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SN65C1168E: Output drive current

dylan stuchbury
Prodigy 10 points
Part Number: SN65C1168E

Tool/software:

The data sheet and application test circuits seems contradictory.

For a typical application with 100Ohm termination, and typical output drive voltage Vod2 of 3.7V , then 37mA would be being sourced / sank.

However the datasheet lists 20mA as recommended and absolute maximum levels (Ioh Iol and Iok) . This 20mA as a 'maximum' seems completely counter-inuitive as with 100Ohm region termination this will always be exceeded.

Is the device intended to operate with the outputs in some form of current limit, and the developed Vod will be whatever is developed across the terminator with the actual current limit (up to Vcc) ?

  

  • 0
    TI__Guru 72521 points

    Hi Dylan,

    dylan stuchbury said:
    However the datasheet lists 20mA as recommended and absolute maximum levels (Ioh Iol and Iok) . This 20mA as a 'maximum' seems completely counter-inuitive as with 100Ohm region termination this will always be exceeded.

    I agree with you on the recommended spec. I'm not sure if this is a typo or if it was categorized incorrectly. The abs max output current however calls out 150mA which is also the device's max short circuit current clamp (Ios). IoK is a clamping current that shouldn't occur during normal operation so we can disregard this one.

    dylan stuchbury said:
    Is the device intended to operate with the outputs in some form of current limit, and the developed Vod will be whatever is developed across the terminator with the actual current limit (up to Vcc) ?

    The device itself should clamp it's own current below 150mA (the IoS current). My guess is the recommended current max for the driver is actually incorrect. This device was designed around the RS485 standard so it should be able to support more than double the recommended. 

    -Bobby