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參數(shù)資料
| 型號： | LM2696 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 3A, Constant On Time Buck Regulator |
| 中文描述： | 第3A，恒定時間降壓穩(wěn)壓器 |
| 文件頁數(shù)： | 10/19頁 |
| 文件大?。?/td> | 833K |
| 代理商： | LM2696 |
Application Information
(Continued)
It can be seen that the average output voltage is higher than
the gained up reference by exactly half the output voltage
ripple. The output voltage may then be appended according
to the voltage ripple. The appended V
OUT
term may be
expressed using the relationship:
One should note that for high output voltages (
>
5V), a load
of approximately 15 mA may be required for the output
voltage to reach the desired value.
INPUT CAPACITOR
Because PV
is the power rail from which the output voltage
is derived, the input capacitor is typically selected according
to the load current. In general, package size and ESR de-
termine the current capacity of a capacitor. If these criteria
are met, there should be enough capacitance to prevent
impedance interactions with the source. In general, it is
recommended to use a low ESR, high capacitance electro-
lytic and ceramic capacitor in parallel. Using two capacitors
in parallel ensures adequate capacitance and low ESR over
the operating range. The Sanyo MV-WX series electrolytic
capacitors and a ceramic capacitor with X5R or X7R dielec-
tric are an excellent combination. To calculate the input
capacitor RMS, one may use the following relationship:
that can be approximated by,
Typical values are 470 μF for the electrolytic capacitor and
0.1 μF for the ceramic capacitor.
AV
IN
CAPACITOR
AV
is the analog bias rail of the device. It should be
bypassed externally with a small (1 μF) ceramic capacitor to
prevent unwanted noise from entering the device. In a shut-
down state the current needed by AV
will drop to approxi-
mately 12 μA, providing a low power sleep state.
In most cases of operation, AV
is connected to PV
IN
;
however, it is possible to have split rail operation where AV
IN
is at a higher voltage than PV
. AV
should never be lower
than PV
. Splitting the rails allows the power conversion to
occur from a lower rail than the AV
IN
operating range.
SOFT-START CAPACITOR
The SS capacitor is used to slowly ramp the reference from
0V to its final value of 1.25V (during shutdown this pin will be
discharged to 0V). This controlled startup ability eliminates
large in-rush currents in an attempt to charge up the output
capacitor. By changing the value of this capacitor, the dura-
tion of the startup may be changed accordingly. The startup
time may be calculated using the following relationship:
Where I
is the soft-start pin source current (1 μA typical)
that may be found in the electrical characteristics table.
While the C
capacitor can be sized to meet the startup
requirements, there are limitations to its size. If the capacitor
is too small, the soft-start will have little effect as the refer-
ence voltage is rising faster than the output capacitor can be
charged causing the part to go into current limit. Therefore a
minimum soft-start time should be taken into account. This
can be determined by:
20153431
FIGURE 2. Average and Ripple Output Voltages
L
www.national.com
10
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2696EVAL | 功能描述:電源管理IC開發(fā)工具 LM2696 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM2696MXA | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2696MXA/NOPB | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 3A,CONSTANT ON TIME BUCK REG 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(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM2696MXAX | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 24V 16-Pin TSSOP EP T/R |
| LM2696MXAX/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
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