Operation
        1. 8.3.11.1 ADC Control and LED Voltage Updating
      12. 8.3.12 Device Functional Modes
        1. 8.3.12.1 Analog Dimming
        2. 8.3.12.2 PWM Dimming
    4. 8.4 Serial Interface
      1. 8.4.1 Command Frame
      2. 8.4.2 Response Frame Formats
        1. 8.4.2.1 Read Response Frame Format
        2. 8.4.2.2 Write Response Frame Format
        3. 8.4.2.3 Write Error/POR Frame Format
        4. 8.4.2.4 SPI Error
    5. 8.5 Registers
      1. 8.5.1  CONTROL Register (Address = 00h) [reset = 00h]
        1. Table 3. CONTROL Register Field Descriptions
      2. 8.5.2  STATUS (FAULT) Register (Address = 01h) [reset = 10h]
        1. Table 4. STATUS Register Field Descriptions
      3. 8.5.3  THERM_WARN_LMT Register (Address = 02h) [reset = 80h]
        1. Table 5. THERM_WARN_LMT Register Field Descriptions
      4. 8.5.4  LED1_PKTH_DAC Register (Address = 03h) [reset = 80h]
        1. Table 6. LED1_PKTH_DAC Register Field Descriptions
      5. 8.5.5  LED2_PKTH_DAC Register (Address = 04h) [reset = 80h]
        1. Table 7. LED2_PKTH_DAC Register Field Descriptions
      6. 8.5.6  LED1_TOFF_DAC Register (Address = 05h) [reset = 80h]
        1. Table 8. LED1_TOFF_DAC Register Field Descriptions
      7. 8.5.7  LED2_TOFF_DAC Register (Address = 06h) [reset = 80h]
        1. Table 9. LED2_TOFF_DAC Register Field Descriptions
      8. 8.5.8  LED1_MAXOFF_DAC Register (Address = 07h) [reset = 80h]
        1. Table 10. LED1_MAXOFF_DAC Register Field Descriptions
      9. 8.5.9  LED2_MAXOFF_DAC Register (Address = 08h) [reset = 80h]
        1. Table 11. LED2_MAXOFF_DAC Register Field Descriptions
      10. 8.5.10 VTHERM Register (Address = 09h) [reset = 0h]
        1. Table 12. VTHERM Register Field Descriptions
      11. 8.5.11 LED1_MOST_RECENT Register (Address = 0Ah) [reset = 0h]
        1. Table 13. LED1_MOST_RECENT Register Field Descriptions
      12. 8.5.12 LED1_LAST_ON Register (Address = 0Bh) [reset = 0h]
        1. Table 14. LED1_LAST_ON Register Field Descriptions
      13. 8.5.13 LED1_LAST_OFF Register (Address = 0Ch) [reset = 0h]
        1. Table 15. LED1_LAST_OFF Register Field Descriptions
      14. 8.5.14 LED2_MOST_RECENT Register (Address = 0Dh) [reset = 0h]
        1. Table 16. LED2_MOST_RECENT Register Field Descriptions
      15. 8.5.15 LED2_LAST_ON Register (Address = 0Eh) [reset = 0h]
        1. Table 17. LED2_LAST_ON Register Field Descriptions
      16. 8.5.16 LED2_LAST_OFF Register (Address = 0Fh) [reset = 0h]
        1. Table 18. LED2_LAST_OFF Register Field Descriptions
      17. 8.5.17 Reset Register (Address = 10h) [reset = 0h]
        1. Table 19. Reset Register Field Descriptions
    6. 8.6 Programming
      1. 8.6.1 TPS92518-Q1 Register Typedef - Sample Code
      2. 8.6.2 Command Frame - Sample Code
      3. 8.6.3 SPI Read/Write - Sample Code
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
    3. 9.3 Dos and Don'ts
  10. 10Power Supply Recommendations
    1. 10.1 Input Source Direct from Battery
    2. 10.2 Input Source from a Boost Stage
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

The TPS92518-Q1 buck current controller is suitable for implementing step-down LED drivers. This section presents a simplified design process for an LED driver with the specifications shown in Design Requirements:

Use the following design procedure to select component values for this and similar buck applications.

