TLV3691: Schmitt trigger circuit ( using TLV3691 Comparator ) is not working if input voltage comes first before the supply voltage.

Hi Lakshmanan,

the problem arises because you violate the common mode input voltage range during the moment of connecting.

Tell more about how you exactly connect the TLV3691 to the circuit. When do you disconnect the TLV3691 from the circuit? Also, what is the exact turn-on and turn-off procedure?

Kai

Thanks for your input Kai!

You are correct about the problem occurring because of violating the input common mode range of the device. As Kai stated, if you can explain your turn on/off procedure it would help us understand your problem better.

Regards,

Jonny

Hello sir,


            We are using TLV3691 Comparator in Schmitt trigger circuit.

We designed schmitt trigger in inverting configuration. we gave input voltage to inverting terminal of comparator.

We using Super Capacitor as power source and it charges from 0 to 4.2V.

Both input and comparator supply voltage from super capacitor.

By using TPS61090RSAR Boost regulator we are converting  5.5V stable output from super capacitor voltage


Our requirement are

We need to Enable the TPS61090RSAR Boost regulator if once super capacitor Charges reach to 4V and regulator should disable if super capacitor voltage below 2V.

So regulator should work only if supper capacitor voltage between 2V to 4V.


To achieve the above requirements we are doing

Schmitt trigger output is LOW when Super capacitor voltage between 2V to 4V

Schmitt trigger output is HIGH when Super capacitor voltage is less then 2V


schmitt trigger tested result:-

Schmitt trigger is working only when supply voltage Initialised first and then the input voltage given next to the comparator.

When the input voltage given first then the supply voltage Initialised - it is not working.

I am attachign the schematic for your reference.

Please give the solution to solve the above issue.

schmitt trigger using TLV3691 & Boost reg.PDF

Regards

Lakshmanan V

Lakshmanan,

Thank you for those details. When testing this solution, did you see these results on the bench or in a simulator? What happens if you bring up the input and supply for the comparator at the same time?

Regards,

Jonny

Hello sir,


                   We tested schmitt trigger circuit in real time. But schmitt trigger output always 0 Volt if we bring up both  input and supply for the comparator at the same time.


Regards

Lakshmanan V

Hi Lakshmanan,

I would power the TLV3691 with a CR2032 lithium cell or similar.

Kai

Lakshmanan,

I will need some more time to investigate this issue. A separate fixed supply as Kai stated would definitely help the ease of design for this circuit.

I would also suggest using 100kohm resistors for your divider/hysteresis network to improve the accuracy of the circuit.

Regards,

Jonny

Hello sir,

                  We have only one source ( that is Super capacitor ).Li-Ion battery is not allowed by our customer.

Schmitt trigger is powered by using TPS7A02 ( 1.8V LDO ). LDO get powered from Super capacitor.

To reduce the Quecient current of this circuit we used all resistor in terms of Mega Ohms.

Our requirement is

Quecient current of the schmitt trigger circuit is less then 1µAmps.

Regards

lakshmanan V

Hi Lakshmanan,

a CR2032 lithium cell is no lithium-ion battery. It's something different. It uses lithium manganese dioxide and is used in long-life data storage applications like mainboards and data loggers.

maxell_cr2032_datasheet.pdf

Kai

Lakshmanan

You have several suggestions and we will await your response to see if you need any further assistance.

Chuck

Lakshmanan

It has been a while since there has been any response on this thread, so I will close the post.  If you need any additional support, please feel free to reopen or start a new thread.

Thanks

Chuck

Hi Lakshmanan,

another option is to force the input voltages of TLV3691 to fall within the allowed common mode input voltage range during power-up by the help of RC low pass filters at the inputs as shown here:

lakshmanan_tlv3691.TSC

Kai

Thanks again Kai for providing more useful information.

Lakshmanan

If you have any additional questions, please let us know.  However, if this issue has been resolved by the responses you have received, please let us know that as well.

Thanks

Chuck