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# TDC7200: Minimum time between STOP signal and the next START signal for the TDC7200 timer

Part Number: TDC7200

I am going to use the TDC7200 to time the time-of-flight (TOF) between a transmitted and reflected RF pulse (Radar). From the data sheet and User's Manual it is unclear as to how fast the TDC7200 can be ready for another START pulse after receiving the previous STOP pulse to process and send out the TOF calculation serially to a receiving unit. In other words, what is the maximum RF pulse rate I can send out and ensure the TDC7200 will be ready to begin a timing cycle without missing the START signal.  100Hz, 1000Hz, 1MHz??  I understand it can't be less than the measured TOF but let's assume the measured TOF is 40nsec. How much time do I need after the reception of the STOP signal to have the TDC7200 ready to receive another START signal for the next RF pulse?? Any help answering this question will be greatly appreciated.

Sincerely,

Mike

• Hey Mike,

Thanks for posting to the sensing forum! As you mentioned it is hard to spec this because you are dependent on the actual ToF.  But assuming you know your max ToF you could calculate the maximum rate. You are limited by the time the time it takes INTB to drop low after the last STOP is received (which can take as long as 2us) this lets you know that your data is ready to be read. So you must factor in the time it takes to read the results from the device, and the minimum time it takes to from receiving TRIG to sending a START pulse which is 5ns.

Other than the limiting factor is the ToF. I hope this helps you in your calculation!

Best,

Isaac

• Thanks for the reply Isaac. The maximum sensing distance I am designing this product for is about 450 ft. So to and from will be about 900 ft which means maximum TOF of approximately 900 ns.  So would the calc. be (900 ns + 2 us + time to dump registers + 5  ns)? Do you by any chance know what the max time for the register dumps to occur?

• Hey Mike,

Of course glad to help out! That sounds about right so far, the max time it takes to read the registers would depend on your SPI interface clock frequency and the number of registers you have to read (this could vary by mode) number of STOPs the device is expecting. Having more STOPs would require you to read more TIME or CLOCK_COUNT result registers  in order to perform the calculation to convert the results into ToF.

It is kind of difficult to state the max measurement frequency as the device depends on a lot of factors but my other suggestion would be to order a TDC7200 EVM to test if the device meets your required measurement frequency: https://www.ti.com/tool/TDC7200EVM

This will help you calculate how fast you can communicate with the device and allow you configure the device the way you intend to in order to obtain the best measurements.

Best,

Isaac