TXB0108: Level-shifter driving current

Shih Scott

Part Number: TXB0108
Other Parts Discussed in Thread: TXU0304, TXS0108E

Hi,

I am designing the circuit that the STM32F4 control chip by SPI passes level-shifter, and the chip has fan-out 4 pcs in the same SPI route. The MCU voltage level is 3.3V, and the level-shifter is 1.8V, below is my schematic. My problem is that the SDO pin should output a voltage level of 1.8V, but only output 0.8V swing; and the SCK output is normal. Is that driving current not enough(Adding pull-up 50k does not affect the result)?

over 1 year ago

+1 Clemens Ladisch over 1 year ago

Guru 243220 points

The TXB has a drive strength of 20 µA. Apparently, there is a pull-down somewhere.

For SPI, use a unidirectional level shifter like the TXU0304.

0 Shih Scott over 1 year ago

Prodigy 70 points

Hi, Clemens

Thanks for your reply. So it might not because of the driving current, or should I change the component? I also found another level-shifter TXS0108E, or using TXU304 better?

+1 Clemens Ladisch over 1 year ago

Guru 243220 points

The lowered voltage shows that something else is pulling the line down.

You need a device with higher drive strength. The TXS generates a high voltage only with pull-up resistors. A unidirectional device like the TXU0304 has buffered outputs.

0 Shih Scott over 1 year ago

Prodigy 70 points

Hi, Clemens

Appreciate your advice, it really helps me.

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TXB0108: Level-shifter driving current