Hello
Can the Dig Gnd of the Open Collector Tx be pulled below the Ana Gnd
by say -1 V or so ?
This would help me in coupling a 0-5V from a High Speed FO Rcvr to
the Comparator Input ..
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Hello
Can the Dig Gnd of the Open Collector Tx be pulled below the Ana Gnd
by say -1 V or so ?
This would help me in coupling a 0-5V from a High Speed FO Rcvr to
the Comparator Input ..
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
Hello Varunesh,
As explained I don't have much information available about the VFC110 as it is a legacy product. When I view the Co/s pin internal circuits on the 1987 schematic, besides the base of one NPN transistor and the emitter of another, there is a 1.2 kilohm resistor and a 50 pF capacitor to the Digital Ground pin. The schematic doesn't indicate their composition. However, since tempco is important for accurate operation I suspect the resistor is a thin film resistor and the capacitor has a an oxide dielectric. The tempco of the thin film resistors is likely in the range of 10 to 20 ppm/deg C, while the 50 pF capacitor would have a tempco similar to an quality external capacitor connected to the pin. I don't have any information how the transistors behave with temperature but it seems that would have been an important factor in the design.
Unfortunately, I do not have any information regarding long term stability of these components.
Regards, Thomas
Precision Amplifiers Applications Engineering
Hello Thomas
Thanks for your reply .
I guess I shall have to contend with what you have painstakingly dug up .
Thanks again for your sincere efforts
With kind regards
Varunesh