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
7.3.12 Shunt Current Sensing
Figure 7-4 illustrates inductor current sensing using a shunt resistor. This configuration continuously monitors the inductor current to provide accurate overcurrent protection across the operating temperature range. For excellent current sense accuracy and overcurrent protection, use a low inductance ±1% tolerance shunt resistor between the inductor and the output, with a Kelvin connection to the LM708x0-Q1 current sense amplifier.
If the peak differential current signal sensed from ISNS+ to VOUT exceeds the current limit threshold of 56mV, the current limit comparator immediately terminates the high-side gate driver output for cycle-by-cycle current limiting. Calculate the shunt resistance using Equation 9.
where
- VCS(TH) is current sense threshold of 56mV.
- IOUT(CL) is the overcurrent setpoint that is set higher than the maximum load current to avoid tripping the overcurrent comparator during load transients.
- ΔILis the peak-to-peak inductor ripple current.
Figure 7-4 Shunt Current Sensing
ImplementationThe typical current sense delay (tDELAY(CS)) is 75ns. Calculate the resultant inductor current overshoot above the overcurrent threhold using Equation 10.
The respective SS voltage is clamped 150mV above FB during an overcurrent condition. 16 overcurrent events must occur before the SS clamp is enabled. This requirement make sure that SS can be pulled low during brief overcurrent events, preventing output voltage overshoot during recovery.