SNVSBZ3 June   2021

1. Features
2. Applications
3. Description
4. Revision History
5. Device Comparison Table
6. Pin Configuration and Functions
7. Specifications
8. Detailed Description
1. 8.1 Overview
2. 8.2 Functional Block Diagram
3. 8.3 Feature Description
4. 8.4 Device Functional Modes
9. Application and Implementation
1. 9.1 Application Information
2. 9.2 Typical Application
1. 9.2.1 Design Requirements
2. 9.2.2 Detailed Design Procedure
3. 9.2.3 Application Curves
10. 10Power Supply Recommendations
11. 11Layout
1. 11.1 Layout Guidelines
2. 11.2 Layout Example
12. 12Device and Documentation Support
13. 13Mechanical, Packaging, and Orderable Information

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### 8.3.4 On-Time Generator

The on time of the LM516x-Q1 high-side FET is determined by the RT resistor and is inversely proportional to the input voltage, VIN. The inverse relationship with VIN results in a nearly constant frequency as VIN is varied. Use Equation 10 to calculate the on time.

Equation 10. ${t}_{ON}\left(µs\right)=\frac{{R}_{T}\left(kΩ\right)}{{V}_{IN}\left(V\right)*2.5}$

Use Equation 11 to determine the RT resistor to set a specific switching frequency in CCM.

Equation 11. ${R}_{T}\left(kΩ\right)=\frac{2500*{V}_{OUT}\left(V\right)}{{F}_{SW}\left(kHz\right)}$

Select RT for a minimum on time (at maximum VIN) greater than 50 ns for proper buck operation and greater than 100 ns for proper fly-buck operation. In addition to this minimum on time, the maximum frequency for this device is limited to 1 MHz.