LSF1010 floating problem

Hello,

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http://e2e.ti.com/group/helpcentral/w/e2e/149.4-3-inserting-an-image-on-e2e

-Francis Houde

Hi Aozer,

Sorry about that. The attachment is here. Note: the VrefA is connecting to 1.8V not 3.3V. Please let me know if you have any questions. Thanks for your support.

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Leroy Song

Hi Aozer,

Thanks for your prompt answer. One more question- if the MCU cannot tolerance the 4V from A1 pin , is there a way to solve the problem? (i.e. higher the value of pull-up resistor on B1 pin?) Thanks again for your time and help.

On second thought, you should not be able to see 4V at the A1 pin. The voltage at the A1 pin should not be able to rise above VrefA. As soon as the voltage on A1 rises above VrefA-0.5 the LSF should act as an open switch which would disable the path between A1 and B1.

If the device is connected as shown in the schematic and you are getting 4V at the A1 pin with VrefA pulled up to 1.8V there may be an issue with your part or you may have a short somewhere. Have you tried testing a second part to see if you get the same results?

Hi Song ,

Without a pullup on the A pin, the A1 should clamp to 1.8V (VrefA) . The low will pass through LSF without change .
I don't see problems with the EN/ VrefB connection. The 200kohm resistor needs to be after 5V into both pins. The 5V has pullups at the B since it is open drain ? if it is pushpull input , you do not need pullups.

Thanks for your ansewer. It really helps me a lot. I will check back with our customer and let you know. Thanks again for your support.

Leroy Song