- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄384654 > MAX1761 (Maxim Integrated Products, Inc.) Small, Dual, High-Efficiency Buck Controller for Notebooks PDF資料下載
參數(shù)資料
| 型號： | MAX1761 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Small, Dual, High-Efficiency Buck Controller for Notebooks |
| 中文描述： | 小型、雙路、高效率buck控制器，用于筆記本電腦 |
| 文件頁數(shù)： | 16/23頁 |
| 文件大?。?/td> | 473K |
| 代理商： | MAX1761 |
M
Small, Dual, High-Efficiency
Buck Controller for Notebooks
16
______________________________________________________________________________________
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered
iron is inexpensive and works well at 250kHz. The core
must be large enough not to saturate at the peak induc-
tor current (I
PEAK
):
I
PEAK
= I
LOAD(MAX)
- 1/2 LIR
I
LOAD(MAX)
=
(1 - 0.5 LIR) I
LOAD(MAX)
Setting Current Limit
The minimum current-limit threshold must be great
enough to support the maximum load current plus
some safety margin. For the circuit in Figure 1, with a
desired 2.5A maximum load current, the worst-case
current limit is set at 3.0A, providing a 20% safety mar-
gin. Under these conditions, the valley of the inductor
current waveform occurs at:
I
VALLEY
= I
LOAD(MAX)
- 1/2 LIR
I
LOAD(MAX)
=
(1 - 0.5 LIR) I
LOAD(MAX)
The required valley current is I
VALLEY
= 3A - 1/2 (0.35)
2.5A = 2.56A. Next, the current-sense feedback volt-
age must be scaled taking into account the tolerance of
the CS_ current-limit threshold and the maximum MOS-
FET drain-source on-resistance (R
DS(ON)
) variation
over temperature. The minimum current-limit threshold
at the CS_ pins is 92mV. The worst-case maximum
value for (R
DS(ON)
) over temperature is 50m
. At
2.56A, the voltage developed across the low-side
switch is 128mV. A resistive voltage-divider with a
0.703 attenuation ratio is necessary to scale this volt-
age to the 92mV CS_ threshold.
A current-sense resistor can be used if a more accu-
rate current limit is needed than is available when using
the MOSFET (R
DS(ON)
(Figure 6). Placing the sense
resistor between the source of the low-side MOSFET
and ground provides a very accurate sense point for
the CS_ inputs. Alternatively, a small sense resistor can
be used in series with the low-side MOSFET to ballast
the device and reduce the temperature coefficient of
the current limit when sensing at the inductor
’
s
switched node. This provides a compromise between
sensing across the MOSFET device alone or using a
large sense resistor.
Output Capacitor Selection
The output filter capacitor must have low enough effec-
tive series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy the stability criterion.
In CPU V
CORE
converters and other applications where
the output is subject to violent load transients, the out-
put capacitor
’
s size depends on how much ESR is
needed to prevent the output from dipping too low
under a load transient. Ignoring the sag due to finite
capacitance:
In non-CPU applications, the output capacitor
’
s size
depends on how much ESR is needed to maintain an
acceptable level of output voltage ripple:
The actual required μF capacitance value relates to the
physical size needed to achieve low ESR as well as to
the chemistry of the capacitor technology. Thus, the
capacitor is usually selected by ESR and voltage rating
rather than by capacitance value (this is true of tanta-
lums, SP, POS, and other electrolytics).
When using low-capacitance filter capacitors, such as
ceramic or polymer types, capacitor size is usually
determined by the capacitance needed to prevent
V
SAG
and V
SOAR
from causing problems during load
transients. Generally, once enough capacitance is
added to meet the V
SOAR
requirement, undershoot at
the rising load edge is no longer a problem (see the
V
SAG
equation in
Design Procedure
). The amount of
overshoot due to stored inductor energy can be calcu-
lated as:
where I
PEAK
is the peak inductor current.
Stability Considerations
Stability is determined by the value of the ESR zero rel-
ative to the switching frequency. The point of instability
is given by the following equation:
=
ESR
π
V
L
(
≈
×
2CV
I
PEAK
OUT
2
)
R
Vp-p
LIR I
ESR
LOAD(MAX)
≤
R
V
I
ESR
DIP
LOAD(MAX)
≤
L
-
=
×
×
=
2 5 20
350
2 5
0 35 2 5
.
20
7 1
.
.
(
kHz
.
)
.
V
V
V
V
A
H
μ
相關PDF資料 |
PDF描述 |
|---|---|
| MAX1761EEE | Replaced by TMS320VC5506 : Digital Signal Processor 100-LQFP |
| MAX1763 | 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter |
| MAX1763EEE | 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter |
| MAX1763EUE | Replaced by TMS320C6410 : Digital Signal Processors 68-PLCC -40 to 85 |
| MAX1765 | Replaced by TMS320C6410 : Digital Signal Processors 68-PLCC -40 to 85 |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX17611GTL+ | 制造商:Maxim Integrated Products 功能描述:IMVP7 CPU AND GRAPHICS CONTROLLER - Rail/Tube |
| MAX17611GTL+T | 制造商:Maxim Integrated Products 功能描述:IMVP7 CPU AND GRAPHICS CONTROLLER - Tape and Reel |
| MAX1761EEE | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1761EEE+ | 功能描述:DC/DC 開關控制器 Dual Buck Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1761EEE+T | 功能描述:DC/DC 開關控制器 Dual Buck Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
發(fā)布緊急采購，3分鐘左右您將得到回復。