Schematic revision 10-11-2011
The questions that arosed in the schematics revision held the 10th November 2011 are answered in this webpage.
Output Blocking
Can we remove the Power MOSFET driver?
Yes, we can remove it.
However we have to take into account that the MOSFET used should be able to be activated with logic levels. In the case of the Power MOSFET tested and used in the design, IRLML0060TRBF, this level is around 2V. Hence, it can be driven directly with SN64BCT25244 --as it has been tested. To reduce the stockage, a BSH103 MOSFET can be used with no side-effects reliability-wise. Indeed, its lower threshold, around 0.8V, is an advantage over IRLML0060L.
All of these changes have been tested in lab thanks to CTRV and a pulse with the following parameters is achieved:
- Rise time of 40us
- Fall time of 333us
- Pulse length of 2us under a load of 50 Ohms
Reducing components in the snubber circuit
One BAS16 diode has been supressed. The snubber resistor used is now 1K to reduce BOM.
Input Blocking
The input blocking is able to supress the DC component that could be coupled and let the pulses pass by derivating slowly the signal.
Antiparallel diode. Why?
The task of the antiparallel diode is to not allow the LED achieve a reverse voltage. In the case of FOD060 this voltage is around 5V, so better using a switching diode like BAS16 rather than the 3.6V schottky one. BOM is reduced.
Modifying the threshold
The most effective way to modify the threshold consist of adding a shunt resistor to the antiparallel diode. This resistor will drain a threshold current from the input according to the working voltage of the FOD060 internal LED. By taking a look to the working curve in the schematics, a threshold of 6V is set by design.
The measures showing the behaviour of the Std. Blocking Generator and input received after the optocoupler can be found at the bottom of this page.
Yellow plot represents the Std. Blocking pulse and the pink plot is the output of the optocoupler.
Input TTL
Now the 3.6V schottky is replaced by a BAR66 which is a better option and already in stock.
Capacitors to improve reliability
Tantalum capacitors are used instead of the electrolitic ones. Voltage rating is added to the schematics.
Missed pullups
The missed pullups are added in the JTAG connector to force the JTAG TAP controller to stay IDLE.
The antiglitches now are revised and the antiglitch pull-down resistor is added for the TTL and Blocking output triggers, which is the SN74BCT25244.
Change of FPGA
We have finally moved to the LX45T as to be the same as SPEC.
Schematics
Checked by compilation. Now are much clearer and beautiful :-)