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參數(shù)資料
| 型號： | LM26480SQ-BF/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 2.4 A SWITCHING REGULATOR, 2400 kHz SWITCHING FREQ-MAX, QCC24 |
| 封裝： | 4 X 4 MM, 0.80 MM HEIGHT, LLP-24 |
| 文件頁數(shù)： | 6/30頁 |
| 文件大?。?/td> | 2447K |
| 代理商： | LM26480SQ-BF/NOPB |
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DC/DC Converters
OVERVIEW
The LM26480 provides the DC/DC converters that supply the
various power needs of the application by means of two linear
low dropout regulators, LDO1 and LDO2, and two buck con-
verters, SW1 and SW2. The table here under lists the output
characteristics of the various regulators.
Supply Specification
Supply
Load
Output
V
OUT Range (V)
I
MAX
Maximum Output
Current (mA)
LDO1
analog
1.0 to 3.5
300
LDO2
analog
1.0 to 3.5
300
SW1
digital
0.8 to 2.0
1500
SW2
digital
1.0 to 3.3
1500
LINEAR LOW DROPOUT REGULATORS (LDOs)
LDO1 and LDO2 are identical linear regulators targeting ana-
log loads characterized by low noise requirements. LDO1 and
LDO2 are enabled through the ENLDO pin.
30040404
NO-LOAD STABILITY
The LDOs will remain stable and in regulation with no external
load. This is an important consideration in some circuits, for
example, CMOS RAM keep-alive applications.
SW1, SW2: Synchronous Step-
Down Magnetic DC/DC Converters
FUNCTIONAL DESCRIPTION
The LM26480 incorporates two high-efficiency synchronous
switching buck regulators, SW1 and SW2, that deliver a con-
stant voltage from a single Li-Ion battery to the portable
system processors. Using a voltage mode architecture with
synchronous rectification, both bucks have the ability to de-
liver up to 1500 mA depending on the input voltage and output
voltage (voltage head room), and the inductor chosen (max-
imum current capability).
There are three modes of operation depending on the current
required - PWM, PFM, and shutdown. PWM mode handles
current loads of approximately 70 mA or higher, delivering
voltage precision of +/-3% with 90% efficiency or better.
Lighter output current loads cause the device to automatically
switch into PFM for reduced current consumption (I
Q = 33 A
typ.) and a longer battery life. The Standby operating mode
turns off the device, offering the lowest current consumption.
PWM or PFM mode is selected automatically or PWM mode
can be forced through the setting of the buck control register.
Both SW1 and SW2 can operate up to a 100% duty cycle
(PMOS switch always on) for low drop out control of the output
voltage. In this way the output voltage will be controlled down
to the lowest possible input voltage.
Additional features include soft-start, under-voltage lock-out,
current overload protection, and thermal overload protection.
CIRCUIT OPERATION DESCRIPTION
A buck converter contains a control block, a switching PFET
connected between input and output, a synchronous rectify-
ing NFET connected between the output and ground
(BCKGND pin) and a feedback path. During the first portion
of each switching cycle, the control block turns on the internal
PFET switch. This allows current to flow from the input
through the inductor to the output filter capacitor and load. The
inductor limits the current to a ramp with a slope of
by storing energy in a magnetic field. During the second por-
tion of each cycle, the control block turns the PFET switch off,
blocking current flow from the input, and then turns the NFET
synchronous rectifier on. The inductor draws current from
ground through the NFET to the output filter capacitor and
load, which ramps the inductor current down with a slope of
The output filter stores charge when the inductor current is
high, and releases it when low, smoothing the voltage across
the load.
SYNC FUNCTION
The LM26480SQ-BF is the only version of the part that has
the ability to use an external oscillator. The source must be
13 MHz nominal and operate within a range of 15.6 MHz and
10.4 MHz, proportionally the same limits as the 2.0 MHz in-
ternal oscillator. The LM26480SQ-BF has an internal divider
which will divide the speed down by 6.5 to the nominal 2MHz
and use it for the regulators. This SYNC function replaces the
internal oscillator and works in forced PWM only. The buck
regulators no longer have the PFM function enabled. When
the LM26480SQ-BF is sold with this feature enabled, the part
will not function without the external oscillator present.
PWM OPERATION
During PWM operation the converter operates as a voltage-
mode controller with input voltage feed forward. This allows
the converter to achieve excellent load and line regulation.
The DC gain of the power stage is proportional to the input
voltage. To eliminate this dependence, feed forward voltage
inversely proportional to the input voltage is introduced.
INTERNAL SYNCHRONOUS RECTIFICATION
While in PWM mode, the buck uses an internal NFET as a
synchronous rectifier to reduce rectifier forward voltage drop
and associated power loss. Synchronous rectification pro-
vides a significant improvement in efficiency whenever the
output voltage is relatively low compared to the voltage drop
across an ordinary rectifier diode.
www.national.com
14
LM26480
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM26480SQX-BF/NOPB | 2.4 A SWITCHING REGULATOR, 2400 kHz SWITCHING FREQ-MAX, QCC24 |
| LM2661M/NOPB | SWITCHED CAPACITOR CONVERTER, 80 kHz SWITCHING FREQ-MAX, PDSO8 |
| LM2660MMX/NOPB | SWITCHED CAPACITOR CONVERTER, 40 kHz SWITCHING FREQ-MAX, PDSO8 |
| LM2661MM/NOPB | SWITCHED CAPACITOR CONVERTER, 80 kHz SWITCHING FREQ-MAX, PDSO8 |
| LM2661MMX/NOPB | SWITCHED CAPACITOR CONVERTER, 80 kHz SWITCHING FREQ-MAX, PDSO8 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM26480SQX-AA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Externally Programmable Dual High-Current Step-Down DC/DC and Dual Linear Regulators |
| LM26480SQX-AA/NOPB | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| LM26480SQX-BF | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Externally Programmable Dual High-Current Step-Down DC/DC and Dual Linear Regulators |
| LM26480SQX-BF/NOPB | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 Externally Pgrm Dual Hi-Current SD DC/DC RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM26484 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Power Management Unit |
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