SC4525DSETRT Semtech, SC4525DSETRT Datasheet - Page 14

• Manufacturer Part Number: SC4525DSETRT
• Description: IC BUCK ADJ 3A 8SOIC
• Manufacturer: Semtech
• Series: -r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of SC4525DSETRT

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1 V ~ 16.74 V
• Current - Output: 3A
• Frequency - Switching: 65kHz ~ 350kHz
• Voltage - Input: 3 V ~ 18 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: SC4525DSETR

Applications Information (Cont.)
(2) Select the open loop crossover frequency, F
10% and 20% of the switching frequency. At F
required compensator gain, A
ceramic output capacitors, the ESR zero is neglected and
the required compensator gain at F
(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
350kHz, 12V to 3.3V/3A converter with 47uF ceramic
output capacitor.
Choose a loop gain crossover frequency of 35kHz, and
place voltage compensator zero and pole at F
(20% of F
required compensator gain at F
Then the compensator parameters are
© 2011 Semtech Corp.
A
A
Z
.
C
C
=
=
−
−
R
R
R
R
C
C
C
C
G
G
C
C
C
C
R
R
A
A
A
A
R
R
C
C
C
C
G
G
C
C
V
V
V
V
C
C
A
A
A
A
V
V
V
V
20
20
7
7
o
o
c
c
PWM
PWM
7
7
C
C
C
C
5
5
8
8
5
5
8
8
7
7
o
o
c
c
PWM
PWM
7
7
C
C
C
C
5
5
8
8
5
5
8
8
m
⋅
⋅
=0.3mA/V is the EA gain of the SC4525D.
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
log
log
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
C
. 0
. 0
1 (
1 (
10
10
), and F
−
−
−
−
2
2
10
10
2
2
2
2
2
2
. 0
. 0
1 (
1 (
≈
≈
−
−
−
−
2
2
2
2
2
2
2
2
≈
≈






g
g
g
g
⋅ π
⋅ π
18.5
18.5
⋅ π
⋅ π
π
π
20
20
20
20
28
28
⋅ π
⋅ π
π
π
20
20
20
20
28
28
⋅ π
⋅ π
π
π
π
π
G
G
+
+
m
m
10
10
G
G
+
+
m
m
10
10
A
A
20
20
F
F
F
F
A
A
20
20
F
F
F
F
C
C
C
C
CA
CA
1
1
1
1
16
16
600
600
CA
CA
1
1
/ s
/ s
1
1
1 Z
1 Z
P
P
16
16
600
600
/ s
/ s
P
P
1 Z
1 Z
⋅
⋅
⋅
⋅
1
1
⋅
⋅
R
R
1
1
⋅
⋅
⋅
⋅
⋅
⋅
R
R
15
15
⋅
⋅
15
15
log
log
log
log
10
10
20
20
⋅
⋅
log
log
log
log
10
10
20
20
⋅
⋅
. 3
. 3
R
R
R
R
G
G
R
R
R
R
9 .
9 .
R
R
G
G
ω
ω
9 .
9 .
R
R
⋅
⋅
ω
ω
⋅
⋅
10
10
7
7
7
7
53
53
10
10
PWM
PWM
7
7
7
7
P1
S
S
1
1
PWM
PWM
p
p
S
S
⋅
⋅
⋅
⋅
p
p


 
 








−
−


 
 








−
−
10
10
= 677kHz. From Equation (9), the
10
10
1 ( )
1 ( )
3
3
,
,
1 ( )
1 ( )
3
3
,
,
G
G
28
28
⋅
⋅
G
G
28
28
10
10
3
3
1
1
3
3
1
1
1 (
1 (
=
=
CA
CA
1 (
1 (
1
1
=
=
CA
CA
1
1
3
3
1
1
3
3
⋅
⋅
+
+
1
1
⋅
⋅
−
−
+
+
⋅
⋅
22
22
22
22
3
3
R
R
⋅
⋅
22
22
22
22
R
R
⋅
⋅
+
+
⋅
⋅
⋅
⋅
6
6
+
+
/ s
/ s
6
6
/ s
/ s
22
22
S
S
22
22
S
S
2
2
1 .
1 .
R s
R s
1 .
1 .
R s
R s
.
.
1 .
1 .
1
1
.
.
1 .
1 .
1
1
⋅ π
⋅ π
k 3
k 3
⋅
⋅
k 3
k 3
C
⋅
⋅
ω
ω
ω
ω
1 .
1 .
. In typical applications with
1 .
1 .
2
2
⋅
⋅
ESR
ESR
2
2
⋅
⋅
ESR
ESR
⋅
⋅
35
35
⋅
⋅
n
n
10
10
n
n
ω
ω
10
10
ω
ω
C
π
π
10
10
π
π
10
10
P1
Q
Q
⋅
⋅
Q
Q
⋅
⋅
p
p
is
F
F
10
10
p
p
F
F
10
10
C
C
⋅
⋅
1
1
C
C
C
, to cancel the ESR zero,
1
1
+
+
10
10
C
C
−
−
+
+
C
C
−
−
.
≈
≈
3
3
≈
≈
O
O
3
3
3
3
O
O
C
C
3
3
C
Z1
C
C
s
s
s
s
)
)
1
1
3
3
3
3
)
)
3
3
R
R
=
=
R
R
can be estimated by
O
O
, between 10% and
=
=
⋅
⋅
2
2
O
O
⋅
⋅
2
2
⋅
⋅
P
P
P
P
P
P
1
1
C
C
=
=
2
2
1
1
C
C
2
2
=
=
. 0
. 0
47
47
/
/
. 0
. 0
⋅
⋅
C
C
/
/
T OT AL
T OT AL
S W
S W
⋅
⋅
O
O
⋅ π
⋅ π
O
O
⋅ π
⋅ π
12
12
ω
ω
V
V
12
12
ω
ω
V
V
V
V
45
45
=
=
V
V
45
45
⋅
⋅
,
,
FB
FB
,
,
FB
FB
2
2
n
n
10
10
O
O
2
2
n
n
=
=
O
O
80
80
D
D
80
80
pF
pF
pF
pF
)
)
)
)
nF
nF
nF
nF
−
−


