ZHCSLJ6A June 2021 – June 2021 LM5145-Q1
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 說明（續）
- 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 LM5145-Q1 begins charging the output to the DC level dictated by the feedback resistor network. The LM5145-Q1 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.