Guide to Choosing the Best DC-to-DC Converter for Your Application
Most portable devices use DC-to DC switching converters. They are efficient in generating different regulated supply voltages to different sub-blocks of the same system board. Many switching converters can be found on a typical portable device system board. There are hundreds of DC-DC converters available from multiple suppliers due to this huge market. There are many options available, from small packaged parts without external components to larger parts that require multiple external components. This makes it difficult to select the right option.
This whitepaper explains how to choose the right DC-DC switching conversion for your application. This white paper explains the basics, performance, as well as optional metrics. You will also find other practical aspects that system designers often overlook. Numerous examples of applications are shown.
INTRODUCTION & BACKGROUND
High-performance applications need a stable, controlled power supply voltage. This is not possible with conventional battery technology. To generate the necessary supply, an intermediate voltage regulator circuit is required. Voltage regulators provide supply regulation and noise isolation between blocks that share the same supply.
The power management technology is concerned with optimizing the design of voltage regulators and voltage monitors as well as voltage references and current references. It is designed to produce the correct voltage and current references, including the voltage supply, for a specific application efficiently and with minimal power loss.
There are three main types of voltage regulators: linear regulators, switching regulators and regulators. Low-dropout regulators, switching regulators and charge pumps are all possible.
Linear regulators can be used in noisesensitive and compact applications, such as RF circuits or highprecision analog circuits. The typical linear regulators are not efficient, especially when they operate at high dropout voltages, which can directly impact the battery life. Most applications that require high efficiency such as processors or memory chips for mobile devices, use switching converters. Switching converters are required for all applications that require DC input-output isolation. Charge pumps are a sub-category within switching converters. However, they can be considered as separate because of their low current capability. They serve different low power applications, such as LEDs. LEDs).
There are many types of switching and linear regulators on the semiconductor market. All system designers have one main question: "How do I choose the right regulator for my application?" This question can be answered by understanding the metrics of a converter. The basic metrics are what most designers use as a starting point. These basic metrics can be used for narrowing the search area but not to achieve the best performance. Next comes the performance metrics. These are what really differentiate one converter from the other. Only an in-depth understanding of the application will lead to the right set of performance metrics. The optional features are the last. These optional features add additional functionality to the converter, increasing its durability and adaptability to different operating situations. The practical aspects are often overlooked by new system designers. Practical aspects require a thorough understanding of the environment and the blocks that are on the same chip or board. These can dramatically increase system costs or affect the performance of neighbouring chips.
This whitepaper is designed to assist system designers in choosing the right DC-DC Boost Converter switching converter. The paper describes all of the metrics and provides a process for making the best choice. Then, you will find real-life examples of application.
Similar white papers are available in the section titled Additional Reading. They provide information on how you can choose the best linear regulator with low dropout (LDO), for your application.
DC DC-DC CONVERTER FEATURES & PARAMETERS
Different applications have different requirements for DC-DC converters. System designers can select the right DC-DC converter to fit their needs by understanding the converter parameters. Below are the most important parameters and features, and their meanings.
Input to Output Voltage Consideration
Different converter types can be chosen based on the difference in input and output voltages. A step-down (BUCK), converter is used if VOUT is lower than VIN. A step-up (BOOST), converter is used if VOUT is higher than VIN. A BUCKBOOST converter can be used if both are needed. Inverting converters are used if VOUT and VIN have polarities that differ.
Input to Output Isolation Feature
Some applications require complete DC isolation between the input and output ports. This is usually done with a transformer-based converter.
DC Line Regulation Parameter
DC line regulation refers to the change in output voltage that results from a change in input voltage. This measurement is done under low power dissipation conditions.
DC Load Regulation Parameter
The DC load regulation refers to the change in voltage for a static change of output (load current).
Efficiency Parameter
The power efficiency of an input is the ratio of the input to the output. It is described as:
A perfect switching converter will achieve 100% efficiency. The relationship between average input currents and average output currents is opposite to that between input voltages and output voltages. This ensures equal input power and output power. The real, practical converter circuitry uses power both dynamically and statically. Therefore, POUT is lower than PIN. To maximize DCDC efficiency, converter's internal losses (static or dynamic) must be minimized.
Range Parameter Input Voltage, (VIN).
The input voltage range is what determines the maximum or minimum input supply to the converter. The converter can be damaged if the input supply exceeds the maximum allowed.
