ZHCSF16S November   2004  – May 2016 LM3671 , LM3671-Q1

PRODUCTION DATA.  

  1. 特性
  2. 应用范围
  3. 说明
  4. 修订历史记录
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings: LM3671
    3. 6.3 ESD Ratings: LM3671-Q1
    4. 6.4 Recommended Operating Conditions
    5. 6.5 Thermal Information
    6. 6.6 Dissipation Ratings
    7. 6.7 Electrical Characteristics
    8. 6.8 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Circuit Operation
      2. 7.3.2 Soft Start
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Operation
        1. 7.4.1.1 Internal Synchronous Rectification
        2. 7.4.1.2 Current Limiting
      2. 7.4.2 PFM Operation
      3. 7.4.3 Shutdown
      4. 7.4.4 Low Dropout Operation (LDO)
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Typical Application: Fixed-Voltage Version
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Inductor Selection
            1. 8.2.1.2.1.1 Method 1
            2. 8.2.1.2.1.2 Method 2
          2. 8.2.1.2.2 Input Capacitor Selection
          3. 8.2.1.2.3 Output Capacitor Selection
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Typical Application: ADJ Version
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Output Voltage Selection for LM3671-ADJ
        3. 8.2.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 DSBGA Package Assembly and Use
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 文档支持
      1. 11.2.1 相关文档
    3. 11.3 相关链接
    4. 11.4 社区资源
    5. 11.5 商标
    6. 11.6 静电放电警告
    7. 11.7 Glossary
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

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 external control of this device is very easy. First make sure the correct voltage been applied at VIN pin, then simply apply the voltage at EN pin according to the Electrical Characteristics to enable or disable the output voltage.

8.2 Typical Application

8.2.1 Typical Application: Fixed-Voltage Version

LM3671 LM3671-Q1 20108401.gif Figure 32. LM3671 Fixed-Voltage Typical Application Circuit

8.2.1.1 Design Requirements

Two ceramic capacitors and one inductor required for this application. These three external components need to be selected very carefully for property operation. Please read Detailed Design Procedure.

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Inductor Selection

There are two main considerations when choosing an inductor; the inductor should not saturate, and the inductor current ripple should be small enough to achieve the desired output voltage ripple. Different saturation current rating specifications are followed by different manufacturers so attention must be given to details. Saturation current ratings are typically specified at 25°C. However, ratings at the maximum ambient temperature of application should be requested from the manufacturer. The minimum value of inductance to specify good performance is 1.76 µH at ILIM (typical) DC current over the ambient temperature range. Shielded inductors radiate less noise and should be preferred.

There are two methods to choose the inductor saturation current rating.

8.2.1.2.1.1 Method 1

The saturation current should be greater than the sum of the maximum load current and the worst case average to peak inductor current. This can be written as

Equation 2. LM3671 LM3671-Q1 20108434.gif

where

  • IRIPPLE: average to peak inductor current
  • IOUTMAX: maximum load current (600 mA)
  • VIN: maximum input voltage in application
  • L : min inductor value including worst case tolerances (30% drop can be considered for method 1)
  • f : minimum switching frequency (1.6 MHz)
  • VOUT: output voltage

8.2.1.2.1.2 Method 2

A more conservative and recommended approach is to choose an inductor that has a saturation current rating greater than the maximum current limit of 1150 mA.

A 2.2-µH inductor with a saturation current rating of at least 1150 mA is recommended for most applications. Inductor resistance should be less than 0.3 Ω for good efficiency. Table 1 lists suggested inductors and suppliers. For low-cost applications, an unshielded bobbin inductor could be considered. For noise critical applications, a toroidal or shielded-bobbin inductor should be used. A good practice is to lay out the board with overlapping footprints of both types for design flexibility. This allows substitution of a low-noise shielded inductor, in the event that noise from low-cost bobbin models is unacceptable.

8.2.1.2.2 Input Capacitor Selection

A ceramic input capacitor of 4.7 µF, 6.3 V is sufficient for most applications. Place the input capacitor as close as possible to the VIN pin of the device. A larger value may be used for improved input voltage filtering. Use X7R or X5R types; do not use Y5V. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and 0603. The minimum input capacitance to specify good performance is 2.2 µF at 3-V DC bias; 1.5 µF at 5-V DC bias including tolerances and over ambient temperature range. The input filter capacitor supplies current to the PFET switch of the LM3671 in the first half of each cycle and reduces voltage ripple imposed on the input power source. A ceramic capacitor’s low ESR provides the best noise filtering of the input voltage spikes due to this rapidly changing current. Select a capacitor with sufficient ripple current rating. The input current ripple can be calculated as:

Equation 3. LM3671 LM3671-Q1 20108426.gif

Table 1. Suggested Inductors and Their Suppliers

MODEL VENDOR DIMENSIONS L × W × H (mm) D.C.R (maximum)(mΩ)
DO3314-222MX Coilcraft 3.3 × 3.3 × 1.4 200
LPO3310-222MX Coilcraft 3.3 × 3.3 × 1 150
ELL5GM2R2N Panasonic 5.2 × 5.2 × 1.5 53
CDRH2D14NP-2R2NC Sumida 3.2 × 3.2 × 1.55 94

8.2.1.2.3 Output Capacitor Selection

A ceramic output capacitor of 10 µF, 6.3 V is sufficient for most applications. Use X7R or X5R types; do not use Y5V. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and 0603. DC bias characteristics vary from manufacturer to manufacturer and dc bias curves should be requested from them as part of the capacitor selection process.

