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SC4501 数据表(PDF) 13 Page - Semtech Corporation

部件名 SC4501
功能描述  2Amp, 2MHz Step-Up Switching Regulator with Soft-Start
PDF  21 Pages
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制造商  SEMTECH [Semtech Corporation]
网页  http://www.semtech.com
标志 SEMTECH - Semtech Corporation

SC4501 数据表(HTML) 13 Page - Semtech Corporation

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© 2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4501
with
V
4
.
1
V
L >
.
Example: Increase the turn on voltage of a V
IN = 3.3V boost
converter from 1.4V to 2.75V.
Using V
H = 2.75V and R4 = 100KΩ in (12),
Ω
=
K
150
R
3
.
The resulting UVLO hysteresis is:
V
69
.
0
K
150
A
6
.
4
R
I
V
3
HYS
HYS
=
Ω
•
µ
=
=
.
SC4501
R4
R3
SHDN
3
+
-
IN
6/8
1.1V
4.6
µA
I HYS
COMPARATOR
Y
SWITCH CLOSED
WHEN Y = “1”
Figure 7. Programmable Hysteretic UVLO Circuit
The turn off voltage is:
V
4
.
1
V
06
.
2
69
.
0
75
.
2
V
V
V
HYS
H
L
>
=
−
=
−
=
.
Frequency Compensation
Figure 8 shows the equivalent circuit of a boost converter
using the SC4501. The output filter capacitor and the load
form an output pole at frequency:
2
OUT
2
OUT
OUT
2
p
C
R
2
C
V
I
2
−
=
−
=
ω
(13)
where C
2 is the output capacitor and
OUT
OUT
OUT
I
V
R
=
is the
equivalent load resistance.
The zero formed by C
2 and its equivalent series resistance
(ESR) is neglected due to low ESR of the ceramic output
capacitor.
There is also a right half plane (RHP) zero at angular
frequency:
(
)
L
D
1
R
2
OUT
2
Z
−
=
ω
(14)
ω
z2 decreases with increasing duty cycle D and increasing
I
OUT. Using the 5V to 12V boost regulator (1.35MHz) in
Figure 1(a) as an example,
Ω
=
≥
8
.
6
A
74
.
0
V
5
R
OUT
POWER
STAGE
REFERENCE
VOLTAGE
1.242V
Gm
-
+
R3
C4
C6
RO
R2
COMP
R1
FB
C5
ESR
C2
R
OUT
V
OUT
V
IN
I
OUT
Figure 8. Simplified Block Diagram of a Boost Converter
Application Information



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