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參數(shù)資料
| 型號： | LM2687MM |
| 英文描述： | IC-SWT CAP VOLT INVERTER |
| 中文描述： | 集成電路SWT第伏逆變器 |
| 文件頁數(shù)： | 6/9頁 |
| 文件大?。?/td> | 244K |
| 代理商： | LM2687MM |
Detailed Device Description
The LM2685 CMOS charge pump voltage converter oper-
ates as an input voltage doubler, +5V regulator and inverter
for an input voltage in the range of +2.85V to +6.5V. It deliv-
ers maximum load currents of 50mA and 15mA for the regu-
lated +5V and the inverted output voltages respectively, with
an operating current of only 800μA. It also has a typical shut-
down current of 6μA. All these performance qualities make
the LM2685 an ideal device for battery powered systems.
The LM2685 has three main functional blocks: a voltage
doubler, a low dropout (LDO) regulator, and a voltage in-
verter. Figure 1shows the LM2685 functional block diagram.
Voltage Doubler
The voltage doubler stage doubles the input voltage V
,
within the range of +2.85V to +5.4V. For V
above 5.4V, the
doubler shuts off and the input voltage is passed directly to
V
DBL
via an internal power switch.
The doubler contains four large CMOS switches which are
switched in a sequence to double the input supply voltage.
Figure 2illustrates the voltage conversion scheme. When S2
and S4 are closed, C1 charges to the supply voltage V
.
During this time interval, switches S1 and S3 are open. In the
next time interval, S2 and S4 are opened at the same time,
S1 and S3 are closed, the sum of the input voltage V
and
the voltage across C1 gives the 2V
and the voltage across
C2 gives the 2V
at V
output. V
supplies the LDO
regulator. It is recommended not to load V
DBL
when V
05
has
a load of 50mA. For proper operation, the sum of V
DBL
and
V
05
loads must not be more than 50mA.
The Schottky diode D1 is only needed for start-up. The inter-
nal oscillator circuit uses the V
DBL
and GND pins. The volt-
age across them must be larger than 1.8V to ensure the op-
eration of the oscillator. During start-up, D1 is used to charge
up the voltage at V
pin to start the oscillator; it also pro-
tects the device from turning on its own parasitic diode and
potentially latching up. The diode should have enough cur-
rent carrying capability to change capacitor C3 at start-up, as
well as a low forward voltage to prevent the internal parasitic
diode from turning on. A Schottky diode like 1N5817 can be
used for most applications. If the input ramp is less than
10V/ms, a smaller schottky diode like MBR0520LT1 can be
used to reduce the circuit size.
+5 LDO Regulator
V
DBL
is the input to an LDO regulator that regulates it to a +5
output voltage at V
. V
is tied to V
through a series
switch PSW. The LDO output capacitor (4.7μF Tantalum)
may be tied to either V
05
or V
PSW
.
Inverter
From the V
output, a 5V output is created at V
by
means of an inverting charge pump. This negative output is
unregulated, meaning that it’s output will droop as the load
current at V
increases. The inverter contains four large
CMOS switches which are in a sequence to invert the input
supply voltage. Figure 3 illustrates the voltage conversion
scheme. When S1 and S3 are closed, C1 charges to the
supply voltage V
. During this time interval, switches S2
and S4 are open. In the second time interval, S1 and S3 are
open;at the same time, S2 and S4 are closed, C1 is charging
C2. After a number of cycles, the voltage cross C2 will be
pumped to V
. Since the anode of C2 is connected to
ground, the output at the cathode of C2 equals (V
) when
there is no load current. The output voltage drop when a load
DS101100-3
FIGURE 1. Functional Block Diagram
DS101100-4
FIGURE 2. Voltage Doubler Principle
L
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM2687MM | 制造商:Texas Instruments 功能描述:VOLT CONVERTER SMD 2687 MSOP8 |
| LM2687MM/NOPB | 功能描述:電荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 輸出電壓:- 1.5 V to - 5.5 V, 3 V to 11 V 輸出電流:100 mA 電源電流:1 mA 最大工作溫度:+ 70 C 封裝 / 箱體:SOIC-8 Narrow 封裝:Tube |
| LM2687MMX | 功能描述:電荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 輸出電壓:- 1.5 V to - 5.5 V, 3 V to 11 V 輸出電流:100 mA 電源電流:1 mA 最大工作溫度:+ 70 C 封裝 / 箱體:SOIC-8 Narrow 封裝:Tube |
| LM2687MMX/NOPB | 功能描述:電荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 輸出電壓:- 1.5 V to - 5.5 V, 3 V to 11 V 輸出電流:100 mA 電源電流:1 mA 最大工作溫度:+ 70 C 封裝 / 箱體:SOIC-8 Narrow 封裝:Tube |
| LM2694EVAL | 功能描述:電源管理IC開發(fā)工具 LM2694 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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