SNVSAF2A February   2016  – February 2016 LM36922H

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 LM36922H
        1. 7.3.1.1 Current Sink Enable
      2. 7.3.2 LM36922H 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 I2C Address Select (ASEL)
      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 Voltage Limitations on LED1, LED2
        3. 7.4.5.3 LED String Short Fault
        4. 7.4.5.4 Overcurrent Protection (OCP)
          1. 7.4.5.4.1 OCP Fault
          2. 7.4.5.4.2 OCP Shutdown
        5. 7.4.5.5 Device Overtemperature
          1. 7.4.5.5.1 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 Community Resources
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 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 LM36922H provides a complete high-performance LED lighting solution for mobile handsets. The LM36922H is highly configurable and can support multiple LED configurations.

8.2 Typical Application

LM36922H LM36922 Application Schematic.png Figure 30. LM36922H 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 (Vƒ) 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 LM36922H boost converter output voltage (VOUT) is calculated: number of series LEDs × Vƒ + 0.23 V. The LM36922H boost converter output current (IOUT) is calculated: number of parallel LED strings × 25 mA. The LM36922H peak input current is calculated using Equation 5.

8.2.2 Detailed Design Procedure

8.2.2.1 Component Selection

8.2.2.1.1 Inductor

The LM36922H requires a typical inductance in the range of 4.7 µH to 10 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 5:

Equation 5. LM36922H 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 5 above.

8.2.2.1.2 Output Capacitor

The LM36922H 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 20 lists possible output capacitors that can be used with the LM36922H. Figure 31 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 6:

Equation 6. LM36922H cout_eff.gif

Table 20. 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.

LM36922H cap_DCbias.png Figure 31. 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 = 4.7 µH (VLF504012-4R7M) or 10 µH (VLF504015-100M) as noted in graphs, D1 = NSR240P2T5G, LEDs are Samsung SPMWHT325AD5YBTMS0, temperature = 25°C, VIN = 3.7 V, unless otherwise noted.
LM36922H C046_SNVSAF3.png Figure 32. Boost Efficiency vs Series LEDs
LM36922H C037_SNVSAF3.png Figure 34. Boost Efficiency vs Series LEDs
LM36922H C033_SNVSAF3.png Figure 36. Boost Efficiency vs Series LEDs
LM36922H C054_SNVSAF3.png Figure 38. Boost Efficiency vs Series LEDs
LM36922H C056_SNVSAF3.png Figure 40. Boost Efficiency vs Series LEDs
LM36922H C001_SNVSA30.png Figure 42. LED Current vs Brightness Code (Exponential Mapping)
LM36922H C022_SNVSAF3.png Figure 44. LED Matching (Exponential Mapping)
LM36922H C024_SNVSAF3.png Figure 46. LED Current Accuracy
LM36922H C044_SNVSAF3.png Figure 48. LED Headroom Voltage (Mis-Matched Strings)
LM36922H C018_SNVSAF3.png Figure 50. Current vs PWM Sample Frequency
LM36922H C039_SNVSAF3.png Figure 33. Boost Efficiency vs Series LEDs
LM36922H C035_SNVSAF3.png Figure 35. Boost Efficiency vs Series LEDs
LM36922H C031_SNVSAF3.png Figure 37. Boost Efficiency vs Series LEDs
LM36922H C055_SNVSAF3.png Figure 39. Boost Efficiency vs Series LEDs
LM36922H C057_SNVSAF3.png Figure 41. Boost Efficiency vs Series LEDs
LM36922H C021_SNVSAF3.png Figure 43. LED Current vs Brightness Code
LM36922H C023_SNVSAF3.png Figure 45. LED Matching (Linear Mapping)
LM36922H C025_SNVSAF3.png Figure 47. LED Current Accuracy
LM36922H C029_SNVSAF3.png Figure 49. LED Headroom Voltage (Mis-Matched Strings)