TPS54678_15 Datasheet, PDF (20/42 Pages) Texas Instruments – 2.95 V to 6 V INPUT, 6 A OUTPUT, 2 MHz, SYNCHRONOUS STEP DOWN SWITCHER WITH INTEGRATED FET ( SWIFT™)

TPS54678
SLVSBF3A – JUNE 2012 – REVISED NOVEMBER 2015
Device Functional Modes (continued)
V_OUT
TPS54678
R1
VSENSE
R2
V_REF
g_M(ea)
+
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COMP
R_{OUT(ea) COUT(ea)}
5 pF
R3 _C2
R3
C1
C1
Type IIA
Figure 29. Types of Frequency Compensation
Type IIB
The design guidelines for TPS54678 loop compensation are as follows:
1. Set up crossover frequency fc.
2. R3 can be determined by Equation 10:
R3 = ^{2p ´ fc ´ VO ´ COUT}
gmea ´ V_REF ´ gmps
where
• gm_ea is the GM amplifier gain,
• gm_PS is the power stage gain (20 A/V).
3. Place a compensation zero at the dominant pole
Equation 11:
fp =
1
C_OUT ´ R_L ´ 2p
(10)
C1 can be determined by
C1 = ^{RL ´ COUT}
R3
(11)
4. C2 is optional. It can be used to cancel the zero from ESR of the Co in Equation 12:
C2 =
R
ESR
´
C
OUT
R3
(12)
20
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