ZHCSKX8B September 2019 – September 2020 LMR36503-Q1
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 Device Comparison Table
- 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 Enable, Start-up and Shutdown
- 8.3.2 External CLK SYNC (with MODE/SYNC)
- 8.3.3 Adjustable Switching Frequency (with RT)
- 8.3.4 Power-Good Output Operation
- 8.3.5 Internal LDO, VCC UVLO, and VOUT/BIAS Input
- 8.3.6 Bootstrap Voltage and VCBOOT-UVLO (CBOOT Terminal)
- 8.3.7 Output Voltage Selection
- 8.3.8 Soft Start and Recovery from Dropout
- 8.3.9 Current Limit and Short Circuit
- 8.3.10 Thermal Shutdown
- 8.3.11 Input Supply Current
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application
- 9.2.1 Design Requirements
- 9.2.2 Detailed Design Procedure
- 9.2.3 Application Curves
- 9.3 What to Do and What Not to Do
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.8 Soft Start and Recovery from Dropout
When designing with the LMR36503-Q1, slow rise in output voltage due to recovery from dropout and soft start should be considered as a two separate operating conditions, as shown in Figure 8-10 and Figure 8-11. Soft start is triggered by any of the following conditions:
- Power is applied to the VIN pin of the device, releasing undervoltage lockout.
- EN is used to turn on the device.
- Recovery from shutdown due to overtemperature protection.
Once soft start is triggered, the IC takes the following actions:
- The reference used by the IC to regulate output voltage is slowly ramped up. The net result is that output voltage, if previously 0 V, takes tSS to reach 90% of the desired value.
- Operating mode is set to auto mode of operation, activating the diode emulation mode for the low-side MOSFET. This allows start-up without pulling the output low. This is true even when there is a voltage already present at the output during a pre-bias start-up.
Figure 8-10 Soft Start With and Without Pre-bias Voltage