Designer’s Guide Community

james_lanren New Member Offline Posts: 2	BGR correctness Jan 04^th, 2013, 1:52am I have designed a bgr which has an output voltage against temp as follows. The output voltage is 1.15 instead of 1.205. Will it be tolerable? Also the curvature is upward facing, is that correct?
Back to top	bgr_v_vs_temp.png IP Logged

yvkrishna

Senior Member

Offline

Posts: 117

Re: BGR correctness
Reply #1 - Jan 4^th, 2013, 8:01am

Hi James,

I assume this is simple BGR design without any curvature compensation used.

o/p voltage will not exactly be 1.205 for every process(depends on lot of things) but usually close it if you design a classical voltage bandgap.

Tolerance is always about the total variations with PVT, absolute value is usually easy to trim and control.

And about curvature facing upwards, it might be to do with the BJT used, did you try to observe if BJT alone has proper temperature characterless.(CTAT nature)
use a different bjt/diode and double check.

you can post your schematic for better replies to your queries.

Regards,
yvkrishna

Back to top

IP Logged

Dan Clement Community Member Offline Posts: 95 Salt Lake City, Utah, USA	Re: BGR correctness Reply #2 - Jan 4^th, 2013, 10:34am This can be normal, it just depends on the tempcos of resistors, offsets, etc. It could also be a sign that your collector current is too high...
Back to top	IP Logged

loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: BGR correctness Reply #3 - Jan 12^th, 2013, 4:11pm suggest posting the schematic. Also have you modeled in you mismatches and offsets? Those can throw the accuracy off a lot more than the tempco variance.
Back to top	Jerry Twomey www.effectiveelectrons.com Read My Electronic Design Column Here Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical IP Logged

analog_wiz Junior Member Offline Posts: 31 Universe	Re: BGR correctness Reply #4 - Jan 14^th, 2013, 4:56am Have you checked the leakage of the startup circuit at high temp?
Back to top	IP Logged

RobG Community Fellow Offline Posts: 570 Bozeman, MT	Re: BGR correctness Reply #5 - Feb 5^th, 2013, 1:28pm A bit late, but something is very messed up. Your curvature is 75 mV and upward. 4 mV and downward is typical.
Back to top	IP Logged

Erez_Sarig

Junior Member

Offline

Posts: 16

Re: BGR correctness
Reply #6 - Feb 7^th, 2013, 1:04pm

Hi,

It looks like you are very close to fine tune the BGREF your PTAT is too high so decrease it and you should get a better level.
Best thing to do is to take aside the BJT and using ideal devices see the real ratio of PTAT and CTAT. also measure the PTAT which should be around 166uV/C.
Still it is hard to conslute without seeing the schematic....

Erez

Back to top

IP Logged