參數(shù)資料
型號(hào): FAN8048
廠商: FAIRCHILD SEMICONDUCTOR CORP
元件分類: 運(yùn)動(dòng)控制電子
英文描述: 2 DC-DC Converter & 4-CH PWM Motor IC
中文描述: DISK DRIVE MOTOR CONTROLLER, 0.5 A, PDSO48
封裝: 7 X 7 MM, LQFP-48
文件頁(yè)數(shù): 21/34頁(yè)
文件大?。?/td> 903K
代理商: FAN8048
FAN8048
21
3-10. Boost (Step-up) converter mode (VIN < VSYS)
The step-up converter keeps the average output voltage VSYS higher than DC input voltage VIN, and its circuit diagram is
shown in Figure 15-a. Figure 15-b shows an operational waveform in case inductor current is steady-state. Since in steady-
state, the integral of the inductor voltage over one time period to zero, this can be expressed by the following formula:
From the above formula, a redefined formula is as follows after dividing by cycle Ts:
Assuming a lossless circuit, input and output power are the same (Pin=Po) and the above formula can be redefined as follows:
This can be expressed as follows using input/output current and duty ratio:
In the boundary condition of continuous mode and discontinuous mode, the inductor's average current is defined as follows:
From the above formula, since inductor current and input current are the same (i
IN
=i
L
), the average output current at the edge
of continuous conduction mode can be redefined as below:
In a practical synchronous step-up converter, the parasitic elements are due to the loss associated with the inductor, the capaci-
tor and the switches; however, in this formula we assume that all components are at ideal conditions.In the continuous mode,
as the output current and peak-peak voltage ripple are considered to be constant, this formula can be redefined as below:
=
Where,
0
)
)
((
)
(
=
×
+
×
OFF
SYS
IN
IN
t
V
V
t
V
ON
]
[
1
1
1
1
V
V
D
V
D
t
T
V
V
IN
SYS
OFF
S
IN
SYS
×
=
=
=
O
SYS
IN
IN
I
V
I
V
=
)
1
D
I
I
IN
O
=
2
,
)
1
2
2
T
1
2
1
D
D
L
V
S
T
L
V
i
i
SYS
ON
IN
peak
L
LB
=
=
=
2
)
1
2
D
D
L
V
T
I
SYS
S
OB
×
=
C
DT
R
V
C
DT
I
C
DT
Q
V
S
SYS
S
O
SYS
=
=
RC
V
V
S
SYS
SYS
=
]
[
=
O
SYS
I
V
R
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