uCurrent: Replace MAX4239AUT -> ASA, change of package SOT23-6 to SO8 - Page 1
Forum section: electronics / projects

author: Jara
author_rank: Newbie
timestamp: October 07, 2014, 12:39:52 pm
content: Hi all,the problem is that MAX4239AUT+T in uCurrent rev5 seems not to be available in small quantities. Similar type MAX4239ASA has the same performance but different package: SO-8 instead of SOT23-6. So I need to modify the PCB design. But I thought maybe somene else already did it?(No, I cannot purchase from Dave's shop because my country is not on the approved list.)-- Jara

author: ang370
author_rank: Newbie
timestamp: March 04, 2015, 05:14:54 pm
content: Hi,I'm facing the same problem as Jara. So I've tried to change the original project, you can see it here:https://www.dropbox.com/s/5svljan0wmmclah/uCurrentRev5a.zip?dl=0This attempt has no presumption to be as good as the original one. I would like to hear your revisions and suggestions, if any.I haven't yet printed and tested the pcb so I can't provide any kind of warranty by now.Angelo

author: kjs
author_rank: Regular Contributor
timestamp: March 05, 2015, 03:37:50 am
content: I changed the design completely and use LTC2051 for it. Much easier to get and same performance. That's a part with two amps in one package but they also have it as a single in SOT23-5 package: LTC2050. That one actually fits onto the same footprint as the shutdown pin of the Maxim isn't used.If you make a PCB don't forget to also add the series resistors in the non-inverting path of the OpAmp. Reduces the effect of the input current and input offset current significantly and very measurable.

author: splin
author_rank: Frequent Contributor
timestamp: March 05, 2015, 04:40:59 pm
content: Quote from: kjs on March 05, 2015, 03:37:50 amTI's LMP2022 may also be worth looking at - its cheaper and has better specs for most parameters, especially .01-10Hz noise - 330nVpp versus 1.5uVpp for the LTC2051. What might be a problem for this application though is that its o/p will only get down to 38mV (typ, 2.5V Vcc) or 65mV (typ, 5V Vcc) compared to 1mV with a 10k load[EDIT: More significantly its maximum supply voltage is limited to 5.5V so can't run it from a 9V battery.]Splin

author: kjs
author_rank: Regular Contributor
timestamp: March 11, 2015, 07:17:23 am
content: The LMP2022 wasn't that good when I tested it but the OPA335AIDBVR is a direct replacement for the LTC2050IS5. Just tested a bunch of them for a project and LTC and OPA are hands down better than the Maxim. Having worked 40 years in the semiconductor industry anything which says "guaranteed by design" and a lame excuse why it can't be tested like the Maxim datasheet tries to lull you in is highly suspect. Not a single one of the Maxim's came even close to the "typical" 1pA input current....Splin, if you need a high voltage version try the LTC2057. Almost as good but can handle 40V supply...... Unfortunatley it's not available in an SOT23-5/-6 package. Only MS8.

author: kjs
author_rank: Regular Contributor
timestamp: March 11, 2015, 09:36:00 pm
content: Forgot to mention: if you can't get the TI TPS3809L30DBVR you can also use the much cheaper APX809-26SAG from Diodes. Does exactly the same job.....And if you use the LTC2050HV or the OPA335 they are rated high enough to just survive a 9V block battery.