PTH08T260W_15 Datasheet, PDF (18/38 Pages) Texas Instruments – 3-A, 4.5-V to 14-V INPUT, NON-ISOLATED, WIDE-OUTPUT, ADJUSTABLE POWER MODULE WITH TurboTrans™

PTH08T260W, PTH08T261W
SLTS272G – DECEMBER 2006 – REVISED AUGUST 2011
TURBOTRANS
www.ti.com
TurboTrans™ Technology
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.
TurboTrans™ Selection
Using TurboTrans requires connecting a resistor, R_TT, 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 used. For the
PTH08T260W, the minimum required capacitance is 200 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
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 10 through Figure 15 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 R_TT, 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 10
through Figure 15 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, C_O, to meet that transient
voltage deviation. The required R_TT 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
R_TT values to meet several values of transient voltage deviation for 25% (0.75 A), 50% (1.5 A), and 75% (2.25 A)
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.
The required R_TT resistor value can be calculated using the equation or selected from the TurboTrans table.
As an example, let's look at a 12-V application requiring a 24 mV deviation during an 1.5 A, 50% load transient.
A majority of 330 μF, 10 mΩ ouput capacitors are used. Use the 12 V, Type B capacitor chart, Figure 12.
Dividing 24 mV by 1.5 A gives 16 mV/A transient voltage deviation per amp of transient load step. Select
16 mV/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 600 μF. The required R_TT resistor value for
600 μF can then be calculated or selected from Table 5. The required R_TT resistor is 8.06 kΩ.
To see the benefit of TurboTrans, follow the 16 mV/A marking across to the 'Without TurboTrans' plot. Following
that point down shows that you would need 3000 μF of output capacitance to meet the same transient deviation
limit. This is the benefit of TurboTrans. A typical TurboTrans schematic is shown in Figure 16.
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