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參數(shù)資料
| 型號： | PC34704BEP |
| 廠商： | FREESCALE SEMICONDUCTOR INC |
| 元件分類： | 電源管理 |
| 英文描述： | 8-CHANNEL POWER SUPPLY MANAGEMENT CKT, QCC56 |
| 封裝： | 7 X 7 MM, 1 MM HEIGHT, 0.40 MM PITCH, ROHS COMPLIANT, QFN-56 |
| 文件頁數(shù)： | 31/50頁 |
| 文件大?。?/td> | 2010K |
| 代理商： | PC34704BEP |
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Analog Integrated Circuit Device Data
Freescale Semiconductor
37
34704
FUNCTIONAL DEVICE OPERATION
COMPONENT CALCULATION
Now calculate the maximum allowed ESR to reach the
desired
VO
r.
1CVG: Use a 47uF capacitor from Ground to VG.
D1: Use a fast recovery schottky diode rated to 10V at 1A.
Regulator 2, 4 and 5 (Synchronous Buck-Boost regulator
with external compensation)
These three regulators are 4-Switch synchronous buck-
boost voltage mode control DC-DC regulator that can
operate at various output voltage levels. Since each of the
regulators may work as a buck or a boost depending on the
operating voltages, they need to be compensated in different
ways for each situation.
Since the 34704 is meant to work using a LiIon battery, the
operating input voltage range is set from 2.7 - 4.2 V, then the
following scenarios are possible:
NOTE: Since these 3 regulators can work as a buck or a
boost in a single application, a good practice to configure
these regulators is to compensate for a boost scenario and
then verify that the regulator is working in buck mode using
that same compensation.
Compensating for Buck operation:
L: A buck power stage can be designed to operate in CCM
for load currents above a certain level usually 5 to 15% of
full load. The minimum value of inductor to maintain CCM
can be determined by using the following procedure:
1. Define IOB as the minimum current to maintain CCM as
15% of full load.
COUT: The three elements of output capacitor that
contribute to its impedance and output voltage ripple are
the ESR, the ESL and the capacitance C. A good
approach to calculate the minimum real capacitance
needed is to include the transient response analysis to
control the maximum overshoot as desired.
1. First calculate the dt_I (inductor current rising time)
given by:
Where the parameter
Io_step is the maximum current
step during the current rising time and is define as:
2. Then the output capacitor can be chosen as follow:
Where
VO
max is the maximum allowed transient
overshoot expressed as a percentage of the output
voltage, typically from 3 to 5% of Vo.
3. Finally find the maximum allowed ESR to allow the
desired transient response:
NOTE: Do not use the parameters
VO
r and VOmax
indistinctly, the first one indicates the output voltage ripple,
while the second one is the maximum output voltage
overshoot (transient response).
R1 and RB: These two resistors help to set the output
voltage to the desire value using a Vref=0.6V, select R1
between 10k and 100K and then calculate RB as follows:
Compensation network. (C1,C2,C3, R2, R3):
For
compensating a buck converter, 3 important frequencies
referring to the plant are:
Regulator
Vo
Input voltage
range
Operation
2
2.8 V
3.0 - 4.2
Buck
3.3 V
2.7 - 3.0
Boost
3.3 V
3.5 - 4.2
Buck
4
1.8 V
2.7 - 4.2
Buck
2.5 V
2.7 - 4.2
Buck
5
3.3 V
2.7 - 3.0
Boost
3.3 V
3.5 - 4.2
Buck
+
≤
OB
r
I
D
Io
Vo
ESR
max
1
[
]
()()
OB
Max
OB
L
LSFET
DSON
I
Vo
T
D
I
T
D
R
Io
Vo
L
2
'
2
'
(
min
_
max
min
≈
+
≥
[H]
step
Io
T
Io
I
dt
_
max
=
[s]
=
L
Vo
Vin
Fsw
D
step
Io
min
max
_
[A]
max
_
Vo
I
dt
Io
C
OUT
≤
[F]
)
1
(
)
)(
(
min
max
D
Vo
L
Fsw
Vo
ESR
r
=
[
]
1
=
Vref
Vo
R
RB
[
]
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