sc4525c Semtech Corporation, sc4525c Datasheet - Page 15

• Manufacturer Part Number: sc4525c
• Description: 28v 3a Step-down Switching Regulator
• Manufacturer: Semtech Corporation

P
P
BST
BST
F
F
R
R
SW
SW
DC
DC
+
+
Applications Information (Cont.)
In addition, the quiescent current loss is
The total power loss of the SC4525C is therefore
The temperature rise of the SC4525C is the product of the
total power dissipation (Equation (12)) and q
which is the thermal impedance from junction to ambient
for the SOIC-8 EDP package.
It is not recommended to operate the SC4525C above
125
P
P
Q
Q
o
C junction temperature.
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
Q
Q
TOTAL
TOTAL
SW
SW
=
=
=
=
=
=
Input Voltage
Input Voltage
=
=
=
=
D
D
=
=
1 (
1 (
V
V
=
=
1 (
1 (
IN
IN
1
1
2
2
D
D
⋅
⋅
12V
12V
24V
24V
28V
28V
−
−
V
V
P
P
1 .
1 .
⋅
⋅
⋅
⋅
⋅
⋅
CESAT
CESAT
) D
) D
C
C
2
2
t
t
V
V
S
S
mA
mA
BST
BST
~
~
+
+
⋅
⋅
⋅
⋅
1
1
P
P
V
V
V
V
⋅
⋅
⋅
⋅
D
D
3 .
3 .
SW
SW
IN
IN
I
I
40
40
O
O
I
I
⋅
⋅
I )
I )
O
O
⋅
⋅
I
I
+
+
⋅
⋅
O
O
I
I
O
O
2
2
O
O
12.5ns
12.5ns
25.3ns
25.3ns
P
P
22ns
22ns
⋅
⋅
BST
BST
⋅
⋅
1A
1A
F
F
R
R
SW
SW
DC
DC
+
+
Load Current
Load Current
P
P
Q
Q
15.3ns
15.3ns
25ns
25ns
28ns
28ns
2A
2A
P
P
Q
Q
=
=
V
V
IN
IN
18ns
18ns
28ns
28ns
31ns
31ns
3A
3A
⋅
⋅
JA
2
2
(11)
mA
mA
(12)
(36
o
C/W),
PCB Layout Considerations
In a step-down switching regulator, the input bypass
capacitor, the main power switch and the freewheeling
diode carry pulse current (Figure 9). For jitter-free
operation, the size of the loop formed by these components
should be minimized. Since the power switch is already
integrated within the SC4525C, connecting the anode of
the freewheeling diode close to the negative terminal of
the input bypass capacitor minimizes size of the switched
current loop. The input bypass capacitor should be placed
close to the IN pin. Shortening the traces of the SW and
BST nodes reduces the parasitic trace inductance at these
nodes. This not only reduces EMI but also decreases
switching voltage spikes at these nodes.
The exposed pad should be soldered to a large ground
plane as the ground copper acts as a heat sink for the
device. To ensure proper adhesion to the ground plane,
avoid using vias directly under the device.
V
IN
Figure 9. Heavy lines indicate the critical pulse
current loop. The stray inductance of this
loop should be minimized.
SC4525C
Z
L
V
OUT
15