SNVS974B April   2013  – October 2015 LM3630A

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-Compatible Timing Requirements (SCL, SDA)
    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 Operation
        1. 7.3.1.1  Control Bank Mapping
        2. 7.3.1.2  PWM Input Polaritiy
        3. 7.3.1.3  HWEN Input
        4. 7.3.1.4  SEL Input
        5. 7.3.1.5  INTN Output
        6. 7.3.1.6  Boost Converter
        7. 7.3.1.7  Boost Switching Frequency Select
        8. 7.3.1.8  Adaptive Headroom
        9. 7.3.1.9  Current Sinks
        10. 7.3.1.10 Current String Biasing
        11. 7.3.1.11 Full-Scale LED Current
        12. 7.3.1.12 Brightness Register
        13. 7.3.1.13 Exponential Mapping
        14. 7.3.1.14 Linear Mapping
      2. 7.3.2 Test Features
        1. 7.3.2.1 Open LED String (LED1 And LED2)
        2. 7.3.2.2 Shorted LED String
        3. 7.3.2.3 Overvoltage Protection (Manufacturing Fault Detection and Shutdown)
      3. 7.3.3 Fault Flags/Protection Features
        1. 7.3.3.1 Overvoltage Protection (Inductive Boost Operation)
        2. 7.3.3.2 Current Limit
        3. 7.3.3.3 Thermal Shutdown
      4. 7.3.4 Initialization Timing
        1. 7.3.4.1 Initialization Timing With HWEN Tied to VIN
        2. 7.3.4.2 Initialization Timing With HWEN Driven by GPIO
        3. 7.3.4.3 Initialization After Software Reset
    4. 7.4 Device Functional Modes
      1. 7.4.1 LED Current Ramping
        1. 7.4.1.1 Start-Up/Shutdown Ramp
        2. 7.4.1.2 Run-Time Ramp
      2. 7.4.2 PWM Operation
        1. 7.4.2.1 PWM Input
        2. 7.4.2.2 PWM Input Frequency
        3. 7.4.2.3 Recommended Settings
        4. 7.4.2.4 Adjustments to PWM Sampler
          1. 7.4.2.4.1 Filter Strength, Register 50h Bits [1:0]
          2. 7.4.2.4.2 Hysteresis 1 Bit, Register 05h, Bit 7
          3. 7.4.2.4.3 Lower Bound Disable, Register 05h, Bit 6
        5. 7.4.2.5 Minimum TON Pulse Width
    5. 7.5 Programming
      1. 7.5.1 I2C-Compatible Interface
        1. 7.5.1.1 Data Validity
        2. 7.5.1.2 Start and Stop Conditions
        3. 7.5.1.3 Transferring Data
    6. 7.6 Register Maps
      1. 7.6.1 LM3630A I2C Register Map
      2. 7.6.2 Register Descriptions
  8. 8 Application 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 Inductor Selection
        2. 8.2.2.2 Maximum Power Output
      3. 8.2.3 Application Curves
    3. 8.3 Initialization Setup
      1. 8.3.1 Recommended Initialization Sequence
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Output Capacitor Placement
      2. 10.1.2 Schottky Diode Placement
      3. 10.1.3 Inductor Placement
      4. 10.1.4 Input Capacitor Selection and 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 Documentation Support
      1. 11.2.1 Related Documentation
    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

Package Options

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

8 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.

8.1 Application Information

The LM3630A is a dual-channel backlight driver. The device has 5-bit full-scale current programmability (5 mA to 30 mA) and for every full-scale current there is 8 bits of LED current adjustment from 0 to IFULL_SCALE. Both current sinks can be independently controlled via two separate full-scale current registers and two separate 8-bit brightness registers, or can be made to track together via a single brightness register.

8.2 Typical Application

LM3630A 30200201.gif Figure 87. LM3630A Typical Application

8.2.1 Design Requirements

For typical white LED applications, use the parameters listed in Table 21.

Table 21. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Minimum input voltage 2.3 V
Minimum output voltage VIN
Output current 28.5 mA per channel
Switching frequency 500 kHz or 1 MHz

8.2.2 Detailed Design Procedure

8.2.2.1 Inductor Selection

The LM3630A is designed to work with a 10-µH to 22-µH inductor. When selecting the inductor, ensure that the saturation rating for the inductor is high enough to accommodate the peak inductor current. Equation 4 calculates the peak inductor current based upon LED current, VIN, VOUT, and efficiency.

Equation 4. LM3630A 30200222.gif

where:

Equation 5. LM3630A 30200223.gif

When choosing L, the inductance value must also be large enough so that the peak inductor current is kept below the LM3630A device's switch current limit. This forces a lower limit on L given by Equation 6.

Equation 6. LM3630A 30200224.gif

ISW_MAX is given in Electrical Characteristics, efficiency (η) is shown in theTypical Characteristics, and ƒSW is typically 500 kHz or 1 MHz.

