Post by thread:Cheep DC/DC, any idea ?

Tal wrote: > I need to implement a DC/DC converter for a cost sensitive > design. Input voltage around 7-9VDC, output voltage 4 to > 6VDC, at least 500ma. Ideally the converter should use > components not heigher then 3-4mm, a relativily small foot > print 1-1.5 square intch) and use surface mount > components. Efficency is not a major requiremnets. How about dropping input voltage requirements down to 2.5-4V to enter mobile system's step-up DC/DC converters world? Cheep & compact. Mike. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Instead of a low power linear regulator, you may use regulating charge pump, MAX1759 mentioned in "Battery Level Monitor" thread for example. Mike. From http://pdfserv.maxim-ic.com/arpdf/MAX1759.pdf -------------- The MAX1759 is a buck/boost regulating charge pump that generates a regulated output voltage from a single lithium-ion (Li+) cell, or two or three NiMH or alkaline cells for small hand-held portable equipment. The MAX1759 operates over a wide +1.6V to +5.5V input voltage range and generates a fixed 3.3V or adjustable (2.5V to 5.5V) output (Dual Mode™). Maxim’s unique charge-pump architecture allows the input voltage to be higher or lower than the regulated output voltage. Despite its high 1.5MHz operating frequency, the MAX1759 maintains low 50µA quiescent supply current. Designed to be an extremely compact buck/boost converter, this device requires only three small ceramic capacitors to build a complete DC-DC converter capable of generating a guaranteed 100mA (min) output current from a +2.5V input. For added flexibility, the MAX1759 also includes an open-drain power-OK (POK) output that signals when the output voltage is in regulation. The MAX1759 is available in a space-saving 10-pin µMAX package that is 1.09mm high and half the size of an 8-pin SO. ---------------------- Tal wrote: {Quote hidden}> The input voltage is also used generate 5V (low current) > to operate a PIC and some digital and analog circuits. > This is done using a low power linear regulator. If we > drop the voltage, we will need another step up to 5V. > > > Tal wrote: > > > I need to implement a DC/DC converter for a cost sensitive > > > design.Input voltage around 7-9VDC, output voltage 4 to > > > 6VDC, at least 500ma. > > > Ideally the converter should use components not heigher > > > then 3-4mm, a relativily small foot print 1-1.5 square > > > intch) and use surface mount components. > > > Efficency is not a major requiremnets. > > > > How about dropping input voltage requirements down to 2.5-4V > > to enter mobile system's step-up DC/DC converters world? > > Cheep & compact. > > > > Mike. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Thanks Mike. This is an interesting chip but seems to be expensive (my guess 1.5 to 2$ in large quantities, please correct me if I am wrong). The direction we are considering now is to use LM3485 (http://www.national.com/pf/LM/LM3485.html) which is about 50C + 15C for a power P Mosfet. This chip seems to work up to 1Mhz and therefore can use a smaller inductor. We are now in the process of studying this chip. One interesting point is that its frequency depends on the ESR of the output capacitor (strange, does it make the component selection more tricky?). It also seems that its design result in noticeable ripple but I am not sure. Does anybody has any experience with the LM3485 or can comment on it ? Thanks, Tal > {Original Message removed}