Monitoring Voltages with Scaling Circuits

John Morton

Other Parts Discussed in Thread: UCD90124, UCD90120A

Hi,

I am using the UCD90124/A, among other things, to monitor multiple voltages. Several of these are > 2.5v so I have scaling circuits so as not to violate the 2.5v max on the Mon inputs.

My question is, do I enter the raw voltage values in Fusion for such things as over/under voltage fault/warning or do I use the scaled values? Are there provisions within Fusion to enter the scaling factors?

Thanks,

John M.

over 14 years ago

0 Eric Wright over 14 years ago

TI__Mastermind 42795 points

Enter the actual raw values into Fusion. You then set the "gain" and "offset" values in Fusion on the "Other Config" tab. For example, if your external voltage divider is a divide by 2 (0.5), then you enter 0.5 for Vout Scale Monitor on the other config tab for the subject rail.

0 dhanasuthan Kaneshapillai over 14 years ago in reply to Eric Wright

Prodigy 60 points

Hi Eric,

I have a question on the setting up "Vout scale monitor" and "Vout Cal monitor". I am monitoring a -5.2V power rail with UCD90120A device. The Vin to UCD90120A is scaled down with 6.04K and 8.25K resistors (other end of the divider tied with +12V). How do I monitor the setting up the scale parameters on this scanario?

0 Spandana Kocherlakota over 14 years ago in reply to dhanasuthan Kaneshapillai

TI__Intellectual 1595 points

Hi Dhanasuthan,

My first suggestion would be using an inverting Op amp between the negative rail and the UCD so that the monitoring input to the MON pin of the sequencer would be the Op amp output which is a positive voltage.

I have attached a schematic showing the implementation. The V4 would be the volatge rail you would be monitoring which is -5.2V.

I'll come up with another solution soon which doesnt involve the use of extra components.

0 Paul Porreca over 13 years ago in reply to Spandana Kocherlakota

Prodigy 80 points

I have the same question as the original post but I will elaborate more I have a 12v rail and a 1v rail I want to feed the 1v rail directly into the ADC and the 12v rail divided down. How do I enter in the scaling for EACH rail (no scaling on 1v rail and 1/6 scaling on the 12v rail). I only see one scale entry. Surely you dont want me to divide the 1v rail down to 1/6 as well? All my thresholds will be in the noise.

0 mike dahlhausen over 13 years ago in reply to Paul Porreca

Prodigy 10 points

I have run into the same question. Is it possible to assign a unique scale factor to each rail? If so, how does one do this?

0 GaryS over 13 years ago in reply to mike dahlhausen

Intellectual 370 points

Although it is not obvious from the miserably inadequate documentation. It is possible.

In the Fusion software do the following.

1. On the 'Vout Config' tab Select the rail you want to scale in the "Select Rail to Edit" window.

2. Now click on the 'Other Config' tab, and scroll down to the "Scaling" section. The "Vout Scale Monitor" is the scaling factor that will be applied to the rail you selected in step 1.

BTW the scaling factor is completely opposite of how I think of a scaling factor. For example to monitor a 12V rail. I used a 34K and 4K resistor divider. This produces a 1.26V at the ADC. I expected the scaling factor to be 12.0/1.26 or 9.5, but the software expects 1/9.5 or 0.105.