TDC1000 / VCOM and COMPIN

Kuramochi Tadahiko

Guru 28715 points

Other Parts Discussed in Thread: TDC1000

Hi,

My customer is evaluating the TDC1000 and has several questions.

Evaluating condition is following;

*******************

VDD:4.97V, VIO:3V, TDC_CLK:8MHz, PGA:Unused(Using external Amp), LNA_FB:capacitor, Receive mode:single echo,

VCOM_SEL:external,VCOM supply:2.5V and connected 1uF & 0.01uF capacitors vs GND.

ECHO_QUAL_THLD(VTHLD):-75mV

5 bursts of sin-wave are inputted as receive signal from the signal generator

*******************

The measured waveforms is following;

1) Why do the STOP-signal rise in the red circle nevertheless the COMPIN-signal doesn't fall below VTHLD?

Is this caused by the error between setting value and actually value?

2) Regarding the additional offset, I refer to the figure 19 on the datasheet, however the VCOM livel and COMPIN offset don't correspond.

The error is occured about 0.02V.

Why is this error occured?

Please let me know if there is any lack of information.

Best Regards,

Kuramochi

over 7 years ago

0 Vishy Viswanathan over 7 years ago

TI__Mastermind 21685 points

Kuramochi-san,

There's 10mv hysteresis (typical) for both the comparators. The VTHLD (75mV) is also a typical value and there can be slight difference to the actual from device to device.

Thanks,
Vishy

0 Kuramochi Tadahiko over 7 years ago in reply to Vishy Viswanathan

Guru 28715 points

Hi Vishy-san,

Thank you for your support.

My customer is thinking that the hysteresis doesn't affected the STOP signal.
Is it wrong?

And regarding condition of output the STOP signal, my customer is recognizing such as following;

1. The COMPIN passes acrross VTHLD from + side to - side.
2. Additionally, the COMPIN passes acrross VTHLD from - side to + side.
3. The COMPIN passes acrross VCOM from - side to + side, then the STOP signal goes high.
4. The COMPIN passes acrross VCOM from + side to - side, then the STOP signal goes high.

Is this recognization correct?
If this is wrong, could you show me correct conditon?

Best Regards,
Kuramochi

0 Kuramochi Tadahiko over 7 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

Hi Vishy-san,

How is this situation?
If there is lack of information, please let me know.

Regards,
Kuramochi

0 Vishy Viswanathan over 7 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 21685 points

Kuramochi-san,
The way you have defined above (for STOP signal generation) is correct except in (4) it should be "then the STOP signal goes low". The extra STOP is happening may be because VTHLD selected and actual are different due to it being a typical value. I wonder if loading on the COMPIN pin also is an issue.
Thanks,
Vishy

0 Kuramochi Tadahiko over 7 years ago in reply to Vishy Viswanathan

Guru 28715 points

Vishy-san,

Thank you for your answer.

> The extra STOP is happening may be because VTHLD selected and actual are different due to it being a typical value.

Could you tell me how much is dispersion of the VTHLD and hysteresis voltage generally ?

Best Regards,
Kuramochi

0 Kuramochi Tadahiko over 7 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

Vishy-san,

is it difficult?

Regards,
Kuramochi

0 Vishy Viswanathan over 7 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 21685 points

Kuramochi-san,

I don't have characterization data on this to provide.

Thanks,
Vishy

0 THINH Nguyen over 6 years ago in reply to Vishy Viswanathan

Prodigy 150 points

Hi TI Team,

My customer are using internal VCOM (VDD/2 = 1.8V). however, VCOM voltage is drops down after we receive the receiver signal about 400us same as picture below. How can we solve this issue?

Thanks.

0 Scott Cummins over 6 years ago in reply to THINH Nguyen

TI__Mastermind 31655 points

Hi Thinh,

I have replied to your other thread here: e2e.ti.com/.../604054 and I will be closing this one.

Regards,

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TDC1000 / VCOM and COMPIN