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PTH04T220WAST Datasheet(PDF) 17 Page - Texas Instruments |
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PTH04T220WAST Datasheet(HTML) 17 Page - Texas Instruments |
17 / 39 page www.ti.com TurboTrans™ Technology TurboTrans™ Selection PTH04T220W, PTH04T221W SLTS275A – DECEMBER 2006 – REVISED FEBRUARY 2007 TurboTrans technology is a feature introduced in the T2 generation of the PTH/PTV family of power modules. TurboTrans optimizes the transient response of the regulator with added external capacitance using a single external resistor. Benefits of this technology include reduced output capacitance, minimized output voltage deviation following a load transient, and enhanced stability when using ultra-low ESR output capacitors. The amount of output capacitance required to meet a target output voltage deviation will be reduced with TurboTrans activated. Likewise, for a given amount of output capacitance, with TurboTrans engaged, the amplitude of the voltage deviation following a load transient will be reduced. Applications requiring tight transient voltage tolerances and minimized capacitor footprint area will benefit greatly from this technology. Utilizing TurboTrans requires connecting a resistor, RTT, between the +Sense pin (pin 5) and the TurboTrans pin (pin 8). The value of the resistor directly corresponds to the amount of output capacitance required. All T2 products require a minimum value of output capacitance whether or not TurboTrans is utilized. For the PTH04T220W, the minimum required capacitance is 220 µF. The minimum required capacitance for the PTH04T221W is 300 µF of ceramic type. When using TurboTrans, capacitors with a capacitance × ESR product below 10,000 µF×mΩ are required. (Multiply the capacitance (in µF) by the ESR (in mΩ) to determine the capacitance × ESR product.) See the Capacitor Selection section of the datasheet for a variety of capacitors that meet this criteria. Figure 12 thru Figure 17 show the amount of output capacitance required to meet a desired transient voltage deviation with and without TurboTrans for several capacitor types; Type A (e.g. ceramic), Type B (e.g. polymer-tantalum), and Type C (e.g. OS-CON). To calculate the proper value of RTT, first determine your required transient voltage deviation limits and magnitude of your transient load step. Next, determine what type of output capacitors will be used. (If more than one type of output capacitor is used, select the capacitor type that makes up the majority of your total output capacitance.) Knowing this information, use the chart in Figure 12 thru Figure 17 that corresponds to the capacitor type selected. To use the chart, begin by dividing the maximum voltage deviation limit (in mV) by the magnitude of your load step (in Amps). This gives a mV/A value. Find this value on the Y-axis of the appropriate chart. Read across the graph to the 'With TurboTrans' plot. From this point, read down to the X-axis which lists the minimum required capacitance, CO, to meet that transient voltage deviation. The required RTT resistor value can then be calculated using the equation or selected from the TurboTrans table. The TurboTrans tables include both the required output capacitance and the corresponding RTT values to meet several values of transient voltage deviation for 25% (2.5 A), 50% (5 A), and 75% (7.5 A) output load steps. The chart can also be used to determine the achievable transient voltage deviation for a given amount of output capacitance. By selecting the amount of output capacitance along the X-axis, reading up to the desired 'With TurboTrans'' curve, and then over to the Y-axis, gives the transient voltage deviation limit for that value of output capacitance. The required RTT resistor value can be calculated using the equation or selected from the TurboTrans table. As an example, let's look at a 5-V application requiring a 50 mV deviation during an 5 A, 50% load transient. A majority of 330 µF, 10 mΩ ouput capacitors will be used. Use the 5-V, Type B capacitor chart, Figure 14. Dividing 50 mV by 5 A gives 10 mV/A transient voltage deviation per amp of transient load step. Select 10 mV/A on the Y-axis and read across to the 'With TurboTrans'' plot. Following this point down to the X-axis gives a minimum required output capacitance of approximately 760 µF. The required R TT resistor value for 760 µF can then be calculated or selected from Table 5. The required RTT resistor is approximately 4.99 kΩ. To see the benefit of TurboTrans, follow the 10 mV/A marking across to the 'Without TurboTrans' plot. Following that point down shows that you would need a minimum of 2700 µF of output capacitance to meet the same transient deviation limit. This is the benefit of TurboTrans. 17 Submit Documentation Feedback |
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