sc2441a Semtech Corporation, sc2441a Datasheet - Page 22

• Manufacturer Part Number: sc2441a
• Description: Sc2441a 1.8v To 20v Input 2-phase Synchronous Step-down Controllers With Step-up Converter
• Manufacturer: Semtech Corporation

As shown in Figure 9, to minimize the switching noise
generated by the step-up converter, the loop formed by
D
And the PGND2 pin should be tied to PGND1 at one
spot close to the PGND1 pin.
Step-up Converter Inductor Selection
For a specified inductor current ripple ratio
peak current ripple v.s. actual input current I
inductor value is
Typically, select
(CCM) operation.
If V
f
s3
POWER MANAGEMENT
Applications Information
1
, C
2006 Semtech Corp.
= 1MHz, then, L
in
= 3.3V, V
1
Figure 9. Step-Up Section Layout Illustration
, SW3 and PGND2 should be as small as possible.
24
PGND1
o3
L
= 5V and I
1
SC2441A
=
C
<2 for a Continous Conduction Mode
1
2
f
= 4.7 H.
s
3
V
V
d
CC
in
3
PGND2
21
I
o
SW3
3
o3
1 (
= 100mA with
-
26
27
V
V
o
in
3
Small
)
Loop
R
V
V
1
o
in
V
3
C
IN
1
.
D
= 1.6 and
L
1
1
(peak-to-
IN
), the
22
Assuming that the efficiency of the boost converter is
and the boost converter is running in CCM with duty ratio
D. The peak inductor current is
The saturation current rating of the selected inductor
should be at least 1.2 times of the calculated peak
current value.
Step-up Converter Capacitor Selection
Input capacitor: : : : : The input capacitance should be large
such that the input transients due to both the step-up
and the step-down converters do not trip the UVLO
threshold 1.71V. Since the SC2441A controls a 2-phase
low input voltage step-down converter, the input
capacitance is sized to handle the input ripple current of
the buck converter. This is usually sufficient for the
auxiliary boost converter because the input current in a
boost converter is continuous.
Output capacitor: Unlike buck converter, pulse current
is delivered to the output of a boost converter. To reduce
the output ripple voltage, low ESR capacitors should be
used. The output capacitor should also be able handle
the output ripple current. The SC2441A is designed to
use multi-layer ceramic capacitor as the sole output
capacitor.
Maximum Output Current of the Step-up Converter
Figure 3 shows that the boost switch current is sensed
with an internal sense resistor Rs and it is internally
limited at 0.6A. So the maximum output current can be
given as ( is the efficiency of the step-up section):
I
L1PEAK
I
o3,
max
=
=
V
V
o3
(
in
0.6A
×
h ×
I
o3
+
-
d
V
L
2
3
in
1
)
×
×
D
V
V
in
×
o3
T
×
SC2441A
h
×
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