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TLV3691: Device functional modes

Prodigy 225 points

Replies: 4

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Part Number: TLV3691

Hello,

I would like to use a comparator to cut the power supply of a section of my circuit.

This comparator must work with the lowest voltage supply possible.

I found 2 suitable chips:

  • TLV3691 (down to Vdd_min=0.9V)
  • TLV7031 (down to Vdd_min=1.6V)

It is very important for me that the chip will keep the output low, even when the Vdd is lower than Vdd_min.

In chapter 7.4 of both datasheet we have the “Device functional modes”

For TLV7031 we have:

“The TLV703x and TLV704x have a power-on-reset (POR) circuit.

While the power supply (VS) is less than the minimum supply voltage, either upon ramp-up or ramp-down, the POR circuitry is activated.

For the TLV703x, the POR circuit holds the output low (at VEE) while activated”

Is this confirming what I need? In case it is not, How low can the POR work, in terms of voltage?

 

For the TLV3691 we have:

“The TLV3691 has a single functional mode and is operational when the power supply voltage is greater than 0.9 V.”

What this mean exactly? What happen at the output when Vdd is less that 0.9V?

Thanks for your clarification.

Kind regards

  • Ciao Alessandro,

    this is usually done by the help of an additional switching stage using a BJT, JFET or MOSFET which needs a minimum voltage to turn-on or turn-off. See figure 14 and 15 of datasheet of TL7705A, e.g.:

    Kai

  • In reply to kai klaas69:

    Ciao Kai,

    are you speaking about the output stage? See picture attached?

    If this is the case, that's actually my question: How low these components can work?

    I need this answer for both TLV7031 and TLV3691.

    Thank you and I wish you a nice day

    Alessandro

  • In reply to Alessandro Bergomi32:

    Alessandro

    While the circuitry of the two devices is different, the way the devices perform once you drop below 0.8 to 0.9V will be similar.  In the case of the TLV7031, there is a POR circuit that you have eluded to that enables around 0.8V and will hold the output pin low in the case of the TLV7031 while the supply is ramping up.  Once the device reaches the operating voltage range, the output will reflect the condition at the inputs.  In the case of the TLV3691, the output reflects the condition of the input at an even lower operating voltage as stated in the datasheet.

    Below the 0.8V to 0.9V range, there is not enough voltage to turn the low side FET on the output stage ON.  So for a supply ramping up from 0V, the output is essentially uncontrolled and floating.  If the circuitry attached to the comparator output is also high impedance while the supply is ramping up, a resistor to ground at the output of the comparator will hold the signal close to ground.  This is generally an acceptable solution when the normal output condition of the comparator is low since no extra power is dissipated across the resistor.  However, if the normal output condition is logic high, some power will be continuously wasted and thus the resistor value needs to be selected with this in mind.

    Chuck

  • In reply to Chuck Sins:

    Thanks for your explanation...now it is clear for me!

    Have a nice day

    Alessandro

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