www.ti.com................................................................................................................................................... SLTS252K – NOVEMBER 2005 – REVISED JUNE 2009
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 (pin6) and the TurboTrans pin
(pin9). 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
PTH08T220W, the minimum required capacitance is 220
µF. The minimum required capacitance for the
PTH08T221W is 300
µF of ceramic type. When using TurboTrans, capacitors with a capacitance × ESR product
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 13 thru Figure 18 show the amount of output capacitance required to meet a desired transient voltage
deviation with and without TurboTrans for several capacitor types; TypeA (e.g. ceramic), TypeB (e.g.
polymer-tantalum), and TypeC (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 13 thru
Figure 18 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%(4A), 50%(8A), and 75%(12A) output
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 RTT 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 40 mV deviation during an 8A, 50% load transient. A
majority of 330
µF, 10mΩ ouput capacitors will be used. Use the 12 V, Type B capacitor chart, Figure 15. Dividing
40mV by 8A gives 5mV/A transient voltage deviation per amp of transient load step. Select 5mV/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 800
µF. The required R
TT resistor value for 800µF can then be
calculated or selected from Table 5. The required RTT resistor is approximately 4.12kΩ.
To see the benefit of TurboTrans, follow the 5mV/A marking across to the 'Without TurboTrans' plot. Following
that point down shows that you would need a minimum of 4500
µF of output capacitance to meet the same
transient deviation limit. This is the benefit of TurboTrans. A typical TurboTrans schematic and waveforms are