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參數(shù)資料
| 型號(hào)： | 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)： | 35/50頁 |
| 文件大小： | 2010K |
| 代理商： | PC34704BEP |
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Analog Integrated Circuit Device Data
40
Freescale Semiconductor
34704
FUNCTIONAL DEVICE OPERATION
COMPONENT CALCULATION
The passive components associated to these frequencies are calculated with the following formulas
On the 34704 VRAMP is half of 1.2V since each operation mode spends only half the ramp.
Regulator 3 (Synchronous Buck - internally
compensated)
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.
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:
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.
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 rip-
ple, while the second one is the maximum output volt-
age 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:
()
=
1
2
1
'
1
0
2
min
R
F
D
V
Vin
C
P
RAMP
π
()
=
1
2
1
2
2 R
F
C
Z
π
()
=
1
2
1
2
1C
F
R
Z
π
()
=
2
1
3
2 R
F
C
P
π
()
=
2
1
3
1C
F
R
P
π
[H]
(
)()
OB
L
LSFET
DSON
I
T
D
R
Io
Vo
L
2
'
(
min
_
max
min
+
≥
OB
Max
I
Vo
T
D
L
2
'
min ≥
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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