ZHCSM29A September 2023 – June 2024 LM70840-Q1 , LM70860-Q1 , LM70880-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 應用
- 3 說明
- 4 說明（續）
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Input Voltage Range (VIN)
- 7.3.2 High-Voltage Bias Supply Regulator (VCC, BIAS, VDDA)
- 7.3.3 Enable (EN)
- 7.3.4 Power-Good Monitor (PG)
- 7.3.5 Switching Frequency (RT)
- 7.3.6 Dual Random Spread Spectrum (DRSS)
- 7.3.7 Soft Start
- 7.3.8 Output Voltage Setpoint (FB)
- 7.3.9 Minimum Controllable On-Time
- 7.3.10 Error Amplifier and PWM Comparator (FB, EXTCOMP)
- 7.3.11 Slope Compensation
- 7.3.12 Shunt Current Sensing
- 7.3.13 Hiccup Mode Current Limiting
- 7.3.14 Device Configuration (CONFIG)
- 7.3.15 Single-Output Dual-phase Operation
- 7.3.16 Pulse Frequency Modulation (PFM) / Synchronization
- 7.3.17 Thermal Shutdown (TSD)
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1
Design 1 – High Efficiency, Wide Input, 400-kHz Synchronous
Buck Regulator
- 8.2.1.1 Design Requirements
- 8.2.1.2
Detailed Design Procedure
- 8.2.1.2.1 Custom Design With WEBENCH? Tools
- 8.2.1.2.2 Custom Design With Excel Quickstart Tool
- 8.2.1.2.3 Buck Inductor
- 8.2.1.2.4 Current-Sense Resistance
- 8.2.1.2.5 Output Capacitors
- 8.2.1.2.6 Input Capacitors
- 8.2.1.2.7 Frequency Set Resistor
- 8.2.1.2.8 Feedback Resistors
- 8.2.1.2.9 Compensation Components
- 8.2.1.3 Application Curves
- 8.2.2 Design 2 – High Efficiency 48V to 12V 400kHz Synchronous Buck Regulator
- 8.2.1
Design 1 – High Efficiency, Wide Input, 400-kHz Synchronous
Buck Regulator
- 8.3 Power Supply Recommendations
- 8.4 Layout
- 9 Device and Documentation Support
- 10Revision History
- 11Mechanical, Packaging, and Orderable Information
7.3.1 Input Voltage Range (VIN)
The LM708x0-Q1 operational input voltage range is from 4.5V to 80V. The device is intended for step-down conversions from 12V, 24V and 48V automotive supply rails. The LM708x0-Q1 uses internal LDOs to provide an 8V or 5V VCC bias rail and a 5V VDDA rail for the gate drive and control circuits.
In high input voltage applications, make sure that the VIN and SW pins do not exceed the absolute maximum voltage rating of 87.5V during line or load transient events. Voltage excursions that exceed the absolute maximum ratings of these pins can damage the IC. Follow PCB board layout recommendations and use high-quality input bypass capacitors to minimize voltage overshoot and ringing.
As VIN approaches VOUT, the LM708x0-Q1 skips tOFF cycles to allow the controller to extend the duty cycle up to approximately 99%. Refer to Dropout Mode Operation.
When in dropout, the output voltage tracks the input voltage and the peak current mode control is open loop. As a result, larger output voltage perturbations due to line and load transients are possible. Additonal output capacitance and more aggressive external compensation can improve the output response.
Use Equation 1 to calculate when the LM708x0-Q1 enters dropout mode.
- tP is the oscillator period
- tOFF is the minimum off time, typical 88ns
Figure 7-1 Dropout Mode Operation