SNVSAN3F August   2017  – November 2020

PRODUCTION DATA

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
3. 9.3 What to Do and What Not to Do
10. 10Layout
1. 10.1 Layout Guidelines
2. 10.2 Layout Example
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

#### Package Options

Refer to the PDF data sheet for device specific package drawings

• RNX|12
• DDA|8
• RNX|12
• DDA|8

### 8.4.3 Minimum Switch On-Time

Every switching regulator has a minimum controllable on-time dictated by the inherent delays and blanking times associated with the control circuits. This imposes a minimum switch duty cycle and, therefore, a minimum conversion ratio. The constraint is encountered at high input voltages and low output voltages. To help extend the minimum controllable duty cycle, the LMR33630 automatically reduces the switching frequency when the minimum on-time limit is reached. This way the converter can regulate the lowest programmable output voltage at the maximum input voltage. An estimate for the approximate input voltage, for a given output voltage, before frequency foldback occurs is found in Equation 2. The values of tON and fSW can be found in Section 7.5. As the input voltage is increased, the switch on-time (duty-cycle) reduces to regulate the output voltage. When the on-time reaches the limit, the switching frequency drops, while the on-time remains fixed. This relationship is highlighted in Figure 8-13 for a nominal switching frequency of 2.1 MHz.

Equation 2.
Figure 8-13 Switching Frequency versus Input Voltage VOUT = 3.3 V