I am looking to use the LTC6994-2 IC to delay a square wave 1600Hz input from 0-320 us. The big deal is having this adjustability across the full range. I am currently evaluating the IC as I write but can not attain the adjustability I am seeking

What resistor values should be used. I assuming to get the adjust, I need to use trim pots. Where to adj? Rset, divder etc..,

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  • 0
    •  Analog Employees 
    on Nov 12, 2019 8:22 PM

    To achieve a single voltage controlled 0-320us delay is not possible with the LTC6994-2. As you can see in table 1 on page 12, the delay range of the LTC6994-2 is split up into 8 ranges with each range covering a 16:1 ratio through the Rset resistor value. By using two resistors and a voltage source you can voltage tune the delay over a 16:1 ratio as described in the "Voltage-Controlled Delay" section on page 17 of the data sheet. Rather than do all of the calculations as shownn on the data sheet, you can use the simple web tool at : http://beta-tools.analog.com/timerblox/LTC6994  You can also control this analog delay setting with a DAC as shown in Figure 11 of the data sheet if this is preferred.

    To cover a very wide range you would need an analog tuning voltage as described above to cover an 8:1 to 16:1 range and also change the  resistors on the DIV pin to change the divider to allow wider delay range (again see table 1). You can do this with simple resistors and a couple of switches. You can use a DAC here as well. This is not shown on the LTC6994 data sheet, but is shown on the related LTC6990 data sheet in the "programming Ndiv Using an 8-bit DAC" application on page 22.

    So, if you need a continuously tunable or swept delay over this wide time range, this is not possible with the LTC6994-2 part. However, if you need to have a settable delay and can use voltage and a couple of switches, then it is possible.

    Last, the extremes of the 0-320us range are not quite possible. The minimum delay for the LTC6994 is 1us and the maximum delay must be slightly less than the input signal's pulse width. In this case that would be half of 1600Hz=312.5us. So, 1 to 312 is possible.

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  • 0
    •  Analog Employees 
    on Nov 12, 2019 8:22 PM

    To achieve a single voltage controlled 0-320us delay is not possible with the LTC6994-2. As you can see in table 1 on page 12, the delay range of the LTC6994-2 is split up into 8 ranges with each range covering a 16:1 ratio through the Rset resistor value. By using two resistors and a voltage source you can voltage tune the delay over a 16:1 ratio as described in the "Voltage-Controlled Delay" section on page 17 of the data sheet. Rather than do all of the calculations as shownn on the data sheet, you can use the simple web tool at : http://beta-tools.analog.com/timerblox/LTC6994  You can also control this analog delay setting with a DAC as shown in Figure 11 of the data sheet if this is preferred.

    To cover a very wide range you would need an analog tuning voltage as described above to cover an 8:1 to 16:1 range and also change the  resistors on the DIV pin to change the divider to allow wider delay range (again see table 1). You can do this with simple resistors and a couple of switches. You can use a DAC here as well. This is not shown on the LTC6994 data sheet, but is shown on the related LTC6990 data sheet in the "programming Ndiv Using an 8-bit DAC" application on page 22.

    So, if you need a continuously tunable or swept delay over this wide time range, this is not possible with the LTC6994-2 part. However, if you need to have a settable delay and can use voltage and a couple of switches, then it is possible.

    Last, the extremes of the 0-320us range are not quite possible. The minimum delay for the LTC6994 is 1us and the maximum delay must be slightly less than the input signal's pulse width. In this case that would be half of 1600Hz=312.5us. So, 1 to 312 is possible.

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