DAC to run o a 5V supply capable of outputting 4.5V

[ernestmyname]

I need a DAC to run o a 5V supply. It also needs to be capable of outputting 4.5V.
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I was originally thinking that I would run 5V to the power and 5V to the reference. But in this datasheet, the recommended operating conditions is for Vref to be Vdd - 1.5V.

Can I run Vdd straight to Vref and obtain 4.5V output? Or do I need to find a different type of DAC?

https://focus.ti.com/lit/ds/symlink/tlc5620.pdf

 

[karesz]

DAC output voltages

Hi,
These ADC has a "Uout=Uref 2x" modus too; if you have 2.5V Ref, your Uout is at max 4.8V (theoretically 5V)...
But can you not change the Vcc to 5.5 or 6V?
These (modius x2 & >5.5V supply) are needed (maybe) for your supplying of Uref too...
K.

 

[ernestmyname]

Re: DAC output voltages

Hi,
These ADC has a "Uout=Uref 2x" modus too; if you have 2.5V Ref, your Uout is at max 4.8V (theoretically 5V)...
But can you not change the Vcc to 5.5 or 6V?
These (modius x2 & >5.5V supply) are needed (maybe) for your supplying of Uref too...
K.

So are you saying that in order for this DAC to output 4.5V, I will ultimately need to supply the DAC with more than 5V?

 

[karesz]

DAC output voltages

The datasheet tels us, that 4.5V is nominell, max at 4.8V...
Check pls figs 9...11 & pp6 (Uout Analog full-scale output voltage, RL,10 kΩ typ. 3.5V, but, you must eventuelly buffer it (Rload>=50KOhm).. .
As sum; I think it is to use as hobby circuit w. your wishes, but as product... Find some other solution.
K.

The datasheet isnt enough detailed to tell exat yes- in relation your problem ..
You wish to take Vcc as reference? Vorget it, then it has lot of changes, isnt referencebar:-(... You need min. a Zener , normally an "referenc source/circuit-IC"!

 

[dick_freebird]

DAC output voltages

How many bits, and how accurate?

I've made rail-rail DACs using CMOS hex inverters and
discrete resistors (R-2R). But these have no appreciable
drive strength.

 

[ernestmyname]

Re: DAC output voltages

The accuracy isn't as much of a concern as being able to output 4.5V when I only have a power supply of 5V running to the ucontroller and DAC. 8 bits is more than enough accuracy for that I'm doing.

So using the same voltage for Vdd and Vref is a bad idea?

Added after 24 minutes:

So I started looking for different DACs. My system is going to be on a noisy 12V system that varies from 12V to ~14V. It will be on an automobile. I found this other DAC that is rail to rail but it runs off a minimum of 11.4V. Will it matter how noisy VDD is? Would this DAC work better and I could just use the 5V as a reference and connect the Vdd straight to the battery?

I'm using a 7805 to get 5V for my uController.

https://www.jameco.com/Jameco/Products/ProdDS/824561.pdf

 

[karesz]

DAC output voltages

Hi,
Automotive apps are relative problematics, than their environment is very stressed, trough EMC, Thermo cycles, vibrations, strong transients! & strong variend supply voltage...
You will need in all cases an efficient transient suppression on the +5/12V and good filtering/separation!
K.

 

[ernestmyname]

Re: DAC output voltages

On the second DAC I linked, the rail to rail, how close should it come to outputting the Vref, 5V? Assuming it is powered by a filtered 12-14V source?

 

[karesz]

DAC output voltages

Hi,
If Im right; It must be no problem!
If your Usuppl. =>11.4V, & your Uref is ander 11.4-4V, also less as 7,4V, you can become the Uref as Uot...
Also, my answer is clear 5V out must be OK with Uref=5V & Us>=+11,4V.
Load must be over 2KOhm!
K.