ZHCSG38A March 2017 – November 2022 TPS65263-1Q1
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 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 PSM
- 7.3.9 Slope Compensation
- 7.3.10 Overcurrent Protection
- 7.3.11 Power Good
- 7.3.12 Thermal Shutdown
- 7.4 Device Functional Modes
- 7.5 Register Maps
- 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 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 there are desired hold-up times for the regulator 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 there is a large, fast increase in the current needs of the load such as a transition from no load to full load. The regulator usually needs two or more clock cycles for the control loop to see the change in load current and output voltage and 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 2 clock cycles while only allowing a tolerable amount of droop in the output voltage. Equation 12 shows the minimum output capacitance necessary to accomplish this.
where
- ΔIout is the change in output current
- ƒsw is the regulators switching frequency
- ΔVout is the allowable change in the output voltage
Equation 13 calculates the minimum output capacitance needed to meet the output voltage ripple specification.
where
- ƒsw is the switching frequency
- Voripple is the maximum allowable output voltage ripple
- Ioripple is the inductor ripple current
Equation 14 calculates 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 increases this minimum value. Capacitors generally have limits to the amount of ripple current they can handle 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 15 to calculate the RMS ripple current the output capacitor must support.
