MSS1048-152NL AD [Analog Devices], MSS1048-152NL Datasheet - Page 21

• Manufacturer Part Number: MSS1048-152NL
• Description: Dual 5 A, 20 V Synchronous Step-Down
• Manufacturer: AD [Analog Devices]

Data Sheet
The
loop to prevent subharmonic oscillations when the duty cycle is
larger than 50%. The internal slope compensation limits the min-
imum inductor value.
For a duty cycle that is larger than 50%, the minimum inductor
value is determined by the following equation:
The inductor peak current is calculated by
The saturation current of the inductor must be larger than the
peak inductor current. For the ferrite core inductors with a
quick saturation characteristic, the saturation current rating of the
inductor should be higher than the current-limit threshold of the
switch to prevent the inductor from entering saturation.
The rms current of the inductor can be calculated by
Shielded ferrite core materials are recommended for low core
loss and low EMI.
Table 9. Recommended Inductors
Vendor
Sumida
Coilcraft
Wurth
Elektronik
ADP2325
I
I
V
PEAK
RMS
OUT
2




f

I
Part No.
CDRH105RNP-0R8N
CDRH105RNP-1R5N
CDRH105RNP-2R2N
CDRH105RNP-3R3N
CDRH105RNP-4R7N
CDRH105RNP-6R8N
MSS1048-152NL
MSS1048-222NL
MSS1048-332NL
MSS1048-472NL
MSS1048-682NL
7447797110
7447797180
7447797300
7447797470
7447797620
1
SW
OUT
I

uses adaptive slope compensation in the current
OUT
D


2


2
I

L
12
I
L
2
Value
(μH)
1.5
2.2
3.3
4.7
6.8
1.5
2.2
3.3
4.7
6.8
1.1
1.8
3.0
4.7
6.2
0.8
I
(A)
13.5
10.5
9.25
7.8
6.4
5.4
10.5
8.4
7.38
6.46
5.94
16
13.3
10.5
8.0
7.5
SAT
I
(A)
9.5
8.3
7.5
6.5
6.1
5.4
10.8
9.78
7.22
6.9
6.01
7.6
7.3
7.0
5.8
5.5
RMS
DCR
(mΩ)
4.3
5.8
7.2
10.4
12.3
18
5.1
7.2
10.1
11.4
15.4
14
16
18
27
30
Rev. 0 | Page 21 of 32
OUTPUT CAPACITOR SELECTION
The output capacitor selection affects both the output voltage
ripple and the loop dynamics of the regulator. For example,
during load step transient on the output, when the load is sud-
denly increased, the output capacitor supplies the load until the
control loop can ramp up the inductor current, which causes an
undershoot of the output voltage. Use the following equation to
calculate the output capacitance that is required to meet the voltage
droop requirement:
where:
Δ I
Δ V
K
Another example is when a load is suddenly removed from the
output and the energy stored in the inductor rushes into the
output capacitor, which causes the output to overshoot. The
output capacitance required to meet the overshoot requirement
can be calculated using the following equation:
where:
Δ V
K
The output ripple is determined by the ESR of the output
capacitor and its capacitance value. Use the following equation to
select a capacitor that can meet the output ripple requirements:
where:
Δ V
R
Select the largest output capacitance given by C
and C
performance.
The selected output capacitor voltage rating must be greater
than the output voltage. The minimum rms current rating of
the output capacitor is determined by the following equation:
ESR
UV
OV
STEP
OUT_UV
OUT_OV
OUT_RIPPLE
is a factor, typically setting K
is a factor, typically setting K
is the equivalent series resistance of the output capacitor.
C
C
C
R
I
OUT_RIPPLE
is the load step.
C
OUT_OV
OUT_RIPPLE
OUT_UV
ESR
OUT
is the allowable undershoot on the output voltage.
is the allowable overshoot on the output voltage.
_

rms
is the allowable output voltage ripple.




V
to meet both load transient and output ripple
OUT_RIPPLE
2

V




12
I
OUT
I
8
L

L
V

K
IN
K

f
UV
OV
SW


V
V



OUT
OUT




I
I
I
V
STEP
STEP
L
_

OUT_RIPPLE
OV

UV
OV

2
2

2
V

= 2.
= 2.


OUT_UV
L
L
V
OUT
2
OUT_UV
ADP2325
, C
OUT_OV
,