ZHCSI53A May 2018 – November 2018 LM5122ZA
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Undervoltage Lockout (UVLO)
- 7.3.2 High-Voltage VCC Regulator
- 7.3.3 Oscillator
- 7.3.4 Slope Compensation
- 7.3.5 Error Amplifier
- 7.3.6 PWM Comparator
- 7.3.7 Soft Start
- 7.3.8 HO and LO Drivers
- 7.3.9 Bypass Operation (VOUT = VIN)
- 7.3.10 Cycle-by-Cycle Current Limit
- 7.3.11 Clock Synchronization
- 7.3.12 Maximum Duty Cycle
- 7.3.13 Thermal Protection
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1
Application Information
- 8.1.1 Feedback Compensation
- 8.1.2 Sub-Harmonic Oscillation
- 8.1.3 Interleaved Boost Configuration
- 8.1.4 DCR Sensing
- 8.1.5 Output Overvoltage Protection
- 8.1.6 SEPIC Converter Simplified Schematic
- 8.1.7 Non-Isolated Synchronous Flyback Converter Simplified Schematic
- 8.1.8 Negative to Positive Conversion
- 8.2
Typical Application
- 8.2.1 Design Requirements
- 8.2.2
Detailed Design Procedure
- 8.2.2.1 Timing Resistor RT
- 8.2.2.2 UVLO Divider RUV2, RUV1
- 8.2.2.3 Input Inductor LIN
- 8.2.2.4 Current Sense Resistor RS
- 8.2.2.5 Current Sense Filter RCSFP, RCSFN, CCS
- 8.2.2.6 Slope Compensation Resistor RSLOPE
- 8.2.2.7 Output Capacitor COUT
- 8.2.2.8 Input Capacitor CIN
- 8.2.2.9 VIN Filter RVIN, CVIN
- 8.2.2.10 Bootstrap Capacitor CBST and Boost Diode DBST
- 8.2.2.11 VCC Capacitor CVCC
- 8.2.2.12 Output Voltage Divider RFB1, RFB2
- 8.2.2.13 Soft-Start Capacitor CSS
- 8.2.2.14 Restart Capacitor CRES
- 8.2.2.15 Low-Side Power Switch QL
- 8.2.2.16 High-Side Power Switch QH and Additional Parallel Schottky Diode
- 8.2.2.17 Snubber Components
- 8.2.2.18 Loop Compensation Components CCOMP, RCOMP, CHF
- 8.2.3 Application Curves
- 8.1
Application Information
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
8.1.4 DCR Sensing
For the applications requiring lowest cost with minimum conduction loss, inductor DC resistance (DCR) is used to sense the inductor current rather than using a sense resistor. Shown in Figure 35 is a DCR sensing configuration using two DCR sensing resistors and one capacitor.
Figure 35. DCR Sensing RCSN and CDCR selection must meet Equation 21 because this indirect current sensing method requires a time constant matching. CDCR is usually selected to be in the range of 0.1 µF to 2.2 µF.
Smaller value of RCSN minimizes the voltage drop caused by CSN bias current, but increases the dynamic power dissipation of RCSN. The DC voltage drop of RCSN can be compensated by selecting the same value of RCSP, but the gain of current amplifier, which is typically 10, is affected by adding RCSP. The gain of current amplifier with the DCR sensing network can be determined as:
Due to the reduced accuracy of DCR sensing, TI recommends FPWM operation when DCR sensing is used.