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參數(shù)資料
| 型號： | AND8079 |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | A Low Cost DDR Memory Power Supply Using the NCP1571 Synchronous Buck Converter and a LM358 Based Linear Voltage Regulator |
| 中文描述： | 一種低成本的DDR記憶體電源使用NCP1571同步降壓轉(zhuǎn)換器和基于線性穩(wěn)壓器1 LM358 |
| 文件頁數(shù)： | 2/20頁 |
| 文件大小： | 150K |
| 代理商： | AND8079 |
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 V
dd
voltage of
1.8 V with a V
tt
and V
REF
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 (V
dd
)
The V
dd
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 V
2
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.
control
Termination Supply Voltage (V
tt
) and Reference
Voltage (V
REF
)
The V
tt
supply voltage is equal to one half of the Vdd
voltage, or approximately 1.25 V. Operational amplifiers
U
2A
and U
2B
function as voltage followers to create the V
tt
voltage. The input to U
2B
is created by the resistive voltage
divider formed by R
5
and R
6
and divides the 2.5 V V
dd
supply by two to form the V
REF
reference voltage. Also, U
2B
provides filtering to remove any of the high frequency
switching noise that is results from the synchronous buck
converter. The V
tt
output of the circuit formed by U
2A
and
transistors Q
4
and Q
5
tracks the voltage at the non-inverting
terminal by virtue of the voltage follower circuit
configuration. Thus, the output of voltage of the V
tt
supply
is referenced to 50% of the 2.5 V V
dd
supply, rather than an
absolute 1.25 V reference.
The sink and source ability of the V
tt
supply is provided
by MOSFETs Q
4
and Q
5
which are used to extend the
current capability of the operational amplifier circuit. When
the V
tt
supply is in the current sinking mode of operation, Q
4
is “OFF” and Q
5
is “ON”. The output of U
2A
will be at a
negative voltage (i.e. –5.0 V) to control the V
gs
of the
P-channel MOSFET (Q
5
) in order to maintain the V
tt
voltage of 1.25 V. In a similar manner, when the V
tt
supply
is in the current sourcing mode of operation, Q
4
is “ON” and
Q
5
is “OFF”. The output of U
2A
will reach a positive voltage
(i.e. + 4.5 V) to control the V
gs
of the N-channel MOSFET
(Q
5
) in order to maintain the V
tt
voltage of 1.25 V. Resistor
R
7
is used to isolate the output of U
2B
from V
tt
and the bulk
capacitor C
20
.
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 V
tt
control loop. Note that the bulk capacitors maintain the V
tt
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 (U
3
)
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.
Q
1
, 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.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AND8079D | A Low Cost DDR Memory Power Supply Using the NCP1571 Synchronous Buck Converter and a LM358 Based Linear Voltage Regulator |
| AND8085 | An Introduction to FST |
| AND8085D | An Introduction to FST |
| AND8090 | AC Characteristics of ECL Devices |
| AND8090D | AC Characteristics of ECL Devices |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AND8079D | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:A Low Cost DDR Memory Power Supply Using the NCP1571 Synchronous Buck Converter and a LM358 Based Linear Voltage Regulator |
| AND8085 | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:An Introduction to FST |
| AND8085D | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:An Introduction to FST |
| AND8090 | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC Characteristics of ECL Devices |
| AND8090D | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC Characteristics of ECL Devices |
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