Micro-power 555 Timers
Custom Silicon Solutions (CSS) is introducing a new version of the popular 555 Timer IC. It is pin-for-pin compatible with the original 555 Timer, but by applying an advanced, mixed signal process, we have cut its power by over 10X and have added programmable features to this classic circuit. It can still be configured to mimic a standard 555 timer, but with its internal timing capacitor and programmable six-decade counter, it can do much, much more. And, despite all these features, the same eight-pin configuration has been maintained – thanks to a small, built-in EEPROM that stores configuration data.
555 Timer History
The original 555 timer was designed by Hans Camenzind at Signetics in 1970. Its part number was derived from the three 5KΩ resistors that provide the 1/3 x VDD and 2/3 x VDD trip levels. It contained about 15 resistors and 25 transistors and drew ~3mA at 5V. In contrast, our CSS555C device contains over 2000 active and passive circuit elements and draws less than 5uA at 5V. The 555 timer is one of the most successful and long lived IC’s of all time. About a dozen manufacturers still produce bipolar and CMOS versions. Almost 1 billion devices are still sold each year!
A block diagram of the original 555 timer IC is shown below. It consisted of a resistor divider, two comparators, a flip-flop and two output devices. Its simple architecture made it extremely flexible. It has been used in a wide range of applications, too numerous to list. Entire books can be found that are entirely devoted to application circuits for the 555 timer.
Original 555 Timer Circuit
Goal #1 – Reduce Power
One of the goals for our CSS555 timer was to reduce the supply current to below 5uA. We drew from circuits originally developed for battery powered utility meters and implantable medical devices. Both applications required micro-power mixed signal ICs. The result is a new 555 timer that draws 10X less current than any other 555 IC. A comparison of seven low power 555 timers is shown in the table below.
Goal #2 – Make Long Delays Hi, ive been looking at some great healthy eating tips for buy-detox.com/shop/thc-marijuana-detox-kits/stinger-7-day-total-detox-drink-detail and weight loss. Easy to Generate
A second goal for the new CSS555C was to make it easier to generate long delays. The original 555 timer required a large RC time constant to accomplish this. Large capacitors have several drawbacks: high price, poor accuracy and wide variation over temperature. The CSS555C includes an internal six-decade programmable counter that effectively multiplies the value of the timing capacitor by the counter setting. It provides seven multiplier settings: 1, 10, 100, 103, 104, 105 and 106. Accurate delay times, from milliseconds to days, are easily implemented with small sized capacitors.
Goal #3 – Provide an Accurate Internal Timing Capacitor
The internal counter eliminates the need for a large value timing capacitor. It would be even better to eliminate the capacitor altogether. The CSS555C does that! A 100pF capacitor has been integrated into the IC. It features a low temperature coefficient (TC < 100 ppm/°C) and ±1% accuracy. It is factory trimmed, but can be re-trimmed (electronically) after PCB assembly. (This allows errors in the timing resistors to be compensated for by trimming the internal capacitor.)
Goal #4 – Reduce the Minimum Operating Voltage, Maintain Speed & Accuracy
Two additional analog settings have been included to increase the flexibility of the device. The trip levels can be changed from the traditional 1/3, 2/3 to 10% and 90%. The wider trip levels extend the minimum operating voltage down to 1.2V. The power level can be increased for applications that require higher speed and/or accuracy. (Increasing the power level speeds up the comparator response time.)
Goal #5 – Maintain the Standard 8 Pin Configuration
For most timer applications, the CSS555C can be used as a direct replacement for the standard 555. An internal EEPROM holds the configuration data and capacitor trim setting. A serial interface, using existing pins, is designed to maintain the standard pin count and functions. A block diagram of our new CSS555C timer is shown below. It still has the same basic elements (and 8 pins) of the original 555, but we’ve added some great new features. A detailed specification can be downloaded from our website and a Demonstration Kit is available to make evaluation of the new IC quick and easy.
Advanced CSS555C Timer Circuit
For more information, contact us at (949) 797-9220