New Bipolar Boost TX and Front End

[KingJL]

This sounds like a very good idea. I like it a lot.
I currently use the LT1371 in a number of circuits and have a design ready to go, I have a few rails of this device too.
The device is good for 3 amps, current limiting and soft start. Its been a nice reliable part for me.
We probably won't require the inrush limiter using this device.

Sounds like a plan!!!

[KingJL]

This sounds like a very good idea. I like it a lot.
I currently use the LT1371 in a number of circuits and have a design ready to go, I have a few rails of this device too.
The device is good for 3 amps, current limiting and soft start. Its been a nice reliable part for me.
We probably won't require the inrush limiter using this device.

Just so I have the correct parameters for a future redesign of the TX-RX PCB, I will assume the following: (1) we have regulated 5V and regulated 20V with no need for inrush current limiting for either one. (2) The boost regulator supplying power to the 20 linear regulator will be dis-abled starting at TX off and lasting for 20% of PRT time. (3) we are using ADuM4120 for all MOSFET drives except for M5A & M5B, , which will use a single EL7222... six ADuM4160's in all. (4) Will will use a dual JFET ( two opa82 ) pre-amp configured for differential input. (5) we will use the improved TX boost circuitry to achieve true constant current TX. (5) provide test points for MOSFET gate/source on top side of PCB. (6) provide a signal from source of M5 A/B to FPGA via J9.

I will start a new PCB schematic and layout with these changes. This will not affect our current PCB testing efforts, but will be on going in parallel. Are there any other changes needed/desired for the TX-RX PCB?

[Mdtoday]

Just so I have the correct parameters for a future redesign of the TX-RX PCB, I will assume the following: (1) we have regulated 5V and regulated 20V with no need for inrush current limiting for either one. (2) The boost regulator supplying power to the 20 linear regulator will be dis-abled starting at TX off and lasting for 20% of PRT time. (3) we are using ADuM4120 for all MOSFET drives except for M5A & M5B, , which will use a single EL7222... six ADuM4160's in all. (4) Will will use a dual JFET ( two opa82 ) pre-amp configured for differential input. (5) we will use the improved TX boost circuitry to achieve true constant current TX. (5) provide test points for MOSFET gate/source on top side of PCB. (6) provide a signal from source of M5 A/B to FPGA via J9.

I will start a new PCB schematic and layout with these changes. This will not affect our current PCB testing efforts, but will be on going in parallel. Are there any other changes needed/desired for the TX-RX PCB?

This is looking great, I will take a look over my assembly notes and comment soon and will also post the 20v PS circuit in ltspice format for you to have a look at.

[KingJL]

This is looking great, I will take a look over my assembly notes and comment soon and will also post the 20v PS circuit in ltspice format for you to have a look at.

@Mdtoday, when you get a chance, look over this new schematic to implement the changes. In addition to changing the pre-amp to a dual opa828 differential input configuration, I changed the bipolar to unipolar methodology. I eliminated the switching of the coil at the pre-amp input, and added an opa627 inverter to follow the dual opa828 frontend, and used DG333 section A to switch the pre-amp output between the opa828 output and opa627 controlled by the TX_AB switch signal. This has the advantage of effectively nulling out any offset errors of the opa828(s) and only utilizing 1 spdt section of the DG333 where the previous configuration required 2 sections of the DG333 convert bipolar to unipolar. I also removed the DG418 and used the remaing section D of the DG333 for RX blanking.

I think I have included all items that I had previously mentioned. I will post the kicad files when I am sure that I have collected all needed files.

edit: I think I have the kicad files together... if anyone has trouble opening in kicad, please let me know and I will try to resolve the issue(s). Currently the only thing completed is the schematic... the PCB work will probably start tomorrow.

[Mdtoday]

@Mdtoday, when you get a chance, look over this new schematic to implement the changes. In addition to changing the pre-amp to a dual opa828 differential input configuration, I changed the bipolar to unipolar methodology. I eliminated the switching of the coil at the pre-amp input, and added an opa627 inverter to follow the dual opa828 frontend, and used DG333 section A to switch the pre-amp output between the opa828 output and opa627 controlled by the TX_AB switch signal. This has the advantage of effectively nulling out any offset errors of the opa828(s) and only utilizing 1 spdt section of the DG333 where the previous configuration required 2 sections of the DG333 convert bipolar to unipolar. I also removed the DG418 and used the remaing section D of the DG333 for RX blanking.

I think I have included all items that I had previously mentioned. I will post the kicad files when I am sure that I have collected all needed files.

edit: I think I have the kicad files together... if anyone has trouble opening in kicad, please let me know and I will try to resolve the issue(s). Currently the only thing completed is the schematic... the PCB work will probably start tomorrow.

