ZHCSHF3C january 2018 – may 2023 TPS65268-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 应用
- 3 描述
- 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 Adjusting the Output Voltage
- 7.3.2 Enable and Adjusting UVLO
- 7.3.3 Soft-Start Time
- 7.3.4 Power-Up Sequencing
- 7.3.5 V7V Low-Dropout Regulator and Bootstrap
- 7.3.6 Out-of-Phase Operation
- 7.3.7 Output Overvoltage Protection (OVP)
- 7.3.8 Slope Compensation
- 7.3.9 Overcurrent Protection
- 7.3.10 Power Good
- 7.3.11 Thermal Shutdown
- 7.4 Device Functional Modes
- 8 Application and Implementation
- 9 Device and Documentation Support
- 10Mechanical, Packaging, and Orderable Information
8.2.2.2 Output Capacitor Selection
The three primary considerations for selecting the value of the output capacitor are:
- Output capacitor which determines the modulator pole
- Output voltage ripple
- How the regulator responds to a large change in load current
The output capacitance must be selected based on the most stringent of these three criteria.
The desired response to a large change in the load current is the first criterion. The output capacitor must supply the load with current when the regulator cannot. This situation can occur if the desired hold-up times for the regulator occur where the output capacitor must hold the output voltage above a certain level for a specified amount of time after the input power is removed. The regulator is also temporarily not able to supply sufficient output current if the current requirements of the load experience a large, fast increase, such as a transition from no load to full load. The regulator typically requires two or more clock cycles for the control loop to experience a change in load current and output voltage, and to adjust the duty cycle to react to the change. The output capacitor must be sized to supply the extra current to the load until the control loop responds to the load change. The output capacitance must be large enough to supply the difference in current for two clock cycles while only allowing a tolerable amount of droop in the output voltage. Use Equation 10 to calculate the minimum output capacitance (CO) required to accomplish this.
where
- ΔIOUT is the change in output current
- fsw is the regulators switching frequency
- ΔVOUT is the allowable change in the output voltage
Equation 11 calculates the minimum output capacitance required to meet the output voltage ripple specification.
where
- fSW is the switching frequency
- VOUTripple is the maximum allowable output voltage ripple
- IOUTripple is the inductor ripple current
Use Equation 12 to calculate the maximum ESR an output capacitor can have to meet the output voltage ripple specification.
Additional capacitance deratings for aging, temperature, and DC bias must be factored in, which increase this minimum value. Capacitors generally have limits to the amount of ripple current they can support without failing or producing excess heat. The user must specify an output capacitor that can support the inductor ripple current. Some capacitor data sheets specify the root mean square (RMS) value of the maximum ripple current. Use Equation 13 to calculate the RMS ripple current that the output capacitor must support (ICOUTrms).
