New Bipolar Boost TX and Front End

[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..

[Mdtoday]

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

Looking good!

[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)?

[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.

[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]

... 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]

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!

[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!

[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]

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 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?

[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!!!

[Mdtoday]

@Mdtoday, Is there a possibility to have a more robust 20V supply? Here is my thinking... After moving to ADuM4120's for the TX boost and damp MOSFETs, remove the remaining EL7202 (TXA and TXB) and replace it with two ADUM4120's, one for TXA and one for TXB. This has a few advantages: (1) it matches the propagation delays between TXA, TXB, TXA_boost, TXB_boost. This maximizes the efficiency of the boost... currently the ADuM4120,s require a 10 nsec delay to get close to synchronization with the EL7202. 10ns does not quite match the delay needed, but 10 ns is the minimum granularity of the FPGA. (2) It removes the need for the 15V regulator. (3) we could take the 20V input through a inrush protection and isolation diode to a 220uF storage tank and use this voltage as the Vdd2 for the ADuM4120 and for the feeding the boost. This ~18.5V Vdd2 ends up achieving about 14V MOSFET drive for the TX boost MOSFET(s) and the damp MOSFET(s) and 18.5V for the TX MOSFET(s). This makes it so that all grades of the ADuM4120 can be used.

I can take the inrush current limiter that is now in the 5V circuit (it is really not needed now) and put it to the 20V circuit (need to boost the 20V by 1.25V to compensate for the loss across the inrush current limiter). I can remove the 15V regulator circuit. We can set the inrush current limit to about 450mA to allow for initial charging of the storage tank in a somewhat timely fashion (6-8 ms). After the tank is charged the Vdd2 (for all 6 ADuM4120's) current draw and boost supply is only about 40mA. It is only for the inrush that we need to have the capability of ~450mA.

I do not know if the MT3608 can handle the switch current (not sure if the internal switch current is automatically limited) that would be needed for the inrush, but a similar IC (LT1935) can. I have modeled it using your current 22uH inductor and using blanking for 20% of PRT. I am not sure what we need for the 20V regulator.

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.

[KingJL]

@Mdtoday, Is there a possibility to have a more robust 20V supply? Here is my thinking... After moving to ADuM4120's for the TX boost and damp MOSFETs, remove the remaining EL7202 (TXA and TXB) and replace it with two ADUM4120's, one for TXA and one for TXB. This has a few advantages: (1) it matches the propagation delays between TXA, TXB, TXA_boost, TXB_boost. This maximizes the efficiency of the boost... currently the ADuM4120,s require a 10 nsec delay to get close to synchronization with the EL7202. 10ns does not quite match the delay needed, but 10 ns is the minimum granularity of the FPGA. (2) It removes the need for the 15V regulator. (3) we could take the 20V input through a inrush protection and isolation diode to a 220uF storage tank and use this voltage as the Vdd2 for the ADuM4120 and for the feeding the boost. This ~18.5V Vdd2 ends up achieving about 14V MOSFET drive for the TX boost MOSFET(s) and the damp MOSFET(s) and 18.5V for the TX MOSFET(s). This makes it so that all grades of the ADuM4120 can be used.

I can take the inrush current limiter that is now in the 5V circuit (it is really not needed now) and put it to the 20V circuit (need to boost the 20V by 1.25V to compensate for the loss across the inrush current limiter). I can remove the 15V regulator circuit. We can set the inrush current limit to about 450mA to allow for initial charging of the storage tank in a somewhat timely fashion (6-8 ms). After the tank is charged the Vdd2 (for all 6 ADuM4120's) current draw and boost supply is only about 40mA. It is only for the inrush that we need to have the capability of ~450mA.

I do not know if the MT3608 can handle the switch current (not sure if the internal switch current is automatically limited) that would be needed for the inrush, but a similar IC (LT1935) can. I have modeled it using your current 22uH inductor and using blanking for 20% of PRT. I am not sure what we need for the 20V regulator.

[eclipse]

Thanks it was the LTSpice version. After the upgrade to 03 Dec 2019 I was able to run it.
I'm definitely building this. I'll be using my processor and analog circuitry to get this closer to my knowledge.