Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

MP28248 Datasheet(PDF) 16 Page - Monolithic Power Systems

Part No. MP28248
Description  High-Efficiency, Fast-Transient, 3A, 4.2V-20V Input Synchronous Step-down Converter in a QFN12 (2x3mm) Package
Download  19 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  MPS [Monolithic Power Systems]
Homepage  http://www.monolithicpower.com
Logo 

MP28248 Datasheet(HTML) 16 Page - Monolithic Power Systems

 
Zoom Inzoom in Zoom Outzoom out
 16 / 19 page
background image
MP28248 – 3A, 4.2V-20V INPUT, FAST-TRANSIENT SYNCHRONOUS STEP-DOWN CONVERTER IN QFN12 (2X3mm)
MP28248 Rev. 1.0
www.MonolithicPower.com
16
1/5/2012
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
Figure 12: Simplified Ceramic Capacitor Circuit
with DC Blocking Capacitor
Input Capacitor
The input current to the step-down converter is
discontinuous and therefore requires a capacitor
to supply the AC current to the step-down
converter while maintaining the DC input voltage.
Ceramic capacitors are recommended for best
performance and should be placed as close to
the VIN pin as possible. Capacitors with X5R and
X7R ceramic dielectrics are recommended
because they are fairly stable with temperature
fluctuations.
The capacitors must also have a ripple current
rating greater than the maximum input ripple
current of the converter. The input ripple current
can be estimated as follows:
OUT
OUT
CIN
OUT
IN
IN
VV
II
(1
)
VV

 
(17)
The worst-case condition occurs at VIN = 2VOUT,
where:
OUT
CIN
I
I
2
(18)
For simplification, choose an input capacitor with
an RMS current rating greater than half of the
maximum load current.
The input capacitance value determines the input
voltage ripple of the converter. If there is an input
voltage ripple requirement in the system, choose
the input capacitor that meets the specification.
The input voltage ripple can be estimated as
follows:
OUT
OUT
OUT
IN
SW
IN
IN
IN
IV
V
ΔV=
1-
fC
V
V



(19)
Under worst-case conditions where VIN = 2VOUT:
OUT
IN
SW
IN
I
1
ΔV=
4f
C
(20)
Output Capacitor
The output capacitor maintains the DC output
voltage. Use ceramic or POSCAP capacitors for
best results. The output voltage ripple can be
estimated as:

 

OUT
OUT
OUT
ESR
SW
IN
SW
OUT
VV
1
V(1
) (R
)
fL
V
8 f
C
(21)
For 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 as:

 
 
OUT
OUT
OUT
2
SW
OUT
IN
VV
V(1
)
8f
L C
V
(22)
The output voltage ripple caused by ESR is very
small and requires an external ramp to stabilize
the system. The external ramp can be generated
through resistor R4 and capacitor C4 following
equations 5, 8 and 9.
For POSCAP capacitors, the ESR dominates the
impedance at the switching frequency. The ramp
voltage generated from the ESR is high enough
to stabilize the system and therefore does not
need an external ramp. Use a minimum ESR
value of around 12mΩ to ensure stable converter
operation. For simplification, the output ripple can
be approximated as:

 
OUT
OUT
OUT
ESR
SW
IN
VV
V(1
) R
fL
V
(23)
The application design must also consider the
maximum output capacitor value. If the output
capacitor value is too high, the output voltage
can’t reach the designated value during the soft-
start time, and then the device will fail to regulate.
The maximum output capacitor value CO_MAX can
be approximately by:

O_ MAX
LIM _ AVG
OUT
ss
OUT
C(I
I
) t / V
(24)
Where ILIM_AVG is the average start-up current
during soft-start period and tss is the soft-start
time.


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19 


Datasheet Download




Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn