ZHCSMC1B october 2020 – august 2023 LM5157-Q1 , LM51571-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 说明（续）
- 6 Device Comparison Table
- 7 Pin Configuration and Functions
- 8 Specifications
-
9 Detailed Description
- 9.1 Overview
- 9.2 Functional Block Diagram
- 9.3
Feature Description
- 9.3.1 Line Undervoltage Lockout (UVLO/SYNC/EN Pin)
- 9.3.2 High Voltage VCC Regulator (BIAS, VCC Pin)
- 9.3.3 Soft Start (SS Pin)
- 9.3.4 Switching Frequency (RT Pin)
- 9.3.5 Dual Random Spread Spectrum – DRSS (MODE Pin)
- 9.3.6 Clock Synchronization (UVLO/SYNC/EN Pin)
- 9.3.7 Current Sense and Slope Compensation
- 9.3.8 Current Limit and Minimum On Time
- 9.3.9 Feedback and Error Amplifier (FB, COMP Pin)
- 9.3.10 Power-Good Indicator (PGOOD Pin)
- 9.3.11 Hiccup Mode Overload Protection (MODE Pin)
- 9.3.12 Maximum Duty Cycle Limit and Minimum Input Supply Voltage
- 9.3.13 Internal MOSFET (SW Pin)
- 9.3.14 Overvoltage Protection (OVP)
- 9.3.15 Thermal Shutdown (TSD)
- 9.4 Device Functional Modes
- 10Application and Implementation
- 11Power Supply Recommendations
- 12Layout
- 13Device and Documentation Support
- 14Mechanical, Packaging, and Orderable Information
9.3.4 Switching Frequency (RT Pin)
The switching frequency of the device can be set by a single RT resistor connected between the RT and the AGND pins. The resistor value to set the RT switching frequency (fRT) is calculated as shown in Equation 5.
Equation 5. 
The RT pin is regulated to 0.5 V by the internal RT regulator when the device is enabled.