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SN74HC595: Can it support 20mA current output under 3.3V power supply

Gary Zeng
Intellectual 1960 points

Part Number: SN74HC595
Other Parts Discussed in Thread: SN74LVC541A, TPIC6B595

Hi team,

We want to use SN74HC595 to drive seven-segment numerical tube LED as below.

image.png

Each moment, they will only drive one segment for 100us. But they need 20mA current. Which means each time there is only one output of SN74HC595.

Q1: Do you have test data that if SN74HC595 can support 20mA/3.3V for long term(up to 3years)

Q2: If 20mA is not allowed, what is the maximum value of current?

  • 0
    Guru 325560 points

    The absolute maximum rating is 35 mA, so the device will not be damaged. But for output currents above 4 mA, the output voltage is not guaranteed.

    You could add a strong buffer like the SN74LVC541A. Alternatively, use the TPIC6B595 and drive the LEDs from the cathode.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 1960 points

    Hi Clemens,

    Thanks for your support.

    Customer wants us provide the test data of lifetime if they use below two situations:

    1. 8ch output driver(4mA) at the same time, which can keep IC's health for 3years?

    2. Only 1ch output driver(30mA) for 100us and then turn to another channel, which can keep IC's health for 3years?

  • 0 in reply to Gary Zeng
    Guru 325560 points

    In both cases, the absolute maximum ratings are not being exceeded, so the lifetime will not be reduced at all.