LDC1612EVM: The sensor frequency shown in the UI

The sensor frequency is calculated from equation 6 in the datasheet, but where fref is the selected clock frequency. Note that since changing the clock frequency does not change anything on the EVM itself, you should either:

- leave it at the default if you haven't supplied your own clock, or
- change it to the frequency of clock that you supply.

If the frequency still isn't matching, then please double check that the INx amplitude is between 1.2V and 1.8V (this can be adjusted with the IDRIVE setting).

Hi Clancy,

Thanks for your reply.
I agree with your points. For external clock, I change it to the frequency that I provided in the UI, which in this case is 3MHz. The amplitude measured at IN0A varies a lot... at one point I am getting about 13V, some others about 1.2V. The IDRIVE setting in my UI shows code 17 (current 196uA). This seems to be a problem... Since I am using a function generator as external clock, I am giving it 10Vpp amplitude (for 3MHz), otherwise anything lower does not provide a stable frequency. Is this 10Vpp ok?

Ali,

What is the single-ended maximum and minimum voltage when you measure the clock signal? You should not supply more than VDD + 0.3V or less than -0.3V on any pin. Violating this can cause unexpected behavior, and this could be why you are seeing 13V on INx (which is much too high).

Hi Clancy,

Ok, I understand. If I apply about 2V amplitude (within the range), nothing as far as the measured frequency is displayed in the UI... I have tried this several times and that is why I stated in my previous why I applied more than 8V as amplitude to the clock signal. Let's say if I am applying amplitude in the range per datasheet, why am I not able to see the measured frequency?
BTW. I have another post on here relating to frequency being changed via firmware and Bala Ravi is the engineer who supported me. Perhaps by looking at this post, it can provide some history.
Thanks.

Regards,
Ali

Ali,

Can you link to that post?

Also, can you look at the INx waveforms using an oscilloscope while you are using the correct clock input range? This will tell us if you are at least getting a valid drive signal now.

Hi Clancy,

When I apply 3MHz with amplitude of 3VPP (1.5V) at input, it seems that I had some grounding issue (not sure yet)... now I am able to see about 67kHz oscillation frequency at IN0. This is good. I placed the ground of my external clock (function generator) at one of the pins of IN0... otherwise I wouldn't be able to see any activity on oscillation frequency.

Here is the link to the post I was referring to earlier: https://e2e.ti.com/support/sensors/f/1023/p/733254/2821596?tisearch=e2e-sitesearch&keymatch=LDC1612EVM#2821596. Thanks.

Regards,
Ali

Hi Clancy,

So what do you think is the issue with my connection (described in last post)? When I apply the function generator's GND to the GND of external clock on the board (5-pin connector as shown in the schematics), I am not able to get a clear signal... but when connecting the function generator's GND to the IN0 pin, I am seeing some activity in the UI and I am able to get a clear signal on scope.

Regards,
Ali

Ali,

The GND of the external clock should not be connected to the IN0 pin. It should be connected to the board ground. With the function generator, you need to use an oscilloscope to make sure that you are applying the correct signal to the clock input. For instance, do you have the offset correct on the function generator? Otherwise, it may be trying to force a negative voltage onto the clock input.

Hi Clancy,

I did use an oscilloscope to make sure I have the function generator's signal is matching what shows on the scope. To answer your question, yes I do have the correct offset on the function generator.

Regards,
Ali

Ali,

This still doesn't make sense to me. Are you getting correct measurements when you use the internal clock?

If you are still having trouble, will you please post waveforms of CLKIN and INx?