SNVSA29 May   2015 LM36922

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 I2C Timing Requirements
    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 Enabling the LM36922
        1. 7.3.1.1 Current Sink Enable
      2. 7.3.2 LM36922 Start-Up
      3. 7.3.3 Brightness Mapping
        1. 7.3.3.1 Linear Mapping
        2. 7.3.3.2 Exponential Mapping
      4. 7.3.4 PWM Input
        1. 7.3.4.1 PWM Sample Frequency
          1. 7.3.4.1.1 PWM Resolution and Input Frequency Range
          2. 7.3.4.1.2 PWM Sample Rate and Efficiency
            1. 7.3.4.1.2.1 PWM Sample Rate Example
        2. 7.3.4.2 PWM Hysteresis
        3. 7.3.4.3 PWM Step Response
        4. 7.3.4.4 PWM Timeout
      5. 7.3.5 LED Current Ramping
      6. 7.3.6 Regulated Headroom Voltage
    4. 7.4 Device Functional Modes
      1. 7.4.1 Brightness Control Modes
        1. 7.4.1.1 I2C Only (Brightness Mode 00)
        2. 7.4.1.2 PWM Only (Brightness Mode 01)
        3. 7.4.1.3 I2C + PWM Brightness Control (Multiply Then Ramp) Brightness Mode 10
        4. 7.4.1.4 I2C + PWM Brightness Control (Ramp Then Multiply) Brightness Mode 11
      2. 7.4.2 Boost Switching Frequency
        1. 7.4.2.1 Minimum Inductor Select
      3. 7.4.3 Auto Switching Frequency
      4. 7.4.4 Backlight Adjust Input (BL_ADJ)
        1. 7.4.4.1 Back-Light Adjust Input Polarity
      5. 7.4.5 Fault Protection/Detection
        1. 7.4.5.1 Overvoltage Protection (OVP)
          1. 7.4.5.1.1 Case 1 OVP Fault Only (OVP Threshold Hit and All Enabled Current Sink Inputs > 40 mV)
          2. 7.4.5.1.2 Case 2a OVP Fault and Open LED String Fault (OVP Threshold Occurrence and Any Enabled Current Sink Input ≤ 40 mV)
          3. 7.4.5.1.3 Case 2b OVP Fault and Open LED String Fault (OVP Threshold Duration and Any Enabled Current Sink Input ≤ 40 mV)
          4. 7.4.5.1.4 OVP/LED Open Fault Shutdown
          5. 7.4.5.1.5 Testing for LED String Open
        2. 7.4.5.2 LED String Short Fault
        3. 7.4.5.3 Overcurrent Protection (OCP)
          1. 7.4.5.3.1 OCP Fault
          2. 7.4.5.3.2 OCP Shutdown
        4. 7.4.5.4 Device Overtemperature (TSD)
          1. 7.4.5.4.1 Overtemperature Shutdown
    5. 7.5 Programming
      1. 7.5.1 I2C Interface
        1. 7.5.1.1 Start and Stop Conditions
        2. 7.5.1.2 I2C Address
        3. 7.5.1.3 Transferring Data
        4. 7.5.1.4 Register Programming
    6. 7.6 Register Maps
  8. 8 Applications and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Component Selection
          1. 8.2.2.1.1 Inductor
          2. 8.2.2.1.2 Output Capacitor
          3. 8.2.2.1.3 Input Capacitor
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Input Supply Bypassing
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Boost Output Capacitor Placement
      2. 10.1.2 Schottky Diode Placement
      3. 10.1.3 Inductor Placement
      4. 10.1.4 Boost Input Capacitor Placement
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8 Applications 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.

8.1 Application Information

The LM36922 provides a complete high-performance LED lighting solution for mobile handsets. The LM36922 is highly configurable and can support multiple LED configurations.

8.2 Typical Application

LM36922 LM36922 Application Schematic.pngFigure 32. LM36922 Typical Application

8.2.1 Design Requirements

DESIGN PARAMETER EXAMPLE VALUE
Minimum input voltage (VIN) 2.7 V
LED parallel/series configuration 2 × 8
LED maximum forward voltage (Vf) 3.2 V
Efficiency 80%

The number of LED strings, number of series LEDs, and minimum input voltage are needed in order to calculate the peak input current. This information guides the designer to make the appropriate inductor selection for the application. The LM36922 boost converter output voltage (VOUT) is calculated as follows: number of series LEDs × Vƒ + 0.23 V. The LM36922 boost converter output current (IOUT) is calculated as follows: number of parallel LED strings × 25 mA. The LM36922 peak input current is calculated using Equation 6.

