sc4524d Semtech Corporation, sc4524d Datasheet - Page 15

• Manufacturer Part Number: sc4524d
• Description: 18v 2a Step-down Switching Regulator
• Manufacturer: Semtech Corporation

P
P
BST
BST
F
F
R
R
SW
SW
DC
DC
+
+
switching time of the NPN transistor (see Table 4).
In addition, the quiescent current loss is
The total power loss of the SC4524D is therefore
The temperature rise of the SC4524D 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 SC4524D above
125
input voltage and high output current, the switching
frequency may need to be reduced to meet the thermal
requirement.
P
P
Q
Q
o
C junction temperature. In the applications with high
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
=
=
D
D
=
=
1 (
1 (
V
V
=
=
1 (
1 (
IN
IN
1
1
2
2
D
D
⋅
⋅
−
−
V
V
P
P
1 .
1 .
⋅
⋅
⋅
⋅
⋅
⋅
12V
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
P
P
⋅
⋅
12.5ns
BST
BST
⋅
⋅
F
F
Load Current
R
R
1A
SW
SW
DC
DC
+
+
P
P
Q
Q
15.3ns
2A
P
P
Q
Q
Fig.9
=
=
V
V
IN
IN
⋅
⋅
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 SC4524D, 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
Figure 9. Heavy lines indicate the critical pulse
IN
current loop. The stray inductance of this
loop should be minimized.
Vin
SC4524D
Z
L
V
OUT
15
Cu