Datasheet

MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
______________________________________________________________________________________ 23
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 10).
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 B: AC-COUPLED CURRENT-SENSE COMPENSATION
OPTION A: DC-COUPLED CURRENT-SENSE COMPENSATION
DC COMPENSATION
<> FEWER COMPENSATION COMPONENTS
<> CREATES OUTPUT LOAD LINE
<> LESS OUTPUT CAPACITANCE REQUIRED
FOR TRANSIENT RESPONSE
AC COMPENSATION
<> NOT DEPENDENT ON ACTUAL DCR VALUE
<> NO OUTPUT LOAD LINE
C
IN
L
C
OUT
R
SENA
R
SENB
C
SEN
PWR
PWR
PWR
PWR
BST
LX
TON
DH
DL
FB
GND
AGND
STABILITY REQUIREMENT
MAX8792
OUTPUT
INPUT
FEEDBACK RIPPLE IN-PHASE WITH INDUCTOR CURRENT
C
IN
L
C
OUT
R
SEN
R
COMP
C
COMP
C
SEN
PWR
PWR
PWR
PWR
BST
LX
TON
DH
DL
FB
GND
AGND
STABILITY REQUIREMENT
MAX8792
OUTPUT
INPUT
FEEDBACK RIPPLE IN PHASE WITH INDUCTOR CURRENT
Figure 10. Feedback Compensation for Ceramic Output Capacitors
L
RRC
C
f
AND LOAD LINE
RR
RR
SENA SENB SEN
OUT
SW
SENB DCR
SENA SENB
||
()
⎛
⎝
⎜
⎞
⎠
⎟
≥=
+
1
2
L
RC
C
f
AND R C
SEN SEN
OUT
SW
COMP COMP
⎛
⎝
⎜
⎞
⎠
⎟
≥=
1
2
3xxto xT
SW
5