Hysteresis adjustment for 8x ADCMP609

Hello,

I woud like to use the Hysteresis adjustment of the ADCMP609 comparator.

I have 8 comparators that shall be adjusted to the same hysteresis.

Is it possible to short all eight HYS pins and set the hysteresis with a single resistor resistor or current source?

How does this affect Figure 6 in the ADCMP609 data iheet?

Do you have a sggestion for controlling the HYS pin voa DAC?

Regards,
Niels

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  • 0
    •  Analog Employees 
    on Feb 10, 2021 12:22 PM

    Hi,

    The datasheet mentioned in page 9 that

    The HYS pin appears as a 1.25 V bias voltage seen through a series resistance of 7 kΩ ± 20% throughout the hysteresis control range.

    Yes, it is possible but shorting all eight HYS pins would mean that the current going into the single hysteresis setting resistor  would be a factor of 8x. The 7k ohms series resistance internal to each of the ADCMP609 comparator would be in parallel, Rseries equivalent would then be 7k/8. Therefore, the hysteresis setting resistor should be divided by 8 or R/8 to be able to set the desired hysteresis or no deviation from the target hysteresis. To put into numbers, for example connecting a Rhys = 200k, hysteresis of a single ADCMP609 is around 40mV. When two ADCMP609 hysteresis pins would be connected, hysteresis is decreased to half around 20mV. So to maintain the 40mV hysteresis, Rhys should be half equal to 100k.

    In regards to controlling the HYS pin with a DAC, you could try to use AD5676R and set it below midscale Vref/2 or 1.25V.

Reply
  • 0
    •  Analog Employees 
    on Feb 10, 2021 12:22 PM

    Hi,

    The datasheet mentioned in page 9 that

    The HYS pin appears as a 1.25 V bias voltage seen through a series resistance of 7 kΩ ± 20% throughout the hysteresis control range.

    Yes, it is possible but shorting all eight HYS pins would mean that the current going into the single hysteresis setting resistor  would be a factor of 8x. The 7k ohms series resistance internal to each of the ADCMP609 comparator would be in parallel, Rseries equivalent would then be 7k/8. Therefore, the hysteresis setting resistor should be divided by 8 or R/8 to be able to set the desired hysteresis or no deviation from the target hysteresis. To put into numbers, for example connecting a Rhys = 200k, hysteresis of a single ADCMP609 is around 40mV. When two ADCMP609 hysteresis pins would be connected, hysteresis is decreased to half around 20mV. So to maintain the 40mV hysteresis, Rhys should be half equal to 100k.

    In regards to controlling the HYS pin with a DAC, you could try to use AD5676R and set it below midscale Vref/2 or 1.25V.

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