In 2001, the first SWIFT (Switchers With Integrated FET Technology) IC developed by TI was released for the market with the model designation TPS54610. Since then, this IC and its growing product family have enjoyed increasing popularity. The interactive software has undoubtedly played a major part in this success. SWIFT development software has existed since March 2001. Over the years it has been increasingly refined, and many additional functions have been added. It will continue to be designed in order to make developments even easier. The product family currently encompasses 37 SWIFT derivatives, all of which are step-down converters. These cover an input voltage range of 2.2 to 20V with output currents of 1.5 to 14A and, thanks to synchronous rectification, allow an efficiency of over 90%. They are manufactured in an HTSSOP housing with a Power Pad (metal substrate under the housing for heat dissipation into the PCB), with 16 to 28 pins. The ICs can be operated either with two external adjustable fixed frequencies or synchronised at up to 700kHz using an external signal. The output voltage can be set down to as low as 900mV for most of the derivatives or may be pre-programmed for fixed values for the most common processor voltages from 0.9 to 5V. In addition, there are converters for special applications such as generating termination voltage for DDR RAMs or the perfect sequencing of multiple supply voltages.

Interactive Development software

As mentioned earlier, the SWIFT software is an interactive development software that allows both inexperienced and experienced developers to work their way through component selection to a virtual circuit in a very short time. For this, the software requires only simple input values, such as output voltage, maximum output current and input voltage range. These three parameters are all that is needed for the software to calculate a proposal after the user has selected the product family as shown in Figure 1 (step 1). At the same time, this selection establishes the permitted input voltage range. In the second step, the output voltage, the maximum required output current and the minimum/maximum input voltage must be entered as decimal values. You can now go straight to step 5 and click «Go". The software then calculates and displays a proposal. However, users also have the possibility to go through steps 3 and 4 in order to further customise the design via several advanced selections. In step 3, you can specify whether the design is to be oriented towards maximum efficiency or minimum size. You can also determine whether only SMD components, only wired components or a mix of SMD and wired components may be used in the design. In capacitor selection, it is possible to specify ceramic capacitors or electrolytic capacitors only, or to allow the two to be mixed. From here you can once again go to step 5 and click «Go" to get a result. However, you can also specify further parameters in block 4, optional settings. Here, the developer can select the slow start time, the maximum output voltage ripple, the switching frequency, the input voltage ripple, the minimum margin for loop gain, minimum phase and maximum permitted component height. If you place the cursor over the input field, a dialog box appears showing the input range available. The value chosen must be within this input range. Once you have set some or all these parameters in accordance with your requirements you c can go to step 5 and click «Go". Via the stored component database, the software then calculates the optimal design taking into account the parameters entered by the user.

Comprehensive circuit analysis

Figure 2 shows the user interface after calculation. The manufacturer or model of all the externally calculated components that are marked with a blue placeholder can now be changed in this window. To do this, click on the placeholder, and the component database for the component in question opens in a separate window. In the example shown, this is the output inductor. All the parameters assigned to the relevant inductor are shown here, too. New and customer-specific components can also be added in order to include them in the calculation or select them in this window. A corresponding component database exists for the capacitors used as input and output capacitors. Figure 3 shows detailed views of the circuit analysis that can be obtained by clicking the relevant buttons in the status bar. Details of the design analysis such as the actual minimum and maximum values resulting from the component tolerances can be displayed. The stress analysis shows the thermal distribution so that the layout can be designed according to power loss and heat dissipation. The loop response graph presents the Bode plot with the stability criterion. The current running across switching nodes as well as the input and output voltage ripple can be shown in graphical form. The efficiency can be indicated in a graph as a function of the load current, while the bill of materials is displayed as a table. All windows can be printed out using the «Print" button or copied to the clipboard for later use. The bill of materials can also be exported into an Excel table with a simple click.

Find the right component

As mentioned earlier, the SWIFT family has various derivatives for special tasks. To simplify the classification of the modules, it is useful to know how the component numbers are allocated. Components in the SWIFT family always start with the component designation TPS54. The third digit then specifies the continuous maximum output current. If the third digit is a one, it is a component with a maximum output current of 1.5A; if it is a three, the current is 3A, if a six, 6A, and so on. A zero as the third digit represents an output current of 14A. The last two digits describe the function or the output voltage of the relevant SWIFT module. Ending 10 or 50 indicate adjustable step-down converters with an external compensation network. These can be set down to a minimum output voltage of 900mV. In the 50 variant, the user can choose, via external circuit elements, between a cheaper conventional step-down converter with an external freewheeling diode and a highly efficient step-down converter with synchronous rectification by an external FET. The driver for this FET is already integrated into the IC. Endings 11 to 16 and 52 to 57 refer to the fixed voltage versions with an internal compensation network. The last digit here specifies the fixed voltage. Ending 11 represents an output voltage of 900mV; ending 12/52: 1.2V; ending 13/53: 1.5V; ending 14/54: 1.8V; ending 15/55: 2.5V; ending 16/56: 3.3. V; and ending 57: 5.0 V. Ending 72 designates SWIFT modules designed for generating the DDR-RAM termination voltage. The module allows the output voltage to follow an externally applied reference voltage. In addition, the module can act as a continuous power source and current sink. Ending 73 represents a SWIFT module that disables synchronous rectification during the start-up phase and activates it only when the programmed nominal voltage is reached. This version can therefore only act as a current source during the start-up phase, not as a current sink, thereby allowing the e precharged form of the sequencing of several supply voltages for DSPs, FPGAs or other multiple voltage systems. In this type of sequencing, the different voltages are «jammed" together via one or more diodes. Use of the special 73-model SWIFT prevents these from working against each other when running up the voltage. A component of the SWIFT family with the ending 80 describes a module with what is known as the tracking function, which allows the supply voltage to be powered up and down as defined. The module has a multiplexer between the reference voltage source and the error amplifier, the second input of the multiplexer being executed as a TRACKIN pin. A ramp can be applied at this TRACKIN pin, and the output of the converter will follow this ramp during power-up and power-down. As soon as the voltage applied at the TRACKIN pin exceeds the internal reference voltage source, the multiplexer switches the internal reference to the error amplifier.