Datasheet

ESR OUT
R C
C2 =
R3
´
´
L OUT
R C
C1 =
R3
¦
´ ´ p
OUT L
1
p =
C R 2
OUT OUT
ea ref ps
2 × c V C
R3 =
gm V gm
p ¦ ´ ´
´ ´
¦
¦ ¦ ´
C
sw
= p mod
2
¦ ¦ ´ ¦
C
= p mod z mod
ESR OUT
1
z mod =
2 R C
¦
p ´ ´
OUT
OUT OUT
I max
p mod =
2 V C
¦
p ´ ´
TPS54318
SLVS975A –SEPTEMBER 2009–REVISED SEPTEMBER 2013 www.ti.com
The design guidelines for TPS54318 loop compensation are as follows:
1. The modulator pole, fpmod, and the ESR zero, fz1 must be calculated using Equation 11 and Equation 12.
Derating the output capacitor (C
OUT
) is required if the output voltage is a high percentage of the capacitor
rating. Use the capacitor manufacturer information to derate the capacitor value. Use Equation 13 and
Equation 14 to estimate a starting point for the crossover frequency, fc. Equation 13 is the geometric mean of
the modulator pole and the ESR zero and Equation 14 is the mean of modulator pole and the switching
frequency. Use the lower value of Equation 13 or Equation 14 as the maximum crossover frequency.
(11)
(12)
(13)
(14)
2. R3 can be determined by Equation 15.
Where
• gm
ea
is the amplifier gain (225 μA/V)
• gm
ps
is the power stage gain (13 A/V) (15)
3. Place a compensation zero at the dominant pole . C1 can be determined by
Equation 16.
(16)
4. C2 is optional. C2 is used to cancel the zero from the C
O
ESR.
(17)
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