SC4525ASETRT Semtech, SC4525ASETRT Datasheet - Page 14

• Manufacturer Part Number: SC4525ASETRT
• Description: IC STEP-DWN SW REG 3A 28V 8-SOIC
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC4525ASETRT

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 3A
• Frequency - Switching: 300kHz ~ 1.3MHz
• Voltage - Input: 8 ~ 28 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Power - Output: -
• Other names: SC4525ASETR

Applications Information (Cont.)
(3) Place the compensator zero, F
20% of the crossover frequency, F
(4) Use the compensator pole, F
F
(5) Then, the parameters of the compensation network
can be calculated by
where g
Example: Determine the voltage compensator for an
800kHz, 2V to 3.3V/3A converter with 47uF ceramic
output capacitor.
Choose a loop gain crossover frequency of 80kHz, and
place voltage compensator zero and pole at F
(20% of F
required compensator gain at F
Then the compensator parameters are
Select R
Compensator parameters for various typical applications
are listed in Table 5. A MathCAD program is also available
upon request for detailed calculation of the compensator
parameters.
Z
C
C
C
C
G
G
R
R
C
C
C
C
A
A
A
A
R
R
V
V
V
V
.
C
C
C
C
5
5
8
8
o
o
c
c
PWM
PWM
7
7
5
5
8
8
7
7
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
10
10
1 (
1 (
−
−
−
−
. 0
. 0
2
2
2
2
2
2
2
2
≈
≈
g
g
C
C
C
C
G
G
R
R
C =
C =
C
C
G
G
R
R
C
C
C
C
A
A
A
A
R
R
⋅ π
⋅ π
20
20
20
20
⋅ π
⋅ π
V
V
V
V
π
π
π
π
V
V
V
V
28
28
+
+
G
G
m
m
A
A
20
20
F
F
F
F
10
10
7
7
7
o
o
c
c
PWM
PWM
7
7
5
5
8
8
o
o
c
c
PWM
PWM
5
5
8
8
m
C
C
C
C
7
7
5
5
8
8
C
C
5
5
CA
CA
1
1
1
1
16
16
600
600
s
s
Z
Z
P
P
=3.4k, C
1
1
1
1
=0.28mA/V is the EA gain of the SC4525A.
⋅
⋅
⋅
⋅
R
R
=
=
=
=
⋅
⋅
=
=
=
=
=
=
/
/
=
=
=
=
=
=
=
=
=
=
=
=
=
=
log
log
log
log
⋅
⋅
19
19
20
20
10
10
R
R
R
R
G
G
ω
ω
R
R
C
⋅
⋅
7
7
10
10
10
10
7
7
10
10
), and F
PWM
PWM
1 (
1 (
1 (
1 (
2
2
2
2
S
S
2
2
2
2
2
2
2
2
−
−
−
−
. 0
. 0
⋅
⋅
p
p
≈
≈
≈
≈


 
 








−
−
10
10
)
)
g
g
g
g
,
,
3
3
G
G
28
28
⋅ π
⋅ π
1 (
1 (
⋅ π
⋅ π
⋅ π
⋅ π
⋅ π
⋅ π
π
π
π
π
20
20
20
20
3
3
1
1
28
28
G
G
G
G
+
+
m
m
+
+
m
m
1 (
1 (
CA
CA
=
=
1
1
A
A
A
A
20
20
F
F
3
3
20
20
F
F
10
10
1
1
⋅
⋅
+
+
C
C
C
C
CA
CA
CA
CA
1
1
1
1
1
1
⋅
⋅
31
31
16
16
16
16
600
600
R
R
600
600
s
s
s
s
Z
Z
P
P
31
31
⋅
⋅
+
+
4
4
s
s
1
1
1
1
⋅
⋅
⋅
⋅
31
31
R
R
R
R
S
S
⋅
⋅
/
/
/
/
1 .
1 .
s
s
log
log
log
log
/
/
5
⋅
⋅
1
1
10
10
4 .
4 .
⋅
⋅
.
.
19
19
20
20
R
R
R
R
R
R
⋅
⋅
k 8
k 8
=0.33nF, and C
G
G
G
G
R
R
ω
ω
ω
ω
R
R
ω
ω
⋅
⋅
4 .
4 .
⋅
⋅
2
2
⋅
⋅
ESR
ESR
7
7
⋅
⋅
10
10
10
10
7
7
n
n
PWM
PWM
10
10
PWM
PWM
ω
ω
S
S
S
S
P
p
p
⋅
⋅
p
p
π
π
10
10
⋅
⋅