9.2 Typical Application

TPS92518-Q1 TPS92518_TypApp_Schematic.gif Figure 56. Typical Application Schematic

9.2.1 Design Requirements

Buck converter topology.

Table 20. Design Requirements

PARAMETER VALUE UNIT
VIN Input voltage 50 V
ILED LED current 1.6 A
VLED LED voltage 9.4 V
ΔIL-PP Ripple voltage change 12.5%
LEDx_PK_DAC[7:0] Target switching frequency 550 kHz
VEN/UV 40 V
VEN/UV-HYST 5 V

9.2.2 Detailed Design Procedure

TPS92518-Q1 Design Equations and sample Calculations.

Start by calculating the converter Duty Cycle

  1. Calculate D:
      Equation 37. TPS92518-Q1 TPS92518_Example_D.gif
  2. Calculate Off Time Estimate:
    1. Using Switching Period (T)
      1. T = tOFF + tON = tOFF + (D x T), and T = 1/fSW

        2. then:

        Equation 38. TPS92518-Q1 TPS92518_Example_toff.gif
  3. Compute the off-time register value:
    4. Equation 39. TPS92518-Q1 TPS92518_Example_LEDx_TOFF_DAC.gif
  4. Calculate the inductance: Where ΔIL-PP is in Amps.
    5. Equation 40. TPS92518-Q1 TPS92518_Example_deltaL.gif
    Equation 41. TPS92518-Q1 TPS92518_Example_L.gif

    The user has the option of choosing a value of 68µH, however, this design uses the next common value of 100 µH in order to meet the ripple requirements. When selecting an inductor, ensure both the average and peak current values are met with adequate margin.

  5. Calculate the sense resistor:For the highest current set-point, set the peak threshold register to be as high as possible. Use [LEDx_PKTH_DAC] = 255 (the maximum value) if possible to increase the converter accuracy. Only use something lower if it is possible the average current level requires adjustment after the design is complete and the BOM is complete. For example, if the production flow includes a trimming step.
    6. Equation 42. TPS92518-Q1 TPS92518_Example_ILXpeak.gif
    Equation 43. TPS92518-Q1 TPS92518_Example_Rsense.gif
  6. Calculate the UVLO Resistors: Considering the turn-on point of 40 V and a 5 V hysteresis values for the UVLO resistors can be selected. ( Refer to Figure 31 for configuration details.)
    7. Equation 44. TPS92518-Q1 R2_UVLO_Numbers_Use.gif
    Equation 45. TPS92518-Q1 R3_UVLO_Numbers_Use.gif

9.2.3 Application Curves

TPS92518-Q1 ForDesign1.png
A.
CH4 (Green) : Inductor Current (500 mA per division) CH1 (Blue) : SWx Node (20 V per division) Time Base: 4µs per division
Figure 57. TPS92518-Q1 Start-Up
TPS92518-Q1 ForDesign2.png
A.
CH4 (Green) : Inductor Current (500 mA per division) CH1 (Blue) : SWx Node (20 V per division) Time Base: 2µs per division
Figure 58. TPS92518-Q1 Normal Steady-State Operation

TPS92518-Q1 Useful Equations:

Converter Output Equation (A) (Ideal)

Equation 46. TPS92518-Q1 TPS92518_ILED.gif

Converter Output Equation (A) (With error sources)

Equation 47. TPS92518-Q1 TPS92518_ILED_wError.gif

9.3 Dos and Don'ts

Do:

  • Check the TPS92518-Q1 case and junction temperature during and after prototyping of any solution.
  • Check the soldering of the device thermal pad (DAP) in production

Don't:

  • Don't write 0 (zero) to any of the off-time registers ([LEDx_TOFF_DAC] or LEDxMAXOFF_DAC] unless the use case is well understood and tested.