1
www.semtech.com
SC4911
Bias/Primary Side PWM Controller
with Ultra Low Start-up Current
POWER MANAGEMENT
Revision: July 22, 2003
Description
Features
Applications
Typical Application Circuit
Programmable switching frequency
Line UVLO Protection
Undervoltage Lockout
Low startup current (max. 50A)
Cycle by cycle current limit
Operation up to 500KHz
8 pin MSOP
The SC4911 is a highly integrated bias/primary side PWM
controller designed for off-line or isolated dc-dc convert-
ers in telecommunication and data communication ap-
plications. The high degree of integration minimizes the
amount of discrete parts needed and leads to substan-
tial cost and space saving converter designs.
The circuitry of the SC4911 includes line voltage UVLO
featuring startup current less than 50A and program-
mable switching frequency. The device supply is derived
from an auxiliary winding on the transformer. The auxil-
iary winding could also provide output feedback informa-
tion if an optocoupler is not used.
Vout
R5
R9
C3
R1
R7
C6
D2
C2
D1
U1 SC4911
1
2
3
4
5
6
7
8
LUVLO
RT
FB
COMP
ILIM
GND
OUT
VCC
C4
R4
Vin
C7
C1
R8
R2
Q1
R6
T1
C8
R3
C5
Telecom isolated converters
Offline isolated power supplies
Instrumentation power supplies
Battery chargers
2
2003 Semtech Corp.
www.semtech.com
SC4911
POWER MANAGEMENT
Absolute Maximum Ratings
Electrical Characteristics
r
e
t
e
m
a
r
a
P
s
n
o
i
t
i
d
n
o
C
t
s
e
T
n
i
M
p
y
T
x
a
M
t
i
n
U
y
l
p
p
u
S
r
e
w
o
P
e
g
a
tl
o
V
n
O
-
n
r
u
T
c
c
V
5
.
0
1
5
.
1
1
5
.
2
1
V
s
i
s
e
r
e
t
s
y
H
c
c
V
4
V
t
n
e
r
r
u
C
g
n
it
a
r
e
p
O
f
s
d
a
o
l
o
N
,
z
H
k
0
0
2
=
3
.
2
5
.
2
7
.
2
A
m
t
n
e
r
r
u
C
p
u
t
r
a
t
S
0
3
5
3
0
5
A
e
g
a
tl
o
V
t
n
u
h
S
r
e
n
e
Z
C
C
V
I
C
C
A
m
0
1
=
5
1
6
1
7
1
V
O
L
V
U
e
n
i
L
d
l
o
h
s
e
r
h
T
t
u
o
k
c
o
L
R
A
M
7
.
2
=
R
,
B
k
0
0
1
=
4
2
.
1
5
2
.
1
8
2
.
1
V
t
n
e
r
r
u
C
s
a
i
B
V
O
L
V
U
L
V
5
2
.
1
<
5
7
1
A
n
s
i
s
e
r
e
t
s
y
H
O
L
V
U
R
A
M
7
.
2
=
R
,
B
k
0
0
1
=
0
6
0
8
5
8
V
m
r
e
i
f
il
p
m
A
r
o
r
r
E
e
g
a
tl
o
V
t
u
p
n
I
k
c
a
b
d
e
e
F
R
1
B
F
K
3
8
3
=
R
,
2
B
F
k
0
0
1
=
5
4
.
2
0
5
.
2
5
5
.
2
V
t
n
e
r
r
u
C
s
a
i
B
t
u
p
n
I
R
1
B
F
K
3
8
3
=
R
,
2
B
F
k
0
0
1
=
0
0
1
A
n
e
c
n
a
t
c
u
d
n
o
c
s
n
a
r
T
r
e
if
il
p
m
A
V
B
F
V
5
.