Q
Q






⋅
⋅
−
−
10
10
10
10
F
F
p
p
)
)
)
)
10
10
C
C
,
,
,
,
=600kHz. From Equation (9), the
1
1
3
3
G
G
28
28
+
+
1 (
1 (
1 (
1 (
C
C
−
−
≈
≈
3
3
3
3
O
O
3
3
3
3
1
1
C
C
s
s
1 (
1 (
1 (
1 (
)
)
CA
CA
3
3
1
1
1
1
=
=
R
R
=
=
O
O
3
3
3
3
⋅
⋅
2
2
⋅
⋅
1
1
⋅
⋅
+
+
+
+
1
1
C
C
2
2
⋅
⋅
=
=
22
22
. 0
. 0
31
31
R
R
31
31
/
/
⋅
⋅
⋅
⋅
⋅
⋅
+
+
+
+
O
O
⋅ π
⋅ π
4
4
s
s
s
s
V
V
8
8
ω
ω
22
22
V
V
31
31
31
31
S
S
,
,
FB
FB
1 .
1 .
5 .
5 .
O
O
2
2
n
n
s
s
s
s
/
/
/
/
1 .
1 .
1
1
80
80
4 .
4 .
.
.
)
)
R
R
R
R
⋅
⋅
k 8
k 8
nF
nF
pF
pF
ω
ω
ω
ω


 
 


4 .
4 .
1 .
1 .
2
2
⋅
⋅
ESR
ESR
ESR
ESR
⋅
⋅
⋅
⋅
⋅
⋅
n
n
n
n
10
10
C
ω
ω
ω
ω
10
10
10
10
π
π
10
10
P
Q
Q
Q
Q
⋅
⋅
⋅
⋅
is
F
F
p
p
p
p
10
10
10
10
8
C
C
C
C
, to cancel the ESR zero,
C
1
1
1
1
3
3
=0pF for the design.
+
+
+
+
C
C
.
−
−
≈
≈
3
3
≈
≈
3
3
O
O
O
O
Z
⋅
⋅
3
3
ω
ω
C
C
s
s
47
47
s
s
)
)
)
)
3
3
3
3
Z
Z
R
R
R
R
, between 0% and
=
=
O
O
⋅
⋅
2
2
2
2
P
P
P
P
P
P
P
P
P
P
P
P
=
=
1
1
1
1
C
C
C
C
2
2
=
=
=
=
⋅
⋅
. 0
. 0
TOTAL
TOTAL
C
C
SW
SW
BST
BST
D
D
IND
IND
/
/
/
/
⋅
⋅
10
10
R
R
O
O
O
O
⋅ π
⋅ π
12
12
8
8
ω
ω
ω
ω
V
V
ESR
ESR
V
V
=
=
=
=
31
31
,
,
,
,
−
−
1
1
FB
FB
5 .
5 .
O
O
2
2
n
n
2
2
n
n
=
=
6
6
=
=
D
D
=
=
1 (
1 (
C
C
80
80
pF
pF
)
)
)
)
⋅
⋅
nF
nF
pF
pF
O
O
=
=
1 (
1 (








