Behavior of LSF0204 when VrefA open

Tomohiro Nagasawa

Other Parts Discussed in Thread: LSF0204

Dear support team

My customer use LSF0204 as 5V↔3.3V level shifter.

There is the time VrefA is open in their application , then internal SW is turned on in spite of EN being pulled-down to GND.

And VrefB voltage appear on VrefA pin.

Is there the method to prevent the VrefB voltage from appearing on VrefA pin?

Regards

Tomohiro Nagasawa

over 7 years ago

0 Eric Hackett over 7 years ago

TI__Guru 69802 points

Nagasawa-san,

This thread has been moved to the Voltage Translation/Level Shifters Forum for more appropriate support.

Regards,

0 aozer over 7 years ago

TI__Mastermind 26875 points

Hello Tomohiro,

I have notified the appropriate engineer about your post. They should respond as soon as they are available.

0 Tomohiro Nagasawa over 7 years ago in reply to aozer

Expert 1710 points

Eric-san

Thank you for response.

Your immediate response is highly appreciated.

Regards

Tomohiro Nagasawa

0 ShreyasRao over 7 years ago in reply to Tomohiro Nagasawa

TI__Guru 58230 points

Hi Tomohiro san ,

With VrefA open not a recommended operation condition , we cannot guarantee the operation. VrefB is connected internally to the gate and drain of internal nmos. The transistor is turned on and the vrefA is pulled to VrefB-Vt most likely when VrefA is floating.

0 Tomohiro Nagasawa over 7 years ago in reply to ShreyasRao

Expert 1710 points

Hello Shreyas-san

Thank you for strong support.

Customer is going to attach an external circuit so that vrefA does not open. And I have one question.

How much is threshold Vt of the transistor between VrefA and VrefB?

Your prompt reply would be appreciated.

Regards

Tomohiro Nagasawa

0 Ron Michallick over 7 years ago in reply to Tomohiro Nagasawa

TI__Guru*** 148806 points

Tomohiro san.

I would guess about 0.5V (maybe less) It doesn't matter however.
A pull down resistor on VrefA could easily pull down the current from VrefB that passes through a internal 200k
With Vref A pulled down, the channels will be off.

Logic

Logic forum

Behavior of LSF0204 when VrefA open