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SN74AXC8T245: Output Current Drive

Intellectual 2445 points

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Part Number: SN74AXC8T245

Team,

Using the SN74AXC8T245 in a design and I am curious what the maximum current drive is on an output pin.  The datasheet shows an absolute max of +/-50 mA and then farther down there is a test with a 2k Ohm load resistor but is there a recommended maximum current that this part can drive?

Also I just realized that the vendor that made the board for the customer tied DIR1, DIR2 and OE_N directly to GND or VCC. The application circuit shows that these are usually pulled up or down with 10k resistors.  Any issues with these direct ties to power or GND?  It doesn’t sit great with me but we don’t see crazy increases in current when we apply power to this part of the board.

  • The recommended maximum current is specified as the test condition for VOL/VOH; when you are trying to draw more current, there is no guarantee for the voltage drop.

    The datasheet says:

    To ensure the high-impedance state of the level shifter I/Os during power up or power down, OE should be tied to VCCA through a pullup resistor.

    If you do not care about the state of the I/Os during power up or power down, then you can connect OE directly to GND.

    Pull-up or pull-down resistors allow to override the voltage; even if your circuit does not do this, you might want to do this when debugging. The device itself does not care; CMOS inputs have a very high impedance.