2
=
0
0
0
1
o
h
m
t
n
e
r
r
u
C
e
c
u
o
S
r
e
if
il
p
m
A
0
5
4
0
0
5
0
0
6
A
t
n
e
r
r
u
C
k
n
i
S
r
e
if
il
p
m
A
0
5
4
0
0
5
0
0
7
A
n
i
a
G
e
g
a
tl
o
V
p
o
o
L
n
e
p
O
V
B
F
V
5
.
2
=
0
5
B
d
r
e
t
e
m
a
r
a
P
l
o
b
m
y
S
m
u
m
i
x
a
M
s
t
i
n
U
e
g
a
tl
o
V
y
l
p
p
u
S
V
C
C
8
1
V
t
n
e
r
r
u
C
y
l
p
p
u
S
I
C
C
0
2
A
m
e
g
a
tl
o
V
O
L
V
U
e
n
i
L
V
C
C
V
P
M
O
C
d
n
a
M
I
L
I
,
B
F
6
o
t
3
.
0
-
V
k
n
i
S
r
o
e
c
r
u
o
S
t
n
e
r
r
u
C
t
u
p
t
u
O
0
5
2
A
m
e
g
n
a
R
e
r
u
t
a
r
e
p
m
e
T
e
g
a
r
o
t
S
T
G
T
S
0
5
1
+
o
t
0
6
-
C
e
g
n
a
R
e
r
u
t
a
r
e
p
m
e
T
n
o
it
c
n
u
J
T
J
0
5
1
+
o
t
0
4
-
C
.
c
e
S
0
1
)
g
n
ir
e
d
l
o
S
(
e
r
u
t
a
r
e
p
m
e
T
d
a
e
L
T
D
A
E
L
0
6
2
C
)l
e
d
o
M
y
d
o
B
n
a
m
u
H
(
g
n
it
a
R
D
S
E
D
S
E
2
V
k
Unless specified: T
A
=
T
J
= -40C to 105C, V
CC
= 12V, R
T
= 100K
,
V
FB
= 2.4V.
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied.
4
2003 Semtech Corp.
www.semtech.com
SC4911
POWER MANAGEMENT
Pin Configuration
Ordering Information
Pin Descriptions
r
e
b
m
u
N
t
r
a
P
e
g
a
k
c
a
P
T
(
e
g
n
a
R
.
p
m
e
T
J
)
R
T
S
M
I
1
1
9
4
C
S
8
-
P
O
S
M
C
5
2
1
+
o
t
C
0
4
-
Note:
Only available in tape and reel packaging. A reel
contains 2500 devices.
ILIM
GND
OUT
VCC
COMP
FB
RT
LUVLO
#
n
i
P
e
m
a
N
n
i
P
n
o
i
t
c
n
u
F
n
i
P
1
O
L
V
U
L
.t
u
o
k
c
o
l
e
g
a
tl
o
v
r
e
d
n
u
e
n
i
L
2
T
R
.
y
c
n
e
u
q
e
r
f
r
o
t
a
ll
i
c
s
o
g
n
i
m
m
a
r
g
o
r
p
r
o
F
3
B
F
.
k
c
a
b
d
e
e
F
4
P
M
O
C
.
n
o
it
a
s
n
e
p
m
o
c
k
c
a
b
d
e
e
F
5
M
I
L
I
.
e
s
n
e
s
ti
m
il
t
n
e
r
r
u
C
6
D
N
G
.
d
n
u
o
r
G
7
T
U
O
.
O
L
V
U
L
r
o
O
L
V
U
g
n
ir
u
d
w
o
L
.t
u
p
t
u
o
e
v
ir
d
e
t
a
G
8
C
C
V
.
e
g
a
tl
o
v
y
l
p
p
u
S
(MSOP- 8 PIN)
TOP VIEW
Part Number Code (Example: AAxx)
yyww = Date Code (Example: 0012)
xxxx = Semtech Lot No. (Example: E901
xxxx 01-1)
Marking Information
PDF 
ZIP
