MCP1702-5002 LDO High Quiescent Current - Page 1
Forum section: electronics / projects

author: embed4
author_rank: Newbie
timestamp: December 08, 2022, 04:35:02 pm
content: I am using a MCP1702-5002 to drop 6V battery source to a 5V supply.I am seeing a quiescent current of around 20uA and not the 2uA typical I am expecting. Have cut the cct down to the bare LDO and ceramic caps and measuring through a switched resistor. I have tried 3 devices all with the same result.Any ideas?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 08, 2022, 05:05:19 pm
content: Tried different capacitors?Tim

author: Peabody
author_rank: Super Contributor
timestamp: December 08, 2022, 05:09:50 pm
content: What does "measuring through a switched resistor" mean exactly?

author: mk_
author_rank: Regular Contributor
timestamp: December 08, 2022, 05:26:20 pm
content: Quote from: embed4 on December 08, 2022, 04:35:02 pmwe had a kind of latchup with the MCP1710-3V3 when load-jump occured (from 200nA to 2,2ma), about 50% of the used MCP showed this on a 500pcb-run. Microchip was very surprised and after some more testing (use more capacity, use less capacity, use other caps, that kind of "suggestions") we gave them some boards for their own testing... finaly they told us that they saw this too and it was definitly theri fault because they didn`t test this scenario during production :-(.So... from the experience we had with them ask them to check this behavior. Document everything and be persistent...

author: embed4
author_rank: Newbie
timestamp: December 08, 2022, 06:22:37 pm
content: I have a 47K resistor in-line on the Vin with a parallel switch. Device is powered on with the switch on and then flicked off so as to measure quiescent current across the resistor when its in its steady state

author: Kleinstein
author_rank: Super Contributor
timestamp: December 08, 2022, 06:38:52 pm
content: Some oscillation of the output could caus excessibe power consumption. An 1 µF capacitor (espeally if small size) under DC bias may show degradation of the capacitance. So it may be woth adding a 2nd capacitor in parallel.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 08, 2022, 08:25:26 pm
content: This LDO is claimed to be stable with ceramic output caps, so I would doubt oscillation here. Now a quick look with a scope doesn't hurt.But I would question the measurement before questioning the regulator.

author: Peabody
author_rank: Super Contributor
timestamp: December 08, 2022, 09:31:27 pm
content: Quote from: SiliconWizard on December 08, 2022, 08:25:26 pmYes, particularly since it's off by a factor of 10. If it's really 20uA, then the voltage drop across 47K would be 0.94V (check my math). But that assumes the meter is on the right range, and the resistor is really 47K. And particularly if you get the same result on multiple new parts. Not saying they aren't all counterfeits, or bad copies, but just make sure the test results are valid.

author: embed4
author_rank: Newbie
timestamp: December 10, 2022, 09:43:46 am
content: Quote from: Kleinstein on December 08, 2022, 06:38:52 pmIt's all clean on the scope. On the actual design there is plenty more decoupling capacitors on the board.Any ideas?

author: embed4
author_rank: Newbie
timestamp: December 10, 2022, 09:45:31 am
content: Quote from: Peabody on December 08, 2022, 09:31:27 pmYes -the same "is it me" went through my mind. Checked by adding known load onto regulator and the current tallied.

author: magic
author_rank: Super Contributor
timestamp: December 10, 2022, 10:00:46 am
content: 1. It's fake.2. Your resistor pushes it into hard dropout, increasing power consumption for some reason. Why not 10kΩ?3. Your resistor makes it unstable, but you only scoped with the resistor bypassed. Make sure there is a cap from Vin to ground, after the resistor.4. Your lab is haunted by ghosts, runeditTo my eye, the datashit contains a strong hint that 2 is the case.(If not, my bets are on 4, 1, 3 - in this order).

author: iMo
author_rank: Super Contributor
timestamp: December 10, 2022, 10:06:43 am
content: Power it out from 10V and do use 10k, or 1k or 100ohm..