TL431B-Q1: Special Usage

Dear, Ethan-san.

Thank you so much for your reply and so sorry ask you quite obscure question.

This simulation circuit is not a formal application circuit. It is a kind of the simplified
testing fixture circuit involving TL431B-Q1.

I tried to simulate it, so find a concern as below. Please give your advice, again.

Question :
Reference voltage would be lower than Anode voltage of TL431B-Q1, around 10mV.
Cathode voltage is defined the positive with respected Anode.
Is it no problem(no damage) if Reference voltage become lower 10mV from Anode?

Best Regards,
H. Sakai

Hi Sakai-san,

What will be actual voltages of of the reference and anode pins? I am not concern of the anode voltage pin being higher than reference pin, but the possible current sourcing of the reference pin violating abs maximum. I would recommend a series resistor on the reference pin to limit the current.

I can test this, but i am not sure the instance in which the phenomena happens. Please provide a test circuit if you would like me to test this on the bench for some typical characterization.

Regards,

Ethan

Dear, Ethan-san. 

Thank you so much for your mentioning. 

I tried to simulate as the circuit as below. 

SW1 turns ON 10ms, SW2 turns ON 11ms later. 

OUT=20V is expecting because TL431B-Q1 is OFF. 

They also expecting no abnormal behavior between 10ms to 11ms. 

I could see Anode > Reference around 40mV, no much current flow from Reference &

no abnormal behavior. 

Before You mentioned that Anode > Reference is no impact on the device breakdown. 

So no problem SW1 & SW2 ON timing defference, I think. 

How do you think? 

Best Regards, 

H. Sakai

Hi Sakai-san,

What is the value of AM1 in this simulation. Since you have the positive terminal at the reference pin, a positive current measurement would mean a sourcing current from the reference pin. The datasheet specs this only up 50uA so if the number is greater than an absolute max rating is violated. 

Regards,

Ethan

Dear, Ethan-san. 

Thank you so much for your pointing out. 

AM1 current is 0A according the simulation. 

It is meaning no violation for sink/source current on Reference pin. 

Correct?

Best Regards, 

H. Sakai

Hi Sakai-san,

This is most likely because there is 1ms between the time switches. After that the reference and anode pin are shorted. Is the simulation working as intended?

Although there is no current shown in the simulation, I see a voltage transient on VM1 which indicates there could be some current and the model does not support this circuit application. What is the VM1 voltage from the high point to the transient at the low point where the switches turn around 10ms?

Regards,
Ethan

Dear, Ethan-san.

Thank you for your advice.

The simulation working is as my intended.

VM1 voltage is due to leakage current from Anode.

The peak current will be due to SW1 on which is a kind of in-rush.

Ioff & Figure 22 are defined as the operating condition on the datasheet,

but not sure about its maximum ratings.

I wonder it is violated against TL431B-Q1 specification?

Best Regards,

H. Sakai