Electronic Components Datasheet Search
Selected language     English  ▼
Part Name
         Description


AND8079 Datasheet(PDF) 2 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 

 
 2 page
background image
AND8079/D
http://onsemi.com
2
Many industry experts have predicted that DDR memory
will soon become the standard for desktop computers, with
notebooks shortly behind. Next generation DDR-II
generation systems are likely to have a lower Vdd voltage of
1.8 V with a Vtt and VREF voltage equal to 900 mV. This
lower voltage will be required to satisfy the consumer’s
requirement for more memory without a large increase in
required power.
Supply Voltage (Vdd)
The Vdd 2.5 V power supply is created with the NCP1571
low voltage synchronous buck controller. The NCP1571
controller contains the required circuitry for a synchronous
N-channel MOSFET buck regulator. The V2t control
method is used to achieve a fast 200 ns transient response
and an output regulation of
±1.0%. The IC operates at a fixed
internal frequency of 200 kHz. In addition, the NCP1571
provides the following features: undervoltage lockout
protection, programmable soft start, power good signal with
delay and overvoltage protection. Note the NCP1570 and
NCP1571 are functionally and pin for pin equivalent. The
NCP1571’s under voltage lockout operation (UVLO)
feature has been modified for applications that require a
parallel standby power supply in addition to the main power
supplied by the buck converter.
Termination Supply Voltage (Vtt) and Reference
Voltage (VREF)
The Vtt supply voltage is equal to one half of the Vdd
voltage, or approximately 1.25 V. Operational amplifiers
U2A and U2B function as voltage followers to create the Vtt
voltage. The input to U2B is created by the resistive voltage
divider formed by R5 and R6 and divides the 2.5 V Vdd
supply by two to form the VREF reference voltage. Also, U2B
provides filtering to remove any of the high frequency
switching noise that is results from the synchronous buck
converter. The Vtt output of the circuit formed by U2A and
transistors Q4 and Q5 tracks the voltage at the non-inverting
terminal by virtue of the voltage follower circuit
configuration. Thus, the output of voltage of the Vtt supply
is referenced to 50% of the 2.5 V Vdd supply, rather than an
absolute 1.25 V reference.
The sink and source ability of the Vtt supply is provided
by MOSFETs Q4 and Q5 which are used to extend the
current capability of the operational amplifier circuit. When
the Vtt supply is in the current sinking mode of operation, Q4
is “OFF” and Q5 is “ON”. The output of U2A will be at a
negative voltage (i.e. –5.0 V) to control the Vgs of the
P-channel MOSFET (Q5) in order to maintain the Vtt
voltage of 1.25 V. In a similar manner, when the Vtt supply
is in the current sourcing mode of operation, Q4 is “ON” and
Q5 is “OFF”. The output of U2A will reach a positive voltage
(i.e. + 4.5 V) to control the Vgs of the N-channel MOSFET
(Q5) in order to maintain the Vtt voltage of 1.25 V. Resistor
R7 is used to isolate the output of U2B from Vtt and the bulk
capacitor C20.
The slew rate of the operational amplifier and the ability
of the bulk capacitors to hold the voltage at 1.25 V under the
load conditions control the transient response of the Vtt
control loop. Note that the bulk capacitors maintain the Vtt
voltage at approximately 1.25 V; therefore, the operational
amplifier is only required to slew its output a relatively small
amount; therefore, the relatively slow slew rate of the
LM358 operational amplifiers is not a limiting factor in the
design.
Standby Power Operation
The demonstration PCB has the provision of providing a
low power standby mode of operation to the DDR memory
system. This mode could be used to provide a 2.5 V low
current standby voltage to the memory ICs when the main
5.0 V input power is not available. A MC33375 (U3)
300 mA low dropout voltage regulator (LDO) was chosen
for the design to provide the 2.5 V standby power. The
MC33375 has an ON/OFF enable pin and is available in a
SOT-223 package. The performance of the standby
regulator was not verified.
Q1, a N-Channel MOSFET, serves as a diode to prevent
current flow back to the main 5.0 volt input power supply
during the standby mode. The MOSFET was chosen instead
of a Schottky diode in order to minimize the voltage drop
and power consumption of the diode.




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