Datasheet

TPS40055-EP
www.ti.com SGLS310D –JULY 2005–REVISED FEBRUARY 2012
Figure 14. Type III Compensation Configuration Figure 15. Type III Compensation Gain and Phase
The poles and zeros for a Type III network are described in Equation 25.
(25)
The value of R1 is somewhat arbitrary, but influences other component values. A value between 50 kΩ and
100 kΩ usually yields reasonable values.
The unity gain frequency is described in Equation 26.
(26)
where G is the reciprocal of the modulator gain at f
C
.
The modulator gain as a function of frequency at f
C
, is described in Equation 27.
(27)
Minimum Load Resistance
Care must be taken not to load down the output of the error amplifier with the feedback resistor, R2, that is too
small. The error amplifier has a finite output source and sink current, which must be considered when sizing R2.
Too small a value does not allow the output to swing over its full range.
(28)
CALCULATING THE BOOST AN BP10 BYPASS CAPACITOR
The BOOST capacitance provides a local, low impedance source for the high-side driver. The BOOST capacitor
should be a good quality, high-frequency capacitor. The size of the bypass capacitor depends on the total gate
charge of the MOSFET and the amount of droop allowed on the bypass capacitor. The BOOST capacitance is
described in Equation 29.
(29)
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