MSS1048-152NL AD [Analog Devices], MSS1048-152NL Datasheet - Page 25

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

Data Sheet
To meet the ±5% overshoot and undershoot requirement, use
the following equation to calculate the capacitance:
For estimation purposes, use K
use C
use C
For the 1.2 V rail, ESR of the output capacitor must be smaller
than 8.3 mΩ, and the output capacitance must be larger than
188 µF. It is recommend that three 100 µF, X5R, 6.3 V ceramic
capacitors be used, such as the GRM32ER60J107ME20 from
Murata, with an ESR = 2 mΩ.
For the 3.3 V rail, the ESR of the output capacitor must be
smaller than 23 mΩ, and the output capacitance must be
larger than 55 µF. It is recommended that two 47 µF, X5R,
6.3 V ceramic capacitors be used, such as the Murata
GRM32ER60J476ME20, with an ESR = 2 mΩ.
LOW-SIDE MOSFET SELECTION
A low R
solutions. The MOSFET breakdown voltage must be greater
than 1.2 V × V
1.2 V × I
It is recommended that a 30 V, N-channel MOSFET be used, such
as the FDS8880 from Fairchild. The R
4.5 V driver voltage is 12 mΩ, and the total gate charge is 12 nC.
COMPENSATION COMPONENTS
For better load transient and stability performance, set the
cross frequency, f
therefore, the f
For the 1.2 V rail, the 100 µF ceramic output capacitor has
a derated value of 64 µF.
By choosing standard components where R
1500 pF, no C
C
C
C
C
R
OUT_OV1
OUT_OV2
C1
OUT_OV
OUT_UV
C1
CP1
DSON
LIMIT
=
=
=
2
(
. 0
. 0
N-channel MOSFET is selected for high efficiency
= 188 µF and C
= 55 µF and C
.
×
CP1
=
=
24
001
π
C
0.6
IN
(
2
is set to 50 kHz.
V
, and the drain current must be greater than
×
Ω
is needed.
C
28
×
1
Ω
OUT
V
, to f
+
2 .
(
V
9 .
×
×
. 0
V
K
K
28
IN
500
+
3
kΩ
SW
001
OV
UV
×
×
∆
9 .
−
/10. In this case, f
3
64
V
V
μS
kΩ
×
×
×
Ω
OUT_UV2
OUT
OUT
μF
∆
∆
OUT_UV1
64
)
×
×
I
OV
I
STEP
8.33
_
STEP
3
μF
)
=
OV
= K
×
×
6
= 21 µF.
×
2
∆
64
)
2
6 .
= 21 µF. For V
A/V
2
×
UV
V
50
×
DSON
−
pF
μF
L
OUT
L
V
= 2. For V
kHz
OUT
of the FDS8880 at a
=
_
C1
UV
1598
SW
2
= 28 kΩ and C
=
runs at 500 kHz;
28
pF
OUT1
9 .
OUT2
kΩ
= 1.2 V,
= 3.3 V,
C1
Rev. 0 | Page 25 of 32
=
Figure 52 shows the 1.2 V rail bode plot at 5 A. The cross
frequency is 42 kHz and the phase margin is 50°.
For the 3.3 V rail, the 47 µF ceramic output capacitor has a
derated value of 32 µF.
By using standard component values of R
C
Figure 53 shows the 3.3 V rail bode plot at 5 A. The cross
frequency is 55 kHz and phase margin is 67°.
C2
–12
–24
–36
–48
–60
–12
–24
–36
–48
–60
60
48
36
24
12
60
48
36
24
12
= 1500 pF, no C
0
0
1k
1k
R
C
C
C2
C2
CP2
=
=
=
2
(
. 0
. 0
×
66
001
π
0.6
×
Ω
Figure 52. Bode Plot for 1.2 V Rail
Figure 53. Bode Plot for 3.3 V Rail
26
10k
Ω
10k
3
V
+
3 .
CP2
5 .
×
×
. 0
V
26
2
500
kΩ
001
FREQUENCY (Hz)
is needed.
FREQUENCY (Hz)
×
×
5 .
2
32
kΩ
μS
Ω
×
1
μF
2 3
)
×
×
1
8.33
2
μF
100k
=
100k
×
2
×
32
4 .
A/V
50
μF
pF
kHz
=
C2
1594
=
= 27 kΩ and
2
2
1M
26
1M
pF
5 .
kΩ
ADP2325
180
144
108
72
36
0
–36
–72
–108
–144
–180
180
144
108
72
36
0
–36
–72
–108
–144
–180