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ADP2323ACPZ-R7 数据表(PDF) 23 Page - Analog Devices

部件名 ADP2323ACPZ-R7
功能描述  Dual 3 A, 20 V Synchronous Step-Down Regulator with Integrated High-Side MOSFET
PDF  32 Pages
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制造商  AD [Analog Devices]
网页  http://www.analog.com
标志 AD - Analog Devices

ADP2323ACPZ-R7 数据表(HTML) 23 Page - Analog Devices

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Data Sheet
ADP2323
Rev. A | Page 23 of 32
DESIGN EXAMPLE
This section explains design procedure and component selection as
shown in Figure 50; Table 11 provides a list of the required
settings.
Table 11. Dual Step-Down DC-to-DC Regulator Requirements
Parameter
Specification
Channel 1
Input Voltage
V
IN1 = 12.0 V ± 10%
Output Voltage
V
OUT1 = 1.2 V
Output Current
I
OUT1 = 3 A
Output Voltage Ripple
ΔV
OUT1_RIPPLE = 12 mV
Load Transient
±5%, 0.5 A to 3A, 1 A/µs
Channel 2
Input Voltage
V
IN2 = 12.0 V ± 10%
Output Voltage
V
OUT2 = 3.3 V
Output Current
I
OUT2 = 3 A
Output Voltage Ripple
ΔV
OUT2_RIPPLE = 33 mV
Load Transient
±5%, 0.5 A to 3 A, 1 A/µs
Switching Frequency
f
SW = 500 kHz
OUTPUT VOLTAGE SETTING
Choose a 10 kΩ top feedback resistor (RTOP); calculate the bottom
feedback resistor by using the following equation:
−
×
=
6
.
0
6
.
0
OUT
TOP
BOT
V
R
R
To set the output voltage to 1.2 V, the resistor values are RTOP1 = 10
kΩ and RBOT1 = 10 kΩ. To set the output voltage to 3.3 V, the
resistors values are RTOP2 = 10 kΩ and RBOT2 = 2.21 kΩ.
CURRENT-LIMIT SETTING
For 3 A output current operation, the typical peak current limit
is 4.8 A. In this case, no RILIM is required.
FREQUENCY SETTING
To set the switching frequency to 500 kHz, use the following
equation to calculate the resistor value, ROSC:
( )
(
)
kHz
000
,
60
kΩ
SW
OSC
f
R
=
Therefore, ROSC =100 kΩ.
INDUCTOR SELECTION
The peak-to-peak inductor ripple current, ΔIL, is set to 30% of
the maximum output current. Use the following equation to
estimate the value of the inductor:
(
)
SW
L
OUT
IN
f
I
D
V
V
L
×
∆
×
−
=
For VOUT1 = 1.2 V, Inductor L1 = 2.4 µH, and for VOUT2 = 3.3 V,
Inductor L2 = 5.3 µH.
Select the standard inductor value of 2.2 µH and 4.7 µH for the
1.2 V and 3.3 V rails.
Calculate the peak-to-peak inductor ripple current as follows:
(
)
SW
OUT
IN
L
f
L
D
V
V
I
×
×
−
=
∆
For VOUT1 = 1.2 V, ΔIL1 = 0.98 A. For VOUT2 = 3.3 V, ΔIL2 = 1.02 A.
Find the peak inductor current by using the following equation:
2
L
OUT
PEAK
I
I
I
∆
+
=
For the 1.2 V rail, the peak inductor current is 3.49 A, and for
the 3.3 V rail, the peak inductor current is 3.51 A.
The rms current through the inductor can be estimated by
12
2
2
L
OUT
RMS
I
I
I
∆
+
=
The rms current of the inductor for both 1.2 V and 3.3 V is
approximately 3.01 A.
For the 1.2 V rail, select an inductor with a minimum rms
current rating of 3.01 A and a minimum saturation current
rating of 3.49 A. For the 3.3 V rail, select an inductor with a
minimum rms current rating of 3.01 A and a minimum
saturation current rating of 3.51 A.
Based on these requirements, for the 1.2 V rail, select a 2.2 µH
inductor, such as the Sumida CDRH105RNP-2R2N, with a
DCR = 7.2 mΩ; for the 3.3 V rail, select a 4.7 µH inductor, such
as the Sumida CDRH105RNP-4R7N, with a DCR = 12.3 mΩ.
OUTPUT CAPACITOR SELECTION
The output capacitor is required to meet the output voltage
ripple and load transient requirement. To meet the output
voltage ripple requirement, use the following equation to
calculate the ESR and capacitance:
RIPPLE
OUT
SW
L
RIPPLE
OUT
V
f
I
C
_
_
8
∆
×
×
∆
=
L
RIPPLE
OUT
ESR
I
V
R
_
∆
=
For VOUT1 = 1.2 V, COUT_RIPPLE1 = 20 µF and RESR1 = 12 mΩ. For
VOUT2 = 3.3 V, COUT_RIPPLE2 = 7.7 µF and RESR2 = 32 mΩ.
To meet the ±5% overshoot and undershoot requirement, use
the following equation to calculate the capacitance:
(
)
2
2
_
2
_
OUT
OV
OUT
OUT
STEP
OV
OV
OUT
V
V
V
L
I
K
C
−
∆
+
×
∆
×
=
(
)
UV
OUT
OUT
IN
STEP
UV
UV
OUT
V
V
V
L
I
K
C
_
2
_
2
∆
×
−
×
×
∆
×
=
For estimation purposes, use KOV = KUV = 2. For VOUT1 = 1.2 V, use
COUT_OV1 = 191 µF and COUT_UV1 = 21 µF. For VOUT2 = 3.3 V, use
COUT_OV2 = 54 µF and COUT_UV2 = 20 µF.



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