The minimum output capacitance to specify good performance is 5.75 µF at 1.8-V DC bias including tolerances and over ambient temperature range. The output filter capacitor smoothes out current flow from the inductor to the load, helps maintain a steady output voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with sufficient capacitance and sufficiently low ESR to perform these functions.

The output voltage ripple is caused by the charging and discharging of the output capacitor and by the RESR and can be calculated as:

Voltage peak-to-peak ripple due to capacitance can be expressed by Equation 4:

Equation 4. LM3671 LM3671-Q1 20108427.gif

Voltage peak-to-peak ripple due to ESR can be expressed by Equation 5:

Equation 5. VPP-ESR = (2 × IRIPPLE) × RESR

Because these two components are out of phase the rms (root mean squared) value can be used to get an approximate value of peak-to-peak ripple.

The peak-to-peak ripple voltage, rms value can be expressed by Equation 6:

Equation 6. LM3671 LM3671-Q1 20108428.gif

Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series resistance of the output capacitor (RESR).

The RESR is frequency dependent (as well as temperature dependent); make sure the value used for calculations is at the switching frequency of the part.

Table 2. Suggested Capacitors and Their Suppliers

MODEL TYPE VENDOR VOLTAGE RATING (V) CASE SIZE
INCH (mm)
4.7 µF for CIN
C2012X5R0J475K Ceramic, X5R TDK 6.3 0805 (2012)
JMK212BJ475K Ceramic, X5R Taiyo-Yuden 6.3 0805 (2012)
GRM21BR60J475K Ceramic, X5R Murata 6.3 0805 (2012)
C1608X5R0J475K Ceramic, X5R TDK 6.3 0603 (1608)
10 µF for COUT
GRM21BR60J106K Ceramic, X5R Murata 6.3 0805 (2012)
JMK212BJ106K Ceramic, X5R Taiyo-Yuden 6.3 0805 (2012)
C2012X5R0J106K Ceramic, X5R TDK 6.3 0805 (2012)
C1608X5R0J106K Ceramic, X5R TDK 6.3 0603 (1608)

8.2.1.3 Application Curves

LM3671 LM3671-Q1 20108420.png
Figure 33. PFM-to-PWM Mode Change by Load Transients
LM3671 LM3671-Q1 20108421.png
Figure 34. PWM-to-PFM Mode Change by Load Transients

8.2.2 Typical Application: ADJ Version

LM3671 LM3671-Q1 20108431.gif Figure 35. Typical Application Circuit for ADJ Version

8.2.2.1 Design Requirements

DESIGN PARAMETER EXAMPLE VALUE
Input voltage range 2.7 V to 5.5 V
Input capacitor 4.7 µF
Output capacitor 10 µF
Inductor 2.2 µH
ADJ programmable output voltage 1.1 V to 3.3 V

8.2.2.2 Detailed Design Procedure

8.2.2.2.1 Output Voltage Selection for LM3671-ADJ

The output voltage of the adjustable parts can be programmed through the resistor network connected from VOUT to FB, then to GND. VOUT is adjusted to make the voltage at FB equal to 0.5 V. The resistor from FB to GND (R2) should be 200 kΩ to keep the current drawn through this network well below the 16-µA quiescent current level (PFM mode) but large enough that it is not susceptible to noise. If R2 is 200 kΩ, and VFB is 0.5 V, the current through the resistor feedback network will be 2.5 µA. The output voltage of the adjustable parts ranges from 1.1 V to 3.3 V.

The formula for output voltage selection is:

Equation 7. LM3671 LM3671-Q1 20108435.gif

where

  • VOUT: output voltage (volts)
  • VFB : feedback voltage = 0.5 V
  • R1: feedback resistor from VOUT to FB
  • R2: feedback resistor from FB to GND

For any output voltage greater than or equal to 1.1 V, a zero must be added around 45 kHz for stability. The formula for calculation of C1 is:

Equation 8. LM3671 LM3671-Q1 20108436.gif

For output voltages higher than 2.5 V, a pole must be placed at 45 kHz as well. If the pole and zero are at the same frequency the formula for calculation of C2 is:

Equation 9. LM3671 LM3671-Q1 20108437.gif

The formula for location of zero and pole frequency created by adding C1 and C2 is given below. By adding C1, a zero as well as a higher frequency pole is introduced.

Equation 10. LM3671 LM3671-Q1 20108438.gif
Equation 11. LM3671 LM3671-Q1 20108439.gif

See the Table 3 table.

Table 3. LM3671-ADJ Configurations for Various VOUT
(Circuit of Figure 35)

VOUT (V) R1 (kΩ) R2 (kΩ) C1 (pF) C2 (pF) L (µH) CIN (µF) COUT (µF)
0.9 160 200 22 none 2.2 4.7 10
1.1 240 200 15 none 2.2 4.7 10
1.2 280 200 12 none 2.2 4.7 10
1.3 320 200 12 none 2.2 4.7 10
1.5 357 178 10 none 2.2 4.7 10
1.6 442 200 8.2 none 2.2 4.7 10
1.7 432 178 8.2 none 2.2 4.7 10
1.8 464 178 8.2 none 2.2 4.7 10
1.875 523 191 6.8 none 2.2 4.7 10
2.5 402 100 8.2 none 2.2 4.7 10
2.8 464 100 8.2 33 2.2 4.7 10
3.3 562 100 6.8 33 2.2 4.7 10

8.2.2.3 Application Curves

LM3671 LM3671-Q1 20108424.gif
Figure 36. Start-Up into PWM Mode
LM3671 LM3671-Q1 20108419.gif
Figure 37. Start-Up into PFM Mode