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TXB0108: Low level between C2000's I / O and TXB 0108 is 0.6 V.

ACGUY
Guru 11170 points
Part Number: TXB0108
Other Parts Discussed in Thread: TMS320F28027,

Hello E2E,

Our customer has plan to use the C2000(TMS320F28027) and TXB0108 for new board.
However, a problem occurred in the circuit. The low level between C2000 and the level shifter is 0.6V.
Both of the datasheets VOLs  are max 0.4V.

Though they are communicating, characteristics that are not specs have appeared, so customers will stop diverting to other designing products.

Why are not 0.4V?

Regards,
ACGUY

  • 0
    Guru 316940 points
    The VOL values are specified for a certain current. The VOL can be larger if the current is larger. In any case, any VOL below the VIL is OK.

    In theory, for plain CMOS I/Os, the level should be exactly 0 V. Is there a current flowing? Are there any pull-up resistors?
  • 0
    TI__Guru 62160 points
    Clemens , appreciate your inputs and i agree.

    Please refer to the app note 'Effects of External Pullup and Pulldown Resistors on TXS and TXB Devices' here below .
    www.ti.com/.../scea054.pdf

    hope this might answer your question and resolve the issue.
  • 0 in reply to ShreyasRao
    Guru 11170 points
    Hello specialist,

    Thank you for reply.

    I have any additional information.
    - Customers are using the C2000 internal serial communication module. Other GPIO ports are no issue connected to TXB0108.
    - Connected I/Os are Pulled-down by 100-kΩ resistor to GND.
    - If two TXB0108s to serial, that issue no happend. VOL is less than 0.4V.


    Regards,
    ACGUY
  • 0 in reply to ACGUY
    TI__Guru 62160 points
    ACGUY ,

    Did we verify that the Vol is at the rated current as per the datasheet?
    when 2 are connected together, the IO ports are driving into hi-z ports, and hence the Vol can be maintained below the spec value as there is negligiable current draw.