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SN74AHCT08: Higher Output Current

Brian Wang0928
Genius 14020 points
Part Number: SN74AHCT08
Other Parts Discussed in Thread: SN74LVC1G08, ISOM8110

Tool/software:

Team,

Does TI have other AND gate IC that is pin-to-pin compatible with the “SN74AHCT1G08DBVR” and with a higher output current, increasing from 8 mA to around 10 mA(at least 9mA)?

  • 0
    Prodigy 100 points

    Hi Brian,

    One more condition: the Vcc should remain between 4.5 V and 5.5 V. We want to avoid a board re-layout, so changing Vcc to, for example, 3.3 V is not an option.

    Thank you.

  • 0 in reply to Nick Dai
    Guru 316380 points

    There is no P2P device. The SN74LVC1G08 would require higher input voltages.

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    Could you please help check whether the “SN74AHCT1G08DBVR” is sufficient under the following conditions?
    I believe the 8 mA output current limitation in recommended condition table is due to the ambient temperature (Ta) being 125 °C. If the ambient temperature is reduced to 100 °C, the IOH current might be increased.

    We also cross-checked the absolute maximum output current, which is 25 mA. The conditions we are using seem to have a small margin below this limit.
    Currently, we are using the SN74AHCT1G08DBVR to drive a photocoupler, but we need to increase the output current to around 9 mA to 10 mA.
    I’m wondering if this IC can withstand this condition.
    Thank you.

     

    • IOH or IOL = 9mA ~ 10mA
    • Ta = 80degC ~100degC
    • Vcc = 4.97V ~ 5.27V
  • 0 in reply to Nick Dai
    Guru 316380 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:

    The datasheet specifies a worst-case output resistance of 87.5 Ω (high) or 55 Ω (low) for loads up to 8 mA. You can assume that at 10 mA, it will not be much larger.

    (Why does the photocoupler need so much current? Increased current will increase thermal degradation. Something like the ISOM8110 would require less input current.)

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    I understand that the voltage drop will increase as the output current increases.
    Given Ta = 100°C, the calculated junction temperature Tj is:

    Tj = 100°C + (10 mA)² × 87.5 Ω × 180.5 °C/W = 101.58°C

    It seems that the Tj result (101.58°C) is well below the Tj maximum specification (150°C) under a 10 mA output current condition.

    Could you please confirm if this calculation is correct? Are there any other specifications we need to consider?

    Also, how can we estimate the lifetime of this IC?
    Can you please confirm whether the IC can operate reliably under the following conditions?

    • Ambient Temperature (Ta): 80–100°C

    • Output Current (Iout): 10 mA

    • Supply Voltage (Vcc): 4.97–5.27 V

    • Required Lifetime: 48,000 hours

  • 0 in reply to Nick Dai
    Guru 316380 points

    The Tj estimate is correct.

    For lifetime estimations, see Reliability and its subsections. As long as you stay away from the absolute maximum ratings, you are safe.

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    Thank you for your reply.

    Could you please help confirm whether the function will operate normally at a 10 mA output current?

    Does this IC have any protection features that would limit its operation at a 10 mA output current?

  • 0 in reply to Nick Dai
    Guru 316380 points

    At 10 mA, it will operate normally, but VOL/VOH can be exceeded.

    There are not protection features for 10 mA or any other current. (When you exceed 25 mA, the device can get damaged.)