MAX15053_11 Datasheet, PDF (16/21 Pages) Maxim Integrated Products – High-Efficiency, 2A, Current-Mode Synchronous, Step-Down Switching Regulator

High-Efficiency, 2A, Current-Mode
Synchronous, Step-Down Switching Regulator
1ST ASYMPTOTE
R2 × (R1 + R2)^-1 × 10^AVEA(dB)/20 × gMC × RLOAD × {1 + RLOAD × [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1
2ND ASYMPTOTE
GAIN
R2 × (R1 + R2)^-1 × gMV × (2GCC)^-1 × gMC × RLOAD × {1 + RLOAD × [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1
3RD ASYMPTOTE
R2 × (R1 + R2)^-1 × gMV × (2GCC)^-1 × gMC × RLOAD × {1 + RLOAD × [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1 ×
(2GCOUT × {RLOAD-1 + [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1)^-1
4TH ASYMPTOTE
R2 × (R1 + R2)^-1 × gMV × RC × gMC × RLOAD × {1 + RLOAD × [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1 ×
(2πCOUT × {RLOAD-1 + [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1)^-1
UNITY
1ST POLE
[2GCC × (10^AVEA(dB)/20 - gMV-1)]^-1
3RD POLE (DBL) 2ND ZERO
0.5 × f_SW (2GC_OUTESR)^-1
fCO
FREQUENCY
2ND POLE
fPMOD*
1ST ZERO
(2GCCRC)^-1
5TH ASYMPTOTE
R2 × (R1 + R2)^-1 × g_MV × R_C × g_MC × R_LOAD × {1 + R_LOAD × [K_S × (1 - D) - 0.5] × (L × f_SW)^-1}^-1 ×
(2GCOUT × {RLOAD-1 + [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1)^-1 × (0.5 × fSW)² × (2Gf)^-2
NOTE:
ROUT = 10^AVEA(dB)/20 × gMV-1
fPMOD = [2GCOUT × (ESR + {RLOAD-1 + [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1)]^-1
WHICH FOR
ESR << {R_LOAD-1 + [K_S × (1 - D) - 0.5] × (L × f_SW)^-1}^-1
BECOMES
f_PMOD = [2GC_OUT × {R_LOAD-1 + [K_S × (1 - D) - 0.5] × (L × f_SW)^-1}^-1]^-1
fPMOD = (2GCOUT × RLOAD)^-1 + [KS × (1 - D) - 0.5] × (2GCOUT × L × fSW)^-1
6TH ASYMPTOTE
R2 × (R1 + R2)^-1 × g_MV × R_C × g_MC × R_LOAD × {1 + R_LOAD × [K_S × (1 - D) - 0.5] × (L × f_SW)^-1}^-1 ×
ESR × {RLOAD-1 + [KS × (1 - D) - 0.5] × (L × fSW)^-1}^-1 × (0.5 × fSW)² × (2Gf)^-2
Figure 3. Asymptotic Loop Response of Current-Mode Regulator
As previously mentioned, the power modulator’s domi-
nant pole is a function of the parallel effects of the load
resistance and the current-loop gain’s equivalent imped-
ance:
which can be expressed as:
f_PMOD
≈
2π
×
1
C _OUT
× R_LOAD
+
K _S × (1− D) − 0.5
2π × f_SW × L × C_OUT
f_PMOD
=
2π
× C_OUT
×

_ESR

+
1


1
R_LOAD
+
K _S
× (1− D) −
f_SW × L
0.5


−1_



And knowing that the ESR is typically much smaller than
the parallel combination of the load and the current loop:
Note: Depending on the application’s specifics, the
amplitude of the slope compensation ramp could have
a significant impact on the modulator’s dominate pole.
For low duty-cycle applications, it provides additional
damping (phase lag) at/near the crossover frequency
(see the Closing the Loop: Designing the Compensation
Circuitry section). There is no equivalent effect on the
ESR <<


1
 _RLOAD
+
K _S
×
(1−
D)
−
0.5


−1
f_SW × L

power modulator zero, fZMOD.
f_ZMOD
=
f_ZESR
=
2π
1
× C_OUT
× ESR
f_PMOD
≈
2π
× C_OUT
×


1
R_LOAD
1
+
K _S
× (1− D) −
f_SW × L
0.5


−1
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