LDC1000: OSC DEAD bit set, even though oscillations are found at output

Dean Velasco

We're trying to get our LDC1000 to work correctly, but we have been encountering some problems. The proximity data and frequency readings all come out to zero.

Further investigation shows that the OSC DEAD bit within register 0x20 is set. However, our oscilloscope shows that are are getting oscillations at the output when a belt is plugged in.

Any suggestions regarding what is going on?

over 10 years ago

0 Evgeny Fomin over 10 years ago

TI__Genius 9300 points

What is the oscillation amplitude and the amplitude setting (Reg. 04) ?
Most likely, the former does not reach the setting value.

0 Dean Velasco over 10 years ago in reply to Evgeny Fomin

Intellectual 890 points

I set the oscillation amplitude to 2V, based on the recommendations of our hardware engineers. It's possible that we are misinterpreting how this parameter is used.

0 Dean Velasco over 10 years ago in reply to Dean Velasco

Intellectual 890 points

Here is the latest news. According to our scope, we're getting pulses that are about 1V high at the outputs. Their frequency is about 1.95 MHz.

Based on this information, I set the LDC configuration (reg 4) to 0x03. I set register 3 to 0xC7. Registers 1 and 2 are at 0x00 and 0x3F, respectively, so that Rp_MAX would be at its highest value and Rp_MIN at its lowest.

Any ideas?

0 Evgeny Fomin over 10 years ago in reply to Dean Velasco

TI__Genius 9300 points

Hello,

Please try setting RpMAX to x19 - x1C

0 Dean Velasco over 10 years ago in reply to Evgeny Fomin

Intellectual 890 points

I tried all values within that range, but there's been no change.

I did notice that the INTB signal appears to be constantly high. I need to doubly verify this, but in the meantime... is this something we should normally expect when the OSC DEAD bit is set?

Also, I'm getting a reading of 0xF0 from the status register, so this bit is most definitely set. However, we are seeing distinct pulses at the output. Why would this be the case?

0 Evgeny Fomin over 10 years ago in reply to Dean Velasco

TI__Genius 9300 points

Ok, let's take a look at your sensor.
What is the inductance, capacitance and physical parameters of the coil?
If you have a way to measure it on impedance analyzer, it would be very helpful! resonant frequency and equivalent parallel resistance at that frequency.

0 Dean Velasco over 10 years ago in reply to Evgeny Fomin

Intellectual 890 points

Thanks. According to one of our hardware engineers, the parameters are as follows:

Inductance: 3.58uH at 100kHz

DC resistance: 1.5 ohms

Parallel capacitance: 2200pF

0 Evgeny Fomin over 10 years ago in reply to Dean Velasco

TI__Genius 9300 points

Hello,

Such sensor violates minimum Rp requirement, and thus triggers OSC_DEAD flag.

Is it possible to reduce cap value to 300pF? Or increase the inductance?

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LDC1000: OSC DEAD bit set, even though oscillations are found at output