VFC110: VFC110 Open Collector Dig Gnd

Hello Varunesh,

The VFC110 is a legacy product from the 1980s and there isn't much information about the product remaining. I did locate an internal schematic for the device and it looks like the analog and digital grounds are separate but there are some connections between each other via transistor/diode junctions. The paths are complex so it is difficult to know how moving them apart by a small voltage will affect the VFC operation. However, doing so doesn't look like it will damage the device provided the voltage difference is kept small.

The digital ground connects into the one-shot stage and the TTL output. Therefore, making the digital ground slightly negative may affect the one-shot behavior. If you try applying a small negative voltage to digital ground I wouldn't make the voltage any more negative than necessary; preferably -1 V or less. Then, see how the VFC behaves.

TI cannot make any assurances about what will happen or how the electrical performances will change because the connection you are considering falls outside the datasheet recommendations. If you are willing to experiment you may find it does what you need.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello Thomas 

Many thanks for your efforts to dig up the old archives .

Greatly appreciate ..

I will certainly do that experiment to satisfy my curiosity ;

but since it might fall outside the guaranteed Specs ; I shall

use an alternative Soln ; which I subsequently worked out .

Whilst on the Subject ; I do have a related Q .

What is the TEMPCO and the Long Term Stability of the 

internal Rin and the Cos that determines the One Shot Timer ?

If there was no internal Cos ; the TEMPCO and the LT Stability

would depend entirely on the external Cos ; but since the internal 

Cos comes in parallel ; it does have that dependence .

Rin dependence can be eliminated ; thanks to the Inv Input coming out ;

but Cos ; there is precious little one can do about .

Hence this Q reg TEMPCO & LT stability .

Once again sincere thanks for your efforts to dig up old archival data 

Regards

Varunesh