TL3474: 1 channel use as comparator

Hi Hung,

can you show a schematic please?

Kai

Hello Hsu-san,

I have no data for TL3474 comparator usage. The schematic in the data sheet has similarities to LM324. Therefore I suspect that the overload recovery time (same concept as propagation delay time) may vary considerably with non-inverting input voltage.

See section 6.1 to see how this works on the LM324 

Is the noise question related to comparator mode or the other linear amplifiers. How much noise will be present?

Hi Kai 

I've sent it to you in private. Please check it. Thanks.

Regards, 

Jo

For input voltage less than 0V that can bais parasitic diode(s) may cause the output to change to an undesired state. (phase reversal)

It is very unlikely that the issue will affect any other properly biased channel.

Hi Ronald

Thanks for the reply.

Customer is asking which parasitic diode(s) in following TL3474 schematic may be conducted during minus input voltage applied? 

And also do you have data showing when output will have phase reversal after how much minus input voltage applied? Customer is asking it for reference. 

Regards,

Jo

Jo,

The voltage needed is temperature dependent because a diode forward bias voltage varies with temperature. Any data I gathered would be sample data so there would be no process wide values. 

I see just three options. 

1) Check for proper layout to minimise transients.

2) Filter the transients to a much smaller level.

3) Try TLV9304 or TLV9104 because they were designed to be phase reversal resistant. (similar web 1ku price) 

Hi Ronald

Thanks for the reply.

So the "parasitic diode" you mentioned appears due to layout but not originally inside TL3474? 

Could you help review customer's layout? I'll get the file from customer. 

Regards,

Jo

Jo,

The parasitic diode is not on the schematic. It occurs due to how integrated circuits isolated different components from each other.

Yes, I can look at the layout. In the meantime they can sample the alternative devices to see how they perform.

Hi Ronald

Could you show an example for parasitic diode due to isolation between ICs? Shouldn't it be parasitic capacitance here?

I looked up on the Net but I can only find the info about parasitic diode in MOSFET. 

Unfortunately, customer said they can't provide layout. 

Customer is adding RC filter on +input of OPAMP, customer is asking will it work better to add RC filter on -input of OPAMP also in order to reduce transient?

I'll send you the schematic by mail. 

Thanks.

Regards,

Jo

Hi Ronald

That makes sense for me. Thanks for the explanation. 

For OPAMP use case of TL3474, could you also help confirm following question from customer? 

Customer is adding RC filter on +input of OPAMP, customer is asking will it work better to add RC filter on -input of OPAMP also in order to reduce transient?

Thanks.

Regards,

Jo