SNVS653E July   2011  – August 2015 LM3532

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 Specifications (SCL, SDA)
    7. 6.7 Switching Characteristics
    8. 6.8 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 40-V Boost Converter
      2. 7.3.2 Hardware Enable Input
      3. 7.3.3 Feedback Enable
      4. 7.3.4 LM3532 Current Sink Configuration
      5. 7.3.5 PWM Inputs
      6. 7.3.6 Full-Scale LED Current
      7. 7.3.7 Interrupt Output
      8. 7.3.8 Protection Features
        1. 7.3.8.1 Overvoltage Protection
        2. 7.3.8.2 Current Limit
    4. 7.4 Device Functional Modes
      1. 7.4.1  LED Current Ramping
      2. 7.4.2  Start-up and Shutdown Current Ramping
      3. 7.4.3  Run-Time Ramp Rates
      4. 7.4.4  LED Current Mapping Modes
      5. 7.4.5  Exponential Current Mapping Mode
      6. 7.4.6  Linear Current Mapping
      7. 7.4.7  LED Current Control
        1. 7.4.7.1 I2C Current Control
        2. 7.4.7.2 I2C Current Control With PWM
      8. 7.4.8  Assigning and Enabling a PWM Input
      9. 7.4.9  Enabling a Current Sink
      10. 7.4.10 Ambient Light Sensor Current Control
        1. 7.4.10.1  ALS Resistors
        2. 7.4.10.2  Ambient Light Zone Boundaries
        3. 7.4.10.3  Ambient Light Zone Hysteresis
        4. 7.4.10.4  PWM Enabled for a Particular Zone
        5. 7.4.10.5  ALS Operation
        6. 7.4.10.6  ALS Input Select and ALS ADC Input
        7. 7.4.10.7  ALS ADC Readback
        8. 7.4.10.8  ALS Averaging
        9. 7.4.10.9  ALS ADC Average Readback
        10. 7.4.10.10 Initializing the ALS
        11. 7.4.10.11 ALS Operation
        12. 7.4.10.12 Direct ALS Control
      11. 7.4.11 Down Delay
    5. 7.5 Programming
      1. 7.5.1 I2C-Compatible Interface
        1. 7.5.1.1 Start and Stop Conditions
        2. 7.5.1.2 I2C-Compatible Address
        3. 7.5.1.3 Transferring Data
    6. 7.6 Register Maps
      1. 7.6.1  Output Configuration
      2. 7.6.2  Start-up/Shutdown Ramp Rate
      3. 7.6.3  Run-Time Ramp Rate
      4. 7.6.4  Control A PWM
      5. 7.6.5  Control B PWM
      6. 7.6.6  Control C PWM
      7. 7.6.7  Control A Brightness Configuration
      8. 7.6.8  Control B Brightness Configuration
      9. 7.6.9  Control C Brightness Configuration
      10. 7.6.10 Control A, B, and C Full-Scale Current
      11. 7.6.11 Feedback Enable
      12. 7.6.12 Control Enable
      13. 7.6.13 ALS1 and ALS2 Resistor Select
      14. 7.6.14 ALS Down Delay
      15. 7.6.15 ALS Configuration
      16. 7.6.16 ALS Zone Readback / Information
      17. 7.6.17 ALS Zone Boundaries
      18. 7.6.18 Zone Target Registers
  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 Capacitor Selection
        3. 8.2.2.3 Diode Selection
        4. 8.2.2.4 Maximum Output Power
          1. 8.2.2.4.1 Peak Current Limited
          2. 8.2.2.4.2 Output Voltage Limited
      3. 8.2.3 Application Curves
  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 Examples
  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 LM3532 incorporates a 40-V (maximum output) boost, three high-voltage, low-side current sinks, and programmable dual ambient light sensor inputs with internal-sensor gain selection. The device can drive up to 3 parallel high-voltage LED strings with up to 90% efficiency. The adaptive current regulation method allows for different LED currents in each current sink, thus allowing for a wide variety of backlight-with-keypad applications.

