LSF0204D: Leakage current rises 1.8V rail voltage?

Kazuki Itoh

Genius 9175 points

Part Number: LSF0204D
Other Parts Discussed in Thread: SN74AXC4T774, TXS0104E, SN74AXC4T245, TXB0104

Hello,

My customer is trying to translate 1.8V and 3.3V with LSF0204DPWR.

VREFB = 3.3V and VREFA = 1.8V.

The customer observed issue that the 1.8V rail rises to 2.1V.

My customer removed LSF0204DPWR and then the 1.8V rail returned to 1.8V.

1.8V is coming from TLV70018 which is powered by the 3.3V.

I guess this is due to leakage current from VrefB to VrefA.

How my customer improve his design?

Regards,

Itoh

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 243980 points

There is leakage current of about 3 µA. I doubt that this is large enough to be a problem.

But if that current is the problem, then a 470 kΩ resistor between 1.8 V and GND will help.

0 Kazuki Itoh over 4 years ago in reply to Clemens Ladisch

TI__Genius 9175 points

Hello Clemens-san,

Thank you for the reply. Could you please review my customer's schematic?

I'd like to send it to you via email.

I cannot find your name from the directory, so could you please search my name and reach out to me?

Regards,

Itoh

0 Clemens Ladisch over 4 years ago in reply to Kazuki Itoh

Guru 243980 points

I am not a TI employee.

0 Kazuki Itoh over 4 years ago in reply to Clemens Ladisch

TI__Genius 9175 points

Hi Clemens-san,

Wow, thank you for your volunteer!

100kΩ resistor between 1.8V and GND worked.

But my customer don't like this solution because it increases leakage.

Do you happen to come up with other solution?

Regards,

Itoh

0 Clemens Ladisch over 4 years ago in reply to Kazuki Itoh

Guru 243980 points

With LSF translators, the leakage current is unavoidable due to the architecture of the reference transistor:

It should be possible to replace it with the TXS0104E. If automatic direction sensing and open-drain signals are not needed, a direction-controlled translator like the SN74AXC4T245 or SN74AXC4T774 would be a better solution.

0 Kazuki Itoh over 4 years ago in reply to Clemens Ladisch

TI__Genius 9175 points

Hi,

Is TXB0104 or TXS0104E capable of driving 6kΩ external pull-up resistor?

Regards,

Itoh

0 Clemens Ladisch over 4 years ago in reply to Kazuki Itoh

Guru 243980 points

The TXB cannot drive more than 20 µA.

The TXS uses passive switches, so the 6 kΩ pull-up will work if your other devices are capable of driving it. (And the TXS has internal pull-up resistors and does not need external ones.)

0 Dylan Hubbard over 4 years ago in reply to Clemens Ladisch

TI__Mastermind 42670 points

Hi Itoh-san,

What communication protocol are they using? The TXB/TXS families don't like having pull-ups/pull-downs are the signal lines., especially ones as strong as 6 kohm. If its something like I2C and they can avoid using external pull-ups then I believe the TXS would be the best choice.

0 Kazuki Itoh over 4 years ago in reply to Dylan Hubbard

TI__Genius 9175 points

Hi Dylan-san,

I'd like to send the schematic to you offline. Please accept my friend request.

Regards,

Itoh

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LSF0204D: Leakage current rises 1.8V rail voltage?