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SN74AHC1G125: Output current

Roy Hsu
Genius 9320 points
Part Number: SN74AHC1G125
Other Parts Discussed in Thread: SN74LVC1G125

Hi Team,

What's the output current of this device? It seems to be 8 mA from the datasheet. However, in an application when the output is connected to Pin 5 of ACSL-6420 (an opto-coupler), my customer measured the current and found it to be about 53 mA. (The measurement was done with a digital multi-meter)

Here's the schematic:

Thanks.

Roy Hsu

  • 0
    Guru 281410 points

    The datasheet recommends that you do not try to draw more than 8 mA from the output, and that is the highest current for which a maximum voltage drop is guaranteed. If you draw more, you get a higher voltage drop:

    53 mA widely exceeds the absolute maximum ratings of both the SN75AHC1G125 (25 mA) and the ACSL-6420 (15 mA).

    I suspect that the circuit drives the optocoupler's LED without a current-limiting resistor. (See pages 17/18 of the ACSL-6420 datasheet for example drive circuits.)

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 44665 points

    Hi Roy,

    I believe they are using the SN74LVC1G125 based on the schematic. What Clemens said still applies to this device as well if they indeed using it.