MAX15035 Datasheet, PDF (23/27 Pages) Maxim Integrated Products – 15A Step-Down Regulator with Internal Switches

15A Step-Down Regulator with Internal Switches
Ceramic capacitors have a high-ESR zero frequency,
but applications with sufficient current-sense compen-
sation may still take advantage of the small size, low
ESR, and high reliability of the ceramic chemistry. Using
the inductor DCR, applications using ceramic output
capacitors may be compensated using either a DC
compensation or AC compensation method (Figure 11).
The DC-coupling requires fewer external compensation
capacitors, but this also creates an output load line that
depends on the inductor’s DCR (parasitic resistance).
Alternatively, the current-sense information may be AC-
coupled, allowing stability to be dependent only on the
inductance value and compensation components and
eliminating the DC load line.
OPTION A: DC-COUPLED CURRENT-SENSE COMPENSATION
IN
INPUT
BST
C_IN
PWR
DC COMPENSATION
<> FEWER COMPENSATION COMPONENTS
<> CREATES OUTPUT LOAD LINE
<> LESS OUTPUT CAPACITANCE REQUIRED
FOR TRANSIENT RESPONSE
LX
PGND
MAX15035
PWR
FB
GND
AGND
PWR
R_SENA
L
R_SENB
C_SEN
C_OUT
PWR
OUTPUT
STABILITY REQUIREMENT
( ) ^⎛
⎝⎜
L
R_SENA ||R_SENB
⎞
C_{SEN ⎠⎟}^COUT
≥¹
2f_SW
AND LOAD LINE
=
R_SENBR_DCR
R_SENA + R_SENB
FEEDBACK RIPPLE IN PHASE WITH INDUCTOR CURRENT
OPTION B: AC-COUPLED CURRENT-SENSE COMPENSATION
IN
C_IN
BST
PWR
INPUT
AC COMPENSATION
<> NOT DEPENDENT ON ACTUAL DCR VALUE
<> NO OUTPUT LOAD LINE
LX
PGND
MAX15035
PWR
FB
GND
AGND
PWR
L
R_SEN
C_SEN
C_COMP
C_OUT
PWR
OUTPUT
R_COMP
STABILITY REQUIREMENT
⎛
⎝⎜
L
R_SENC_SEN
⎞
⎠⎟
C_OUT
≥
1
2f_SW
AND
R_COMPC_COMP
≥
1
f_SW
FEEDBACK RIPPLE IN PHASE WITH INDUCTOR CURRENT
Figure 11. Feedback Compensation for Ceramic Output Capacitors
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