LDC2114EVM: ESD from an equipment

We make our devices to be resistant to EMI, but damage is always possible from handling or EMI strikes.

Before we assume there is damage and give up on the EVM, let's try a few things.

1. Check to see if the green LED indicator on the MCU section of the EVM (where the USB attaches) is lit. 
   If it is not lit, then there is a problem with that portion of the EVM, or with the USB connectivity.
   
   
2. Uninstall and reinstall the Sensing Solutions EVM GUI software and retry connecting to the FDC2114 EVM.
   
   
3. If items 1 or 2 get the GUI to show the EVM is "Connected", but the GUI isn't behaving properly, try updating the firmware for the FDC2114 using the GUI.
   To do this, connect the EVM, start the GUI, go to MENU/Firmware, click the upward-pointing arrow and in the pop-up window navigate to 
   C:\ti\Sensing Solutions EVM GUI-1.10.0\EVM Firmware\FDC2114 if you installed the GUI software in the default location.
   Click the file EVM_FDC2114.txt and select Open, and in the GUI click Upload Firmware, and your GUI firmware for this device will be updated. 
   If the GUI does not show the EVM is connected, then the problem could be with the EVM.
   
   

Please give these steps a try and let us know how it goes.

Regards,
John

Hi, Miller

Thank you for your reply!

First of all, I don't know FDC2114. I only have LDC2114EVM.  Is FDC2114EVM same as LDC2114EVM?

Regards,

Murakami

Hi John

Thanks,  I'll try your suggestion soon.

Regards,

Hi John

I tried your 3steps and the results are the followings,

1. Green LED D2 & D11 were lit before uninstall.

2. I did uninstall and reinstall it.

3. Before upload firmware>>> The EVM is "Connected" and the DATA0/1/2/3 waveforms are always 0.

    After upload firmware>>> The EVM is still "Connected" and red LED D12 is ON for a few seconds, the DATA0/1/2/3 waveforms are 0 or 0/-1. 

Can I get your advice again?

Regards,

Murakami,

My EVM was was not plotting DATA out either until after updating the firmware and restarting the GUI.
After updating the firmware and restarting the GUI, it took about 20 seconds for the data to start plotting.

Have you connected a sense coil to the EVM? If you have, what frequency is it?

Regards,
John

John,

Yes, I connect some Coils to the EVM, which are 10uH or 20uH.  I don't touch any Resonance caps on the EVM.

Regards,

Murakami 

Murakami,

Can you look at the sensor waveform with an oscilloscope?
If so, what is the DC voltage, peak-to-peak voltage and frequency?
Regards,
John

John,

Yes. I looked waveforms for INn pin with reference to COM

for 20uH coil, 1.64Vpp & 1.9MHz 

for 10uH coil, 1.88Vpp & 3.57MHz

They look larger amplitude and lower frequency.

Regards,

Murakami 

Murakami,

Is it possible to check the self-resonant frequencies of your coils?
Assuming the resonant caps on the EVMs are still 47pF, the measured frequencies look a bit low, compared to the coil inductance.

Also, would it be possible to add a snapshot of the coil waveforms to this thread?

Regards,
John

John,

I've observed waveforms again and saved 2 snapshots.

TEK00003.TIF is 2.94898MHz & 1.6Vpp for 20uF coil.  

TEK00007.TIF is 3.80084MHz &  1.9Vpp for 10uF coil.

They are different from data which I wrote in previous message. I don't know the reason.

But I think data this time are more reliable.   

By the way, there are 2 LDC2114EVMs which seem damaged due to ESD.

The 2 snapshots were taken from different the EMV.

Regards,

Murakami

Murakami,

Thank you for uploading the waveform images to this thread.
The waveforms' frequencies are okay, but I'm not sure of the amplitudes.
Were the signals measured between INx and COM, or INx and GND?

Also, would you please try adjusting the RPx bit in the SENSORx_CONFIG register to see if it changes the waveform amplitude, and post the result to this thread?

Regards,
John

John,

I want to know why the frequencies are OK.

The input cap is  total ~70pF ( 47pF(on EVM) + 17pF(CIN) + 12pF(probe)) 

So the frequencies should be ~6.0MHz for 10uF,  ~4.3MHz for 20uH. Am I right? 

