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WEBENCH® Tools/TXB0104: Connection of OE Pin

Nithin James
Prodigy 160 points
Part Number: TXB0104


Tool/software: WEBENCH® Design Tools

Hi,

 we are using TXB0104 for GSM  Modem TX and RX voltage level shifting (3.3v to 1.8v), we have doubt about the connection of OE pin of TX0104 ( presently it is connected to VCCA and pull downed through 47k ).

please review the attached schematic and suggest update if any required.

Also VCCA is generated through resistor voltage divider of from 3.3v (47k and 58.3k combination)

please suggest whether this approach is fine or not . 

  • 0
    TI__Guru* 97046 points
    Hi Nithin,
    The OE pin of TXB0104 is a high-impedance CMOS input referenced to VCCA, which means that the thresholds are determined by VCCA. The shown connection will ensure that all channels are always enabled when the device has power.

    Connecting VCCA to a voltage divider probably won't be an issue (if the output is low current/low capacitance and the switching speed is slow), however it's not something we would recommend to do. Every time the device switches, current is drawn from the supply, and that will cause a large change in the supply voltage and could cause issues. Our recommendation would be to use a low power LDO regulator for this conversion, such as the TLV74118PDBVR, which will guarantee that the supply remains at the correct voltage regardless of the transient current.