Cannot find an accurate DCDC module for 12Vin to 24Vout (<1W) - Page 1
Forum section: electronics / beginners

author: opampsmoker
author_rank: Regular Contributor
timestamp: November 18, 2020, 02:19:52 pm
content: We are using 10 ADG1438 multiplexors and feeding them 24V to VDD and -5V to VSS.Abs Max for VDD is 25V.The total current draw will be <10mA for all ten of them.Our power source is 12V…..As such, we are trying to find a 12Vin to 24Vout, <1W DCDC module.However, every single one I find on the web has a poor load regulation of 10%. This means it could blow up our ADG1438’s.As such , we are wondering if we are going to need a discrete MC33063A based boost converter. The software engineers prefer a simple DCDC module but it looks like I must tell them that no suitable DCDC modules exist?ADG1438 datasheethttps://www.analog.com/media/en/technical-documentation/data-sheets/ADG1438_1439.pdfMC33063A datasheethttps://www.ti.com/lit/ds/symlink/mc33063a.pdf?ts=1605685193740&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FMC33063A

author: fcb
author_rank: Super Contributor
timestamp: November 18, 2020, 03:16:13 pm
content: Go with a higher voltage and then a linear regulator. This will lower the chance of overshoot anyway.L78M24 typically +/- 2%, so you're worst case is +/-0.48V

author: fcb
author_rank: Super Contributor
timestamp: November 18, 2020, 03:19:12 pm
content: Quote from: opampsmoker on November 18, 2020, 02:19:52 pmThere's been quite a bit of hate for the 34063 and brethren on this forum. I like the IC personally as it works and it's economical - there are much better parts though.

author: Benta
author_rank: Super Contributor
timestamp: November 18, 2020, 06:02:43 pm
content: Buy a Traco regulated module. Not Alibaba price but very good.Example:https://www.tracopower.com/de/series/tdn-1wism<1% regulation error.

author: Zero999
author_rank: Super Contributor
timestamp: November 20, 2020, 10:03:59 pm
content: Quote from: opampsmoker on November 18, 2020, 02:19:52 pmJust a potentially silly question: why? The ADG1438 is not specified to work with a VDD of 24V. Yes, it might have an absolute maximum rating of 25V, as in it won't blow up, but no characteristic is specified above 15V, so I wouldn't expect it to behave very well at much higher voltages and quite likely won't meet the specification in terms of leakage current.What's it used for? Is it possible to bias/level shift the signal, so it fits within +12V and -5V? Or just reduce VDD to <20V, which still isn't ideal, but much less marginal.Failing that, use a higher voltage rated part. There doesn't seem to be anything quite like the ADG1438 but properly rated to +24V/-5V.There are small parts with one or two channels such as the MAX4659/MAX4660, ADG5236 and DG449.http://www.farnell.com/datasheets/74730.pdfhttps://www.analog.com/media/en/technical-documentation/data-sheets/ADG5236.pdfhttps://www.vishay.com/docs/73897/dg449.pdfThen there are higher voltage rated part such as the HV2801/HV2901 and HV209, which are much larger. Be ware that some have biasing resistors built-in, which you might not want.http://ww1.microchip.com/downloads/en/DeviceDoc/HV2801-HV2901-32-Channel-Low-Charge-Injection-High-Voltage-Analog-Switches-Data-Sheet-20005840A.pdfhttps://www.mouser.com/datasheet/2/268/supertex_hv209-1181153.pdf

author: mariush
author_rank: Super Contributor
timestamp: November 20, 2020, 10:27:55 pm
content: Is it a problem if it's slightly less than 24v ?You could just use voltage doubler ICs, which will give you 2x the input, minus the voltage drop on the diodes used.Here's a bunch of them -https://www.digikey.com/short/z0w29r- from the cheapest that are maximum 20mA (so I guess you could use one per IC) and there's some that can do up to 800mA but will be more expensive.For example LT1054 ... does 100mA and Vout = 2 x Vin - max 1.1v - 2 x diode loss, so around 22v is doable with just a bunch of ceramic capacitors and 2 diodes.See page 17 in the datasheet:https://www.ti.com/lit/ds/symlink/lt1054.pdfFor lower currents, you have TC7662 with max 20mA and closer to 24v output :https://www.digikey.com/en/products/detail/microchip-technology/TC7662BCOA713/443296See page 6 ofhttps://ww1.microchip.com/downloads/en/DeviceDoc/21469a.pdfRunning at 10..35kHz, it would be much easier to filter the output with a pi filter or something, if it's really important to have a cleaner output.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 20, 2020, 10:30:29 pm
content: Quote from: Zero999 on November 20, 2020, 10:03:59 pmThe part is specified for +/- 15V so it supports a total supply-to-supply voltage of 30 V. You could also create a virtual ground at 10V and use logic level translators for the digital signals. That would keep it in the specified operating range.

author: Zero999
author_rank: Super Contributor
timestamp: November 20, 2020, 10:46:46 pm
content: Quote from: ejeffrey on November 20, 2020, 10:30:29 pmThe absolute maximum rating for VDD-VSS is 35V, but only 25V between 0V and VDD. There will be valid reasons for this and the fact it's only specified with a VDD of up to 15V, indicates it's not designed for +24V/-5V so might not work very well at that voltage. Pushing VDD a bit higher than 15V isn't an issue, but taking it to within 1V of its absolute maximum rating is a bad idea.QuoteSounds much more complicated, than simply using an appropriately rated part in the first place.