ZHCSA20C October   2011  – June 2019 LMR10510

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化应用
  4. 4 修订历史记录
  5. 5 说明（续）
  6. 6 Pin Configuration and Functions
    1.     Pin Description: 5-Pin SOT-23
    2.     Pin Descriptions 6-Pin WSON
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Recommended Operating Ratings
    3. 7.3 Electrical Characteristics
    4. 7.4 Typical Performance Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Soft Start
      2. 8.3.2 Output Overvoltage Protection
      3. 8.3.3 Undervoltage Lockout
      4. 8.3.4 Current Limit
      5. 8.3.5 Thermal Shutdown
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Detailed Design Procedure
        1. 9.2.1.1 Custom Design With WEBENCH® Tools
        2. 9.2.1.2 Inductor Selection
        3. 9.2.1.3 Input Capacitor
        4. 9.2.1.4 Output Capacitor
        5. 9.2.1.5 Catch Diode
        6. 9.2.1.6 Output Voltage
        7. 9.2.1.7 Calculating Efficiency, and Junction Temperature
      2. 9.2.2 Application Curves
      3. 9.2.3 Other System Examples
        1. 9.2.3.1 LMR10510x Design Example 1
        2. 9.2.3.2 Lmr10510X Design Example 2
        3. 9.2.3.3 LMR10510Y Design Example 3
        4. 9.2.3.4 LMR10510Y Design Example 4
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Definitions
    4. 10.4 WSON Package
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 开发支持
        1. 11.1.1.1 使用 WEBENCH® 工具创建定制设计
    2. 11.2 接收文档更新通知
    3. 11.3 社区资源
    4. 11.4 商标
    5. 11.5 静电放电警告
    6. 11.6 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

9.2.1.7 Calculating Efficiency, and Junction Temperature

The complete LMR10510 DC/DC converter efficiency can be calculated in the following manner.

LMR10510 30165620.gif

Or

LMR10510 30165622.gif

Calculations for determining the most significant power losses are shown below. Other losses totaling less than 2% are not discussed.

Power loss (PLOSS) is the sum of two basic types of losses in the converter: switching and conduction. Conduction losses usually dominate at higher output loads, whereas switching losses remain relatively fixed and dominate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D):

LMR10510 30165610.gif

VSW is the voltage drop across the internal PFET when it is on, and is equal to:

 

VSW = IOUT x RDSON

VD is the forward voltage drop across the Schottky catch diode. It can be obtained from the diode manufactures Electrical Characteristics section. If the voltage drop across the inductor (VDCR) is accounted for, the equation becomes:

LMR10510 30165621.gif

The conduction losses in the free-wheeling Schottky diode are calculated as follows:

PDIODE = VD × IOUT × (1-D)

 

Often this is the single most significant power loss in the circuit. Take care to choose a Schottky diode that has a low forward-voltage drop.

Another significant external power loss is the conduction loss in the output inductor. The equation can be simplified to:

PIND = IOUT2 × RDCR

The LMR10510 conduction loss is mainly associated with the internal PFET:

LMR10510 30165672.gif

If the inductor ripple current is fairly small, the conduction losses can be simplified to:

PCOND = IOUT2 × RDSON x D

Switching losses are also associated with the internal PFET. They occur during the switch on and off transition periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss is to empirically measuring the rise and fall times (10% to 90%) of the switch at the switch node.

Switching Power Loss is calculated as follows:

PSWR = 1/2(VIN x IOUT x FSW x TRISE)
PSWF = 1/2(VIN x IOUT x FSW x TFALL)
PSW = PSWR + PSWF

Another loss is the power required for operation of the internal circuitry:

PQ = IQ x VIN

IQ is the quiescent operating current, and is typically around 3.3mA for the 1.6MHz frequency option.

Typical Application power losses are:

Table 1. Power Loss Tabulation

VIN 5 V
VOUT 3.3 V POUT 3.3 W
IOUT 1 A
VD 0.45 V PDIODE 150 mW
FSW 1.6 MHz
IQ 3.3 mA PQ 17 mW
TRISE 4 ns PSWR 16 mW
TFALL 4 ns PSWF 16 mW
RDS(ON) 150 mΩ PCOND 100 mW
INDDCR 70 mΩ PIND 70 mW
D 0.667 PLOSS 369 mW
η 88% PINTERNAL 149 mW
ΣPCOND + PSW + PDIODE + PIND + PQ = PLOSS
ΣPCOND + PSWF + PSWR + PQ = PINTERNAL
PINTERNAL = 149 mW