|
|
|
# PCB Review Agenda 20-01-2012
|
|
|
|
|
|
|
|
The DEM files of the project 02446 can temporally be found
|
|
|
|
[here](https://www.ohwr.org/project/conv-ttl-blo/wikis/documents).
|
|
|
|
|
|
|
|
In the PCB Review to be held the Friday 20th January the main points to
|
|
|
|
be discussed are:
|
|
|
|
|
|
|
|
- Schematics
|
|
|
|
- Isolation: options and compatibility with legacy boards.
|
|
|
|
- Rear Transition Module pinouts and compatibility with
|
|
|
|
CONV-TTL-RS485: adding RTM passive\[?\] IDs
|
|
|
|
|
|
|
|
<!-- end list -->
|
|
|
|
|
|
|
|
- PCB received from DEM
|
|
|
|
- Issues found: like 3V3\_IC7 power plane, small\[?\] 1V2 plane
|
|
|
|
for FPGA, FOD060L replacement, VME64x spacings.
|
|
|
|
|
|
|
|
## Schematics
|
|
|
|
|
|
|
|
### Isolation
|
|
|
|
|
|
|
|
Different isolation connections are found at CERN. However, there's not
|
|
|
|
an strong agreement of how to specifically do this for the case of
|
|
|
|
either the Blocking boards or the next RS-485. A couple of good
|
|
|
|
references for gaining insight are "Goods for grounding"\[1\], which
|
|
|
|
gives a from a system point of view how to solve grounding issues, and
|
|
|
|
"Noise Reduction Techniques in Electronics Systems"\[2\] that offers a
|
|
|
|
quick and straightforward technical approach for cable grounding.
|
|
|
|
|
|
|
|
The isolation problem found in the schematics lies in the floating state
|
|
|
|
of both the driver and the receiver, which as pointed out in \[1\], can
|
|
|
|
yield problem for an operator. Thus, an acceptable schema for the
|
|
|
|
Blocking board can be as follows:
|
|
|
|
|
|
|
|
- Driver will be isolated (via couple inductors)
|
|
|
|
- Receiver must be grounded
|
|
|
|
|
|
|
|
\[2\] explains that for low frequencies, like the ones expected for the
|
|
|
|
Blocking case (\< 10MHz), breaking the ground loop by only grounding at
|
|
|
|
one end is effective.
|
|
|
|
|
|
|
|
So as to be compatible with legacy boards, **the receiver should be
|
|
|
|
grounded and changes should be done in the Schematics and PCB**.
|
|
|
|
|
|
|
|
Another issue found is the **Fairchild's FOD060L should be replaced**
|
|
|
|
due to difficulties to be supplied immediately. However, pin-to-pin
|
|
|
|
compatible replacements from **Fairchild** (**6N137.S**, HCPL-2601.S,
|
|
|
|
6N136.S) or Avago (HCPL-2611-300E) are widely available.
|
|
|
|
|
|
|
|
### Rear Transition Module
|
|
|
|
|
|
|
|
*Identification**: A proposal can be found in this [wiki
|
|
|
|
page](/RTM-board-detection). **Pull-ups and buffers must be added to the
|
|
|
|
design** and **P2 pinouts should be done**.
|
|
|
|
|
|
|
|
*P2 pinout modification**: so as to build a good generic RTM
|
|
|
|
motherboard a compatible pinout must be set up between CONV-TTL-BLO and
|
|
|
|
CONV-TTL-RS485 projects. A pinout proposal can be found
|
|
|
|
[here](https://www.ohwr.org/935).
|
|
|
|
|
|
|
|
## Layout
|
|
|
|
|
|
|
|
Issues found:
|
|
|
|
|
|
|
|
- Plane 3V3\_IC7 \> Plane 3V3
|
|
|
|
- Possibly 1V2 can be bigger layouted
|
|
|
|
|