SLUSBZ6A April   2016  – August 2016 TPS92515 , TPS92515-Q1 , TPS92515HV , TPS92515HV-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Simplified Buck LED Driver Application
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1. Table 1. Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  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
      2. 8.3.2  Current Sense Comparator
      3. 8.3.3  OFF Timer
      4. 8.3.4  OFF-Timer, Shunt FET Dimming or Shunted Output Condition
      5. 8.3.5  Internal N-channel MOSFET
        1. 8.3.5.1 Drop-Out
      6. 8.3.6  VCC Internal Regulator and Undervoltage Lockout (UVLO)
      7. 8.3.7  Analog Adjust Input
        1. 8.3.7.1 IADJ Pin Clamp
        2. 8.3.7.2 IADJ Pin Clamp Characteristic
        3. 8.3.7.3 Analog Adjust (IADJ Pin) Control Methods
        4. 8.3.7.4 IADJ Control Method Notes
      8. 8.3.8  Thermal Protection
        1. 8.3.8.1 Maximum Output Current and Junction Temperature
      9. 8.3.9  Junction Temperature Relative Estimation
      10. 8.3.10 BOOT and BOOT UVLO
        1. 8.3.10.1 Start-Up, BOOT-UVLO and Pre-Charged Condition
      11. 8.3.11 PWM (UVLO and Enable)
        1. 8.3.11.1 Using PWM for UVLO (Undervoltage Lockout) Protection
          1. 8.3.11.1.1 UVLO Programming Resistors
        2. 8.3.11.2 Using PWM for Digitally Controlled Enable
        3. 8.3.11.3 UVLO: VIN, VCC and BOOT UVLO
        4. 8.3.11.4 Analog and PWM Dimming - Normalized Results and Comparison
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 General Design Procedure
        1. 9.2.1.1 Calculating Duty Cycle
        2. 9.2.1.2 Calculate OFF-Time Estimate
        3. 9.2.1.3 Calculate OFF-Time Resistor ROFF
        4. 9.2.1.4 Calculate the Minimum Inductance Value
        5. 9.2.1.5 Calculate the Sense Resistance
        6. 9.2.1.6 Calculate Input Capacitance
        7. 9.2.1.7 Calculate Output Capacitance
      2. 9.2.2 Design Requirements
      3. 9.2.3 Detailed Design Procedure
        1. 9.2.3.1 Calculating Duty Cycle
        2. 9.2.3.2 Calculate OFF-Time Estimate
        3. 9.2.3.3 Calculate OFF-Time Resistor ROFF
        4. 9.2.3.4 Calculate the Inductance Value
        5. 9.2.3.5 Calculate the Sense Resistance
        6. 9.2.3.6 Calculate Input Capacitance
        7. 9.2.3.7 Verify Peak Current for Inductor Selection
        8. 9.2.3.8 Calculate Output Capacitance
        9. 9.2.3.9 Calculate UVLO Resistance Values
      4. 9.2.4 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 Documentation Support
      1. 12.1.1 Related Documentation
        1. 12.1.1.1 Related Links
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.1 General Operation

The TPS92515 operates using a peak-current, constant OFF-time as described in Figure 11. Two states dictate the high-side FET control. The switch turns on and stays on until the programmed peak current is reached. The peak current is controlled by monitoring the voltage across the sense resistor. When the voltage drop is higher than the programmed threshold, the peak current is reached, and the switch is turned OFF, which initiates the OFF-time period. A capacitor on the COFF pin is then charged through a resistor connected to the output. When the COFF pin voltage reaches the 1-V (typical) threshold, the OFF-time ends. The COFF pin capacitor resets and the main switch turns ON, and the next cycle begins.

TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 92515_inductorI.gifFigure 11. Hysteretic Operation

Although commonly referred to as constant OFF-time, the OFF-time control voltage is normally derived from the output voltage. This connection ensures constant peak-to-peak ripple. To maintain a constant ripple over various input and output voltages, the converter OFF-time becomes shorter or longer resulting in a change in frequency. If the input voltage and output voltage are relatively constant, the frequency also remains constant. If either the input voltage or the output voltage changes, the frequency changes. For a fixed input voltage, the device operates at the maximum frequency at 50% duty cycle and the frequency reduces as the duty cycle becomes shorter or longer. A graphical representation is shown in Figure 12. For a fixed output voltage (VLED), the frequency is always the maximum at the highest input voltage as shown in Figure 13.

TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 FrequencyPeak2.gif
Fixed input voltage
Figure 12. Frequency vs LED Output Voltage
TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 FrequencyPeak_fixedVout.gif
Fixed LED voltage
Figure 13. Frequency vs Input Voltage (VIN)

By making the OFF-time proportional to the output voltage, it is possible to illustrate how VLED can be removed from the output current equation. When VLED >> VOFT , the output ripple can be defined as shown in Equation 1.

Equation 1. ΔIL-PP = (VLED x dt)/L

where

  • dt is defined by the OFF-timer

.

Equation 2. TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 ILED_simple_Der1.gif

Substitute dt in Equation 1 to create Equation 3.

Equation 3. TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 ILED_simple_Der2.gif
Equation 4. TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 ILED_simple_Der3.gif

When VLED >≈ 10 V, use the ILED calculation Equation 4. The Detailed Design Procedure section describes a design example that uses the more detailed equation. A VLED > 10 V ensures a linear charging ramp below 1 V. If VLED <≈10 V, use Equation 5 that considers the exponential charging characteristic.

Equation 5. TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 ILED_closed.gif

Because the control method relies on thresholds to control the main switch, offsets and delays must also be considered when examining the output accuracy. The ILED equation can be expanded to include these error sources as shown in Equation 6. ILED equations include several passive components, so it is important to consider the tolerance of each component. The VCST_Offset parameter is the variation in the VCST threshold between the typical and maximum or minimum values as defined in the Electrical Characteristics table.

Equation 6. TPS92515 TPS92515-Q1 TPS92515HV TPS92515HV-Q1 ILED_closed_err.gif