PLL clock generators multiply

Torex Semiconductor's new XC25BS3 series of high-frequency PLL clock generator ICs, with built-in divider and multiplier circuits, offers designers a low-cost alternative to crystals.

Torex Semiconductor's new XC25BS3 series of high-frequency PLL clock generator ICs, with built-in divider and multiplier circuits, offers designers a low-cost alternative to 'more expensive' traditional crystal oscillators.

Supplied in the space-saving microminiature SOT-26 package, the XC25BS3 is primarily intended to supply clock signals to portable and handheld equipment although it will prove extremely useful for any design that has a crystal requirement.

The new PLL clock generator IC makes use of external clock signals that are to be found in most electronic systems, from the counter of a CPU for example.

Using this low-frequency (a few tens of kHz) clock signal as input, the XC25BS3 is able to output a clock signal of a few tens of MHz that can then be used as the main clock signal to another chip.

The output frequency is a multiplication factor of the input and in sync with it.

Input frequencies can be from 14kHz to 35MHz.

Also, by using a program on the CPU side of the circuit to change the supplied clock input, so it is possible to vary the output clock frequency of the XC25BS3.

Employing low-power CMOS technology, the new XC25BS3 series combines crystal oscillator circuits, divider circuits and multiplier PLL circuits in a single chip.

Advanced laser trimming techniques used in manufacture allow designers to select factory-set divider ratios from 1 to 2047 and multiplier ratios from 20 to 2047, thus giving them the choice of an extremely wide range of frequency multiplication factors.

Another significant result of this trimming is an output clock signal of extremely small jitter - for example 30ps at an output frequency of 80MHz.

The XC25BS3's inherent flexibility lies in its two outputs.

The first, Q0, is equal to the product of the reference oscillation and the chosen mutiplier/divider ratio within a range of 9 to 80MHz.

The second output, Q1, is a tristate output selectable from reference oscillation, comparative frequencies, PLL frequencies/2 or comparative frequencies/2.

Output comparative frequencies cover a 14 to 500kHz range.

The device incorporates a CE function enabling designers to reduce current consumption down to 5uA (maximum) in standby mode.

The new XC25BS3 has an operating voltage range of 3.0 to 5.0V an operating temperature range of -30 to +80C, and a power dissipation of 150mW.

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