OPA548EVM: .

Hi Nicolas, 

Nicolas Fellas said:

the -30V output from the power supply into the AVSS on the dev board

Please explain -30V. Are you using single or dual supply voltage rails for the dev board?

Nicolas Fellas said:

Is there a way I could debug the board and find out if there is something fried on the board

Yes, you need to connect the output to a power resistor that is able to drawing up to 1-5A of load. You need start with higher resistive load, then gradually doing to lower R values. If the voice coil is 4Ω or 8Ω inductive load, you may have issues to drive it properly. For instance, if Vout swing is the same as the input voltage, say 2Vpp, then the output peak current should be approx. 1Vpk/4Ω = 250mApk, it should be able to drive it. However, if the Vout swing is 20Vpp, then the output peak current is going to be 10Vpk/4Ω = 2.5Apk. In theory, it should be able to drive it. But you have consider the power supply %regulation, decoupling capacitors, voice coil inductance, heat sink, power amplifier's case and junction temperature etc.. I am enclosing a OPA548 simulation, and check out the simulation first. 

I think what you did. You are using negative single supply rail to configure the dev board. Please make sure that you setup the Vcm bias properly, otherwise it is not going to work, see the simulation. 

OPA548 E2E 05192023.TSC

Please let me if you have other questions. 

Best,

Raymond

Hi Raymond,

To answer your initial question , 

I am using a dual supply PSU, I was initially using only the negative rail , but that is not really working.  I tried using only the -v and ground , but also tried +-v & ground and it seems thi is not making any difference. 

I was able to get very very low output by changing the function generator amplitude from 2vpp to 20vpp , so i am guessing somewhere along the way of the amplifier something is not going right. Since I am using the opamp in the inverting input , i am following pafge 12 of the manual to be able to get some amplification but it seems not to work. 

The voicecoil is 2 ohms incase this helps. 

I will try the steps you recommended to debug the board but if anything I might have overseen comes up, please mention it and thanks 

Hi Nicolas, 

Nicolas Fellas said:

The voicecoil is 2 ohms

The 5Apk current is the max. current that part is able to source and sink. You would need to provide good size heatsink to dissipate the heat. 

In addition, you need to minimize |Vs| -Vout delta voltage, which smaller difference would be better. There will be Vout voltage swing limit when the peak current is reached 5Apk, see the table inserted in the simulation file. 

If you have the voice coil L,C and R parameters, please send it to me. It may affect the loop stability of the amplifier; it is something that is should be checked out. 

OPA548 E2E 05252023.TSC

If you have additional questions, please let us know. 

Best,

Raymond

I have the following information  : 

Coil resistance : 5.1 Ω

Coil Inductance : 1675 µH

Maximum Current : 0.89 A @ 60 °C
1.90 A @ 200 °C

Thanks

Hi Nicolas, 

Nicolas Fellas said:

Coil resistance : 5.1 Ω

Coil Inductance : 1675 µH

Maximum Current : 0.89 A @ 60 °C

The simulation indicated that the following circuit is stable with 63 degree of phase margin. You did not provide me with winding capacitance parameter, which it may be another parameter to be checked out. 

OPA548 E2E Coil 05252023.TSC

What is the voice coil's operating frequency range. 

Nicolas Fellas said:

1.90 A @ 200 °C

Where does the figure come about? OPA548's junction temperature is only rated up to 150C, and you would need to keep it as low as possible. You would need to provide adequate cooling, else the op amp will be damaged. 

Please let me know what are the current issues, and I will be happy to assist. 

Best,

Raymond

Hello! 

I am unsure of the frequency range of the voice coil and neither the winding capacitance , but we will be using a sinusoidal wave generated by a DAW or a standalone function generator. 

I have not tried a phase shift to the signal yet, but since i am not able to get any initial movement from the voicecoil, could it be that The board is malfunctioning ? 

The voicecoil purchased is the following one  : 

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=14116&pn=VC250/M

They recommended this dev board and some instructions of where to plug what, yet it seems it does not work from the beginning. It could be that the board was damaged while initially testing but my multimeter tests show signal flowing through the circuit. 

Hi Nicolas, 

Please try the following configuration from the EVM. It should operate up to 20kHz range.  You would need to modify the existing EVM feedback capacitor as shown in the simulation below or remove the feedback capacitors completely from EVM. I checked the loop stability, which is simulated at approx.  75degrees as shown in the image below. 

OPA548 Step Transient 06062023.TSC

 If you have additional questions, please let me know. 

Best,

Raymond

Hi & thanks for the reply! 

I will try this today and let you know how it goes.

Thanks for the help

I just checked my board and we have no capacitor in C1, so the pads are soldered but not connected with any capacitor. I would like to try to add a capacitor and see if this helps, do you have any recommended value i should try?

Hi Nicolas, 

Nicolas Fellas said:

do you have any recommended value i should try?

Please jump the OPA548EVM as shown below. 

If you have additional questions, please let me know. 

Best,

Raymond

jumpers have been set to your recommendation. Should i completely remove the 2k resistor and just bridge that and the capacitor pins too? since there is no capacitor, i would just connect both terminals with a blob of solder. 

Hi Nicolas,

Nicolas Fellas said:

Should i completely remove the 2k resistor and just bridge that and the capacitor pins too?

You mentioned that the requirements are -5V/V in the inverting op amp configuration. So R2 needs to be 2kΩ. You can remove R2 of 10kΩ and replace it with 2kΩ resistor. Or you can solder 2.5kΩ in parallel with R2 (10k), which 2.5k||10k is equivalent to 2kΩ. 

It is much easier to jump JP4 and JP5 pins. If you do not have jumpers on hand, you can invert the PCB and shorted JP4 and JP5 jumper to ground (These are through hole parts).  

Please let us know how it drives the voice coil. 

Best,

Raymond