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参数资料
| 型号： | LM2765M6/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHED CAPACITOR CONVERTER, 100 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | LEAD FREE, SOT-23, 6 PIN |
| 文件页数： | 6/9页 |
| 文件大小： | 208K |
| 代理商： | LM2765M6/NOPB |
Circuit Description
The LM2765 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 LM2765 is to double the input
voltage. The range of the input supply voltage is 1.8V 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, and the capacitance and
ESR of C
1 and C2. Since the switching current charging and
discharging C
1 is approximately twice as the output current,
the effect of the ESR of the pumping capacitor C
1 will be
multiplied by four in the output resistance. The output ca-
pacitor C
2 is charging and discharging at a current approxi-
mately 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. R
SW is typically 8 for
the LM2765.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency as well as the capacitance and ESR of
the output capacitor C
2:
High capacitance, low ESR capacitors can reduce both the
output resistance and the voltage ripple.
The Schottky diode D
1 is only needed to protect the device
from turning-on its own parasitic diode and potentially
latching-up. During start-up, D
1 will also quickly charge up
the output capacitor to V
IN minus the diode drop thereby de-
creasing the start-up time. Therefore, the Schottky diode D
1
should have enough current carrying capability to charge the
output capacitor 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 applica-
tions. If the input voltage ramp is less than 10V/ms, a smaller
Schottky diode like MBR0520LT1 can be used to reduce the
circuit size.
Shutdown Mode
A shutdown (SD) pin is available to disable the device and
reduce the quiescent current to 0.1 A. In normal operating
mode, the SD pin is connected to ground. The device can be
brought into the shutdown mode by applying to the SD pin a
voltage greater than 40% of the V+ pin voltage.
Capacitor Selection
As discussed in the
Positive Voltage Doubler section, the
output resistance and ripple voltage are dependent on the
capacitance and ESR values of the external capacitors. The
output voltage drop is the load current times the output resis-
tance, and the power efficiency is
Where I
Q(V+) is the quiescent power loss of the IC device,
and I
L
2R
out is the conversion loss associated with the switch
on-resistance, the two external capacitors and their ESRs.
The selection of capacitors is based on the specifications of
the dropout voltage (which equals I
out Rout), the output volt-
age ripple, and the converter efficiency. Low ESR capacitors
(
Table 1) are recommended to maximize efficiency, reduce
the output voltage drop and voltage ripple.
TABLE 1. Low ESR Capacitor Manufacturers
Manufacturer
Phone
Website
Capacitor Type
Nichicon Corp.
(847)-843-7500
www.nichicon.com
PL & PF series, through-hole aluminum
electrolytic
AVX Corp.
(843)-448-9411
www.avxcorp.com
TPS series, surface-mount tantalum
Sprague
(207)-324-4140
www.vishay.com
593D, 594D, 595D series, surface-mount tantalum
Sanyo
(619)-661-6835
www.sanyovideo.com
OS-CON series, through-hole aluminum
electrolytic
DS101281-14
FIGURE 2. Voltage Doubling Principle
LM2765
www.national.com
6
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相关代理商/技术参数 |
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| LM2765M6X | 功能描述:电荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube |
| LM2765M6X/NOPB | 功能描述:电荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube |
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| LM2766M6 | 功能描述:电荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube |
| LM2766M6/NOPB | 功能描述:电荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube |
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