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SN74ALS00A: Pin Output Current Capability

JIGAR PATEL2
Intellectual 615 points
Part Number: SN74ALS00A

Hello All,

I have used quad NAND gate IC SN74ALS00AD for some logic function.

Now, I want to drive FZT600 transistor's base using one of the NAND gate output pin.

For that I want to use minimum base series resistor to allow maximum current flow through transistor. This is not an issue.

I want to know that how much maximum current,  the pin of  SN74ALS00AD can source?

I  have read the datasheet of it but what i found,

1) high level output current is negative & just 2mA.

2) I dont think so that this IC can source just 2mA. isn't it?

For any IC, in datasheet, the maximum output that can be source by any I/O pin is mentioned. But what is the value for this IC?

in above data, what is IO for whose value is -30mA(min) to -120mA(max)?, if it is output current then why it is negative?

Regards,

Jigar

  • 0
    Intellectual 615 points
    The pic that i have uploaded is from IC's datasheet (page 4).
  • 0 in reply to JIGAR PATEL2
    TI__Guru* 96591 points

    Hi Jigar,

    First, I'm not sure what version of the datasheet you're looking at, but the most recent version of the SN74ALS00A datasheet from TI's site shows these electrical characteristics:

    There's a very detailed application report on the ALS family of logic available here: Advanced Schottky Family

    What you may not know is that the datasheets for these parts were originally released in data books -- those books would include application reports like the one I linked above that described the entire family.  Unfortunately, when we went to computer based datasheets (about 30 years ago) it was decided to separate these documents.

    If you look at Figure 19 in the above linked document, you will see the general output characteristics:

    The datasheet guarantees that you will see at least Vcc - 2V at the output with a 0.4 mA source current, however you can see from this plot that much higher currents are possible - it looks like the short circuit current for this device would be close to 60 mA. I would not recommend running the device at that current, however. It would likely cause damage due to thermal issues.

  • 0 in reply to Emrys Maier
    Intellectual 615 points
    Hi Emrys Maier,
    The graph you have shown explain everything !!! Thanks for that.

    I want to ask about 7th parameter in table:
    What I understand that parameter is:
    If I draw 30mA from output pin then my voltage at pin will be downed to 2.25V !!! is this correct?
    If yes, then what about maximum current 112mA? what it explains?

    Regards,
    Jigar
  • 0 in reply to JIGAR PATEL2
    TI__Guru* 96591 points
    Hey Jigar,
    It means that if you force the output voltage to 2.25V (for example, by using a DC power supply) then the device will output somewhere between 30 and 112mA.
  • 0 in reply to Emrys Maier
    Intellectual 615 points
    Hi Emrys Maier,

    Thanks for the explanation.

    Regards,
    Jigar