TXB0104-Q1: Request information about the output status when the input is floating

Charles Jeon

Expert 2975 points

Part Number: TXB0104-Q1
Other Parts Discussed in Thread: TXB0104, LSF0108

Hi team.

The customer requests data about the status of the output when the input is floating.

for example, if A1 is floating when input status, how is B1 status ?

Customers want products that are equally floating.

Additional inquiries

Is there a dedicated level shift IC for EMMC?

Please recommend if it is.

over 5 years ago

0 ShreyasRao over 5 years ago

TI__Guru 56100 points

Charles,

TXB device acts as a very weak latch, hence the last known state of the B & A port will be retained when the IO ports are floating.

For the MMC specific devices, I have filtered devices from the parametric search here below:

www.ti.com/.../products.html

0 Charles Jeon over 5 years ago in reply to ShreyasRao

Expert 2975 points

HI Shreyas.

The data sheet states that A and B are high-Z when OE is low.
(Datasheet : 8.3.4 Enable and Disable)
If I do not want to affect port B when A port is floating, can I change OE to low?

Thank you.

0 ShreyasRao over 5 years ago in reply to Charles Jeon

TI__Guru 56100 points

Charles,

The OE pin when low places both the IO ports in HiZ by disconnecting A <->B connection. Tying it high enables the normal operation.

0 ShreyasRao over 5 years ago in reply to ShreyasRao

TI__Guru 56100 points

Hi Charles,

A floating port may not have enough drive to overturn the previous logic high to low state. Without OE pulled low, the port B can retain the last known state when A port is floating.
Having a very weak pulldown may also be another option. ( in the order of 100k)

0 Charles Jeon over 5 years ago in reply to ShreyasRao

Expert 2975 points

Hi Shreyas

The customer asks you to confirm that the following situation is possible.

1. Level shift when data communication.

- OE Pin is high

2. Floating when do not data communication.

- OE Pin is Low

3. When OE is low, it should not affect data on both devices.

is it possible?

Thank you!

0 ShreyasRao over 5 years ago in reply to Charles Jeon

TI__Guru 56100 points

OE pin is high = Normal operation -> Level translation between Vcca and Vccb

OE pin is low = High impedance on both the A & B ports, retains the last known state.

0 Charles Jeon over 5 years ago in reply to ShreyasRao

Expert 2975 points

Thank you for your supprot.

I have some question additional.

1. When power on is state while OE Pin is Low, what is the initial state of A & B?

- 0V or VCCA(B) or Unknown?

2. Does the OE pin of TXB0104 have internal pull-up or pull-down resistor.?

3. Does the EN pin of LSF0108 have internal pull-up or pull-down resistor.?

-Thank,

0 ShreyasRao over 5 years ago in reply to Charles Jeon

TI__Guru 56100 points

Charles,

1. Please elaborate on the query, i couldnt understand.

2, 3. No the OE or the En pin doesnt have internal pullup or pulldown resistors.

0 Charles Jeon over 5 years ago in reply to ShreyasRao

Expert 2975 points

Shreyas

The first question is explained in detail.

What is the initial output state of TXB series when operated in the following sequence?

1) VDDA and VDDB is not appled power

2) OE pin fix low using pull-down resistor

3) Power appled VDDA and VDDB

0 ShreyasRao over 5 years ago in reply to Charles Jeon

TI__Guru 56100 points

1) The A B ports are off.

2) The A B ports are disconnected and off since Vcca / Vccb is disconnected

3)When OE is low and supply is powered, the A/B will retain the last retained state.

0 Charles Jeon over 5 years ago in reply to ShreyasRao

Expert 2975 points

I'd like to duuble check your answer

I'm not understand the meaning of the last retained state.

Is "the last retained state" a state before power-off?

If the products mounted first on the board, what is the state of port A & B when OE was low?

0 ShreyasRao over 5 years ago in reply to Charles Jeon

TI__Guru 56100 points

Charles,

It is the last valid known state before the inputs float when the power is on. It can be either high or low.
once the power is off, the state is irrelevant or low( not at the last known state)

Logic

Logic forum

TXB0104-Q1: Request information about the output status when the input is floating