TXS0104E: about one of VCCA and VCCB is not powered up, will it damage device?

Joyce Li

Part Number: TXS0104E

Hi Dear expert,

My customer has a question regarding to TXS0104E, they have one application scenario that VCCA or VCCB is not present, only one supply is on, will it damage the device?

I checked the datasheet, quote below:

"The TXS0104E device does not require power sequencing between VCCA and VCCB during power-up so the power-supply rails can be ramped in any order. A VCCA value greater than or equal to VCCB (VCCA ≥ VCCB) does not damage the device, but during operation, VCCA must be less than or equal to VCCB (VCCA ≤ VCCB) at all times. The output-enable (OE) input circuit is designed so that it is supplied by VCCA and when the (OE) input is low, all outputs are placed in the high-impedance state. To ensure the high-impedance state of the outputs during power up or power down, the OE input pin must be tied to GND through a pulldown resistor and must not be enabled until VCCA and VCCB are fully ramped and stable. The minimum value of the pulldown resistor to ground is determined by the current-sourcing capability of the driver."

So should be ok, right? Looking forward to your reply.

BR, Joyce

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 317000 points

The datasheet is correct. But when V_CCA > V_CCB, current can leak out of V_CCB (see section 1.1 of Biasing Requirements for TXS, TXB, and LSF Auto-Bidirectional Translators).

0 Joyce Li over 4 years ago in reply to Clemens Ladisch

TI__Intellectual 2170 points

Hi Clemens,

so for customer application that VCCA or VCCB is not present, only one supply is on, will it damage the device?

0 Clemens Ladisch over 4 years ago in reply to Joyce Li

Guru 317000 points

The datasheet says that the leakage current does not damage the TXS itself. But the circuit must be able to cope with the leakage current (other devices on V_CCB might get powered up partially).

0 Joyce Li over 4 years ago in reply to Clemens Ladisch

TI__Intellectual 2170 points

Hi Clemens,

Sorry i am not fully clear, so i double confirm with you:

1. if VCCA is present and VCCB is not present, in this case, VCCA > VCCB. In app note, it says: When this occurs, large amounts of current flows through VCCA and into the diode, increasing power consumption and potentially damaging the device.

In datasheet it says "The TXS0104E device does not require power sequencing between VCCA and VCCB during power-up so the power-supply rails can be ramped in any order. A VCCA value greater than or equal to VCCB (VCCA ≥ VCCB) does not damage the device," When VCCA is present, VCC B is not present, so this should be powers are not fully powered up, not in normal working mode.

2. if VCCA is not present, VCCB is present, in this case, should not have the damage risk.

Below snapshot is our competitor datasheet that lists that one of the supply is off, it will not cause damage risk to device, so customer wants to check our device.

Thanks! Looking forward to your reply!

0 Clemens Ladisch over 4 years ago in reply to Joyce Li

Guru 317000 points

The app note and the datasheet contradict each other. But the app note says "potentially", so it does not actually know. Apparently, the only problem could be the power dissipation.

I_OFF applies only to the data I/O pins, and only when at least one supply is at GND. Section 14.5 of the NTS0104 datasheet says the same as the TI datasheet.

0 Joyce Li over 4 years ago in reply to Clemens Ladisch

TI__Intellectual 2170 points

Hi Clemens,

So what should we reply to customer if the app note and datasheet contradict each other?

If does TXS0104 support partially powered down?

Thanks very much for your reply,

Joyce

0 Clemens Ladisch over 4 years ago in reply to Joyce Li

Guru 317000 points

The datasheet should have priority. (But I'm just a random guy on the internet and do not set TI policy.)

The TXS0104E supports partial power down, in the same way as the NTS0104.

Logic

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TXS0104E: about one of VCCA and VCCB is not powered up, will it damage device?