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參數(shù)資料
| 型號： | LM2681MDA |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHED CAPACITOR CONVERTER, 160 kHz SWITCHING FREQ-MAX, UUC |
| 封裝： | DIE |
| 文件頁數(shù)： | 7/11頁 |
| 文件大?。?/td> | 234K |
| 代理商： | LM2681MDA |
Pin Description
Pin
Name
Function
Voltage Doubler
Voltage Split
1
V+
Power supply positive voltage input
Positive voltage output
2
GND
Power supply ground input
Same as doubler
3
CAP
Connect this pin to the negative terminal of the
charge-pump capacitor
Same as doubler
4
GND
Power supply ground input
Same as doubler
5
OUT
Positive voltage output
Power supply positive voltage
input
6
CAP+
Connect this pin to the positive terminal of the
charge-pump capacitor
Same as doubler
Circuit Description
The LM2681 contains four large CMOS switches which are
switched in a sequence to double the input supply voltage.
Energy transfer and storage are provided by external capaci-
tors. Figure 2 illustrates the voltage conversion scheme.
When S
2 and S4 are closed, C1 charges to the supply volt-
age V+. During this time interval, switches S
1 and S3 are
open. In the next time interval, S
2 and S4 are open; at the
same time, S
1 and S3 are closed, the sum of the input volt-
age V+ and the voltage across C
1 gives the 2V+ output volt-
age when there is no load. The output voltage drop when a
load is added is determined by the parasitic resistance (R
d-
s(on)
of the MOSFET switches and the ESR of the capacitors)
and the charge transfer loss between capacitors. Details will
be discussed in the following application information section.
Application Information
Positive Voltage Doubler
The main application of the LM2681 is to double the input
voltage. The range of the input supply voltage is 2.5V to
5.5V.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistance. The
voltage source equals 2V+. The output resistance R
out is a
function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, the capacitance and ESR
of C
1 and C2. Since the switching current charging and dis-
charging C
1 is approximately twice as the output current, the
effect of the ESR of the pumping capacitor C
1 will be multi-
plied by four in the output resistance. The output capacitor
C
2 is charging and discharging at a current approximately
equal to the output current, therefore, its ESR only counts
once in the output resistance. A good approximation of R
out
is:
where R
SW is the sum of the ON resistance of the internal
MOSFET switches shown in Figure 2.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, the capacitance and ESR of the output
capacitor C
2:
High capacitance, low ESR capacitors can reduce both the
output reslistance and the voltage ripple.
The Schottky diode D
1 is only needed for start-up. The inter-
nal oscillator circuit uses the OUT pin and the GND pin. Volt-
age across OUT and GND must be larger than 1.8V to insure
the operation of the oscillator. During start-up, D
1 is used to
charge up the voltage at the OUT pin to start the oscillator;
also, it protects the device from turning-on its own parasitic
diode and potentially latching-up. Therefore, the Schottky di-
ode D
1 should have enough current carrying capability to
charge the output capacitor at start-up, as well as a low for-
ward voltage to prevent the internal parasitic diode from
turning-on. A Schottky diode like 1N5817 can be used for
most applications. If the input voltage ramp is less than 10V/
ms, a smaller Schottky diode like MBR0520LT1 can be used
to reduce the circuit size.
Split V+ in Half
Another interesting application shown in the Basic Applica-
tion Circuits is using the LM2681 as a precision voltage di-
vider. . This circuit can be derived from the voltage doubler
by switching the input and output connections. In the voltage
divider, the input voltage applies across the OUT pin and the
GND pin (which are the power rails for the internal oscillator),
therefore no start-up diode is needed. Also, since the
off-voltage across each switch equals V
in/2, the input voltage
can be raised to +11V.
DS100965-14
FIGURE 2. Voltage Doubling Principle
www.national.com
5
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2682C E WAF | 制造商:Texas Instruments 功能描述: |
| LM2682M | 制造商:Maxim Integrated Products 功能描述:VOLT CONVERTER SMD 2682 SOIC8 |
| LM2682M | 制造商:Maxim Integrated Products 功能描述:VOLT CONVERTER SMD 2682 SOIC8 |
| LM2682M/NOPB | 功能描述:IC REG SWITCHD CAP DBL INV 8SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:3.3V 輸入電壓:4.5 V ~ 24 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:125mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-6 包裝:Digi-Reel® 供應(yīng)商設(shè)備封裝:SOT-6 其它名稱:MAX1836EUT33#TG16DKR |
| LM2682M/NOPB | 制造商:Texas Instruments 功能描述:DC/DC Charge Pump Converter IC |
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