ZHCSLJ7A June 2021 – June 2021 LM5146
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 说明（续）
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 Input Range (VIN)
- 8.3.2 Output Voltage Setpoint and Accuracy (FB)
- 8.3.3 High-Voltage Bias Supply Regulator (VCC)
- 8.3.4 Precision Enable (EN/UVLO)
- 8.3.5 Power Good Monitor (PGOOD)
- 8.3.6 Switching Frequency (RT, SYNCIN)
- 8.3.7 Configurable Soft Start (SS/TRK)
- 8.3.8 Voltage-Mode Control (COMP)
- 8.3.9 Gate Drivers (LO, HO)
- 8.3.10 Current Sensing and Overcurrent Protection (ILIM)
- 8.3.11 OCP Duty Cycle Limiter
- 8.4 Device Functional Modes
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.7 Configurable Soft Start (SS/TRK)
After the EN/UVLO pin exceeds its rising threshold of 1.2 V, the LM5146 begins charging the output to the DC level dictated by the feedback resistor network. The LM5146 features an adjustable soft start (set by a capacitor from the SS/TRK pin to GND) that determines the charging time of the output. A 10-µA current source charges this soft-start capacitor. Soft start limits inrush current as a result of high output capacitance to avoid an overcurrent condition. Stress on the input supply rail is also reduced. The soft-start time, tSS, for the output voltage to ramp to its nominal level is set by Equation 4.
where
- CSS is the soft-start capacitance
- VREF is the 0.8-V reference
- ISS is the 10-µA current sourced from the SS/TRK pin
More simply, calculate CSS using Equation 5.
The SS/TRK pin is internally clamped to VFB + 115 mV to allow a soft start recovery from an overload event. The clamp circuit requires a soft-start capacitance greater than 2 nF for stability and has a current limit of approximately 2 mA.