8.2.2 Detailed Design Procedure

8.2.2.1 Component Selection

8.2.2.1.1 Inductor

The LM36922 requires a typical inductance in the range of 10 µH to 22 µH. When selecting the inductor, ensure that the saturation rating for the inductor is high enough to accommodate the peak inductor current of the application (IPEAK) given in the inductor datasheet. The peak inductor current occurs at the maximum load current, the maximum output voltage, the minimum input voltage, and the minimum switching frequency setting. Also, the peak current requirement increases with decreasing efficiency. IPEAK can be estimated using Equation 6:

Equation 6. LM36922 ipeak.gif

Also, the peak current calculated above is different from the peak inductor current setting (ISAT). The NMOS switch current limit setting (ICL_MIN) must be greater than IPEAK from Equation 6 above.

8.2.2.1.2 Output Capacitor

The LM36922 requires a ceramic capacitor with a minimum of 0.4 µF of capacitance at the output, specified over the entire range of operation. This ensures that the device remains stable and oscillation free. The 0.4 µF of capacitance is the minimum amount of capacitance, which is different than the value of capacitor. Capacitance would take into account tolerance, temperature, and DC voltage shift.

Table 21 lists possible output capacitors that can be used with the LM36922. Figure 33 shows the DC bias of the four TDK capacitors. The useful voltage range is determined from the effective output voltage range for a given capacitor as determined by Equation 7:

Equation 7. LM36922 cout_eff.gif

Table 21. Recommended Output Capacitors

PART NUMBER MANUFACTURER CASE SIZE VOLTAGE RATING (V) NOMINAL CAPACITANCE (µF) TOLERANCE (%) TEMPERATURE COEFFICIENT (%) RECOMMENDED MAX OUTPUT VOLTAGE (FOR SINGLE CAPACITOR)
C2012X5R1H105K085AB TDK 0805 50 1 ±10 ±15 22
C2012X5R1H225K085AB TDK 0805 50 2.2 ±10 ±15 24
C1608X5R1V225K080AC TDK 0603 35 2.2 ±10 ±15 12
C1608X5R1H105K080AB TDK 0603 50 1 ±10 ±15 15

For example, with a 10% tolerance, and a 15% temperature coefficient, the DC voltage derating must be ≥ 0.38/(0.9 × 0.85) = 0.5 µF. For the C1608X5R1H225K080AB (0603, 50-V) device, the useful voltage range occurs up to the point where the DC bias derating falls below 0.523 µF, or around 12 V. For configurations where VOUT is > 15 V, two of these capacitors can be paralleled, or a larger capacitor such as the C2012X5R1H105K085AB must be used.

LM36922 cap_DCbias.pngFigure 33. DC Bias Derating for 0805 Case Size and
0603 Case Size 35-V and 50-V Ceramic Capacitors

8.2.2.1.3 Input Capacitor

The input capacitor in a boost is not as critical as the output capacitor. The input capacitor primary function is to filter the switching supply currents at the device input and to filter the inductor current ripple at the input of the inductor. The recommended input capacitor is a 2.2-µF ceramic (0402, 10-V device) or equivalent.

8.2.3 Application Curves

L1 = 10 µH (VLF403212-100M) or 22 µH (VLF504015-220M) as noted in graphs, D1 = NSR530P2T5G, LEDs are Rohm SML312WBCW1, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
LM36922 C039_SNVSA30.pngFigure 34. Boost Efficiency vs Series LEDs
LM36922 C046_SNVSA30.pngFigure 35. Boost Efficiency vs Series LEDs
LM36922 C054_SNVSA30.pngFigure 36. Boost Efficiency vs Series LEDs
LM36922 C056_SNVSA30.pngFigure 38. Boost Efficiency vs Series LEDs
LM36922 C033_SNVSA30.pngFigure 40. Boost Efficiency vs Series LEDs
LM36922 C037_SNVSA30.pngFigure 42. Boost Efficiency vs Series LEDs
LM36922 C021_SNVSA30.pngFigure 44. LED Current vs Brightness Code
LM36922 C023_SNVSA30.pngFigure 46. LED Matching (Linear Mapping)
LM36922 C025_SNVSA30.pngFigure 48. LED Current Accuracy
LM36922 C029_SNVSA30.pngFigure 50. LED Headroom Voltage (Mis-Matched Strings)
LM36922 C055_SNVSA30.pngFigure 37. Boost Efficiency vs Series LEDs
LM36922 C031_SNVSA30.pngFigure 39. Boost Efficiency vs Series LEDs
LM36922 C035_SNVSA30.pngFigure 41. Boost Efficiency vs Series LEDs
LM36922 C001_SNVSA30.pngFigure 43. LED Current vs Brightness Code (Exponential Mapping)
LM36922 C022_SNVSA30.pngFigure 45. LED Matching (Exponential Mapping)
LM36922 C024_SNVSA30.pngFigure 47. LED Current Accuracy
LM36922 C044_SNVSA30.pngFigure 49. LED Headroom Voltage (Mis-Matched Strings)
LM36922 C018_SNVSA30.pngFigure 51. Current vs PWM Sample Frequency