TL431 - REF pin Absolute Maximum Ratings

Hirotaka Matsumoto

Other Parts Discussed in Thread: TL431

Hi all

Would you mind if we ask TL431?

Our customer would like to know REF pin Absolute Maximum Ratings.
So, is(Absolute Maximum Ratings) it 37V?

Kind regards,

Hirotaka Matsumoto

over 10 years ago

0 Ryan Eslinger over 10 years ago

TI__Guru 55940 points

Please allow for a delay in response due to the US holiday.

Very respectfully,
Ryan

0 Hirotaka Matsumoto over 10 years ago in reply to Ryan Eslinger

Guru 27585 points

Ryan san

Thank you for your update!
We are looking forward to your reply.

Kind regards,

Hirotaka Matsumoto

0 Michael J Schultis over 10 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 24975 points

Matsumoto-san,

You are correct, the absolute maximum rating for the TL431 is 37V.

The recommended maximum is 36V.

Best,
Michael

0 Ron Michallick over 10 years ago in reply to Michael J Schultis

TI__Guru**** 164976 points

Hirotaka-san,Michael is correct about the maximum cathode voltage.
The maximum reference voltage is 2.5V. The reference pin must always have current limited by a series resistor or from a voltage divider tap.
The reference pin draws current when voltage is above +2.5V or below -0.5V

0 Hirotaka Matsumoto over 10 years ago in reply to Ron Michallick

Guru 27585 points

Ron san,

Thank you for your update!

We'd like to confirm as followings;

The voltage of REF pin is 2.5V, so if we add over 2.5V from external voltage, it is not over 2.5V, isn't it?
So, in this case, does it mean "Reference input current range" on the datasheet?

Kind regards,

Hirotaka Matsumoto

0 Ron Michallick over 10 years ago in reply to Hirotaka Matsumoto

TI__Guru**** 164976 points

Hirotaka san

Yes, that is correct.

For inputs less than 2.5V, reference curent is less than 4uA.
For higher input voltage, reference current is about (VIN - 2.5V) / R.
R is the resistor added between input and reference pin.

0 Hirotaka Matsumoto over 10 years ago in reply to Ron Michallick

Guru 27585 points

Ron san,

Thank you for your prompt update and your kindness!

We confirmed our customer why they would like to know Maximum Absolute voltage of REF pin.
They would like to use TL431 as the comparator device.
So, their circuit is the following;

20150911_TL431_Circuit.pdf

On the attachmentfile, +12V_A and +12V_VS are other power sources.
When the +12V_A occurs the overvoltage, they would like to make +12V_VS shut down.

Of course, we can't recommend this method(way) because Absolute Maximum Ratings voltage of REF is 2.5V and power sources are isolated.

And then, we have to explain that our customer use the normal comparator device instead of TL431.

So, if you have some comment, could you let us know?

Kind regards,

Hirotaka Matsumoto

0 Ron Michallick over 10 years ago in reply to Hirotaka Matsumoto

TI__Guru**** 164976 points

Hirotaka san,

The reference drive is OK, even if 12V_A was over 100V.

The reference pin is not driven with a low impedance voltage source therefore the maximum reference voltage does not apply because Vref self regulates when +12V_A is higher than the target voltage of 12.68V

The reference current must be less than 10mA in the worst case.
The 10k resistor uses 0.25mA. So the top resistors could pass up to 10.25mA.
Top resistors add to 40.48k. 10.25mA * 40.48k = 415V.
See the reference pin is safe.

0 Hirotaka Matsumoto over 10 years ago in reply to Ron Michallick

Guru 27585 points

Ron san,

Thank you for your very kind reply!
OK we got it.

If we have some addtional questions, we don't hesitate to ask you.

Kind regards,

Hirotaka Matsumoto.

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TL431 - REF pin Absolute Maximum Ratings