1
1
2
2
D
D
⋅
⋅
1
1
3
3
,
,
−
−
V
V
P
P
0 .
0 .
3 .
3 .
⋅
⋅
1 .
1 .
⋅
⋅
⋅
⋅
CESAT
CESAT
10
10
) D
) D
C
C
t
t
V
V






S
S
Z
BST
BST
~
~
=
=
+
+
1
1
⋅
⋅
=6kHz
3
3
19
19
⋅
⋅
. 1
. 1
P
P
V
V
V
V
ω
ω
⋅
⋅
ω
ω
⋅
⋅
⋅
⋅
D
D
SW
SW
dB
dB
IN
IN
) 3
) 3
47
47
I
I
40
40
O
O
Z
Z
Z
Z
I
I
⋅
⋅
O
O
⋅
⋅
I
I
⋅
⋅
=
=
=
=
+
+
O
O
I
I
I
I
⋅
⋅
O
O
2
2
O
O
10
10
P
P
R
R
R
R
⋅
⋅
BST
BST
⋅
⋅
ESR
ESR
ESR
ESR
F
F
R
R
1
1
1
1
−
−
SW
SW
DC
DC
6
6
C
C
C
C
+
+
Thermal Considerations
For the power transistor inside the SC4525A, the
conduction loss P
circuit loss P
where V
switching time of the NPN transistor (see Table 4).
In addition, the quiescent current loss is
The total power loss of the SC4525A is therefore
The temperature rise of the SC4525A is the product of the
total power dissipation (Equation (2)) and q
which is the thermal impedance from junction to ambient
for the SOIC-8 EDP package.
It is not recommended to operate the SC4525A above
25
input voltage and high output current, the switching
frequency may need to be reduced to meet the thermal
requirement.
⋅
⋅
O
O
O
O
P
P
1
1
3
3
,
,
,
,
Q
Q
0 .
0 .
3 .
3 .
o
C junction temperature. In the applications with high






P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
Table 4. Typical switching time
=
=
C
C
BST
BST
D
D
IND
IND
C
C
BST
BST
D
D
IND
IND
TOTAL
TOTAL
SW
SW
Q
Q
TOTAL
TOTAL
SW
SW
BST
19
19
=
=
=
=
=
=
=
=
=
=
Input Voltage
Input Voltage
is the BST supply voltage and t
=
=
=
=
=
=
=
=
=
=
D
D
D
D
=
=
1 (
1 (
1 (
1 (
V
V
dB
dB
BST,
=
=
1
1
1 (
1 (
=
=
1
1
1 (
1 (
2
2
D
D
IN
IN
2
2
D
D
⋅
⋅
⋅
⋅
12V
12V
24V
24V
28V
28V
−
−
−
−
V
V
V
V
P
P
P
P
1 .
1 .
1 .
1 .
⋅
⋅
⋅
⋅
⋅
⋅
⋅
⋅
⋅
⋅
can be estimated as follows:
CESAT
CESAT
CESAT
CESAT
C
C
) D
) D
C
C
) D
) D
2
2
t
t
V
V
t
t
V
V
S
S
S
S
BST
BST
mA
mA
BST
BST
~
~
~
~
+
+
+
+
C
⋅
⋅
⋅
⋅
⋅
⋅
⋅
⋅
, the switching loss P
. 1
. 1
. 1
. 1
P
P
V
V
P
P
V
V
V
V
V
V
⋅
⋅
⋅
⋅
D
D
⋅
⋅
⋅
⋅
D
D
SW
SW
SW
SW
IN
IN
) 3
) 3
IN
IN
) 3
) 3
I
I
I
I
40
40
40
40
O
O
O
O
I
I
⋅
⋅
I
I
⋅
⋅
O
O
O
O
⋅
⋅
⋅
⋅
I
I
I
I
⋅
⋅
⋅
⋅
+
+
+
+
I
I
O
O
O
O
I
I
I
I
I
I
O
O
O
O
2
2
O
O
2
2
O
O
P
P
12.5ns
12.5ns
25.3ns
25.3ns
P
P
⋅
⋅
22ns
22ns
⋅
⋅
BST
BST
BST
BST
⋅
⋅
⋅
⋅
1A
1A
F
F
F
F
R
R
R
R
SW
SW
SW
SW
DC
DC
DC
DC
+
+
+
+
Load Current
Load Current
P
P
P
P
Q
Q
Q
Q
15.3ns
15.3ns
25ns
25ns
28ns
28ns
2A
2A
P
P
P
P
Q
Q
Q
Q
SW
=
=
=
=
S
is the equivalent
, and bootstrap
V
V
V
V
IN
IN
IN
IN
18ns
18ns
28ns
28ns
31ns
31ns
3A
3A
⋅
⋅
⋅
⋅
JA
2
2
2
2
mA
mA
(0)
()
mA
mA
(2)
(36
o
C/W),
4