ZHCSGO2H September 2003 – November 2018 LM5007
PRODUCTION DATA.
- 1 特性
- 2 應(yīng)用
- 3 說明
- 4 修訂歷史記錄
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Application
- 8.2.1 Design Requirements
- 8.2.2
Detailed Design Procedure
- 8.2.2.1 Custom Design With WEBENCH® Tools
- 8.2.2.2 Custom Design With Excel Quickstart Tool
- 8.2.2.3 Feedback Resistors, RFB1 and RFB2
- 8.2.2.4 Switching Frequency Selection, RON
- 8.2.2.5 Buck Inductor, L1
- 8.2.2.6 Output Capacitor, COUT
- 8.2.2.7 Type I Ripple Circuit, RC
- 8.2.2.8 Input Capacitor, CIN
- 8.2.2.9 Current Limit, RCL
- 8.2.3 Application Curves
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文檔支持
- 12機(jī)械、封裝和可訂購信息
封裝選項(xiàng)
機(jī)械數(shù)據(jù) (封裝 | 引腳)
散熱焊盤機(jī)械數(shù)據(jù) (封裝 | 引腳)
訂購信息
7.3.5 Overcurrent Protection
The LM5007 contains an intelligent current limit off-timer intended to reduce the foldback characteristic inherent with fixed off-time overcurrent protection (OCP) schemes. If the current in the buck switch exceeds 725 mA, the present cycle on-time is immediately terminated (cycle-by-cycle current limit). Following the termination of the cycle a non-resettable current limit off-timer is initiated. The duration of the off-time is a function of the external resistor (RCL) and the FB voltage. When the FB voltage equals zero, the current limit off-time is internally preset to 17 µs. This condition occurs during a short-circuit condition when a maximum amount of off-time is required.
In case of output overload (not a complete short circuit), the current limit off-time is reduced as a function of the output voltage (measured at the FB pin). Scaling the off-time with smaller overloads reduces the amount of foldback and also reduces the initial start-up time. Calculate the current limit off-time for a given FB voltage and RCL resistor using Equation 5.
Select the current limit off-time such that it is less than the MOSFET off-time during normal steady-state switching operation. Applications utilizing low-resistance inductors and/or a low-voltage-drop freewheeling power diodes may require special evaluation at high line, short-circuited conditions. In this special case the preset 17-µs off-time (VFB = 0 V) may be insufficient to provide inductor volt-seconds balance. Additional inductor resistance, output resistance or a larger voltage drop diode may be necessary to balance inductor volt-seconds and limit the short-circuit current.