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PDF LMC7660 Data sheet ( Hoja de datos )
| Número de pieza | LMC7660 | |
| Descripción | Switched Capacitor Voltage Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LMC7660 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
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April 1997
LMC7660
Switched Capacitor Voltage Converter
General Description
The LMC7660 is a CMOS voltage converter capable of con-
verting a positive voltage in the range of +1.5V to +10V to
the corresponding negative voltage of −1.5V to −10V. The
LMC7660 is a pin-for-pin replacement for the
industry-standard 7660. The converter features: operation
over full temperature and voltage range without need for an
external diode, low quiescent current, and high power effi-
ciency.
The LMC7660 uses its built-in oscillator to switch 4 power
MOS switches and charge two inexpensive electrolytic ca-
pacitors.
Features
n Operation over full temperature and voltage range
without an external diode
n Low supply current, 200 µA max
n Pin-for-pin replacement for the 7660
n Wide operating range 1.5V to 10V
n 97% Voltage Conversion Efficiency
n 95% Power Conversion Efficiency
n Easy to use, only 2 external components
n Extended temperature range
n Narrow SO-8 Package
Block Diagram
Pin Configuration
DS009136-1
Ordering Information
Package
8-Lead Molded DIP
8-Lead Molded Small Outline
DS009136-2
Temperature Range
Industrial
−40˚C to +85˚C
LMC7660IN
LMC7660IM
NSC
Drawing
N08E
M08A
© 1997 National Semiconductor Corporation DS009136
www.national.com
1 page  
Application Information (Continued)
DS009136-6
FIGURE 2. Idealized Voltage Converter
Typical Applications
Changing Oscillator Frequency
It is possible to dramatically reduce the quiescent operating
current of the LMC7660 by lowering the oscillator frequency.
The oscillator frequency can be lowered from a nominal 10
kHz to several hundred hertz, by adding a slow-down ca-
pacitor Cosc (Figure 3). As shown in the Typical Performance
Curves the supply current can be lowered to the 10 µA
range. This low current drain can be extremely useful when
used in µPower and battery back-up equipment. It must be
understood that the lower operating frequency and supply
current cause an increased impedance of Cr and Cp. The in-
creased impedance, due to a lower switching rate, can be
offset by raising Cr and Cp until ripple and load current re-
quirements are met.
Synchronizing to an External Clock
Figure 4 shows an LMC7660 synchronized to an external
clock. The CMOS gate overrides the internal oscillator when
it is necessary to switch faster or reduce power supply inter-
ference. The external clock still passes through the ÷2 circuit
in the 7660, so the pumping frequency will be 1⁄2 the external
clock frequency.
FIGURE 3. Reduce Supply Current by Lowering Oscillator Frequency
DS009136-7
FIGURE 4. Synchronizing to an External Clock
Lowering Output Impedance
Paralleling two or more LMC7660’s lowers output imped-
ance. Each device must have it’s own pumping capacitor Cp,
but the reservoir capacitor Cr is shared as depicted in Figure
5. The composite output resistance is:
5
DS009136-8
www.national.com
5 Page 
Physical Dimensions inches (millimeters)
Molded Small Outline Package (M)
Order Number LMC7660IM
NS Package Number M08A
Molded Dual-In-Line Package (N)
Order Number LMC7660IN
NS Package Number N08E
11
www.national.com
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LMC7660.PDF ] | |
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