Maximum Output Current (IOUT) Parameter
This parameter specifies the maximum output current the converter can produce while still meeting the datasheet parameters.
No Loading Current Operation Feature
Many applications require the converter to maintain the output voltage stable under no current load conditions. Applications that keep alive CMOS RAM. Under no load conditions, some converters may experience instability or degraded performance.
Output Voltage Noise Parameter
A switching nature of switching converters results is an output tone that contains harmonics. This tone corresponds with the switching frequency of power transistors. This tone is also the output voltage noise parameter. It is the RMS output voltage voltage that is generated by the converter, including the voltage reference-noise, as it is assumed that the converter contains an integrated reference). The noise is typically between 10 Hz and 100 KHz under constant output current.
Output Voltage, (VOUT), Accuracy Parameter
Output voltage accuracy is the deviation between the nominal converter output voltage and the average output voltage. The output voltage accuracy includes line regulation and load regulation.
Output Voltage Range Parameter
You can adjust the output voltage of your converter. It is important to understand the maximum and minimum output voltages that can be adjusted, as well as the programming steps.
Over-Current Security Feature
This limit restricts the amount of current the converter can draw. This is to protect the converter from a high-current or short-circuit condition.
Over-Temperature Protect Feature
This function shuts down the converter if the temperature of the die exceeds the high temperature limit. When the temperature drops below a safe level, the converter will reactivate.
Power Supply Rejection Rate (PSRR), Parameter
The PSRR measures how well the converter rejects any electrical noise from the power-supply input. It is measured by the change in voltage.
Quiescent Current (IQ) Parameter
The current used to power the converter is called the "quiescent current" or the "ground current". It is not delivered to the load. When the converter is turned on and the output/load current equals zero (0), IQ is measured. To maximize the converter's output efficiency, reduce heat and prolong battery life in battery-operated apps, a small quiescent current must be applied.
Soft-Start Operation Feature
Soft-start ensures that the output voltage ramps up slowly from 0 to the desired output voltage. Soft-start can be used to prevent overload current from causing damage to the converter package and load. For safe load startup, it maintains a monotonic ramp-up. It also avoids false triggers of ESD active power supply clamps.
Soft-Stop Operation Feature
Soft-stop ensures that the output voltage ramps down slowly and in a controlled manner when the converter is disabled.
Shutdown (ISD) Parameter
Shutdown current refers to the current that flows through the converter when it is turned off or disabled.
Turn-On or Start-Up Time Parameter
The time taken between the rising edge and the output voltage reaching 90%, 95% or more of its nominal value is called the start-up time.
Line Transient Regulation Parameter
The line transient regulation parameter measures the converter's ability to maintain a constant output voltage while maintaining a transient step at its input.
Load Transient Regulation Parameter
A load transient regulation refers to a change in the output voltage that results from a dynamic (stepwise) change in the output current. Load transient regulations include overshoot (difference in the maximum VOUT from the initial VOUT when the output voltage changes to a lower level), and undershoot when the output voltage changes to a higher value.
Interface Protocol Feature
This is the digital interface that controls the operation and programmability of the converter. You can choose from I2C (Inter- Integrated Circuit), Voltage Identification (Voltage Identification) or SPI (Serial Perpendicular Interface), just to name a few.
Temperature Coefficient Parameter
The temperature coefficient is the variation in output voltage with respect to temperature. It is often measured in parts per million (ppm). Parameter Output Voltage Ripple Amplification The output voltage ripple amplitude identifies the maximum peak to peak ripple amplitude.
Current Monitor Feature
This allows the converter's signal to be proportional to the average current output.
SELECTING A DC-DC CONVERTER
It is often difficult for system designers with so many parameters to choose the best converter for their application. What parameters are most important? Is there any parameter that could be altered to lower the overall cost? Are there hidden details that can be used to make a product more successful?
We recommend that you divide the parameters of the converter into three groups to make it easier for the user to choose the right converter.
Basic DC Parameters
To provide the functionality required for an application, the DC-DC Buck Converter converter must work within the specified range of DC parameters. The input voltage range, output voltage range and maximum output current are some of the basic DC parameters.
Requirements and AC Performance Parameters
To provide the best performance, the DC-DC converter must have the necessary features. The most common AC performance parameters include efficiency, load transient regulation, and output voltage ripples.
Additional Features
They may be necessary for specific applications. A temperature sensor may not be necessary if the converter is part a large SoC.
