Electronic Components Datasheet Search
Selected language     English  ▼
Part Name
         Description


AND8079 Datasheet(PDF) 4 Page - ON Semiconductor

Part No. AND8079
Description  A Low Cost DDR Memory Power Supply Using the NCP1571 Synchronous Buck Converter and a LM358 Based Linear Voltage Regulator
Download  20 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
Logo 

 
 4 page
background image
AND8079/D
http://onsemi.com
4
Component Selection
Input Inductor
The input inductor (LIN) is used to isolate the input power
supply from the switching portion of the buck regulator. LIN
also limits the inrush current into the bulk input capacitors
and limits the input current slew rate that results from the
transient load. The inductor blocks the ripple current and
transfers the transient current requirement to the bulk input
capacitor bank.
The design equations for LIN are listed below and for
connivance an inductance of 1.0
mH is chosen. The cut-off
frequency of the second order LC filter provides adequate
attenuation for the 200 kHz switching frequency of the
NCP1571.
LIN +
DV
(dI dt)Max
+ 5V * 2.5 V
10 A
5
ms + 1.25 mH
f
* 3db +
1
2
p
LIN CIN
+
1
2
p
1
mH
5400
mF
+ 216 Hz
where:
LIN = input inductor
CIN = bulk input capacitor(s)
dI/dt = 10 A in 5.0
ms
Input Capacitors
The input filter capacitors provide a charge reservoir that
minimizes the supply voltage variations due to the pulsating
current through the MOSFETs. The input capacitors are
chosen primarily to meet the ripple current rating of the
capacitors.
The design equation is listed below.
ICin(RMS) + D
(1
* D)
Iout2
+ .5
(1
* .5)
102
+ 5A
where:
D = duty cycle = VOUT/VIN = 2.5 V/5.0 V = 0.5
IOUT = maximum output current
The Rubycon 10 V 1800
mf capacitors have a ripple
current rating of 2.55 A. Thus only 2 of the capacitors are
needed to meet the ripple requirements; however, 3
capacitors were chosen to be conservative.
Output Inductance
The main criterion in selecting the output filter inductance
(LOUT) is to provide a satisfactory response to the load
transients. The inductance affects the output voltage ripple
by limiting the rate at which the current can either increase
or decrease. The design equation used for selecting LOUT is
listed below. A 2.2
mH inductor was chosen for the design.
LOUT +
(VIN * VOUT)
tr
DI
+
(5 V
* 2.5 V)
10
ms
10 A
+ 2.5 mH
where:
tr = output transient load time
Output Capacitors
The output capacitors are selected to meet the desired
output ripple requirements. The key specifications for the
capacitors are their ESR (Equivalent Series Resistance) and
ESL (Equivalent Series Inductance). In order to obtain a
good transient response, a combination of low value/high
frequency ceramic
capacitors
and
bulk
electrolytic
capacitors are placed as close to the load as possible.
The voltage change during the load current transient is:
DVOUT + DIOUT
ESL
Dt )
ESR
)
tr
COUT
^ DIOUT
ESR
Empirical data indicates that most of the output voltage
change that results from the load current transients is
determined by the capacitor ESR; therefore, the maximum
allowable ESR can be approximated from the following
equation.
ESR max ^
DVOUT
DIOUT
+ 75 mV
10 A
+ 7.5 mW
The number of capacitors is calculated by using the
equation listed below.
Number of capacitors
+
ESRCAP
ESR max
+ 19 mW
7.5 m
W +
2.5
The ESR of the Rubycon 6.3 V 1800
mF capacitors is
specified at 19 m
W; therefore, 3 capacitors are used in the
design.
MOSFET Selection
The output switch MOSFETs are chosen based on the gate
charge/gate-source threshold voltage, gate capacitance, on
resistance, current rating and the thermal capacity of the
package. In this DDR design, the MOSFETs were chosen for
economical reasons and have a current and power rating that
is much better than needed for this design. In addition, the
MOSFETs selected were verified by measuring the thermal
characteristics of the devices on the PCB.
The power dissipation design equation for selecting the
MOSFETs is given below.
P
+ IMAX2
RDS(ON)
D
)
IMAX
VDS
Tr
FS
2
)
IMAX
VDS
Tf
FS
2
where:
Tr = rise time or turn-on time of MOSFET
Tf = fall time or turn-off time of MOSFET
FS = switching frequency




Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20 


Datasheet Download



Related Electronics Part Number

Part NumberComponents DescriptionHtml ViewManufacturer
RT9232PROGRAMMABLE SYNCHRONOUS PWM BUCK CONVERTER WITH 1.5V/2.5V DUAL LOW DROPOUT LINEAR REGULATOR CONTROLLER AND REFERENCE OUTPUT 1 2 3 4 5 MoreRichtek Technology Corporation
FX5545G108The Smallest and Low Profile 0.9V to 4.5V 4A with 570W/in^3 Power Density Efficiency up to 95% DC/DC Buck Converter 1 2 3 4 5 MoreVishay Siliconix
RT9221PROGRAMMABLE SYNCHRONOUS PWM BUCK CONVERTER WITH 1.5V / 2.5V DUAL LOW DROPOUT LINEAR REGULATOR CONTROLLER 1 2 3 4 5 MoreList of Unclassifed Manufacturers
TB7001FLFor high current and low voltage applications Synchronous buck converter module 1 2 3 4 5 MoreToshiba Semiconductor
TPS51116COMPLETE DDR AND DDR2 MEMORY POWER SOLUTION SYNCHRONOUS BUCK CONTROLLER 3-A LDO BUFFERED REFERENCE 1 2 3 4 5 MoreTexas Instruments
RT9222PROGRAMMABLE SYNCHRONOUS PWM BUCK CONVERTER WITH DUAL ADJUSTABLE LOW DROPOUT LINEAR REGULATOR CONROLLER 1 2 3 4 5 MoreList of Unclassifed Manufacturers
SP6120Low Voltage AnyFETTM Synchronous Buck Controller Ideal for 2A to 10A High Performance DC-DC Power Converters 1 2 3 4 5 MoreSipex Corporation
2SC2879TRANSISTOR 2~30MHz SSB LINEAR POWER AMPLIFIER APPLICATIONS LOW SUPPLY VOLTAGE USE 1 2 Toshiba Semiconductor
LDO513IP Library: Power Supply Range 2.9V to 13V Low Power 50mA Low Dropout Voltage Regulator 1 2 3 4 STMicroelectronics
SP6120Low Voltage AnyFETTM Synchronous Buck Controller Ideal for 2A to 10A High Performance DC-DC Power Converters 1 2 3 4 5 MoreSipex Corporation

Link URL

Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Bookmark   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com 2003 - 2017    


Mirror Sites
English : Alldatasheet.com  , 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