Table 22. Inductors

MANUFACTURER PART NUMBER VALUE SIZE CURRENT RATING DC RESISTANCE
TDK VLF4014ST-100M1R0 10 µH 3.8 mm × 3.6 mm × 1.4 mm 1A 0.22 Ω
TDK VLF302512MT-220M 22 µH 3 mm × 2.5 mm × 1.2 mm 0.43A 0.583 Ω

8.2.2.2 Maximum Power Output

The LM3630A device's maximum output power is governed by two factors: the peak current limit (ICL = 1.2 A maximum), and the maximum output voltage (VOVP = 40 V minimum). When the application causes either of these limits to be reached, it is possible that the proper current regulation and matching between LED current strings may not be met.

In the case of a peak current limited situation, when the peak of the inductor current hits the LM3630A device's current limit the NFET switch turns off for the remainder of the switching period. If this happens, each switching cycle the LM3630A begins to regulate the peak of the inductor current instead of the headroom across the current sinks. This can result in the dropout of the feedback-enabled current sinks and the current dropping below its programmed level.

The peak current in a boost converter is dependent on the value of the inductor, total LED current (IOUT), the output voltage (VOUT) (which is the highest voltage LED string + 0.3 V regulated headroom voltage), the input voltage VIN, and the efficiency (Output Power/Input Power). Additionally, the peak current is different depending on whether the inductor current is continuous during the entire switching period (CCM) or discontinuous (DCM) where it goes to 0 before the switching period ends.

For CCM the peak inductor current is given by:

Equation 7. LM3630A 30200219.gif

For DCM the peak inductor current is given by:

Equation 8. LM3630A 30200220.gif

To determine which mode the circuit is operating in (CCM or DCM), a calculation must be done to test whether the inductor current ripple is less than the anticipated input current (IIN). If ΔIL is < IIN, the device operates in CCM. If ΔIL is > IIN then the device is operating in DCM.

Equation 9. LM3630A 30200221.gif

Typically at currents high enough to reach the LM3630A device's peak current limit, the device is operating in CCM.

Application Curves show the output current and output voltage derating for a 10-µH and a 22-µH inductor, at switch frequencies of 500 kHz and 1 MHz. A 10-µH inductor is typically a smaller device with lower on resistance, but the peak currents are higher. A 22-µH inductor provides for lower peak currents, but to match the DC resistance of a 10 µH requires a larger-sized device.

8.2.3 Application Curves

LM3630A C027_SNVS974.png
Frequency = 500 kHz L = 10 µH
Figure 88. Maximum Boost Output Power vs VIN
LM3630A C062_SNVS974.png
Frequency = 500 kHz L = 22 µH
Figure 90. Maximum Boost Output Power vs VIN
LM3630A C028_SNVS974.png
Frequency = 1 MHz L = 10 µH
Figure 89. Maximum Boost Output Power vs VIN
LM3630A C063_SNVS974.png
Frequency = 1 MHz L = 22 µH
Figure 91. Maximum Boost Output Power vs VIN

8.3 Initialization Setup

8.3.1 Recommended Initialization Sequence

The recommended initialization sequence for the device registers is as follows:

  1. Set Filter Strength register (offset = 50h) to 03h.
  2. Set Configuration register (offset = 01h) to enable the PWM and the feedback for Bank A; for example, writing 09h to the Configuration register, enables PWM and feedback for Bank A. Note the Bank B PWM and feedback need to be configured if Bank B is used, otherwise disable the Bank B feedback by clearing bit 4 and disable the Bank B PWM by clearing bit 1.
  3. Configure the Boost Control register (offset = 02h) to select the OVP, OCP and FMODE. For example, writing 78h to the Boost Control register sets OVP to 40 V, OCP to 1.2 A and FMODE to 500 kHz.
  4. Set the full scale LED current for Bank A and Bank B (if used), by writing to the Current A (offset = 05h), and Current B(offset = 06) registers. For example, writing 14h to the Current A register selects a full scale LED current of 20 mA for Bank A.
  5. Set the PWM Sampler Hysteresis to 2 codes by setting Bit 7 of the Current A register. Set the PWM Sampler Lower Bound code to 6 by clearing Bit 6 of the Current A register. Note these settings apply to both Bank A and Bank B. If only Bank B is used, these setting are still necessary when PWM is enabled.
  6. Select the current control and enable or disable the LED Bank A and/or B by writing to Control register(offset = 00h). For example, writing 14h to the Control register select linear current control and enables Bank A.
  7. Set the LED brightness by writing to Brightness A (offset = 03h) and Brightness B (Offset = 04h) registers. For example, writing FFh to Brightness A sets the LED current to 20 mA, with the Current A register set to 14h, and the PWM input is high.