MAX6350 output voltage variation within the input voltage range - Page 1
Forum section: electronics / general

author: deepfryed
author_rank: Unknown
timestamp: July 06, 2023, 08:18:51 am
content: I'm playing with MAX6350 and noticing that the output voltage varies from 4.99999v to 5.00095v as the input voltage changes from 9v to 26v. It is still within the stated spec of 0.02% tolerance but is this something that's normal ?and if I want to build a reference standard, should I pick a stable input voltage at a given temperature before trying to trim it ?Cheers

author: Kleinstein
author_rank: Super Contributor
timestamp: July 06, 2023, 08:52:18 am
content: Some change in the output with a change in the supply is normal. On point is the heat the chip produces and this changes the temperature of the chip if run with a much high supply.There usually is an extra specs for the power supply rejection ratio - not just the overall accuracy specs. Anyway the assumption is usually a small change in the supply.For a really stable reference one should use a regulated supply, usually not much higher than needed. In many cases a normal voltage regulator like 78xx is good enough for this purpose.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: July 06, 2023, 11:10:00 am
content: This behavior is fully consistent with the datasheet:

author: gamalot
author_rank: Super Contributor
timestamp: July 06, 2023, 01:17:55 pm
content: It is normal. I have some MAX6350's that behave just like yours, and that's clearly stated in the datasheet.

author: Andreas
author_rank: Super Contributor
timestamp: July 06, 2023, 07:28:22 pm
content: Quote from: deepfryed on July 06, 2023, 08:18:51 amHello,the tolerance is specified at 25 deg C and exactly 10V input voltage.So the PSRR and the T.C. (and ageing since adjustment at factory) are outside of tolerance specification and may add up additionally.So you should keep input voltage constant (and also keep the heat from the voltage regulator somewhat away from the reference).With best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: July 06, 2023, 08:33:11 pm
content: Interestingly you may fine tune the output voltage by changing the input voltage (see the DS), ie +/-20ppm with +/-3V around 10V input voltage. Pretty handy

author: Andreas
author_rank: Super Contributor
timestamp: July 06, 2023, 09:20:19 pm
content: Hmm,I would not bet on the datasheet values.maybe you have a sweet spot between self heating and PSRR at certain voltages.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: July 06, 2023, 09:50:13 pm
content: Now, the Vin/Vout dependency could be created by a) selfheating (P=Vin*Iqesc), or/and b) because of the poor PSSR..For example with the LT1021-5/10 (epoxy dil8) the Vin/Vout was almost zero in my measurements (10-20V)..It could be my measurements were short enough to not see the a)..

author: Andreas
author_rank: Super Contributor
timestamp: July 07, 2023, 05:22:57 am
content: Hello,so your measurements might be closer to datasheet values.The test conditions for PSRR are usually done with "short pulses" so that there is no self heating visible.with best regardsAndreas