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Designing a voltage regulator GPB with SPI

Posted: 02 Aug 2013     Print Version  Bookmark and Share

Keywords:PCB  general purpose board  GPB  design software  SPI 

One of the important aspects of product development is electrical lab characterisation. It is vital for validating the device’s electrical functionality and ensuring that it meets the specifications. However, typical lab characterisation setup takes a long time to complete using the manual measurement method. To address this concern, this article presents a custom-made test board, called the general purpose board (GPB), with the capability to fulfil the entire datasheet test parameters for lab characterisation. The GPB hardware is composed of a motherboard and a daughterboard. The latter component is included to support characterisation activities for voltage regulators available in various device packages. On the motherboard, serial peripheral interface (SPI) drives all the relays, and in order to perform the characterisation faster, relay matrix concept is applied to swap the testing parameter setup from one state to another.

Figure 1: Voltage regulator product datasheet.

Introduction to GPB
Generally, there are a few types of characterisation boards already available in the lab for evaluation. However, only two types of boards are commonly used by the engineers: the universal test board and a smaller dimension of printed circuit board (PCB) designed for a particular product. The universal board consists of daughterboard and motherboard, making it compatible with several types of product package. Its concept may be identical to the general purpose board (GPB) proposed in this article, but it does not have any external components. It also has limitations such as the manual test up and the need for long cables on the motherboard, which could lead to inaccurate measurement results.

A different type of PCB that can be customised for a specific product is also obtainable in the lab. It is smaller in size and requires some soldering of the device under test (DUT) and cables on the PCB. The advantages of using a dedicated PCB are excellent heat dissipation in the PCB and high accuracy of measurement results. Shorter cables and traces contribute to these precise measurement readings. However, sample preparation needs longer time and measurement is done manually when using this type of PCB.

For new product characterisation, it is important to ensure that the product is functioning well within the datasheet specification [1]. Figure 1 illustrates an example of a voltage regulator product datasheet from which users can obtain as much information as possible such as the product details, application setup and the device's electrical behaviour. During new product characterisation, all datasheet parameters will be tested and the results are compiled to finalise the datasheet before its release. In the past, manual lab measurements method was used to check the device's functionality but this leads to lengthy development cycle time. Also, the conventional method is no longer suitable as new products are becoming more complex.

Test board design
Schematics Design: This is an important criterion in hardware design. Numerous steps need to be carried out when constructing a comprehensive and faultless test board. The types of product that will undergo the test verification need to be identified beforehand. In this project, we will look into voltage regulator products. The identification step is then followed by studying the pin configuration of the available products, as well as learning the test methodology for each and every testing parameter. Typically, the pin configuration for each product varies due to its functionality. During the schematics design, identification of functional pins to the correct resources is essential. This is to avoid any problems caused by equipment limitation during measurement.

Test methodology is necessary to identify the suitable measurement setup for each product characterisation. A complete test parameter list can be obtained from the datasheet and this can be grouped based on similarity in terms of measurement concept. In voltage regulator products, the main parameters will be the same—the output voltage, current consumption, load regulation, line regulation and drop out voltage. For these identical parameters, test circuitry does not differ much even among different products. Indirectly, this could help reduce the complexity of a schematics design.

In this project, the PCB design tool used is EAGLE PCB design software from CadSoft since it is a freeware and is open source. The advantage of this design software is the short learning curve. Also, it offers a large number of components in the library [2] and is easily downloadable from Infineon software database.

Figure 2 elucidates the PCB design flow in EAGLE PCB. It begins with design and prototype, then schematic capture once prototype is available, then followed by physical layout where traces checking are done, and finally the hardware test, which wraps up the PCB design process.

Figure 2: PCB design flow in Eagle.


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