ZHCSPF6B february 2022 – may 2023 LMQ66410 , LMQ66420 , LMQ66430
PRODUCTION DATA
- 1
- 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 Adjustable Switching Frequency (with RT)
- 8.3.3 Power-Good Output Operation
- 8.3.4 Internal LDO, VCC, and VOUT/FB Input
- 8.3.5 Bootstrap Voltage and VBOOT-UVLO (BOOT Terminal)
- 8.3.6 Output Voltage Selection
- 8.3.7 Spread Spectrum
- 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 Synchronous Buck Regulator at 400 kHz
- 9.2.2 Design Requirements
- 9.2.3 Detailed Design Procedure
- 9.2.4 Application Curves
- 9.3 Best Design Practices
- 9.4 Power Supply Recommendations
- 9.5 Layout
- 10Device and Documentation Support
- 11Mechanical, Packaging, and Orderable Information
8.3.8 Soft Start and Recovery from Dropout
When designing with the LMQ664x0, slow rise in output voltage due to recovery from dropout and soft start must be considered as two separate operating conditions, as shown in Figure 8-7 and Figure 8-8. 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
After 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 8-7 Soft Start
with and Without Pre-bias Voltage