Generating 5V Reference for external DAC from lower voltage? - Page 1
Forum section: electronics / projects

author: suku
author_rank: Contributor
timestamp: August 07, 2016, 09:02:11 pm
content: Hi, I'm working on a project where I need a stable reference voltage for the external DAC I use with a microcontroller. The micro is running on 3.8-4.3V and I need a reference voltage of 5V. Should I use a standard DC-to-DC converter or is there a "better" way of doing this? (Preferably as few parts as possible)Thanks!

author: sangvikh
author_rank: Contributor
timestamp: August 07, 2016, 09:08:39 pm
content: A DC to DC converter feeding into a 5v reference should work. I wouldn't use the output of a DC to DC converter directly.You don't really have a choice about using a switching converter if you need a higher voltage than you have.

author: Zero999
author_rank: Super Contributor
timestamp: August 07, 2016, 09:32:06 pm
content: A Schottky diode & capacitor voltage multiplier followed by a low drop-out regulator.

author: ajb
author_rank: Super Contributor
timestamp: August 07, 2016, 09:36:04 pm
content: You can even drive a charge pump from a spare mcu pin if you don't need much current, otherwise there are some 5/6 pin SOT charge pumps that only require two external caps.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 08, 2016, 01:50:44 am
content: see the ltc1043 data sheet.http://www.linear.com/product/LTC1043Precision multiply by 2,3,4.

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2016, 07:39:02 am
content: Quote from: RandallMcRee on August 08, 2016, 01:50:44 amI do not think the LTC1043 can generate an output outside of its supply rails do to integrated protection diodes.One of the various integrated charge pumps would work for this application and would probably be my first choice; some of them support regulated outputs.http://www.linear.com/product/LT1054

author: Ian.M
author_rank: Super Contributor
timestamp: August 08, 2016, 10:09:18 am
content: What DAC is it that works with a reference outside its supply rails? The whole setup sounds fishy to me.It probably needs a regulated DC-DC converter, for the DAC Vdd supply with a tapped coil and an extra diode to get an semi-unregulated rail a volt or so higher to feed the reference.

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2016, 04:39:57 pm
content: Quote from: Ian.M on August 08, 2016, 10:09:18 amMany DACs can work with a reference and output outside of their supply range. Current DACs are a prime example and I think some resistor ladder DACs can as well but they have unbuffered outputs.That does not help if you need a voltage reference higher than the supply voltage of course.

author: Buriedcode
author_rank: Super Contributor
timestamp: August 08, 2016, 06:00:23 pm
content: AS already mentioned, if you want minimum number of parts, the charge pump powered by the 3.8-4.3V feeding an LDO, or shunt reference is probably the easiest. A square wave output form a micro (50% duty, say, 35kHz) with a voltage doubler should provide more than enough current for a 5v shunt regulator. Just make sure the reference is bypassed adequately, and give the charge pump enough time to reach a stable voltage (few ms?).So thats two diodes, two caps, a resistor, and shunt regulator (LM4040, TL431 etc..) + an extra pin on the micro.If your external DAC needs to be powered from this, then use an LDO instead of a shunt reference. Plenty of 5V LDO's have better than 1% line regulation.