rev. 1.0 1/15 copyright ? 2015 by silicon laboratories an856 an856 s ilicon l abs ? ts3004 vs . the cmos 555: d etermining l owest s upply c urrent for b attery -p owered a pplications 1. introduction the 555 timer is the workhorse of ics, with close to a billion of them manu factured every year. introduced in 1972, the 555 is still in widespr ead use because of its ease of use, reasonable price, and good stabilit y. it can be found in a wide variety of applications for oscilla tion, timing and pulse gene ration. but what if you ne ed a timer ic for ultra- long life, low-frequency battery-powered/portable applicatio ns where a low supply current is a requirement? is the CMOS555 timer your best option? in this application note, we will compar e the CMOS555 timer to the silicon la bs? ts3004, a single-supply timer ic fully specified to operate over a supply volta ge range of 1.55 v to 5.25 v while consuming 1.9 a supply current. requiring only a resistor to set the base output freque ncy (or output period) with a 50% duty cycle, the ts3004 timer/oscillator is compact, easy-to-use, and versatile. 2. ts3004 vs. the CMOS555 the ts3004 timer has an output frequency range of 0. 0043 hz to 300 khz while ma intaining a very low supply current. to demonstrate just how low the supply current is for the ts3004, we will compare the supply current consumption of the ts3004 to a CMOS555 timer side-by-si de, with an output frequency of 1 hz for both timers. for this example, a texas instruments lmc555 is used as the cmos version of the industry-standard 555 series of general-purpose timers. the lmc555 offers 1.5 v s upply operating voltage and requires a single external resistor and a capacitor. first, the output frequencies of bo th the ts3004 and CMOS555 were set to 1 hz. to set the ts3004 output frequency to 1 hz, the appropriate frequency divider in put setting must be selected as well as the necessary rset resistance. the equation defining the fout frequenc y is found in the data sheet. as shown in equation 1, fout is defined by only one external component, the rset resistor. equation 1. the frequency divider input table in the data sheet shows that the correct setting to obtain a 1 hz output frequency is 101, which is equivalent to 5. by substituting the appropriate value of 5 for fdiv2:0 into equation [1] and using an output frequency of 1 hz, the appropriate rset value of 3.3 m ? can be calculated. to set the output frequency of the CMOS555 timer to 1 hz, the oscillati ng frequency is defined by two external components, a ?c? capacitor, and an ?r c ? resistor. the equation defining the output frequency is found in the lmc555 data sheet. equation 2. fout 1.08 10 11 ? 8 fdiv2:0 r set ? ---------------------------------------- - = f 1 1.4 c r ? c ? -------------------------------- - =
an856 2 rev. 1.0 substituting the output frequency of 1 hz and a standard capacitor value of 0.1 f, the necessary r c resistance of 7.14 m ? can be calculated. in setting the output frequency of both timers, the ts30 04 offers an advantage because it only requires one component instead of the two external components required by the CMOS555. to compare the supply currents of both timers side-by- side, a few supply voltages were applied while both supply currents were recorded. ta ble 1 displays the results. as shown in table 1, at 1.5 v, the ts3004 consumes a factor of 26 less supply current. with a 2.5 v supply, the ts3004 consumes a factor of 40 less supply current. with a 3.3 v supply, the ts3004 consumes a factor of 38 less supply current. in summary, the CMOS555 ic uses much more supply current than can be supported in battery or portable applications. for all voltages within its supply range, the ts3004 save s a significant amount of s upply current, which can help extend battery life in battery-powered applications. th ese applications include ultra-long life, low-frequency battery-powered/portable applications, such as micropower pwm control, pulse-position modulation control, clock generation, and sequent ial timing. the ts3004 can also be used as a low-parts-count mi cropower oscillator and compact replacement for cryst al and ceramic oscillators. for additional information, see the following: ?? ts3004 timer ic ?? ts3004 data sheet ?? silicon labs? family of timer ics table 1. supply current per supply voltage supply voltage ts3004 supply current CMOS555 supply current 1.5 v 1.9 a50 a 2.5 v 2.0 a8 1 a 3.3 v 2.3 a8 7 a
disclaimer silicon laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the silicon laboratories products. characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "typical" parameters provided can and do vary in different applications. application examples described herein are for illustrative purposes only. silicon laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. silicon laboratories shall have no liability for the consequences of use of the information supplied herein. this document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. the products must not be used within any life support system without the specific written consent of silicon laboratories. a "life support system" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. silicon laboratories products are generally not intended for military applications. silicon laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons. trademark information silicon laboratories inc., silicon laboratories, silicon labs, silabs and the silicon labs logo, cmems?, efm, efm32, efr, energy micro, energy micro logo and combinations thereof, "the world?s most energy friendly microcontrollers", ember?, ezlink?, ezmac?, ezradio?, ezradiopro?, dspll?, isomodem ?, precision32?, proslic?, siphy?, usbxpress? and others are trademarks or registered trademarks of silicon laboratories inc. arm, cortex, cortex-m3 and thumb are trademarks or registered trademarks of arm holdings. keil is a registered trademark of arm limited. all other products or brand names mentioned herein are trademarks of their respective holders. http://www.silabs.com silicon laboratories inc. 400 west cesar chavez austin, tx 78701 usa smart. connected. energy-friendly products www.silabs.com/products quality www.silabs.com/quality support and community community.silabs.com
|
