ZHCSSZ6F august 2008 – june 2020 TPS40210-Q1 , TPS40211-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 應用
- 3 說明
- 5
- 4 Revision History
- 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 Minimum On-Time and Off-Time Considerations
- 7.3.2 Current Sense and Overcurrent
- 7.3.3 Current Sense and Subharmonic Instability
- 7.3.4 Current Sense Filtering
- 7.3.5 Soft Start
- 7.3.6 BP Regulator
- 7.3.7 Shutdown (DIS/ EN Pin)
- 7.3.8 Control Loop Considerations
- 7.3.9 Gate Drive Circuit
- 7.3.10 TPS40211-Q1
- 7.4 Device Functional Modes
-
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 Duty Cycle Estimation
- 8.2.2.2 Inductor Selection
- 8.2.2.3 Rectifier Diode Selection
- 8.2.2.4 Output Capacitor Selection
- 8.2.2.5 Input Capacitor Selection
- 8.2.2.6 Current Sense and Current Limit
- 8.2.2.7 Current Sense Filter
- 8.2.2.8 Switching MOSFET Selection
- 8.2.2.9 Feedback Divider Resistors
- 8.2.2.10 Error Amplifier Compensation
- 8.2.2.11 R-C Oscillator
- 8.2.2.12 Soft-Start Capacitor
- 8.2.2.13 Regulator Bypass
- 8.2.3 Application Curves
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
7.4.1 Setting the Oscillator Frequency
The oscillator frequency is determined by a resistor and capacitor connected to the RC pin of the TPS40210-Q1 device. The capacitor is charged to a level of approximately VDD / 20 by current flowing through the resistor and is then discharged by a transistor internal to the TPS40210-Q1 device. The required resistor for a given oscillator frequency is found from either Figure 6-1 or Equation 31.
where
- RT is the timing resistance in k?
- fSW is the switching frequency in kHz
- CT is the timing capacitance in pF
For most applications, a capacitor in the range of 68 pF to 120 pF gives the best results. Resistor values should be limited to between 100 k? and 1 M? as well. If the resistor value falls below 100 k?, decrease the capacitor size and recalculate the resistor value for the desired frequency. As the capacitor size decreases below 47 pF, the accuracy of Equation 31 degrades, and empirical means may be needed to fine tune the timing component values to achieve the desired switching frequency.