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Looking for a level shifter that supports 1.8V<-->1.8V and 1.8V<--->3.3V

Muthu Shankar
Prodigy 235 points
Other Parts Discussed in Thread: TXB0104, TXS0102, LSF0102, SN74AXC4T774, LSF0204D, LSF0204

Hi,

I need a level translator for my SPI and I2C interface...I have seen that, for I2C, TI have specific devices because of the load capacitance limitation...I have selected TXB0104 for SPI and TXS0102 for I2C.

I want to know the above devices support 1.8V to 1.8V... Please suggest.

Thanks,

Muthu

  • 0
    Guru 316760 points

    The TXS0102 does not go below 2.3 V on the B side. You can use the LSF0102 instead (which requires that the voltage on Vref_B is higher than that on Vref_A, but this does not restrict the signal voltages).

    The TXB0104 might work for SPI, but its weak output drivers introduce many restrictions (see the datasheet). A more robust solution is the SN74AXC4T774.

  • 0 in reply to Clemens Ladisch
    Prodigy 235 points

    Hi Ladisch,

    Thanks.

    But I am seeing same drive strength in the datasheets for both TXB0104 and SN74AXC4T774...

    Since TXB0104 does not have direction pins, I want to use that part for my GPIO and SPI interface.Please let me know

  • 0 in reply to Muthu Shankar
    Guru 316760 points

    What you have shown are the absolute maximum ratings. These are the currents at which the device can blow up; you will not be able to draw these currents from a working circuit. (With the TXB's output impedance of 4 kΩ, you would need to apply 200 V.)

    The TXB's guaranteed drive strength is 20 µA, the AXC's, 8 mA (see the test conditions for VOL/VOH).

    All translators with automatic direction sensing must compromise their output drivers in some way to allow the other devices to override the voltage level (TXS/LSF use open-drain outputs; TXB uses weak drivers). If possible, use a direction-controlled translator.

  • 0 in reply to Clemens Ladisch
    Prodigy 235 points

    Hi,

    Thanks for your prompt response.

    Actually, we want to use a single device for SPI, I2C and GPIO which needs 1.8V <---> 1.8V and 1.8V <--->3.3V translation. I have gone through LSF010x datasheet.If you take LSF device for 1.8V <---> 1.8V application, VCCA is 1.8V and VCCB should be VCCA+0.8V, and the pull-up voltage on the B side should be 1.8V to translate 1.8V <---> 1.8V right?...For 1.8V <---> 3.3V, we can simply change the B side pull-up voltage to 3.3V right?

    We want to use the same part for SPI interface as well...Please let me know that it is good to go with LSF...

    Regards,

    Muthu

  • 0 in reply to Muthu Shankar
    Guru 316760 points

    Yes, you can use the LSF in this way. You can even use it for GPIO and SPI (if the pull-up resistors are sized correctly for the desired speed, and if the other devices' output drivers are strong enough).

    I²C has different electrical characteristics; it would make sense to use a different translator.

  • 0 in reply to Clemens Ladisch
    Prodigy 235 points

    Hi Ladisch,

    Thanks for your support.

    In the previous reply, I wrongly mentioned that I am going to use LSF010x.Actually, I want to go with LSF0204D,to use it for SPI,I2C and GPIO.

    Q1: In your first reply, you suggested to go with LSF part for I2C. But, in the latest reply, it seems that you are telling not to use LSF for I2C.Can you clarify this?

    Q2: It looks both LSF010x and LSF0204 are same, functionality wise. So, instead LSF010x, I can use LSF0204 right?

    Regards,

    Muthu

  • 0 in reply to Muthu Shankar
    Guru 316760 points

    What I was trying to say was that LSF is not the optimal solution for GPIO and SPI.

    The I/Os work the same with the LSF010x and LSF0204. The difference is that the LSF0204 has the 200 kΩ resistor integrated, and that the EN pin is a proper digital input.