2 channel dc dc question - Page 1
Forum section: electronics / general

author: reaper38
author_rank: Newbie
timestamp: July 11, 2016, 04:31:06 pm
content: Hello, got problem, on my board i have 9-20v dc in and i need 3.3 and 1.2 supply for converter.Any suggestion about small 2 channel dc-dc?

author: uncle_bob
author_rank: Unknown
timestamp: July 12, 2016, 12:29:32 am
content: HiOr do the wide range to 3.3V and then take the 3.3 to 1.2V. A lot depends on how much power you need at each voltage.Bob

author: reaper38
author_rank: Newbie
timestamp: July 12, 2016, 11:25:45 am
content: i already use 2 converters, wide range to 3.3 and 3.3 to 1.2, but it takes a lot of space on board, one 2 channel will be much more convenient to use.

author: Signal32
author_rank: Frequent Contributor
timestamp: July 12, 2016, 11:34:56 am
content: Quote from: reaper38 on July 12, 2016, 11:25:45 amI'm not sure where you think the space savings will be. Only thing different is that you will use 2 IC's instead of 1. If your current design was originally designed for compactness, then you're probably already using a SC-70(2x2 mm) for the buck IC's. Replacing these two with a say DFN-8(3x3mm) won't give you much space savings.

author: reaper38
author_rank: Newbie
timestamp: July 12, 2016, 11:44:18 am
content: i use 2 dc-dc in big bulky sot23 and sop8 packages, because it is cheap and easy to get.Something like one in qfn will be much better.

author: uncle_bob
author_rank: Unknown
timestamp: July 12, 2016, 10:26:25 pm
content: Quote from: reaper38 on July 12, 2016, 11:44:18 amHiAre you running below 50 ma on the 1.2V supply?Bob

author: reaper38
author_rank: Newbie
timestamp: July 13, 2016, 06:34:42 pm
content: 70 ma top on 1.2 line

author: uncle_bob
author_rank: Unknown
timestamp: July 14, 2016, 12:42:30 am
content: Quote from: reaper38 on July 13, 2016, 06:34:42 pmHiDrop in a 1 or 1.5 mm square linear.Bob

author: reaper38
author_rank: Newbie
timestamp: July 14, 2016, 08:57:35 am
content: a have found just the right thing, tps51220a in qfn package

author: uncle_bob
author_rank: Unknown
timestamp: July 14, 2016, 03:14:03 pm
content: HiIf the objective was to reduce board area ... that's one massive circuit ....Bob

author: mariush
author_rank: Super Contributor
timestamp: July 14, 2016, 04:20:25 pm
content: I agree with using a 1.2v LDO if the current is so low. Here's a 1mm x 1mm one, for example:http://uk.farnell.com/on-semiconductor/ncp103amx120tcg/ldo-fixed-1-2v-0-15a-udfn-4/dp/2454534Or something bigger but easier to solder:http://uk.farnell.com/microchip/mcp1703at-1202e-cb/ldo-2-7-16vin-0-25a-1-2v-2-3sot23/dp/2218569RL

author: reaper38
author_rank: Newbie
timestamp: July 14, 2016, 11:48:12 pm
content: Quote from: mariush on July 14, 2016, 04:20:25 pmgood one, i never thought about it.What about small wide range to 3.3, max current will be about 200ma?

author: uncle_bob
author_rank: Unknown
timestamp: July 15, 2016, 12:14:53 am
content: Quote from: uncle_bob on July 14, 2016, 12:42:30 amBobLinear = Linear regulator, run from 3.3 to 1.2V. You can get them in very small packages ....Bob

author: sporadic
author_rank: Regular Contributor
timestamp: July 17, 2016, 02:03:56 pm
content: Maybe a TPS62175 for 3.3v then your LDO for 1.2? It's U1 on the attached board, pretty low part count to use it.

author: uncle_bob
author_rank: Unknown
timestamp: July 17, 2016, 07:40:25 pm
content: HiTry:http://www.mouser.com/ProductDetail/Texas-Instruments/TPS79912YZUR38 cents each at 1K pieces.http://www.ti.com.cn/cn/lit/ds/symlink/tps799.pdf1.0 mm x 1.37 mm, handles 200 ma. 2.2 uF output cap, can be a 0402 ceramic. In 0402 you still have X7R available. If 0402 is to big, you can drop down to 0201 and an X5R dielectric. Not a lot of board space used at all.If the BGA gives you heartburn, there are other packages you can use. There are also dozens of similar sized parts out there.Bob