Datasheet

TPS40055-EP
www.ti.com SGLS310D –JULY 2005–REVISED FEBRUARY 2012
(73)
Select the close-loop 0 dB crossover frequency (f
C
). For this example, f
C
= 20 kHz.
Select the double zero location for the Type III compensation network at the output filter double pole at 4.93 kHz.
Select the double pole location for the Type III compensation network at the output capacitor ESR zero at
73.7 kHz.
The amplifier gain at the crossover frequency of 20 kHz is determined by the reciprocal of the modulator gain
AMOD at the crossover frequency from Equation 74.
(74)
And also from Equation 75.
(75)
Choose R1 = 100 kΩ
The poles and zeros for a type III network are described in Equation 25 and Equation 26.
(76)
(77)
(78)
(79)
(80)
Calculate the value of R
BIAS
from Equation 81 with R1 = 100 kΩ.
(81)
CALCULATING THE BOOST AND BP10V BYPASS CAPACITANCE
The size of the bypass capacitor depends on the total gate charge of the MOSFET being used and the amount
of droop allowed on the bypass cap. The BOOST capacitance for the Si7860DP, allowing for a 0.5-V droop on
the BOOST pin from Equation 29 is:
(82)
and the BP10V capacitance from Equation 32 is
Copyright © 2005–2012, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Link(s): TPS40055-EP