поискавой системы для электроныых деталей
  Russian  ▼
ALLDATASHEETRU.COM

X  

Preview PDF HTML

SC4525FEVB датащи(PDF) 10 Page - Semtech Corporation

номер детали SC4525FEVB
подробное описание детали  18V, 3A, 350kHz Step-Down Switching Regulator
PDF  23 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
производитель  SEMTECH [Semtech Corporation]
домашняя страница  http://www.semtech.com
Logo SEMTECH - Semtech Corporation

SC4525FEVB датащи(HTML) 10 Page - Semtech Corporation

Back Button SC4525FEVB Datasheet HTML 6Page - Semtech Corporation SC4525FEVB Datasheet HTML 7Page - Semtech Corporation SC4525FEVB Datasheet HTML 8Page - Semtech Corporation SC4525FEVB Datasheet HTML 9Page - Semtech Corporation SC4525FEVB Datasheet HTML 10Page - Semtech Corporation SC4525FEVB Datasheet HTML 11Page - Semtech Corporation SC4525FEVB Datasheet HTML 12Page - Semtech Corporation SC4525FEVB Datasheet HTML 13Page - Semtech Corporation SC4525FEVB Datasheet HTML 14Page - Semtech Corporation Next Button
Zoom Inzoom in Zoom Outzoom out
 10 / 23 page
background image
SC4525F
0
Applications Information (Cont.)
the latch B
3. The soft-start capacitor is discharged with
(I
D - IC) (Figure 3). If the inductor current falls below the
current limit and the PWM comparator instead turns off
the switch, then latch B
3 will be reset and IC will recharge
the soft-start capacitor. If over-current condition persists
or OC becomes asserted more often than PWM over
a period of time, then the soft-start capacitor will be
discharged below .9V. At this juncture, comparator B
4
sets the overload latch B
2. The soft-start capacitor will be
continuously discharged with (I
D - IC). The COMP pin is
immediately pulled to ground. The switching regulator is
shut off until the soft-start capacitor is discharged below
.0V. At this moment, the overload latch is reset. The
soft-start capacitor is recharged and the converter again
undergoes soft-start. The regulator will go through soft-
start, overload shutdown and restart until it is no longer
overloaded.
If the FB voltage falls below 0.8V because of output
overload, then the switching frequency will be reduced.
Frequency foldback helps to limit the inductor current
when the output is hard shorted to ground.
During normal operation, the soft-start capacitor is
charged to 2.4V.
Setting the Output Voltage
The regulator output voltage, V
O, is set with an external
resistive divider (Figure ) with its center tap tied to the FB
pin. For a given R
6 value, R4 can be found by
CESAT
D
IN
D
O
V
V
V
V
V
D
−
+
+
=
−
=
1
V
0
.
1
V
R
R
O
6
4
1
SW
D
O
L
L
F
)
D
1
(
)
V
V
(
I
⋅
−
⋅
+
=
D
SW
O
D
O
1
F
I
%
20
)
D
1
(
)
V
V
(
L
⋅
⋅
−
⋅
+
=
)
D
1
(
D
I
I
O
CIN
_
RMS
−
⋅
⋅
=


⋅
⋅
+
⋅
D
=
D
O
SW
L
O
C
F
8
1
ESR
I
V
SW
IN
O
IN
F
V
4
I
C
⋅
D
⋅
>
,
R
G
R
G
S
CA
PWM
⋅
≈
)
/
s
Q
/
s
1
()
/
s
1
(
)
C
R
s
1
(
G
V
V
2
n
2
n
p
O
ESR
PWM
c
o
ω
+
ω
+
ω
+
+
=
7
1
Z
5
R
F
2
1
C
π
=
7
1
P
8
R
F
2
1
C
π
=
,
C
R
1
O
p ≈
ω
,
C
R
1
O
ESR
Z =
ω
k
3
.
22
10
28
.
0
10
R
3
7
20
9
.
15
=
⋅
=
−
nF
45
.
0
10
1
.
22
10
16
2
1
C
3
3
5
=
⋅
⋅
⋅
⋅
π
=
pF
12
10
1
.
22
10
600
2
1
C
3
3
8
=
⋅
⋅
⋅
⋅
π
=


⋅
π
⋅
⋅
−
=
O
FB
O
C
S
CA
C
V
V
C
F
2
1
R
G
1
log
20
A
dB
9
.
15
3
.
3
0
.
1
10
22
10
80
2
1
10
1
.
6
28
1
log
20
A
6
3
3
C
=
⋅
⋅
⋅
⋅
⋅
π
⋅
⋅
⋅
⋅
−
=
−
−
m
7
g
10
R
20
C
A
=
Minimum On Time Consideration
The operating duty cycle of a non-synchronous step-
down switching regulator in continuous-conduction
mode (CCM) is given by
whereV
IN is the input voltage, VCESAT is the switch saturation
voltage, and V
D is voltage drop across the rectifying
diode.
CESAT
D
IN
D
O
V
V
V
V
V
D
−
+
+
=
−
=
1
V
0
.
1
V
R
R
O
6
4
1
SW
D
O
L
L
F
)
D
1
(
)
V
V
(
I
⋅
−
⋅
+
=
D
SW
O
D
O
1
F
I
%
20
)
D
1
(
)
V
V
(
L
⋅
⋅
−
⋅
+
=
)
D
1
(
D
I
I
O
CIN
_
RMS
−
⋅
⋅
=


