ncp3127 ON Semiconductor, ncp3127 Datasheet - Page 9

• Manufacturer Part Number: ncp3127
• Description: Ncp3127 2 A Synchronous Pwm Switching Converter
• Manufacturer: ON Semiconductor

MOSFET
Design Procedure
important to collect as much information as possible about
the behavior of the input and output before starting the
design.
tool available online under the design tools section of the
NCP3127 product page. The tool allows you to capture your
design point and optimize the performance of your regulator
based on your design criteria.
that are LC filtered to produce a lower DC output voltage
V
on time relative to the switching period T or switching
frequency. The ratio of high side switch on time to the
switching period is called duty ratio D. Duty ratio can also
Low Side
PHASE
VOCTH
Table 4. DESIGN PARAMETERS
OUT
Current
Input voltage
Output voltage
Input ripple voltage
Output ripple voltage
Output current rating
Operating frequency
When starting the design of a buck regulator, it is
ON Semiconductor has a Microsoft Excel® based design
The buck converter produces input voltage V
Drive
. The output voltage can be changed by modifying the
BG
0 V
Design Parameter
−
+
Figure 20. Current Limit Trip
VOCTH
(V
(V
(V
(V
(I
(F
OUT
SW
IN
OUT
INRIPPLE
OUTRIPPLE
)
)
)
BG
)
)
)
10.8 V to 13.2 V
Example Value
350 kHz
300 mV
40 mV
3.3 V
2 A
APPLICATION SECTION
IN
Current
http://onsemi.com
Flow
pulses
9
be calculated using V
Drop V
D
F
T
T
T
V
V
V
V
Inductor Selection
rule of thumb for the design where the percentage of ripple
current in the inductor should be between 10% and 40%.
When using ceramic output capacitors, the ripple current
can be greater because the ESR of the output capacitor is
smaller, thus a user might select a higher ripple current.
F
D +
D +
SW
OFF
ON
SW
HSD
IN
LSD
OUT
When selecting an inductor, the designer can employ a
+ 1
T
V
T
ON
IN
LSD
T
V
* V
OUT
and (1 * D) +
, and the High Side Switch Voltage Drop V
HSD
) V
) V
= Duty cycle
= Switching frequency
= Switching period
= High side switch off time
= High side switch on time
= High side switch voltage drop
= Input voltage
= Low side switch voltage drop
= Output voltage
LSD
OUT
LSD
, V
T
[ D +
OFF
IN
T
, the Low Side Switch Voltage
V
V
OUT
IN
³ 27.5% +
(eq. 2)
(eq. 3)
(eq. 4)
3.3 V
12 V
HSD
.