SNVS787I January   2012  – August 2021

PRODUCTION DATA

1. Features
2. Applications
3. Description
4. Revision History
5. Pin Configuration and Functions
6. Specifications
7. Detailed Description
1. 7.1 Overview
2. 7.2 Functional Block Diagram
3. 7.3 Feature Description
4. 7.4 Device Functional Modes
8. Application and Implementation
1. 8.1 Application Information
2. 8.2 Typical Applications
1. 8.2.1 Application Circuit: 12.5- to 95-V Input and 10-V, 300-mA Output Buck Converter
1. 8.2.1.1 Design Requirements
2. 8.2.1.2 Detailed Design Procedure
3. 8.2.1.3 Application Curves
2. 8.2.2 Typical Isolated DC-DC Converter Using LM5018
1. 8.2.2.1 Design Requirements
2. 8.2.2.2 Detailed Design Procedure
3. 8.2.2.3 Application Curves
9. Power Supply Recommendations
10. 10Layout
11. 11Device and Documentation Support
1. 11.1 Device Support
1. 11.1.1 Development Support
2. 11.2 Documentation Support
4. 11.4 Support Resources
6. 11.6 Electrostatic Discharge Caution
7. 11.7 Glossary
12. 12Mechanical, Packaging, and Orderable Information

#### Package Options

• DDA|8
• NGU|8
• DDA|8
##### 8.2.1.2.6 Type II Ripple Circuit

A type II ripple circuit, as described in the Section 7.3.11, section is chosen for this example. For a constant on-time converter to be stable, the injected in-phase ripple must be larger than the capacitive ripple on COUT.

Using type II ripple circuit equations with a minimum FB pin ripple of 25 mV, the values of the series resistor RC and ac coupling capacitor Cac can calculated.

Equation 16.

Assuming RFB2 = 6.98 kΩ and RFB1 = 1 kΩ, the calculated minimum value of Cac is 0.013 µF. A standard value of 0.1 µF is selected for Cac = C8. The value of the series output resistor RC is calculated for the minimum input voltage condition when the inductor ripple current as at a minimum. Using Equation 13 and assuming VIN = 12.5 V, the minimum inductor ripple current is 27 mA. The calculated minimum value of RC is 0.93 Ω. A standard value of 1.5 Ω is selected for RC = R2 to provide additional ripple for stable switching at low VIN.