AIC1341 Analog Intergrations Corporation, AIC1341 Datasheet - Page 10

• Manufacturer Part Number: AIC1341
• Description: High Performance/ Triple-Output/ Auto-Tracking Combo Controller
• Manufacturer: Analog Intergrations Corporation

After the initial transient, the ESL dependent term
drops off. Because the strong relationship be-
tween output capacitor ESR and output load tran-
sient, the output capacitor is usually chosen for
ESR, not for capacitance value. A capacitor with
suitable ESR will usually have a larger capaci-
tance value than is needed for energy storage.
A common way to lower ESR and raise ripple cur-
rent capability is to parallel several capacitors. In
most case, multiple electrolytic capacitors of
small case size are better than a single large
case capacitor.
Output Inductor Selection
Inductor value and type should be chosen based
on output slew rate requirement, output ripple r e-
quirement and expected peak current. Inductor
value is primarily controlled by the required current
response time. The AIC1341 will provide either 0%
or 85% duty cycle in response to a load transient.
+3.3V
V
OUT2
IN
C
OUT2
V
OUT3
+
Q4
C
OUT3
+
Fig.6 Printed circuit board power planes and islands
+12V
+
Css
Q3
VIN2
GATE3
GATE2
SS
VCC
+
GND
Power Plane Layer
Circuit Plane Layer
Via Connection to Ground Plane
OCSET
UGATE
PHASE
LGATE
PGND
The response time to a transient is different for the
application of load and remove of load.
Where
In a typical 5V input, 2V output application, a 3 H
inductor has a 1A/ S rise time, resulting in a 5 S
delay in responding to a 5A load current step. To
optimize performance, different combinations of
input and output voltage and expected loads may
require different inductor value. A smaller value of
inductor will improve the transient response at the
expense of increase output ripple voltage and i n -
ductor core saturation rating.
Peak current in the inductor will be equal to the
maximum output load current plus half of inductor
ripple current. The ripple current is approximately
equal to:
t
RISE
Q2
Q1
V
L
I
IN
OUT
V
I
OUT
is transient load current step.
OUT
+
C
,
L
IN
OUT
t
FALL
+5V
+
IN
=
C
OUT
L
V
OUT
V
OUT
AIC1341
I
OUT
.
10