SN74AVC4T774: High quiescent current in sleep mode with new controller, question regarding OE settings

Florian Eberhard

Part Number: SN74AVC4T774
Other Parts Discussed in Thread: TXU0204

Tool/software:

Hello,

we are using the level-shifter to transfer from 1,8V to 3,3V logical uart level. With our old controller, we had no problems regarding high Iq. now, after controller switch we got high Iq on the UART pins with high impedance imputs, where we propose different controller behaviour, but this maybe connected top linked thread.

to my question:
At the moment, we have OE tied to ground, setting the level shifter to always on. In the datasheet, OE can be set to high to disable the device. However, it was unclear, how much power needed to keep the device in the deactivated state, when e.g. a 100k pullup is used. The schematics are attached below.

regards

10 months ago

0 Clemens Ladisch 10 months ago

Guru 317370 points

/OE disables only the outputs, so it does not affect this.

The input buffers on both sides are always active, so you should ensure that all pins have a valid voltage. Add pull-up resistors to any signal that could be floating.

0 Florian Eberhard 10 months ago in reply to Clemens Ladisch

Prodigy 10 points

So it is recommended to have /OE pullup and all pins that are in Input Configuration equipped with pullups as well? One side of the level shifter is only active when the device on this side is active, as the 1.8V are only available when the device it self is powered on.

+1 Clemens Ladisch 10 months ago in reply to Florian Eberhard

Guru 317370 points

You need a pullup on /OE only if you want to disable the device during power up.

I/O pins need pullups only if they could be floating (when powered) otherwise.

(The TXU0204 would be simpler and cheaper.)

+1 Joshua Salinas 10 months ago in reply to Florian Eberhard

TI__Mastermind 23600 points

Hello Florian,

I agree what Clemens said. You only need a pull-up on OE pin if you plan to disable the device. Another reason for a high Iq could be IOs are left floating. Please make sure IOs are at a known state. FAQs below provide additional information

[FAQ] How does a slow or floating input affect a CMOS device?

[FAQ] What should be done with unused I/O pins of the level translator devices?

For UART applications, I would also recommend the TXU0204. Much smaller (since you don't need 4 direction pins) and has internal pull-downs.

Regards,

Josh