8.2 Typical Application

LM3532 301154100.gifFigure 23. LM3532 Typical Application

8.2.1 Design Requirements

For typical white LED applications, use the parameters listed in Table 20:

Table 20. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Input voltage range 2.7 V to 5.5 V
Output current 500 MHz typical
Boost switching frequency 2 MHz

8.2.2 Detailed Design Procedure

Table 21. Suggested Application Circuit Component List

COMPONENT MANUFACTURER'S PART NUMBER VALUE SIZE CURRENT/VOLTAGE
RATING (RESISTANCE)
L COILCRAFT
LPS4018-103ML		 10 µH 3.9 mm x 3.9 mm x 1.7 mm 1 A (RDC = 0.2 Ω)
COUT Murata
GRM21BR71H105KA12L		 1 µF 0805 50 V
CIN Murata
GRM188R71A225KE15D		 2.2 µF 0603 10 V

8.2.2.1 Inductor Selection

The LM3532 is designed to work with a 10-µH to 22-µH inductor. When selecting the inductor, ensure that the saturation rating is high enough to accommodate the applications peak inductor current . The inductance value must also be large enough so that the peak inductor current is kept below the LM3532's switch current limit. See Maximum Output Power for more details. Table 22 lists various inductors that can be used with the LM3532. The inductors with higher saturation currents are more suitable for applications with higher output currents or voltages (multiple strings). The smaller devices are geared toward single string applications with lower series LED counts.

Table 22. Suggested Inductors

MANUFACTURER PART NUMBER VALUE SIZE CURRENT RATING DC RESISTANCE
TDK VLS252010T-100M 10 µH 2.5 mm × 2 mm × 1 mm 590 mA 0.712 Ω
TDK VLS2012ET-100M 10 µH 2 mm × 2 mm × 1.2 mm 695 mA 0.47 Ω
TDK VLF301512MT-100M 10 µH 3.0 mm × 2.5 mm × 1.2mm 690 mA 0.25 Ω
TDK VLF4010ST-100MR80 10 µH 2.8 mm × 3 mm × 1 mm 800 mA 0.25 Ω
TDK VLS252012T-100M 10 µH 2.5 mm × 2 mm × 1.2mm 810 mA 0.63 Ω
TDK VLF3014ST-100MR82 10 µH 2.8 mm × 3 mm × 1.4mm 820 mA 0.25 Ω
TDK VLF4014ST-100M1R0 10 µH 3.8 mm × 3.6 mm × 1.4 mm 1000 mA 0.22 Ω
Coilcraft XPL2010-103ML 10 µH 1.9 mm × 2 mm × 1 mm 610 mA 0.56 Ω
Coilcraft LPS3010-103ML 10 µH 2.95 mm × 2.95 mm × 0.9 mm 550 mA 0.54 Ω
Coilcraft LPS4012-103ML 10 µH 3.9mm × 3.9mm × 1.1mm 1000 mA 0.35 Ω
Coilcraft LPS4012-223ML 22 µH 3.9 mm × 3.9 mm × 1.1 mm 780 mA 0.6 Ω
Coilcraft LPS4018-103ML 10 µH 3.9 mm × 3.9 mm × 1.7 mm 1100 mA 0.2 Ω
Coilcraft LPS4018-223ML 22 µH 3.9 mm × 3.9 mm × 1.7 mm 700 mA 0.36 Ω

8.2.2.2 Capacitor Selection

The LM3532’s output capacitor has two functions: filtering of the boost converter's switching ripple, and to ensure feedback loop stability. As a filter, the output capacitor supplies the LED current during the boost converter's on time and absorbs the inductor's energy during the switch's off time. This causes a sag in the output voltage during the on time and a rise in the output voltage during the off time. Because of this, the output capacitor must be sized large enough to filter the inductor current ripple that could cause the output voltage ripple to become excessive. As a feedback loop component, the output capacitor must be at least 1µF and have low ESR; otherwise, the LM3532's boost converter can become unstable. This requires the use of ceramic output capacitors. Table 23 lists part numbers and voltage ratings for different output capacitors that can be used with the LM3532.

Table 23. Input/Output Capacitors

MANUFACTURER PART NUMBER VALUE SIZE RATING DESCRIPTION
Murata GRM21BR71H105KA12 1 µF 0805 50 V COUT
Murata GRM188B31A225KE33 2.2 µF 0805 10 V CIN
TDK C1608X5R0J225 2.2 µF 0603 6.3 V CIN

8.2.2.3 Diode Selection

The diode connected between the SW and OUT pins must be a Schottky diode and have a reverse breakdown voltage high enough to handle the maximum output voltage in the application. Table 24 lists various diodes that can be used with the LM3532.

Table 24. Diodes

MANUFACTURER PART NUMBER VALUE SIZE RATING
Diodes Inc. B0540WS Schottky SOD-323 40/500 V/mA
Diodes Inc. SDM20U40 Schottky SOD-523 (1.2 mm × 0.8 mm × 0.6 mm) 40/200 V/mA
On Semiconductor NSR0340V2T1G Schottky SOD-523 (1.2 mm × 0.8 mm × 0.6 mm) 40/250 V/mA
On Semiconductor NSR0240V2T1G Schottky SOD-523 (1.2 mm × 0.8 mm × 0.6 mm) 40/250 V/mA

8.2.2.4 Maximum Output Power

The LM3532 device's maximum output power is governed by two factors: the peak current limit (ICL = 880 mA minimum), 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.

