acquisitionZONE Products for the week of November 26, 2001
Dallas Semiconductor (Maxim) Says . . .
Programmable, All-Silicon Oscillator Runs up to 66.6MHz
with No External Components
Dallas Semiconductor introduced the DS1077L, the only oscillator
IC that can accurately generate dual synchronous output frequencies from
4kHz to 66.6MHz without the use of external crystals, resistors, or other
discrete components. The 3V DS1077L provides a low-cost alternative to modular
crystal-based clock oscillators using a minimum of board space. The DS1077L
may be used as a processor peripheral device through a 2-wire interface
for dynamic frequency changes or it may be preprogrammed and used as a fixed-frequency
oscillator.
The DS1077L's internal master oscillator is factory trimmed from 40MHz to 66.6MHz with standard frequencies available off-the-shelf. This, in combination with a programmable 3-bit prescaler and a 1 to 1025 divider, allows virtually limitless combinations of output frequencies.
Dual control pins can be set to act as power-down or output-enable controls,
depending on the application. In the power down mode, the DS1077L uses less
than 5µA of standby current, making it ideal for power-sensitive applications.
All oscillator settings are stored in EEPROM memory providing default conditions
during power-up. The DS1077L has better than 1% absolute frequency accuracy
over temperature or voltage.
analogZone Says . . .
This takes out all the fun of building oscillators: That always seems to start with paying a premium for fast turn around of the only crystal frequency you don't seem to have in your drawer; but that is the whole point. Here is a solution for getting out of the world of crystals in a very large number of applications with an oscillator stability that is tight enough for many of those uses. It is a tidy, convenient, low-cost solution that requires little to no thought and no external components -- that makes it an admirable part. If you are looking for two synchronized frequencies it is a total no-brainer, and if you have an application where you need to change frequencies in real time get on line for a sample now!
The DS1077L is being shipped in four standard master frequencies off-the-shelf at 40.000 MHz, 50.000 MHz, 60.000 MHz, and 66.666 MHz. The lowest divisible frequency from those standards are 4.87 kHz, 6.09 kHz, 7.32 kHz, and 8.13 kHz. The master clock feeds a Mux and two prescalers; the first pre-scaler feeds the same Mux which can be set to select either the main oscillator as an output or a divide of 2, 4, or 8 version of it. The second pre-scaler can be set to 1, 2, 4, or 8 and can then be fed directly to the second output or it can pass through a divider that can be set for any integer from 2 to 1025. The settings that are selected are stored in EEPROM for application at power-up. Control is over a 2-wire interface and frequency changes can be made on the fly. The serial clock can be either 100 kHz, or a fast mode at 400 kHz.
The parts are designed for a 2.7 to 3.6 V supply but the sweet spot looks to be 3.1 V for the standard parts. The rail could also be used for small frequency corrections -- up to about +/-0.2% for the 66 MHz part and as much as +0.6%/-0.8% for the 40 MHz part -- which might allow you to use a standard part for your application instead of a special order frequency. The tempcos also look like they are all optimized for 25 degrees C. With a 3.1-V supply the quiescents increase with the standard frequencies from about 8 mA, to 10 mA, to 11 mA, to 12.5 mA, although the data sheet maximums are about double those numbers. A shutdown mode reduces the drain to 5 uA (max). The outputs swing between 0.4 V (max) to 2.4 V (min).
The DS1077L is in production in SO-8 and micro-SOP-8
and are priced at $1.22 and $1.27, respectively, in 1000-piece lots. Chip-scale
is also available. A higher voltage (5 V) version, the DS1077 is under development.