Datasheet

LMC7660
www.ti.com SNOSBZ9C –APRIL 1997–REVISED APRIL 2013
Figure 11. 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 capacitor C
osc
(Figure 12). 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 C
r
and C
p
. The increased impedance, due to a lower switching rate, can be offset by
raising C
r
and C
p
until ripple and load current requirements are met.
SYNCHRONIZING TO AN EXTERNAL CLOCK
Figure 13 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 interference. The external clock still passes through
the ÷2 circuit in the 7660, so the pumping frequency will be ½ the external clock frequency.
Figure 12. Reduce Supply Current by Lowering Oscillator Frequency
Figure 13. Synchronizing to an External Clock
Copyright © 1997–2013, Texas Instruments Incorporated Submit Documentation Feedback 7
Product Folder Links: LMC7660