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ADP5014ACPZ-R7 数据表(PDF) 24 Page - Analog Devices

部件名 ADP5014ACPZ-R7
功能描述  Integrated Power Solution with Quad Low Noise Buck Regulators
PDF  34 Pages
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制造商  AD [Analog Devices]
网页  http://www.analog.com
标志 AD - Analog Devices

ADP5014ACPZ-R7 数据表(HTML) 24 Page - Analog Devices

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ADP5014
Data Sheet
Rev. A | Page 24 of 34
OUTPUT CAPACITOR SELECTION
The selected output capacitor affects both the output voltage
ripple and the loop dynamics of the regulator. For example, during
load step transients on the output, when the load is suddenly
increased, the output capacitor supplies the load until the
control loop can ramp up the inductor current, causing an
undershoot of the output voltage.
The output capacitance required to meet the voltage droop
requirement (COUT_UV) is calculated using the following equation:

UV
OUT
OUT
IN
STEP
UV
UV
OUT
V
V
V
L
I
K
C
_
2
_
2
where:
KUV is a factor (typically set to 2).
ΔISTEP is the load step.
ΔVOUT_UV is the allowable undershoot on the output voltage.
Another example of the effect of the output capacitor on the loop
dynamics of the regulator is when the load is suddenly removed
from the output. The energy stored in the inductor rushes into
the output capacitor, causing an overshoot of the output voltage.
The output capacitance required to meet the overshoot
requirement (COUT_UV) is calculated using the following equation:

2
2
2
_
OUT
OUT_OV
OUT
STEP
OV
OV
OUT
V
V
V
L
I
K
C
where:
KOV is a factor (typically set to 2).
ΔISTEP is the load step.
ΔVOUT_OV is the allowable overshoot on the output voltage.
The output voltage ripple is determined by the equivalent series
resistance (ESR) of the output capacitor and its capacitance
value. Use the following equation to select a capacitor that can
meet the output ripple requirements:
RIPPLE
OUT
SW
L
RIPPLE
OUT
V
f
I
C
_
_
8
L
RIPPLE
OUT
ESR
I
V
R
_
where:
ΔVOUT_RIPPLE is the allowable output voltage ripple.
RESR is the ESR of the output capacitor.
Select the largest output capacitance given by COUT_UV, COUT_OV,
and COUT_RIPPLE to meet both load transient and output ripple
requirements.
The selected output capacitor voltage rating must be greater
than the output voltage. The minimum rms current rating of
the output capacitor (ICOUT_rms) is determined by the following
equation:
ICOUT_rms =
12
L
I
INPUT CAPACITOR SELECTION
The input decoupling capacitor attenuates high frequency noise
on the input and acts as an energy reservoir. This capacitor is a
ceramic capacitor and must be placed close to the PVINx pins.
The loop composed of the input capacitor, the high-side MOSFET,
and the low-side MOSFET must be kept as small as possible.
The voltage rating of the input capacitor must be greater than
the maximum input voltage. The rms current rating of the
input capacitor (ICIN_rms)is larger than the following equation:
ICIN_rms = IOUT ×
)
1
(
D
D
where D is the duty cycle (D = VOUT/VIN).
PROGRAMMING THE UVLO INPUT
The precision enable input can be used to program the UVLO
threshold of the input voltage, as shown in Figure 32.
The precision turn on threshold is 0.6 V. Use the following
equations to calculate RTOP_EN and RBOT_EN:
RTOP_EN = (0.57 V × VIN_RISING − 0.6 × VIN_FALLING)/(0.57 V ×
4 μA − 0.6 × 1 μA)
RBOT_EN = (0.6 V × RTOP_EN)/(VIN_RISING – RTOP_EN × 4 μA − 0.6 V)
where:
RTOP_EN is the resistor from PVINx to ENx.
VIN_RISING is the VIN rising threshold.
VIN_FALLING is the VIN falling threshold.
RBOT_EN is the resistor from ENx to ground.
COMPENSATION COMPONENTS DESIGN
For the peak current-mode control architecture, the power stage
can be simplified as a voltage controlled current source that
supplies current to the output capacitor and load resistor. The
simplified loop is composed of one domain pole and a zero
contributed by the ESR of the output capacitor. The control to
output transfer function (Gvd) is shown in the following equations:
p
z
VI
COMP
OUT
vd
f
s
f
s
R
A
s
V
s
V
G
2
1
2
1
)
(
)
(
)
s
(
OUT
ESR
z
C
R
f
2
1

OUT
ESR
p
C
R
R
f
2
1
where:
AVI = 16.67A/V for Channel 1 or Channel 2, and 8.33 A/V for
Channel 3 or Channel 4.
R is the load resistance.
fz is the frequency of the zero.
COUT is the output capacitance.
RESR is the equivalent series resistance of the output capacitor.
fp is the frequency of the pole.



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