Ok will do JL, that’s fair parts reduction , nice work!

[Mdtoday]

Ok will do JL, that’s fair parts reduction , nice work!

@KingJL, I had a reasonable look over the schematic and it looks good.
The only query I have is the value of C22, I thought there was a post regarding the change to that area but I can't find it, is 2n2F correct?

I will have another look over the schematic again but it looks Ok JL, thanks for sharing, great work!

[KingJL]

... The only query I have is the value of C22, I thought there was a post regarding the change to that area but I can't find it, is 2n2F correct?

Actually 22nF (original was 220n) I had changed the footprint, but failed to correctly state the value.

I will have another look over the schematic again but it looks Ok JL...

There is one other error on the posted version... the pins for the ADuM4120 are incorrectly numbered. I didn't notice it until I tried to place the input capacitor between pins 1 & 3! I am also going to remove all TP's from the schematic and add them later after component placement. Will post updated files/schematic after some more checking.

[Mdtoday]

Actually 22nF (original was 220n) I had changed the footprint, but failed to correctly state the value.There is one other error on the posted version... the pins for the ADuM4120 are incorrectly numbered. I didn't notice it until I tried to place the input capacitor between pins 1 & 3! I am also going to remove all TP's from the schematic and add them later after component placement. Will post updated files/schematic after some more checking.

No problems JL, yes, I hadn't compared the schematic to footprints on data sheets for the newly added devices yet and I didn't realise that the ADuM4120 is a 6 pin device, good that you caught that one!

[KingJL]

... Will post updated files/schematic after some more checking.

The corrected kicad files. The PCB is still a work in progress, I need to tweak/relax the layout.

[eclipse]

Can you please upload PDF on the latest revision.
Is REF voltage regulator LM317 needed (= resistor divider)?
Can a stock DD (minelab) coil be used with this (or shielding connections will be a problem)?

[Mdtoday]

The corrected kicad files. The PCB is still a work in progress, I need to tweak/relax the layout.

Looking good!

[Mdtoday]

Can you please upload PDF on the latest revision.
Is REF voltage regulator LM317 needed (= resistor divider)?
Can a stock DD (minelab) coil be used with this (or shielding connections will be a problem)?

@Eclipse, here is a PDF copy of KingJL's last posted Kicad schematic files.
Kicad_TX_ADUM_drive(12-21-2019).pdf

As you have thought, The standard ML DD and mono coil shielding wiring being referenced to gnd and tied to one side of coil winding will be a problem without mods in coil to shield connection to isolate the winding from gnd..

[KingJL]

Can you please upload PDF on the latest revision.

TX_ADuM.pdf

Is REF voltage regulator LM317 needed (= resistor divider)?

It is there for accurate adjustment of the voltage to the ADC. Using the voltage divider will work, but you'll have to adjust your ADC output to account for any offset voltage from the opa627 (the offsets of all others should filter out).

Can a stock DD (minelab) coil be used with this (or shielding connections will be a problem)?

They should work as long as the shield connections are not connected to GND of the TX-RX board. Not sure how effective shielding will be. Ideally, shield should not be connected to any of the coil leads, but be separately connected to chassis GND, with independant conductors for the coil leads.

[KingJL]

TX with ADum4120 MOSFET driver

... The PCB is still a work in progress, I need to tweak/relax the layout...

The schematic and board layout is completed. I added test points (all accessible from the top side of PCB) for 5V, 20V, Vdd, REF, M5A&B source, M1 gate & M1 sorce, M3 gate & M3 source, M2 gate, M4, gate, m6 gate & M6 source, M7 gate & M7 source, and pre-amp out. I added an output line to J9 for the signal at the source of M5A&B. The TX current from the end of TX boost until TX off can be measured (voltage drop across R2, R3, R4, and R5) at this point. If we use the old IF board, we have to cut the trace from from J1-5 to PIO40 to prevent damaging the CMOD-A7 (we need a new I/F board).
Schematic:
TX_ADuM.pdf

Board top view:


Board bottom view:


Kicad arcive and gerbers:
Kicad_TX_ADUM_drive(12-22-2019).zip
TX(ADuM)-Gerbers(12-22-2019).zip


@Mdtoday (and anyone else so inclined) would you put your eagle eye to the board layout when you get time. Again, none of this is time critical.

[waltr]

Wow, looks good.

Is there a timing diagram of all the drive signals?
I am thinking of trying this TX/pre-amp circuit but run the timing from a PIC32 instead of the FPGA.