MSS1048-152NL AD [Analog Devices], MSS1048-152NL Datasheet - Page 24

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

ADP2325
DESIGN EXAMPLE
This section describes the design procedure and component
selection for the example application shown in Figure 54, and
Table 11 provides a list of the required settings.
Table 11. Dual Step-Down DC-to-DC Regulator Requirements
Parameter
Channel 1
Channel 2
Switching Frequency
OUTPUT VOLTAGE SETTING
Choose a 10 kΩ top feedback resistor (R
bottom feedback resistor using the following equation:
To set the output voltage to 1.2 V, the resistor values are R
10 kΩ and R
the resistors values are R
CURRENT-LIMIT SETTING
For 5 A output current operation, the typical peak current
limit is 8 A. In this case, no R
FREQUENCY SETTING
To set the switching frequency to 500 kHz, use the following
equation to calculate the resistor value, R
Therefore, R
INDUCTOR SELECTION
The peak-to-peak inductor ripple current, ΔI
of the maximum output current. Use the following equation
to estimate the value of the inductor:
For V
Inductor L2 = 3.2 µH.
Select the standard inductor value of 1.5 µH and 3.3 µH for
the 1.2 V and 3.3 V rails.
Input Voltage
Output Voltage
Output Current
Output Voltage Ripple
Load Transient
Input Voltage
Output Voltage
Output Current
Output Voltage Ripple
Load Transient
R
R
L
OUT1
OSC
BOT
=
(
= 1.2 V, Inductor L1 = 1.4 µH, and for V
( )
V
kΩ
=
IN
BOT1
OSC
∆
R
TOP
−
I
=
L
=120 kΩ.
V
= 10 kΩ. To set the output voltage to 3.3 V,
×
f
OUT
×
SW
60
f




SW
V
,
(
)
000
kHz
×
OUT
TOP2
D
0
6 .
)
−
= 10 kΩ and R
0
ILIM
6 .




Specification
V
V
I
ΔV
±5%, 1 A to 4 A, 1 A/µs
V
V
I
ΔV
±5%, 1 A to 4 A, 1 A/µs
f
is required.
OUT1
OUT2
SW
IN1
OUT1
IN2
OUT2
OUT1_RIPPLE
OUT2_RIPPLE
= 500 kHz
= 12.0 V ± 10%
= 12.0 V ± 10%
= 5 A
= 5 A
= 1.2 V
= 3.3 V
TOP
); calculate the
BOT2
OSC
:
= 12 mV
= 33 mV
= 2.21 kΩ.
L
, is set to 30%
OUT2
= 3.3 V,
TOP1
Rev. 0 | Page 24 of 32
=
Calculate the peak-to-peak inductor ripple current as follows:
For V
Find the peak inductor current using the following equation:
For the 1.2 V rail, the peak inductor current is 5.73 A, and for
the 3.3 V rail, the peak inductor current is 5.73 A.
The rms current through the inductor can be estimated by
The rms current of the inductor for both the 1.2 V and 3.3 V
rails is approximately 5.02 A.
For the 1.2 V rail, select an inductor with a minimum rms
current rating of 5.01 A and a minimum saturation current
rating of 5.73 A. For the 3.3 V rail, select an inductor with a
minimum rms current rating of 5.02 A and a minimum
saturation current rating of 5.73 A.
Based on these requirements, for the 1.2 V rail, select a
1.5 µH inductor, such as the Sumida CDRH105RNP-1R5N,
with a DCR = 5.8 mΩ; for the 3.3 V rail, select a 3.3 µH
inductor, such as the Sumida CDRH105RNP-3R3N, with a
DCR = 10.4 mΩ.
OUTPUT CAPACITOR SELECTION
The output capacitor is required to meet the output voltage
ripple and load transient requirements. To meet the output
voltage ripple requirement, use the following equation to
calculate the capacitance and ESR:
For V
V
OUT2
∆
C
R
I
I
OUT1
OUT1
= 3.3 V, C
PEAK
RMS
I
OUT_RIPPLE
ESR
L
=
= 1.2 V, ΔI
= 1.2 V, C
=
=
=
(
V
∆
I
I
IN
V
OUT
OUT
OUT
OUT_RIPPLE2
L
−
=
I
×
V
2
+
8
L
_
L1
OUT_RIPPLE1
OUT
+
×
RIPPLE
f
∆
SW
= 1.44 A. For V
∆
2
f
I
12
SW
L
I
)
L
×
= 11 µF and R
2
×
D
∆
∆
V
I
= 30 µF and R
L
OUT
_
RIPPLE
OUT2
ESR2
= 3.3 V, ΔI
= 23 mΩ.
ESR1
= 8.3 mΩ. For
Data Sheet
L2
= 1.45 A.