TXB0102: TXB0102 output waveform decayed when speed go to 500KHz or higher

Garrick Dai

Part Number: TXB0102
Other Parts Discussed in Thread: SN74AXC8T245, SN74AVC4T774

My customer use TXB0102 to voltage tranlate SPI Clock signal, from A port 1.8V(external MCU) to B port 3.3V. But found if the Clock signal is higher than about 500KHz, the output signal waveform decayed. If the clock go high to 5MHz, the output almost distorted. Customer tried to connect or disconnect external pull-high resistors(R169,170), but see no any improvement. Also tried to disconnect the output load from port B, but still no improvement, as below. The exxternal MCU IO(connected to port A) can drive 2mA current. So what is the reason and how to solve this? Many thanks.

over 5 years ago

0 ShreyasRao over 5 years ago

TI__Guru 55990 points

Hi Garrick,

Please send any scope shots and the schematics if available.
TXB is suggested for SPI (push-pull architecture), however, it cannot support a load as you have mentioned here.
It can only support 20uA of DC drive and is not suggested to have more than 70pF of loading(including board, pin, trace capacitance)

Since the SPI is 4 line signal with push-pull architecture, you can also consider SN74AXC8T245 which has 2 DIR control for controlling the bank of 4 channels each.
There is also SN74AVC4t774 having DIR control on each of the IO port suited for SPI interface.

0 Garrick Dai over 5 years ago in reply to ShreyasRao

TI__Intellectual 1660 points

0 Garrick Dai over 5 years ago in reply to Garrick Dai

TI__Intellectual 1660 points

Please check the output waveform and customer circuit. Already disconnect external load, and there is no more than 70pF load, but the output still no change. The only way to improve the output is to slower the clock speed. So not sure why TXB0102 cannot buffer just 500KHz SPI Clock?

0 ShreyasRao over 5 years ago in reply to Garrick Dai

TI__Guru 55990 points

Garrick,

what is the probe capacitance while measuring?

could the customer also disconnect the series resistors before measuring at the device pin?

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TXB0102: TXB0102 output waveform decayed when speed go to 500KHz or higher