Good LDO Regulator/Buck Converter with Low Quiescent Current? - Page 1
Forum section: electronics / projects

author: LabSpokane
author_rank: Super Contributor
timestamp: May 19, 2015, 03:56:06 am
content: I have a battery powered device that I'm working on and need a 5V SMD voltage regulator with a reasonably low quiescent current. Hopefully under 100uA.What is a good, mainstream choice? Mouser's search criteria doesn't include quiescent current, so I'm not sure if what I'm finding is oddball or not.Thanks!================================Better specs:Vin = 12.6VVout = 5VuC draw = 100 uA sleep / 10mA operatingAuxiliary draw = 500 mA / 1.5A? short peaks

author: Unknown
author_rank: Unknown
timestamp: May 19, 2015, 04:32:54 am
content: Quote from: LabSpokane on May 19, 2015, 03:56:06 amHave you looked at manufacturer's parametric search tools e.g.TI,ST, etc? Most include quiescent current, and it's pretty easy to pick the the mainstream / available parts (e.g. LP2951) out of the results.

author: georges80
author_rank: Frequent Contributor
timestamp: May 19, 2015, 04:49:35 am
content: Max current requirement? Input voltage?Micrel MIC5235 is a nice regulator family if it meets your current/input voltage needs. Reverse polarity protected as well.cheers,george.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 19, 2015, 04:59:22 am
content: Oh geez, of course.Vin<20V. Vout=5V. Iout 250-500mA.I'll look at the vendor websites tonight. I just wish the distys had better search tools. So much easier to compare everyone in one spot.Thanks again.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 19, 2015, 05:31:00 am
content: Quiescent current is only significant when you're running a few mA or uA through the thing.But, what do you think about an LP2980?

author: georges80
author_rank: Frequent Contributor
timestamp: May 19, 2015, 05:48:07 am
content: Do a power dissipation calc. If you have 5V out and even 10V input at 500mA you have 2.5W losses in the linear regulator....Seems a little weird to be worried about very low quiescent current if you are tossing away a bunch of runtime in a linear regulator versus a switcher.So, what's the actual duty cycle here, i.e. on time at 250mA - 500mA versus off time (sleep/standby)? What is the actual input voltage, versus <20V which could mean 19.999V...cheers,george.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 19, 2015, 06:15:40 am
content: Application is a 328P microcontroller that will be asleep 99+% of the time. Vin in 12.8V. I've tried off the shelf switchers (as a time saver) and the quiescent current is in the mA, which is far too high. I just need enough to handle the peak draw of the micro and a few ICs. I think the short term losses through the Vreg will be better than the long term load of the switcher.The 500mA was to handle as cell modem, but the more I look, I think it will be better to split that off into its own regulator. So I'm down to maybe 80mA of draw, so a 125mA LDO should be fine. I want to be able to keep the device alive even while the batts are close to dead, hence the LDO.And I did do the power calc and I'll lose 1/2W during the few minutes a day it's in operation. I'm fine with that.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 19, 2015, 06:28:46 am
content: You can power the 328p using the LP2980-alike, and use a different higher current ldo or switchmode with EN pin for the GSM module.Assuming you do not source power trough the 328p's IO's.The LP2980 is transparent when you go below Vout, so you can literally run until the battery is below Vcc-min for the 328p.But with nominal 12V batteries, this will not happen. When lead-acid batteries are 6 Volt, they're dead. You cannot draw current. You cannot recharge. Maybe keep the 328p awake, but I wouldn't guarantee the GSM module to work.

author: matseng
author_rank: Frequent Contributor
timestamp: May 19, 2015, 06:49:22 am
content: Quote from: LabSpokane on May 19, 2015, 06:15:40 amThat must be a nice gms module that only pulls 500 mA - doesn't most of them pull upwards to 1.5 - 2 amps in "sustained spikes"? (can't find a better word for something that is not continuous, but definitely longer than like a mS or two....)

author: LabSpokane
author_rank: Super Contributor
timestamp: May 19, 2015, 02:10:25 pm
content: Quote from: matseng on May 19, 2015, 06:49:22 amWell...I don't have the modules yet, so you may well be right. I'm looking at the MultiTech embedded series which claim in the neighborhood of 500mA.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 19, 2015, 02:15:58 pm
content: Quote from: Jeroen3 on May 19, 2015, 06:28:46 amThanks! Will check the LP2980 out. I really appreciate the tips.I'm actually going to use disposable batts for now, so running nearly dead is ok.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 20, 2015, 04:10:59 am
content: Guess what I just found on the shelf?I had a pre-fab buck converter using the MP2467.Datasheet:http://www.monolithicpower.com/DesktopModules/DocumentManage/API/Document/getDocument?id=311100uA quiescent current. Vinmax = 36V. Ioutmax = 2.5A (My version is 1.5A, but no problem)And I know that this is not "low current," but it will be perfect for what I'm doing, and it's a one regulator conversion.============================================================================If in the future, I want a converter with lower quiescent current, but need a beefy current output on occasion (1/2AMP). What's the best way to handle that off a single power supply? Do I have two regulators/converters and enable/disable as appropriate, then prevent back feeding the "off" converter?