TurboTrans™ Technology

TurboTrans™ Selection

PTH08T255W

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 is 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 is reduced. Applications requiring tight transient voltage tolerances

and minimized capacitor footprint area benefits greatly from this technology.

(pin19). 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

PTH08T255W, the minimum required capacitance is 1000

µF. 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

m

Ω) to determine the capacitance × ESR product.) See the Capacitor Selection section of the datasheet for a

variety of capacitors that meet this criteria.

Figure 7 and Figure 8 show the amount of output capacitance required to meet a desired transient voltage

deviation with and without TurboTrans for several capacitor types; TypeB (e.g. polymer-tantalum) and TypeC

limits and magnitude of your transient load step. Next, determine what type of output capacitors to 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 7 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

calculated using the equation or selected from the TurboTrans table. The TurboTrans tables include both the

deviation for 25%(10A), 50%(20A), and 75%(30A) output load steps.

The chart can also be used to determine the achievable transient voltage deviation for a given amount of output

capacitance. Selecting the amount of output capacitance along the X-axis, reading up to the 'With TurboTrans'

curve, and then over to the Y-axis, gives the transient voltage deviation limit for that value of output capacitance.

As an example, let's look at a 12-V application requiring a 80 mV deviation during an 20A load transient. A

majority of 560

µF, 10mΩ ouput capacitors are used. Use the 12 V, Type C capacitor chart, Figure 8. Dividing

80mV by 20A gives 4mV/A transient voltage deviation per amp of transient load step. Select 4mV/A on the

Y-axis and read across to the 'With TurboTrans' plot. Following this point down to the X-axis gives us a minimum

required output capacitance of approximately 1700

µF. The required R

To see the benefit of TurboTrans, follow the 4mV/A marking across to the 'Without TurboTrans' plot. Following

that point down shows that you would need a minimum of 5500

µF of output capacitance to meet the same

transient deviation limit. This is the benefit of TurboTrans.

Copyright © 2008, Texas Instruments Incorporated

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