 
 


=
=
1
1
2
2


 
 


⋅
⋅
6
6
V
V
⋅
⋅
P
P
⋅
⋅
⋅
⋅
⋅
⋅
C
10
10
(10)
C E S AT
C E S AT
10
10
C
C
, between
t
t
1
1
3
3
C
, find the
0 .
0 .
S
S
3 .
3 .
+
+
(9)
1
1
1
1
Z1
3
3
3
3
⋅
⋅






P
P
V
V
=7kHz
⋅
⋅
ω
ω
⋅
⋅
ω
ω
=
=
⋅
⋅
S W
S W
IN
IN
22
22
22
22
I
I
Z
Z
Z
Z
7
7
O
O
I
I
O
O
⋅
⋅
=
=
dB
dB
=
=
+
+
I
I
⋅
⋅
⋅
⋅
O
O
10
10
R
R
10
10
P
P
R
R
⋅
⋅
B S T
B S T
ESR
ESR
F
F
ESR
ESR
1
1
−
−
1
1
S W
S W
−
−
6
6
6
6
C
C
C
C
+
+
Select R
Compensator parameters for various typical applications
are listed in Table 4. A MathCAD program is also available
upon request for detailed calculation of the compensator
parameters.
Thermal Considerations
For the power transistor inside the SC4525D, the
conduction loss P
circuit loss P
where V
switching time of the NPN transistor (see Table 3).
In addition, the quiescent current loss is
The total power loss of the SC4525D is therefore
⋅
⋅
⋅
⋅
O
O
O
O
P
P
1
1
3
3
1
1
3
3
,
,
,
,
Q
Q
0 .
0 .
3 .
3 .
0 .
0 .
3 .
3 .












R
R
C
C
C
C
P
P
P
P
P
P
P
P
P
P
P
P
P
P
Table 3. Typical switching time
=
=
Table 3: Typical Switching Time
Table 3: Typical Switching Time
=
=
C
C
B S T
B S T
D
D
IND
IND
T OT AL
T OT AL
S W
S W
7
BST
Q
Q
7
7
5
5
8
8
=7.32k, C
15
15
15
15
Input Voltage
Input Voltage
=
=
=
=
=
=
=
=
=
=
=
=
is the BST supply voltage and t
=
=
=
=
D
D
=
=
1 (
1 (
V
V
9 .
9 .
9 .
9 .
BST,
2
2
=
=
1
1
1 (
1 (
2
2
2
2
D
D
IN
IN
. 0
. 0
⋅
⋅
12V
12V
dB
dB
−
−
⋅ π
⋅ π
dB
dB
5V
5V
V
V
⋅ π
⋅ π
P
P
1 .
1 .
⋅
⋅
⋅
⋅
⋅
⋅
can be estimated as follows:
3
3
C E S AT
C E S AT
) D
) D
C
C
2
2
10
10
t
t
V
V
7
7
677
677
S
S
B S T
B S T
~
~
mA
mA
+
+
⋅
⋅
5
C
⋅
⋅
⋅
⋅
=3.3nF, and C
, the switching loss P
⋅
⋅
10
10
10
10
20
20
. 1
. 1
7
7
P
P
V
V
V
V
⋅
⋅
⋅
⋅
S W
S W
D
D
⋅
⋅
IN
IN
) 3
) 3
I
I
−
−
10
10
40
40
3
3
O
O
I
I
⋅
⋅
3
3
1
1
⋅
⋅
O
O
⋅
⋅
I
I
⋅
⋅
+
+
7.4
7.4
I
I
O
O
1
1
3
3
I
I
O
O
6.86ns
6.86ns
12.5ns
12.5ns
2
2
O
O
=
=
P
P
⋅
⋅
⋅
⋅
1A
1A
7.4
7.4
B S T
B S T
⋅
⋅
F
F
7
7
R
R
⋅
⋅
S W
S W
10
10
4 .
4 .
DC
DC
+
+
Load Current
Load Current
⋅
⋅
10
10
k
k
3
3
P
P
8
= 33pF for the design.
9.71ns
9.71ns
15.3ns
15.3ns
Q
Q
3
3
=
=
2A
2A
www.semtech.com
3
3
P
P
=
=
1 .
1 .
Q
Q
32
32
SW
nF
nF
=
=
S
is the equivalent
12.5ns
12.5ns
SC4525D
, and bootstrap
V
V
18ns
18ns
pF
pF
3A
3A
IN
IN
⋅
⋅
2
2
(11)
(12)
mA
mA
14