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SN74ACT244: Driving LED using non-inverting buffer IC such as SN74ACT244

Krunal Zala
Prodigy 50 points
Part Number: SN74ACT244
Other Parts Discussed in Thread: SN74LVC2G07, SN74LXC8T245, TPL7407LA, TPS22996, TPS22960, TXU0104, SN74LXC2T45, CSD13381F4

Tool/software:

Hello,

I have 8 LED and each LED can have a forward current of 25mA with forward voltage as 1.7V.

I want to turn on or off each LED independently using Microcontroller IO where IO follows 1.8V logic level (i.e. High = 1.8V and Low = 0V)

The LED can be powered using 3.3V source.

Is there a non-inverting buffer which I can use for such purpose?

Regards,

  • 0
    TI__Genius 9601 points

    Hi Krunal,

    To translate from 1.8V inputs to a 3.3V output, you would need to use an open drain buffer. Doing the calculations, for a 3.3V power supply, the resistor in series with the LEDs would need to be 64 ohms, and the device would need to sink 51 mA of current when off, which is more than our buffers' maximum current sink. Would it be possible to use a 70 ohm resistor for a LED current of 23 mA? This decreases the buffer sink current to an acceptable amount. In this case, the best solution for this application in our portfolio is the SN74LVC2G07.

    I'm sending this question to one of my colleagues with level translation to see if they have a non-open drain 1.8V to 3.3V solution that may be more applicable.

  • 0
    Guru 317060 points

    The SN74LXC8T245 can output 24 mA per channel, with a total current limit of 200 mA, which is just barely OK.

    Consider using stronger devices. The TPL7407LA has open-drain outputs, but only 7 channels. For high-side switching, there are load switches like the TPS22996 or TPS22960, with 2 channels each.

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Hello,

    SN74LXC8T245 can meet my requirement as I can lower the LED forward current to 20mA as well. It will not affect brightness significantly and hence it is okay for me.

    However, is there another low cost buffer that function same as SN74LXC8T245 ?

    I mean, I don't need bi-directional buffer as in my application, signal direction is fixed.

    Just trying to make sure I select a product that is cost competitive as well. You can refer 1K price while suggesting an alternative TI part number.

    Also, if there is dual channel/2bits buffer available meeting same technical requirement as mentioned above is my additional requirement.

    Regards,

  • 0 in reply to Krunal Zala
    Guru 317060 points

    Many level shifters allow two directions. The TXU0104 is unidirectional, but with a lower drive strengh.

    The SN74LXC2T45 has two channels.

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Hello Clemens,

    Thank you for your reply.

    TXU0104 does not work for me as drive strength is 12mA @5V.

    Basically, SN74LXC8T245 meets my technical requirements but it's cost is at higher side and hence I am exploring if I can get another TI IC which offers same technical requirement but at lesser cost and therefore I mentioned that I don't need a bidirectional feature as it is present in SN74LXC8T245 

    Thank you for pointing me to SN74LXC2T45 for two channels requirements.

    Please help me as I requested above.

  • 0 in reply to Krunal Zala
    Guru 317060 points

    There is no such integrated device. You could drive the LEDs with discrete MOSFETs, but 8× CSD13381F4 would not be much cheaper.