MP2143 – 3A, 5.5V, 1.2MHz, 40μA I
Q
, COT SYNCHRONOUS STEP-DOWN SWITCHER
MP2143 Rev. 1.07 www.MonolithicPower.com 13
7/4/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
Selecting the Output Capacitor
The output capacitor (C2) maintains the output
DC voltage. Use ceramic capacitors. Low-ESR
capacitors keep the output voltage ripple low.
The output voltage ripple can be estimated by:
OUT OUT
OUT ESR
S1 IN S
VV
1
V1R
fL V 8fC2
Where L
1
is the inductor value and R
ESR
is the
equivalent series resistance of the output
capacitor.
Using ceramic capacitors, the impedance at the
switching frequency is dominated by the
capacitance. The output voltage ripple is mainly
caused by the capacitance. For simplification,
the output voltage ripple can be estimated by:
OUT OUT
OUT
2
IN
S1
VV
V1
V
8f L C2
For tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency. For simplification, the output ripple
can be approximated as:
OUT OUT
OUT ESR
IN
S1
VV
V1R
fL V
The characteristics of the output capacitor also
affect the stability of the regulation system.
PCB Recommendation of MP2143
Proper layout of the switching power supplies is
very important, and sometimes critical for
proper operation. For high-frequency switching
converters, poor layout could lead to poor line
or load regulation and stability issues.
The high current paths (GND, VIN, and SW)
should be placed very close to the device using
short, direct, and wide traces. The input
capacitor needs to be as close as possible to
the VIN and GND pins. The external feedback
resistors should be placed next to the FB pin.
Keep the switching node SW short and away
from the feedback network.
8
7
6
5
L1
C
2
C
2
A
R
1
R
4
R
3
R
2
1
2
3
4
OUT
VIN
GND
SW
C1C1A
Figure 3: Layout Recommendation
TYPICAL APPLICATION CIRCUITS
MP2143
VIN 2.5-5.5V
R3
100k
R2
200k
R1
200k
R4
499k
U1
SW
VOUT
GND
C2A
NS
1206
IN
EN
PG
PGND AGND
FB
OUT
SW
2
8
1
46
7
5
3
GND
EN
PG
VIN
Figure 4: MP2143 Typical Application Circuit
