application note ts3v555 : a low cost 2v to 5v step up converter AN850/0299 by g. augustoni ? the ts3v555 is the cmos 3 volt version of the famous versatile 555 timer which has the ability to work with voltage as low as 2v. this application note shows how to use this feature to build a micropower low cost step-up converter from 2v up to 5v. the ts3v555 is used in a schematic that multiplies the supply voltage by a constant ratio fixed by an external resistor bridge. the figure 1 circuit supply current is 100 m a not loaded and is able to deliver 10ma with 50% efficiency. applications include power conversion with input voltage from 2v to 16v and output voltage only limited by external npn voltage rating, 5v to 12v introduction figure 1 : electrical schematic conversion for flash programmation, boost voltage for high side nmos driving, ... description ts3v555 has two threshold voltages determined by an internal accurate resistor bridge, trigger (2) and threshold (6). the trigger input is used for output voltage regu- lation, the threshold level is 0.7v (1/3 of vcc). output voltage is compared via r1/r2 resistor bridge to this level during output (3) low cycle, switching it to high when voltage drop below trig- ger threshold level.the output voltage is vout = (1+r2/r1) x vcc/3. the threshold input is triggered at 1.3v (2/3 of vcc), on the saturation voltage of the npn, during the inductor charge cycle. as 1.3v is a high satu- 1/2
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