TurboTrans Technology
TurboTrans Selection
SLTS263I – AUGUST 2007 – REVISED MARCH 2009 ...................................................................................................................................................... www.ti.com
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. The, 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 benefit from this technology.
Utilizing TurboTrans requires connecting a resistor, RTT, between the +Sense pin (pin10) and the TurboTrans pin
(pin13). 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
PTH05T210W, the minimum required capacitance is 470
F. When using TurboTrans, capacitors with a
capacitance × ESR product below 10,000
F × m are required. (Multiply the capacitance (in F) by the ESR (in
m
) 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 through
Figure 9, 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 the
required transient voltage deviation limits and magnitude of the 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 the total output capacitance.) Knowing this information, use the chart in
Figure 7through
Figure 9 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 the 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 the transient
voltage deviation. The required RTT resistor value can then be calculated using Equation 2 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%(7.5A), 50%(15A), and 75%(22.5A)
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 RTT resistor value can be calculated using Equation 2 or selected from the TurboTrans table. As an example, let's look at a 12-V application requiring a 60mV deviation during a 15A, 50% load transient. A
majority of 330
F, 10m output capacitors are used. Use the 12V, TypeB capacitor chart,
Figure 8. Dividing
60mV by 15A 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 1350
F. The required R
TT resistor value for 1350F can then be
calculated or selected from Figure 8. The required RTT resistor is approximately 9.31k. To see the benefit of TurboTrans, follow the 4mV/A marking across to the 'Without TurboTrans' plot. Following
that point down shows that more than 10,000
F of output capacitance is required to meet the same transient
deviation limit. This is the benefit of TurboTrans. A typical TurboTrans application schematic is shown in
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