TXB0108: GND Level Translation

Sofia R.

Part Number: TXB0108

Good afternoon ladies and gents,

I'm currently testing a design which features a TXB0108 voltage level shifter. Vcc on the A side is +2.5V and on the B side is +3.3V.

I have noticed that when I pull to GND one of the A inputs, the output on the B side is not pulled to GND, and it stays at 1V instead.

It is my understanding that this part shifts the level of the input signal on the A side to the appropriate level depending on Cvv on the B side, but GND stays the same. Is that correct?

I believe the issue might be related with the use of a pull-up resistor on the B side (10k pull-up to 3.3V) as I see on the datasheet that it states "Any external pulldown or pullup resistors are recommended to be larger than 50kΩ"?

Would anyone please be able to confirm that GND translated to GND on this device? Kind regards,

Sofia

over 6 years ago

0 Emrys Maier over 6 years ago

TI__Guru* 96947 points

Hello Sofia,
Today is a US holiday. I have asked our translation expert to take a look, but he won't be in until tomorrow.

0 Clemens Ladisch over 6 years ago

Guru 292610 points

To allow external devices to override the TXB's outputs, the TXB has deliberately weak output drivers (about 4 kΩ resistors in series with its outputs).

When you're using a strong pull-up, it forms a voltage divider with the TXB output impedance.

0 ShreyasRao over 6 years ago in reply to Clemens Ladisch

TI__Guru 59350 points

Thanks Clemens and I agree on your inputs.

Sofia,

Please read the app note on effects of external pullups on TXB here below.
www.ti.com/.../scea054a.pdf

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TXB0108: GND Level Translation