DRV8662: DRV8662 with sensing circuit

Hi Shozo,

we have received your questions. I will get back to you after check with the team.

Br,

Wenbin

Hi, Shozo,

Could you provide the details about the sensing circuit you are using? Usually, our evaluation modules don't include a sensing circuit. Just single test points to measure the output with scope probes.

It is important to consider that the DRV8662 output has some bandwidth limitations if the output capacitance increases. If the sensing circuit capacitance is high, this would explain the voltage dropping.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

I attached the design file.

Without DRV8662, we can detect the output of the piezo element.

But with DRV8662 connected, the output magnitude greatly decrease.

Two diodes are connected to protect our receiver cricuit from high voltage of DRV8662.

The capacitance of our piezo element is 10 to 30 nF, not to large.

If you have any seggestion ,please let me know.

Regards,

Shozo

DRV8662+receiver.pdf

Hi Luis,

You called me, right?

Sorry to intrrupt you.

If possible, would you please send me by e-mail?

If you will tell me your e-mail, I will send you by e-mail.

Now I am in the open space room.

If necessary, I will move to the private room and I can call you by phone.

I prefer to use e-mail.

Thanks,

Shozo

My e-mail address is 

sootera@murata.com

Thanks,

Shozo

Hi, Shozo,

I sent you a friendship invite through the e2e chat. We can talk privately through the chat.

In addition, if you use a scope to monitor the piezo element output, do you also see changes on the voltage level?

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

I am going to monitor the voltalge level.

I will let you know the result later.

I want to confirm one thing. That is when DRV8662 does not ouput, the impedance of the output terminal is high or low or not stable?

And I want to ask you one thing.

How can I do chat in this E2E? And what time is convenient for you?

There may be time lag between Japan and your location.

Thanks,

Shozo

Hi Luis,

I attahced the output of our receiver.

The output is a little bit noisy. It depends on the grounding and shielding.

As you see, after DRV8662 is connected, the bias voltage remains constant but the variation of the voltage get smaller.

We want to get the same level of variation even after DRV8662 is connected.

Regards,

Shozo

Sensor Output.pdf

Hi, Shozo,

You can use E2E chat anytime you want. I can take a look at the messages in my work time.

Have you tried with the scope probe that I mentioned previously in order to see if you get the same results? In addition, what is the purpose of the 1k resistor connected between the piezo element and the operational amplifier?

The DRV8662 output should be placed in high-impedance when the device is disabled.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

E2E chat means this post message? Or are there any other communication mechanism? Sorry I am not familiar with this kind of SNS.

And I am not familiar with the scope probe? Does that mean that measruring voltage by usiing osciloscope probe?

You mean that we should add some pull-up resistor in the DRV8662 output or that pull-up resistor is connected in DRV8662 circuit?

If we add the pull-up resistor, that resistor should be connceted betweeen the output and boost-up voltage?

The purose of the 1k resistor is to avoid the decrese in the output voltage of DRV8662 with the receiver circuit connected.

But to tell the truth, we are not sure htat this measure or the value of the resistance is appropirate or not.

So I want TE to show us some recommendeted circuit for this purpose.

Regards,

Shozo

Hi, Shozo,

Yes, the E2E chat allows to send direct messages to me instead of using a public forum.

I requested a voltage measurement with a oscilloscope probe in order to verify if the voltage dropping is caused by your sensing circuit or your piezo load. If you are able to monitor the voltage level correctly with the help of the oscilloscope, then the problem should be the sensing circuit.

No need to add resistors to the DRV8662 output due to the high voltage that the device handles.

Best regards,
Luis Fernando Rodríguez S.

Hi, Shozo,

Please let me know if you have questions or comments about my previous response.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

We tried to measure the impedance between the output ports of DRV8662 with EN Low.

We expected that the impedance would be high when the EN is low.

We measured that about 20mA flows when 3 V is applied between the output ports.

From this measurements, I think the impedance between the ouput ports with EN low is not hig.

So when we measure the output voltage which is derived the piezo element, the magnitude of the voltage signififantly decrese.

And we are concerned that if my idea is right, we will not be able to measure the output voltage of the piezo element with DRV8662 is connected.

I want to confirm that my idea is right or not.

And if this idea is right, we want to know how to avoid such inconvenience.

We need the circuit configuration where the piezo element is connected to DRV8662 and the output voltage derived from the piezo element can be measured.

In our circuit, we use two diodes for limiting high voltage. We have checked it is working well.

But the problem is the output impedance of DRV8662.

Would you please show us some example of the circuit?

Regards,

Shozo

Hi, Shozo,

I'm taking a look at this. I will provide a response shortly.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

I am waiting for you repsonce.

I want to modify the electirc circuit I sent you before.

The need to use DRV8662 with sensing circuit would be high, I think.

Your suggestion will help us to use DRV8662 in other application.

Regards,

Shozo

Hi, Shozo,

Sorry for the late response. Our team is still taking a look at this request. We will come back to you shortly.

Best regards,
Luis Fernando Rodríguez S.

Hi, Shozo,

If you are capable to measure the output of the DRV8662 with an oscilloscope (no additional components between the piezo load and the scope) and without any voltage dropping, then you would only need of an operational amplifier with enough input impedance to measure the output level.

Have you already monitored the output with an oscilloscope? Do you see a proper output signal without voltage dropping?

Please remember that the DRV8662 output is directly affected by the connected loads. Capacitive loads will affect the output bandwidth, so make sure that there are no additional capacitance levels in the components you add in your circuit.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

I already monitored the ouput with an osilloscope and ascertained a proper output signal.

I evaluated that the detection circuit does not affect the DRV8662 operation.

The problem is that the DRV8662 affect the detection circuit.

To make it clear about my question, I list my qeustions I asked you in my last chatting.

1) The output impedance of DRV8662 with EN terminal low is high, low, or unstable?

2) Do you have any example circuit diagram for driving a piezo element with DRV8662 and detecting the output voltage of the piezo element concurrently?

Other provider's IC can drive piezo element and, at the same time, detect the output of piezo element.

I know that DRV8662 does not provide the detecting function.

I want to know what circuit should be added to DRV8662 to obtain the same function as other provider's IC.

I appreciate you if you can give me the replies.

Regards,

Shozo