4 Design Support

This section summarizes documents that help the application designer to understand the capabilities and limitations of buck-boost devices, apart from the basic topology calculations given in the previous section.

Understanding the Absolute Maximum Ratings of the SW Node: SLVA494

This application note explains the operation of a synchronous converter, demonstrates why the switch-node negative rating might be exceeded during switching operation, gives guidance for properly measuring the node voltage, and provides good PCB layout practices. The report discusses buck converter, but the same basic principles are also valid for buck-boost converter.

I_Q: What It Is, What It Isn’t, and How to Use It: SLYT412

This article discusses one of the most misunderstood parameter, the quiescent current I_Q. The article shows how I_Q is defined and measured, and how I_Q translates to the no-load input current and the efficiency at light loads.

Understanding Undervoltage Lockout in Power Devices:SLVA769

Many integrated circuits include an undervoltage lockout (UVLO) function to disable the device at low supply voltages. Below the minimum supply voltage the function and performance of a device may be undefined, making it impossible to predict system behavior. This application note explains how to correctly understand the undervoltage lockout specification in the data sheets of TI's power products.

Extending the Soft Start Time Without a Soft Start Pin: SLVA307

In many applications, extending the soft start time can be crucial to a glitch-free start-up. This application report demonstrates a simple circuit that extends the soft start time and reduces the inrush current, taking a boost converter as an example. The same principle can be applied to buck-boost converters as long as the output voltage is set with a resistive feedback divider.

Achieving a Clean Startup by Using a DC/DC Converter With a Precise Enable-Pin Threshold: SLYT730

This article explains some common EN-pin threshold specifications found in device data sheets and describes several application circuits that provide a clean startup, with or without using a converter with a precise EN-pin threshold.

Methods of Output-Voltage Adjustment for DC/DC Converters: SLYT777

Changing the output voltage can optimize power delivery, reduce power consumption, or properly bias analog circuits. This article demonstrates three basic techniques to adjust the output voltage of a device that uses voltage feedback divider for setting the output voltage.

Design Considerations for a Resistive Feedback Divider in a DC/DC Converter: SLYT469

The resistive feedback divider is the most common network in any DC/DC converter’s feedback system. However, it is often misjudged as a circuit that simply sets the output voltage by scaling it down to a reference voltage. This article discusses the design considerations for the resistive divider in a feedback system and how the divider affects a converter’s efficiency, output voltage accuracy, noise sensitivity, and stability

Prevent Battery Overdischarge With Precise Threshold Enable Pin: SLVAE79

This application report shows how to set precise battery cut-off voltage in order to protect a battery from overdischarge, by using precise EN-pin thresholds.

Precise Start-Up Delay Using Enable Pin with Precise Voltage Threshold: SLVAEA3

This application report shows how to set precise start-up delay for devices that implement precise EN-pin thresholds.

Choosing an Appropriate Pull-Up and Pull-Down Resistor for Open Drain Outputs: SLVA485

Many TI buck-boost devices have open drain output pins to indicate proper operation. These outputs require the use of an external pull-up resistor to keep the digital output in a defined logic state. This application report discusses factors that should be considered when selecting a pull-up resistor, and how to calculate a valid range for the value of the resistor.

Optimizing Transient Response of Internally Compensated DC-DC Converters With Feedforward Capacitor: SLVA289

This application report describes how to choose the feedforward capacitor value of an internally compensated DC/DC converter to achieve optimum transient response. The described procedure provides guidance in optimizing transient response by increasing converter bandwidth while retaining acceptable phase margin.

Improving Load Transient Response of DC/DC Converters Powering Controlled Loads: SLVAEE0

This application report shows a way of improving the load transient response that can be used when other methods are not effective or possible. This method can be used for a DC/DC converter that supplies a controlled load and uses an external voltage feedback divider.

Extending Battery Life With Low Quiescent Current and Dynamic Voltage Scaling: SLVAER8

When designing a battery powered system, maximizing battery life is often one of the most important design goals. Selecting the right converter to obtain a fixed system voltage in such a case is often based on the quiescent current parameter I_Q. This application report shows that, besides having low quiescent current, the battery life can be further extended by dynamically scaling the output voltage.