• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 3424 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

About the Vref of TLC7524

ma yiqing
Prodigy 80 points
Other Parts Discussed in Thread: TLC7524, LM339

Hello everybody,

Thanks a lot for your attention to my question about the use of the component TLC7524.

Generally I use it for my design of the controler of stepper motor.

The dac is used to translate the datas digital to analog. And the 

signal analog is connected to the comparator LM339 as the pole positif.

 

this photo shows my datas digital hex. it varies from 0x03 to 0xFE

This photo shows the datas analogic.But in this photo it can't precisely show what i want.Then i turn to look what's going on at the voltage reference.

H

In this photo you see my voltage reference. It should be constant but it's not. I think here is the reason why i can't get a correct result.

This photo is my connection the the component.  I used the mode voltage. I've tried to pose a cap between OUT1 and gnd, but it doesn't work. then I put a cap between REF and gnd, it doesn't work neither.

Anyone can tell me why? what should i do to relove it? Thank you very much for your help.

 

Best regards.

 

Yiqing

  • 0
    TI__Mastermind 43915 points

    Hi Yiqing,

    The TLC7524 is designed as an MDAC and carries the internal properties of a MDAC as it is meant to have the Vref driven with a reference voltage and Iout1 and Iout2 as the current outputs. Since the TLC7524 is designed as a MDAC, the internal switches are designed and expected to switch between ground and virtual ground. When used in "voltage mode," the converter is configured as a back DAC and you are going to see small glitches which come from a combination of the switching synchronization and the switch charge injection. As a back DAC, each leg is switching from ground to Vref and vice verse which will lead to a glitching behavior. Now, the glitch you show in these screen shots seems fairly large. This may be because the parts switches are designed for use as a MDAC and you are back driving it to be a back DAC or it may be something else. It may have to do with the drive capability of the reference. Notice, in "voltage mode," you are now having the converter switch each leg between ground and Vref, essentially changing the load impedance seen by the reference. A reference does not like to see a change in impedance and, in some cases, may have trouble settling out. Having a buffer there will help.

    Regards,

    Tony Calabria