Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

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

Status
Not open for further replies.
E

ernestmyname

Member level 1
Joined
Nov 19, 2009
Messages
33
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Location
Clemson
Activity points
1,548
I need a DAC to run o a 5V supply. It also needs to be capable of outputting 4.5V.
ff
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
 

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.
 

Re: DAC output voltages

karesz said:
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.
Click to expand...

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?
 

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"!
 

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.
 

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
 

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.
 

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?
 

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.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top