It is crucial to be able to distinguish between the performance metrics and the parameters of DC-DC converters when reviewing their features and parameters. This will help you to set realistic expectations for the DC/DC converter that is best suited for your application.
Low output voltage ripples require larger offchip L or C components, which in turn requires a larger area on the PCB and a higher cost.
High efficiency: Larger switch sizes are required and thus a larger area of the die.
A smaller number of off-chip components means higher switching frequencies, which can lead to greater dynamic losses and efficiency degradation.
High output power: Larger die areas are required for larger switches.
Practical Aspects
There are many practical aspects to consider, in addition to the parameters mentioned above. Below are some of these aspects:
External EMI Reduction circuits
Some devices require off-chip components to deal with extreme EMI and maintain device reliability (e.g. off-chip filters).
Area
For a minimum area of PCB, verify all off-chip component values, costs, and sizes. For optimum performance and EMI reduction, make sure to check the size and type of the packaging and the PCB design restrictions provided by the supplier.
Input Voltage Ripples
Pulsed current is drained from the input voltage source by switching converters. The pulsed current can cause large voltage ripples. These ripples are suppressed by an input capacitor at a minimum value. Is this the right value for your application? Brownout activity can occur in other blocks that share the same supply voltage input, causing system instability or multiple resets.
Operating Temperature
The system designer must know the operating temperature of the switch converter, the ambient temperature of the application, the package type and its thermal resist, as well as the system casing. This information can be used to determine if a heat dissipation device (e.g. Heat sinks This will directly impact the system's cost.
Failure Rate
How long is this converter's MTTF (mean Time to failure)? Is it reliable? Will it cause a bottleneck in a product with a short life expectancy?
Output Ripple Frequency
If the frequency of the converter is not within your application's range, large output ripples will not be significant. You should check the frequency of the converter to determine its effect on your application. For multi-tone environments, a detailed analysis of harmonic distribution and inter-modulation is required.
Other Protection Features
Do you have any concerns specific to your application? Is it possible for input supply to exceed capacity due to sharing of supply with other converters? Over-voltage protection can be a necessity in some cases for reliable operation.
Number of Switching Converters Per App
The high-performance switching converters can be expensive and bulky. It is not recommended to use a single switch converter to power as many blocks as possible unless there is a performance limit.
Isolated Versus Non-Isolated Conversions
For isolated converters, a transformer must be sized to meet the maximum current requirements. Only use an isolated converter when absolutely necessary.
Converter Selection Procedure
The following five steps will help you choose the right converter for your application:
Choose a group that meets the requirements of your application. What is the input voltage and output range required? Is it necessary to have input-output isolation? What is your maximum current requirement?
The performance columns of Table 1 should be arranged in priority order according to the importance of your application. Next, select the converters that match the parameters you have arranged in Step 1.
This step narrows down your selection to the performance parameter most relevant for your application.
To help you choose the right converter for you, be sure to review all of the details.
Once you've made your selection of a converter, discover which additional parameters it offers for your application.
CONVERTER EXAMPLES
Below are some examples of switching converter applications. Each one has its own performance parameters. If your application is not covered in this whitepaper, please contact Vidatronic sales@vidatronic.com. We are happy to assist you with any aspect of your application.
AMOLED (Active Matrix LED) Displays in Wearable Devices
Wearable devices have a limited circuit board area and a long-lasting battery life. System efficiency is crucial in the design of these products. Wearable devices require DC-DC switching converters with high power efficiency and precise output voltage accuracy to power AMOLED displays.
DDR SDRAM Memory
DDR-SDRAM memory is dependent on DC-DC switching converts that meet tight accuracy and can support fast load transients.
USB Charging Ports/Battery Chargers for Portable Devices
Everybody wants their phone, tablet or portable battery pack charged quickly and without overheating their devices. This application can be done with a synchronous BUCK convertor. A micro USB port is the most common type of charging port for mobile devices. It can accept a regulated 5V.
DVFS (Dynamic Volume Frequency Scaling).
Switching converters are used to manage the performance-power tradeoff in digital signal processing circuits and microprocessors. The digital circuit supply can be increased to increase performance (speed), but dynamic power consumption will decrease.
Energy Harvesting Systems
Energy harvesting systems require high efficiency switching converters. This is the best method to regulate voltage in low-power systems. For MPPT (Maximum power point tracking) operation, boost converters with clock-controlled input resistance are used.