MAX8792 Maxim Integrated Products, MAX8792 Datasheet - Page 23

• Manufacturer Part Number: MAX8792
• Description: Single Quick-PWM Step-Down Controller
• Manufacturer: Maxim Integrated Products

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