REF31-Q1: REF31-Q1 Output Capacitance Limit

Hi Jackson, you are right. I want to use 16-bit adc option for VREFHIA, B,C and D so 4 pieces 22uF is needed(Totally min. 88uF). I want to use one adc referance generator and i want to generate this ref 3V from VDDA 3.3V. In order to generate 3.3V to 3V it should be used low dropout LDO(50-100mv max. dropout). 

In REF31-Q1 datasheet, below sentence is written

"The REF31xx-Q1 does not require a load capacitor and is stable with any capacitive load"

Considering all this, can't I use REF31-Q1? Because of REF5030 and REF50E series dropout voltage bigger than 0.3V. 

In section 7.11.2.3.1, VREFHI minimum voltage is given 2.4V. If we give VREFHI between 2.4V to 3V are there any wrong conversion or problem?

My second question: I need more than 88uF output capacitor usage so only REF50E series is useful with max. permissible 100uF output capacitance, is it true? 

Mt third question, In F28386 datasheet 190uA is nominal input current of VREFHI. What is the max. input current of VREFHI? Are you say any max. input current in extreme conditions?

Thanks,

Hi Ozan,

Ozan Güney Düşmezer said:

My second question: I need more than 88uF output capacitor usage so only REF50E series is useful with max. permissible 100uF output capacitance, is it true? 

If you want to only use one VREF, then this is true that only REF50E of the options I mentioned goes to 100µF.

For the other questions, I will loop in the F28386 team and they can provide more details. 

Thanks,

Jackson

Thanks, F28386 team suggestions are important for me. Actually "The REF31xx-Q1 does not require a load capacitor and is stable with any capacitive load" sentence is telling me REF31 load capacitance can be 100uF. If you can say me REF31-Q1 maximum load capacitance limit. This solution is the best for me.

Secondly, Is LM4040C30QDBZR usable for 100uF load capacitance and F28386Q VREFHI supplying?

Hello Ozan,

Your understanding of both the REF31 and LM4040 datasheets regarding load capacitor is correct. For a 16-bit ADC and using large capacitive loads, however, my recommendations remain as REF50 or REF50E for best performance.

Thanks,

Jackson

Can you explain in detail why you recommend REF50? 

Hi Ozan,

Of course. REF50 has three main benefits when compared to REF31:

1. Temperature Drift: 8 ppm/°C

2. Noise: 3 ppm p-p

3. Initial accuracy: ±0.1%

These improvements in performance when compared to REF31-Q1 are typically more fitting for what is typically needed for a 16-bit ADC in terms of expected measurement accuracy due gain error and ENOB.

REF50E is the enhanced version of REF50 with even more performance improvements.

Based off of this information, you can decide which device fits your system best. 

I will now allow the F28386 team to answer your remaining questions. 

Thanks,

Jackson

Ok, i am waiting for thinking of F28386 team.

Thanks for explaining Masoud. Can you suggest me an reference generator for using 16 bit single adc operation of all VREFHI terminals?

Hey Ozan,

I think it’s best if Jackson answer to this question since we can only provide info about our own products. They’ve got more insights on their offerings. We do have some reference designs you can look at for a general idea, but we don't suggest using those directly in your product design.

Best Regards,
Masoud.

Hi Ozan,

I believe you have reached out to a member of our team via email and are having discussions with them in regards to the best voltage reference. Please refer to that correspondence going forward for our recommendations on this topic. 

Thanks,

Jackson