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Keywords: DS1077, power reduction, econoscillator, roboclock, LTC1799, programmable oscillator

APPLICATION NOTE 171

Using Programmable Oscillators to Generate and

Control System Clocks

May 28, 2002

Abstract: In a processor-controlled system, power consumption is directly proportional to the clock speed

of the processor. If the computational load on the processor is small, most of this power is wasted.

Modulating the processor speed to the slowest possible frequency while maintaining the minimum

frequency generator. The frequency of the two, synchronous, oscillator outputs are user adjustable in

sub-multiples of the master frequency through the use of two on-chip programmable prescalers and

divider. The frequency and mode settings are configurable "on-the-fly" and stored in EEPROM using a

2-wire serial interface which can address up to eight DS1077s on a single 2-wire bus. Two digital control

inputs, CTRL0 and CTRL1 are also capable of controlling the frequency or mode. Also available is the

DS1077L, which is a 3V version of the DS1077 and is capable of generating frequencies from 4.87kHz

up to 66.66MHz. Throughout the remainder of this document, unless otherwise specified, both the 3V

and 5V versions of the DS1077 will be referred to as the DS1077.

This application note will show several examples of using a DS1077. It will show how a DS1077 can be

used in place of a crystal to clock an 8051 microcontroller and a Microchip PIC™ microcontroller. This

independent of each other, they are both controlled by a common 2-wire master. This 2-wire master can

be part of a larger system that needs control of its subsystems. The master can decide to reduce the

operating frequencies of the subsystems that are not currently needed in order to conserve power,

reduce heat in some cases, or maybe even reduce EMI radiation. It is sometimes advantageous to use a

DS1077 to avoid running high frequency clocks throughout a large system, like over a backplane. It is