Are my coil designs good for LDC1614?

Hi Santosh,

The sensors seem reasonable, although Coil 0 does have a rather small sensor cap. Try using an oscilloscope and check INAx to ground and see what the frequency and signal amplitude are. Make sure you have the channel current drive settings set. Can you post the register values you are using?

Regards,

ChrisO

Hello Chris,

Coil 0, 2 are giving me the inductance values but the problem is with coil 1,3. Coil 1,3 always gives me approx 0 value. Here is a screenshot of the register values.

coil 0 on channel 0 and so on.

Hi Santhosh,

It seems like Coil 1 and 3 are getting saturated. Can you use an oscilloscope between the Capacitor and ground to check the sensor frequency and amplitude for both these channels?

If this is outside the range, offset, reference count and gain values can be changed to get the sensor frequency within the range.

-Best Regards,

 Suhas R C

Hi Santosh,

In addition, please check the errors tab on the GUI to see if a particular error is being reported. Also, I recommend setting the reference and sensor dividers to 1 for all channels.

Regards,

ChrisO

Hello Chris,

I have accidentally restored the configuration from defaults(using restore from defaults button on the top right corner). Now, not even a single channel is working. Can you point me to a document which can help me to fix the configuration back to normal. 

Hello Suhas
Do you mean probe across the capacitor? I can certainly do that but I have a new issue now. I have restored the configuration from defaults and all of a sudden, I can't start streaming. Do you know how can I set it back to normal. Unfortunately, I did not save a screenshot of the previous configuration.
Thanks.

Santosh,

You need to use a differential probe if you are probing across the capacitor. Otherwise, you can probe between capacitor and ground using a normal probe. This will still provide you the sensor frequency.

I suppose you have posted your register settings on this E2E post earlier. Can you try rewriting the registers using those values?

-Best Regards,

 Suhas R C

 

 

These are the errors that are reported by the GUI.

Hi Santosh,

That doesn't seem to indicate any issue. Have you made any progress in driving the two sensors? Have you tried swapping the channels?

Regards,

ChrisO

Hi Chris,

I did try swapping the channels but the two coils are not working on any channel. I also tried the working coils on all the channels and they work fine. Currently, I am sticking to the two working coils and writing code to interface it to msp430g2553. My application is to read from ldc and write it to console using UART. I have configured UART and I2C but am not really clear on the timing diagram in the datasheet and how to configure, read inductance form ldc1614.  

Is this the forum where I can get help with my code or I have to seek help from other forums? If so, point me in the right direction.

Hello Santosh,

Please reduce the value of the sensor capacitor - try using ~800pF and see if that resolves your issue. Your sensor Q is very low at 72kHz; increasing the frequency should help.

Regards,

ChrisO

Hello Chris,

For the following coil below, I have calculated the values for the registers as follows:

RCOUNT_CH0 = 0x0406

SETTLECOUNT_CH0 = 0x0064

CLOCK_DIVIDERS_CH0 = 0x1002

ERROR_CONFIG = 0x0001

MUX_CONFIG = 0x0201

DRIVE_CURRENT_CH0 = NOT SURE.

CONFIG = 0x1401

Rp value = 145468 (calculated from Q = Rp*sqrt(C/L))

Fref: 20MHz 

according to the figure 14 in the datasheet, I dont find any corresponding Idrive value for my Rp. 

Can you verify my register setting and suggest me on how to obtain Idrive value for my coil design.

Thanks.

Hello Santosh,

I recommend checking the capacitance of coils 1 & 3 to ~800 pF as it seems that the two sensors which do not work have larger capacitor values. We can also try putting a 20kohm resistor in parallel with the sensor capacitor to see if this helps the oscillation.

Regards,

ChrisO

Chris,

I am asking about coil 0, coils 1, 3 will work if i change the capacitors. 

My issue here is how to calculate Rp and IDRIVE from figure 14 in the datasheet. for coil 0 which has a capacitor of 73pF, the Rp was calculated to be 145468 ohms and I don't see any corresponding IDRIVE value from the graph in figure 14 of the datasheet. I will be using only one coil. All the other coils are just for evaluation.

In my previous post I have posted some register values for single channel mode. Can you review them?

Thanks. 

Hello Santosh,

Refer to section 7.3.3 of the datasheet for more information on the current drive setting for the LDC161x. Also, there is an app-note for setting the current drive - www.ti.com/.../snaa221.

Regards,

ChrisO

If you look at table 1. of the above said application note, it give you the Rp vs IDRIVE for Rp between 0.9 kohms to 90 kohms. But for my coils, the Rp value is 145 Kohms. For now, I am having 0 as drive current decimal which corresponds to 90 Kohms.

In the same page of table 1, there is a procedure for auto calibration which should be used if one doesn't know the Rp.

Hi Santosh,

As long as the sensor amplitude is not exceeding the LDC161x maximum spec, then setting code 0 is fine with the higher RP. Also, the RP will decrease with target interaction. If the amplitude is too high, then increase the sensor capacitance by a ~10%.

Regards,

ChrisO