⋅
⋅
+
⋅
D
=
D
O
SW
L
O
C
F
8
1
ESR
I
V
SW
IN
O
IN
F
V
4
I
C
⋅
D
⋅
>
,
R
G
R
G
S
CA
PWM
⋅
≈
)
/
s
Q
/
s
1
()
/
s
1
(
)
C
R
s
1
(
G
V
V
2
n
2
n
p
O
ESR
PWM
c
o
ω
+
ω
+
ω
+
+
=
7
1
Z
5
R
F
2
1
C
π
=
7
1
P
8
R
F
2
1
C
π
=
,
C
R
1
O
p ≈
ω
,
C
R
1
O
ESR
Z =
ω
k
3
.
22
10
28
.
0
10
R
3
7
20
9
.
15
=
⋅
=
−
nF
45
.
0
10
1
.
22
10
16
2
1
C
3
3
5
=
⋅
⋅
⋅
⋅
π
=
pF
12
10
1
.
22
10
600
2
1
C
3
3
8
=
⋅
⋅
⋅
⋅
π
=


⋅
π
⋅
⋅
−
=
O
FB
O
C
S
CA
C
V
V
C
F
2
1
R
G
1
log
20
A
dB
9
.
15
3
.
3
0
.
1
10
22
10
80
2
1
10
1
.
6
28
1
log
20
A
6
3
3
C
=
⋅
⋅
⋅
⋅
⋅
π
⋅
⋅
⋅
⋅
−
=
−
−
m
7
g
10
R
20
C
A
=
CESAT
D
IN
D
O
V
V
V
V
V
D
−
+
+
=
−
=
1
V
0
.
1
V
R
R
O
6
4
1
SW
D
O
L
L
F
)
D
1
(
)
V
V
(
I
⋅
−
⋅
+
=
D
SW
O
D
O
1
F
I
%
20
)
D
1
(
)
V
V
(
L
⋅
⋅
−
⋅
+
=
)
D
1
(
D
I
I
O
CIN
_
RMS
−
⋅
⋅
=


⋅
⋅
+
⋅
D
=
D
O
SW
L
O
C
F
8
1
ESR
I
V
SW
IN
O
IN
F
V
4
I
C
⋅
D
⋅
>
,
R
G
R
G
S
CA
PWM
⋅
≈
)
/
s
Q
/
s
1
()
/
s
1
(
)
C
R
s
1
(
G
V
V
2
n
2
n
p
O
ESR
PWM
c
o
ω
+
ω
+
ω
+
+
=
7
1
Z
5
R
F
2
1
C
π
=
7
1
P
8
R
F
2
1
C
π
=
,
C
R
1
O
p ≈
ω
,
C
R
1
O
ESR
Z =
ω
k
3
.
22
10
28
.
0
10
R
3
7
20
9
.
15
=
⋅
=
−
nF
45
.
0
10
1
.
22
10
16
2
1
C
3
3
5
=
⋅
⋅
⋅
⋅
π
=
pF
12
10
1
.
22
10
600
2
1
C
3
3
8
=
⋅
⋅
⋅
⋅
π
=


⋅
π
⋅
⋅
−
=
O
FB
O
C
S
CA
C
V
V
C
F
2
1
R
G
1
log
20
A
dB
9
.
15
3
.
3
0
.
1
10
22
10
80
2
1
10
1
.
6
28
1
log
20
A
6
3
3
C
=
⋅
⋅
⋅
⋅
⋅
π
⋅
⋅
⋅
⋅
−
=
−
−
m
7
g
10
R
20
C
A
=
In peak current-mode control, the PWM modulating
ramp is the sensed current ramp of the power switch.
This current ramp is absent unless the switch is turned
on. The intersection of this ramp with the output of the
voltage feedback error amplifier determines the switch
pulse width. The propagation delay time required to
immediately turn off the switch after it is turned on is the
minimum controllable switch on time (T
ON(MIN)).
Closed-loop measurement shows that the SC4525F
minimum on time is about 20ns at room temperature for
A load current (Figure 4). If the required switch on time
is shorter than the minimum on time, the regulator will
either skip cycles or it will jitter.
Figure 4. Variation of Minimum On Time
with Ambient Temperature
To allow for transient headroom, the minimum operating
switch on time should be at least 20% to 30% higher than
the worst-case minimum on time.
Minimum Off Time Limitation
The PWM latch in Figure 2 is reset every cycle by the
clock. The clock also turns off the power transistor to
refresh the bootstrap capacitor. This minimum off time
limits the attainable duty cycle of the regulator at a given
switching frequency. The measured minimum off time is
38ns typically. If the required duty cycle is higher than
the attainable maximum, then the output voltage will not
be able to reach its set value in continuous-conduction
mode.



Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23


датащи скачать

Go To PDF Page


ссылки URL



Вашему бизинису помогли Аллдатащит?  [ DONATE ] 

Что такое Аллдатащит   |   реклама   |   контакт   |   Конфиденциальность   |   Ссылка на техническое описание    |   обмен ссыками   |   поиск по производителю
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com