SNVSA30A March   2015  – October 2016 LM36923

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 LM36923
        1. 7.3.1.1 Current Sink Enable
      2. 7.3.2 LM36923 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 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

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 LM36923 provides a complete high-performance LED lighting solution for mobile handsets. The LM36923 is highly configurable and can support multiple LED configurations.

8.2 Typical Application

LM36923 LM36923 Application Schematic.png Figure 32. LM36923 Typical Application

8.2.1 Design Requirements

DESIGN PARAMETER EXAMPLE VALUE
Minimum input voltage (VIN) 2.7 V
LED parallel/series configuration 3 × 5
LED maximum forward voltage (Vf) 3.2 V
Efficiency 82%

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 LM36923 boost converter output voltage (VOUT) is calculated as follows: number of series LEDs × Vƒ + 0.23 V. The LM36923 boost converter output current (IOUT) is calculated as follows: number of parallel LED strings × 25 mA. The LM36923 peak input current is calculated using Equation 6.

8.2.2 Detailed Design Procedure

Table 21. Typical Application Component List

CONFIGURATION L1 D1 COUT
3p7s, 3p8s VLF504012MT-100M
VLF504012MT-150M 		NSR0530P2T5G C2012X7R1H105K085AC
3p6s VLF504012MT-220M NSR0530P2T5G C2012X7R1H105K085AC
3p5s VLF403210MT-100M NSR0530P2T5G C2012X7R1H105K085AC
3p4s VLF302510MT-100M NSR0530P2T5G C2012X7R1H105K085AC

8.2.2.1 Component Selection

8.2.2.1.1 Inductor

The LM36923 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. LM36923 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 LM36923 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 22 lists possible output capacitors that can be used with the LM36923. 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. LM36923 cout_eff.gif

Table 22. 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.

LM36923 cap_DCbias.png Figure 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.
LM36923 C038_SNVSA30.png Figure 34. Boost Efficiency vs Series LEDs
LM36923 C045_SNVSA30.png Figure 36. Boost Efficiency vs Series LEDs
LM36923 C039_SNVSA30.png Figure 35. Boost Efficiency vs Series LEDs
LM36923 C046_SNVSA30.png Figure 37. Boost Efficiency vs Series LEDs
LM36923 C050_SNVSA30.png Figure 38. Boost Efficiency vs Series LEDs
LM36923 C051_SNVSA30.png Figure 40. Boost Efficiency vs Series LEDs
LM36923 C052_SNVSA30.png Figure 42. Boost Efficiency vs Series LEDs
LM36923 C030_SNVSA30.png Figure 44. Boost Efficiency vs Series LEDs
LM36923 C032_SNVSA30.png Figure 46. Boost Efficiency vs Series LEDs
LM36923 C034_SNVSA30.png Figure 48. Boost Efficiency vs Series LEDs
LM36923 C036_SNVSA30.png Figure 50. Boost Efficiency vs Series LEDs
LM36923 C001_SNVSA30.png Figure 52. LED Current vs Brightness Code (Exponential Mapping)
LM36923 C016_SNVSA30.png Figure 54. LED Matching (Exponential Mapping)
LM36923 C019_SNVSA30.png Figure 56. LED Current Accuracy
LM36923 C028_SNVSA30.png Figure 58. LED Headroom Voltage (Mis-Matched Strings)
LM36923 C018_SNVSA30.png Figure 60. Current vs PWM Sample Frequency
LM36923 C054_SNVSA30.png Figure 39. Boost Efficiency vs Series LEDs
LM36923 C055_SNVSA30.png Figure 41. Boost Efficiency vs Series LEDs
LM36923 C056_SNVSA30.png Figure 43. Boost Efficiency vs Series LEDs
LM36923 C031_SNVSA30.png Figure 45. Boost Efficiency vs Series LEDs
LM36923 C033_SNVSA30.png Figure 47. Boost Efficiency vs Series LEDs
LM36923 C035_SNVSA30.png Figure 49. Boost Efficiency vs Series LEDs
LM36923 C037_SNVSA30.png Figure 51. Boost Efficiency vs Series LEDs
LM36923 C021_SNVSA30.png Figure 53. LED Current vs Brightness Code
LM36923 C017_SNVSA30.png Figure 55. LED Matching (Linear Mapping)
LM36923 C020_SNVSA30.png Figure 57. LED Current Accuracy
LM36923 C027_SNVSA30.png Figure 59. LED Headroom Voltage (Mis-Matched Strings)