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 C

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 C

creased impedance, due to a lower switching rate, can be

offset by raising C

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

clock frequency.

Lowering Output Impedance

Paralleling two or more LMC7660’s lowers output imped-

ance. Each device must have it’s own pumping capacitor C

but the reservoir capacitor C

5. The composite output resistance is:

DS009136-6

FIGURE 2. Idealized Voltage Converter

DS009136-7

FIGURE 3. Reduce Supply Current by Lowering Oscillator Frequency

DS009136-8

FIGURE 4. Synchronizing to an External Clock

5

www.national.com