TXB0104: TXB0104

Moshe Levy

Part Number: TXB0104
Other Parts Discussed in Thread: TXU0104

Tool/software:

Hi,

I am using the TXB0104 in my design (schematic attached.
in my design VCCB is 5V and VCCA is 3.3V

- The input to VCCB is off / 24V fed to the pins via resistor split as shown in attached picture.(i,e: 44.2K and 10K to GND)

The issue is that i expected to get 4.42V and i get 1.5V ( I verified and the reason is the connection to the IC).

I tried also to alter the circuit and place on the input pin a p.d of 53.6K to GND and then find resistor so the overall divider will give me >3.25V (Vih min per datasheet)

1. I failed to find any combination to meet my needs.

2. my calculations assumed that maybe there is internal resistance in parallel to the 10K....i got ~4K)....and based on that tried to make divider to get correct Vi...but no success

3. why is it not that straight forward.

4. i also tried to change the device to TXS0104...with external P.U...and no success

3 months ago

0 Clemens Ladisch 3 months ago

Guru 295240 points

The outputs have clamping diodes to VCCB. Applying a voltage above VCCB violates the absolute maximum ratings and can damage the device.

To ensure that the B-side I/Os are in the high-impedance state, pull OE low.

0 Moshe Levy 3 months ago in reply to Clemens Ladisch

Prodigy 30 points

Thank you Clemens,

but my issue is not the output. it is the input. instead of having 4.42V i get 1.5V (voltage divider of the 24V input)

0 Clemens Ladisch 3 months ago in reply to Moshe Levy

Guru 295240 points

All I/O pins of the TXB are both inputs and outputs.

0 Moshe Levy 3 months ago in reply to Clemens Ladisch

Prodigy 30 points

Hi Clemens,

I know that each I/O is both input & output.

So how come if my voltage divider supplies <5V it is still trimmed to 1.5V?

0 Jack Guan 3 months ago in reply to Moshe Levy

TI__Mastermind 30616 points

Hi Moshe,

It is not recommended to use external pullups/ pulldowns stronger than 50kohms with the TXB/TXS devices due to pullups (TXS) and series resistance (TXB) internally. The effects are documented here in this app note: www.ti.com/.../scea054a.pdf

Regards,
Jack

0 Clemens Ladisch 3 months ago in reply to Moshe Levy

Guru 295240 points

The voltage is clamped through a diode to VCCB. (When VCCB is off, the current flowing through the diode will raise VCCB.)

For unidirectional signals, you should use a unidirectional translator like the TXU0104.

0 Moshe Levy 3 months ago in reply to Clemens Ladisch

Prodigy 30 points

Dear Clemens,

I think I managed to resolve my issue.

In The datasheet pull up/down it is stated:
"8.3.5 Pullup or Pulldown Resistors on I/O Lines The device is designed to drive capacitive loads of up to 70 pF. The output drivers of the TXB0104 device have low dc drive strength. If pullup or pulldown resistors are connected externally to the data I/Os, their values must be kept higher than 50 kΩ to ensure that they do not contend with the output drivers of the TXB0104 device."

Does it mean only the output driver has this requirement? in the input I can have smaller value P.D? or will it cause malfunction?

0 Clemens Ladisch 3 months ago in reply to Moshe Levy

Guru 295240 points

The input buffers and output drivers on both sides are always active (when OE is high).

0 Moshe Levy 3 months ago in reply to Clemens Ladisch

Prodigy 30 points

noted.

in my case. where Side B is the input buffer. and A is the driver. is it problematic that the input buffer P.D is less than 50K?

+1 Clemens Ladisch 3 months ago in reply to Moshe Levy

Guru 295240 points

Yes, because the output driver at the same pin might pull the line into the other direction.

Logic

Logic forum

TXB0104: TXB0104