MAX8717ETI Maxim Integrated, MAX8717ETI Datasheet - Page 23

• Manufacturer Part Number: MAX8717ETI
• Description: Current & Power Monitors & Regulators
• Manufacturer: Maxim Integrated

The output filter capacitor must have low enough equiv-
alent series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy stability requirements. The output capaci-
tance must be high enough to absorb the inductor
energy while transitioning from full-load to no-load con-
ditions without tripping the overvoltage fault protection.
When using high-capacitance, low-ESR capacitors (see
the Output-Capacitor Stability Considerations section),
the filter capacitor’s ESR dominates the output voltage
ripple. So the output capacitor’s size depends on the
maximum ESR required to meet the output-voltage-rip-
ple (V
In Idle Mode, the inductor current becomes discontinu-
ous, with peak currents set by the idle-mode current-
sense threshold (V
no-load output ripple can be determined as follows:
Figure 8. Current-Sense Configurations
Interleaved High-Efficiency, Dual Power-Supply
RIPPLE(P-P)
V
RIPPLE(P-P)
) specifications:
______________________________________________________________________________________
IDLE
Output Capacitor Selection
a) OUTPUT SERIES RESISTOR SENSING
b) LOSSLESS INDUCTOR SENSING
= R
= 0.2V
ESR
MAX8716
MAX8717
MAX8756
MAX8757
MAX8716
MAX8717
MAX8756
MAX8757
Controllers for Notebook Computers
I
LIMIT
LOAD(MAX)
CSH_
PGND
CSH_
PGND
). In Idle Mode, the
CSL_
CSL_
DH_
DH_
LX_
DL_
LX_
DL_
LIR
N
N
N
N
H
H
L
L
R
BIAS =
D
C
C
D
L
IN
IN
L
INPUT (V
R
EQ
INPUT (V
The actual capacitance value required relates to the
physical size needed to achieve low ESR, as well as to
the chemistry of the capacitor technology. Thus, the
capacitor is usually selected by ESR and voltage rating
rather than by capacitance value (this is true of tanta-
lums, OS-CONs, polymers, and other electrolytics).
When using low-capacity filter capacitors, such as
ceramic capacitors, size is usually determined by the
capacity needed to prevent V
causing problems during load transients. Generally,
once enough capacitance is added to meet the over-
shoot requirement, undershoot at the rising load edge
is no longer a problem (see the V
tions in the Transient Response section). However, low-
capacity filter capacitors typically have high-ESR zeros
that may effect the overall stability (see the Output-
Capacitor Stability Considerations section).
IN
)
IN
L
)
R
EQ
INDUCTOR
V
C
RIPPLE P P
R
EQ
SENSE
(
−
)
=
V
C
IDLE ESR
R
OUT
SAG
SENSE
SAG
C
R
OUT
and V
and V
SOAR
SOAR
equa-
from
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