Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

APW7098 Datasheet(PDF) 23 Page - Anpec Electronics Coropration

Part No. APW7098
Description  Two- Phase Buck PWM Controller with Integrated MOSFET Drivers
Download  30 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  ANPEC [Anpec Electronics Coropration]
Homepage  http://www.anpec.com.tw
Logo 

APW7098 Datasheet(HTML) 23 Page - Anpec Electronics Coropration

Zoom Inzoom in Zoom Outzoom out
 23 / 30 page
background image
Copyright
© ANPEC Electronics Corp.
Rev. A.6 - Oct., 2009
APW7098
www.anpec.com.tw
23
Application Information (Cont.)
Output Inductor Selection (Cont.)
IN
OUT
V
V
D
=
Where F
SW is the switching frequency of the regulator.
Although the inductor value and frequency are increased
and the ripple current and voltage are reduced, a tradeoff
exists between the inductor’s ripple current and the regu-
lator load transient response time.
A smaller inductor will give the regulator a faster load tran-
sient response at the expense of higher ripple current.
Increasing the switching frequency (F
SW) also r e d u c e s
the ripple current and voltage, but it will increase the
switching loss of the MOSFETs and the power dissipa-
tion of the converter. The maximum ripple current oc-
curs at the maximum input voltage. A good starting point
is to choose the ripple current to be approximately 30%
of the maximum output current. Once the inductance value
has been chosen, select an inductor that is capable of
carrying the required peak current without going into
saturation. In some types of inductors, especially core
that is made of ferrite, the ripple current will increase
abruptly when it saturates. This results in a larger out-
put ripple voltage.
For two-phase converter, the inductor value (L) determines
the sum of the two inductor ripple currents,
∆I
P-P, and af-
fects the load transient reponse. Higher inductor value
reduces the output capacitors’ripple current and induces
lower output ripple voltage. The ripple current can be
approxminated by:
Output Capacitor Selection
Output voltage ripple and the transient voltage de-
viation are factors that have to be taken into con-
sideration when selecting output capacitors. Higher
capacitor value and lower ESR reduce the output ripple
and the load transient drop. Therefore, selecting high
performance low ESR capacitors is recommended for
switching regulator applications. In addition to high fre-
quency noise related to MOSFET turn-on and turn-off,
the output voltage ripple includes the capacitance
voltage drop
∆V
COUT and ESR voltage drop ∆VESR
caused by the AC peak-to-peak sum of the inductor’s
current. The ripple voltage of output capacitors can be
represented by:
These two components constitute a large portion of the
total output voltage ripple. In some applications, multiple
capacitors have to be paralleled to achieve the desired
ESR value. If the output of the converter has to support
another load with high pulsating current, more capaci-
tors are needed in order to reduce the equivalent ESR
and suppress the voltage ripple to a tolerable level. A
small decoupling capacitor in parallel for bypassing
the noise is also recommended, and the voltage rating
of the output capacitors are also must be considered.
To support a load transient that is faster than the
switching frequency, more capacitors are needed for
reducing the voltage excursion during load step change.
For getting same load transient response, the output
capacitance of two-phase converter only needs around
half of output capacitance of single-phase converter.
Another aspect of the capacitor selection is that the
total AC current going through the capacitors has to be
less than the rated RMS current specified on the ca-
pacitors in order to prevent the capacitor from over-
heating.
Input Capacitor Selection
Use small ceramic capacitors for high frequency
decoupling and bulk capacitors to supply the surge cur-
rent needed each time high-side MOSFET turns on. Place
the small ceramic capacitors physically close to the
MOSFETs and between the drain of high-side MOSFET
and the source of low-side MOSFET.
The important parameters for the bulk input capacitor are
the voltage rating and the RMS current rating. For reliable
operation, select the bulk capacitor with voltage and cur-
rent ratings above the maximum input voltage and larg-
est RMS current required by the circuit. The capacitor volt-
age rating should be at least 1.25 times greater than the
maximum input voltage and a voltage rating of 1.5 times
is a conservative guideline. For two-phase converter, the
IN
OUT
SW
OUT
IN
P
-
P
V
V
L
F
2V
-
V
I
×
×
=
ESR
P
P
ESR
SW
OUT
P
P
COUT
R
I
V
F
C
8
I
V
×
×
=
×
=


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30 


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