The signals were measured between  INx and COM.

For adjusting RPx,  before measuring it, I also want to know the relationship between amplitude and RPx.

Anyway,  I can't control the GUI as I want, although I'm referring to  "LDC2114EVM: Cannot configure LDC2114EVM through Sensing GUI" in this site.

DATAx (connecting to 10uF or 20uF) in data streaming in GUI are still 0/-1 or 0.

Also, I want to know difference of ESD rating between LDC2114 and LDC1314.

For LDC2114, HBM 1KV / CDM 250V, For LDC1314 HBM 2kV/ CDM 750V

Could you tell me the difference of ESD regarding to input circuit?

Regards,

Murakami

Murakami,

When saying the frequencies are okay, I meant on that they are within the ranges published in the data sheets.
They do not agree with the LC calculations.

Is the self-resonant frequency known for your coils?
This is the resonant frequency of the coil without a capacitor.
It may be in the coil specs, perhaps listed as "SRF". 
If that is not possible, can it be measured?
It may be the LC calculations are different because the LC resonance is close to the coil's self-resonant frequency.
We recommend the LC resonant frequency is less than 25%-35% of the coil's self-resonant frequency.

An app note about measuring Rp can be found here.
We don't have an exact formula for Rp and amplitude.
The LDC2114 automatically does the amplitude adjustments based on the sensor's Rp and the RPx bit of the SENSORx_CONFIG register.
I'm not sure how the sensor waveform will look if the RPx bit does not agree with the actual sensor RPx.
For example, if the sensor RPx is 350 ohms, but the RPx bit is '1', then the amplitude may not be as recommended.

The ESD circuits are diodes that provide a path for current resulting from an ESD discharge on a pin. 
The diode parameters are optimized to give the required ESD protection while not interfering with the normal operation of the pin.

Regards,
John

John,

SRF is 20MHz for 10uH, 12.5MHz for 20uH.

So the parasitic CAP is 6.3pF for 10uH, 8.1pF.

I don't think  the parasitic CAPs change the frequencies largely.

To change Rp, I have to know a correct procedure to change the registers using the GUI

Is there any manuals to change the resisters surely?

Regards,

Murakami 

John,

For Rp in previous measurements, 350< Rp <4k Ohms.

After changed 800<Rp<10k Ohms,  

For 20uH, don't oscillate,,

For 10uH, the amplitude & frequency didn't change. 

I also want to know how to check if the resister Rp changes correctly.

(Sometimes the Rp returns to original value on its own... )   

Anyway, I want to hear your opinion of EDS damage in these EVMs at this moment.

and also want to know how to improve immunity for ESD from outside. 

Regards,

Murakami

Hello, 

For changing the Rp register settings, make sure to put the EVM in configuration mode first before changing any of the settings: 

To check the Rp value change, you can check the registers tab of the GUI or close the GUI and reopen without removing power from the EVM it so the values in the configuration tab have to be re-read from the device. 

I also had a couple notes on how you are measuring the sensor waveform. You should be measuring between INx and GND with an oscilloscope probe. Unless you are using a differential probe, most oscilloscope GNDs are connected to earth GND and will tie the COM pin to GND if connected that way. Additionally, you can decouple the capacitance of the oscilloscope probe by adding a 1kOhm resistor in between the sensor INx and the oscilloscope probe. This will prevent the probe from having an impact on the oscillation frequency. 

In regards to immunity for ESD from outside, what type of application is this in and what is the use case where you expect ESD beyond the spec in the datasheet to be an issue? 

Best Regards, 
Justin Beigel

Hi Justine,

Thank you for your comment.

For changing resisters, I often fail to change resisters..

I think some waiting time is needed after changed resisters. Am I right?  

If so, do you know how long the waiting time is?

For measuring waveform, TEST condition in the datasheet is " Measured on the INn pins with reference to COM". 

Is that wrong?   

If I measure  Measured on the INn pins with reference GND pin, what is the TYP amplitude? (Still 0.9Vpp?)

For ESD, I can't tell the application in this forum.

I think we need NDA and confidential communication if I use the LDC for the application.

Could you tell me your company's guideline for confidential questions?

Regards,

Murakami