8.2.2.4.1 Peak Current Limited

In the case of a peak current limited situation, when the peak of the inductor current hits the LM3532's current limit the NFET switch turns off for the remainder of the switching period. If this happens, each switching cycle the LM3532 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 + 0.4 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 5. LM3532 30115429.gif

For DCM the peak inductor current is given by:

Equation 6. LM3532 30115430.gif

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

Equation 7. LM3532 30115431.gif

Typically at currents high enough to reach the LM3532's peak current limit, the device is operating in CCM.

Figure 24, Figure 25, Figure 26, and Figure 27 show the output current and voltage derating for a 10-µH and a 22-µH inductor. These plots take Equation 5 and Equation 6 from above and plot VOUT and IOUT with varying VIN, a constant peak current of 880 mA (ICL min), and a constant efficiency of 85%. Using these curves can give a good design guideline on selecting the correct inductor for a given output power requirement. A 10 µH 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 inductor requires a larger-sized device.

LM3532 30115475.gifFigure 24. Maximum Output Power (22 µH)
LM3532 30115427.gifFigure 26. Maximum Output Power (10 µH)
LM3532 30115483.gifFigure 25. Maximum Output Power (22 µH)
LM3532 30115433.gifFigure 27. Maximum Output Power (10 µH)

8.2.2.4.2 Output Voltage Limited

When the LM3532 output voltage (highest voltage LED string + 400-mV headroom voltage) reaches 40 V, the OVP threshold is hit, and the NFET turns off and remains off until the output voltage drops 1V below the OVP threshold. Once VOUT falls below this hysteresis, the boost converter turns on again. In high output voltage situations the LM3532 begins to regulate the output voltage to the VOVP level instead of the current sink headroom voltage. This can result in a loss of headroom voltage across the feedback enabled current sinks resulting in the LED current dropping below its programmed level.

8.2.3 Application Curves

VIN = 3.6 V, LEDs (VF = 3.2 V at 20 mA, TA = 25°C), COUT = 1 µF, CIN = 2.2 µF, L = Coilcraft LPS4018-103ML (10 µH ) or LPS4018-223M (22 µH), TA = 25°C unless otherwise specified.
LM3532 30115451.gif
ILED = 20.2 mA L = 10 µH
Figure 28. Efficiency vs VIN Single String,
LM3532 30115453.gif
ILED = 20.2 mA L = 10 µH
Figure 30. Efficiency vs VIN Dual String
LM3532 30115455.gif
ILED = 20.2 mA L = 10 µH
Figure 32. Efficiency vs VIN Triple String
LM3532 30115457.gif
ILED = 20.2 mA L = 22 µH
Figure 34. Efficiency vs VIN Single String
LM3532 30115459.gif
ILED = 20.2 mA L = 22 µH
Figure 36. Efficiency vs VIN Dual String
LM3532 30115461.gif
ILED = 20.2 mA L = 22 µH
Figure 38. Efficiency vs VIN Triple String
LM3532 30115463.gif
VIN = 3.6 V L = 10 µH
Figure 40. Efficiency vs ILED Triple String
LM3532 30115465.gif
VIN = 3.6 V L = 22 µH
Figure 42. Efficiency vs ILED Triple String
LM3532 30115452.gif
ILED = 20.2 mA L = 10 µH
Figure 29. Efficiency vs VIN Single String
LM3532 30115454.gif
ILED = 20.2 mA L = 10 µH
Figure 31. Efficiency vs VIN Dual String
LM3532 30115456.gif
ILED = 20.2 mA L = 10 µH
Figure 33. Efficiency vs VIN Triple String
LM3532 30115458.gif
ILED = 20.2 mA L = 22 µH
Figure 35. Efficiency vs VIN Single String
LM3532 30115460.gif
ILED = 20.2 mA L = 22 µH
Figure 37. Efficiency vs VIN Dual String, Iled = 20.2ma Per String L = Lps4018-223ml (22µh)
LM3532 30115462.gif
ILED = 20.2 mA L = 22 µH
Figure 39. Efficiency vs VIN Triple String
LM3532 30115464.gif
VIN = 3.6 V L = 10 µH
Figure 41. Efficiency vs ILED Triple String
LM3532 30115466.gif
VIN = 3.6 V L = 22 µH
Figure 43. Efficiency vs ILED Triple String