SC174MLTRT Semtech, SC174MLTRT Datasheet - Page 20

• Manufacturer Part Number: SC174MLTRT
• Description: IC BUCK SYNC ADJ 4A MLPD-10
• Manufacturer: Semtech
• Series: EcoSpeed™r
• Type: Step-Down (Buck)r

Specifications of SC174MLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.75 ~ 5.23 V
• Current - Output: 4A
• Frequency - Switching: 200kHz ~ 1MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MLPD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC174MLTR

Layout Guideline
Since the SC174 has integrated switches, special consid-
eration should be given to board layout. Let us use the
schematic shown above as an example. The board level
layout is illustrated in the following four layers.
As shown on the top layer layout, U1 is the switching
regulator SC174. C1 and C11 serve as the decoupling ca-
pacitor for the buck converter power train. C11, with a
value between 1nF and 10nF, is the high frequency filter-
ing capacitor. It is recommended to put C1 and C11 as
close as possible to the SC174 to get the best decoupling
performance, with C11 closest. C1, with a value of 10uF,
should be placed no more than 3mm away from the VIN
pin. L1 is the output filtering inductor. C2, C3 and C4 are
the output filtering capacitors. C5 is the boostrap capaci-
tor. Pin 10 (VDD) is the input bias power for the internal
circuits. It is recommended to get the power from VIN
through an RC filtering network consisted of R1, C6 and
C10. The value of R1 can be between 3.01W and 10W and
the capacitance of C10 should be above 1mF. C6, with a
value of 1nF, is the high frequency filtering capacitor. The
© 2010 Semtech Corporation
V
V
V
V
O
O
IN
-
IN
+
-
+
C4
C3
0
C11
C2
C7
C1
0
R4
R3
L1
Schematic for layout illustration
R6
0
C9
C5
locations of C6 and C10 should be as close as possible to
pins 9 and 10, with C6 closest, to get the best possible
filtering result. R2 is the on-time programming resistor.
R2 should be located as close as possible to pin 8 and it
should return to analog ground. The EN/PSV pin is a tri-
state pin. Pull EN/PSV high to enable the part with power
save mode enabled. Connect EN/PSV to AGND to disable
the switching regulator. Leave EN/PSV floating to enable
the IC in forced continuous conduction mode.
Since there are two integrated MOSFETs inside the SC174
that will dissipate a lot of power, to help spread the heat
out of the IC more efficiently, there is a thermal pad un-
derneath the SC174 serving as a heat sink. To enlarge the
heat sinking area, a large copper plane under the thermal
pad as shown on the top layer is recommended.
On inner layer 2, a large analog ground plane (AGND) on
the right hand side is connected to the thermal pad un-
derneath the SC174 using vias. Thus the heat generated
inside the SC174 can be spread through the vias to the
0
R7
2
3
4
5
1
1
5
2
3
4
C8
SC174
BST
VIN
LX
PGND
PGOOD
U1
EN/PSV
AGND
VDD
TON
FB
R1
10
9
7
6
0
10
9
8
7
6
C10
C6
R2
SC174
EN/PSV
20