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SN74ACT244-Q1: Noninverting buffers & drivers to control of LEDs

Francisco Vera
Prodigy 100 points
Part Number: SN74ACT244-Q1
Other Parts Discussed in Thread: SN74LV541A-Q1, SN74LVC1G07, SN74LVC2G06-Q1

Hello, my name is Francisco, engineer of the R+D+i Department of the Rother Industries & Technology company.

I would want to use a device through the 3.3V GPIOs signals of my microcontroller enable and disable LEDs. This device and LEDs must be supplied at 5V and they must support a maximum current of 20mA. I have investigated your products and I have found that the Noninverting buffers & drivers would be perfect for controlling LEDs.

In the following document discusses its implementation: https://www.ti.com/lit/an/scaa142/scaa142.pdf?ts=1682579657969&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252Fes-mx%252FSN74LVC1G07

On option that I could use, it would be the SN74ACT244-Q1. I want to ask if this device would be suitable for the previously commented requirements.

Another option but with lower output current (16 mA) is SN74LV541A-Q1, Would this device be suitable?

On the other hand, I would want you to confirm me that I can get outputs of 5V if I apply a 3.3V input to each input pin of SN74ACT244IPWRG4Q1 and SN74LV541A-Q1. Please confirm me both cases, this requirement is fundamental for me. I am not sure about this specifically in the case of SN74LV541A-Q1 because in its datasheet appears the following information that I mark and I attach you.

On the other hand, I would want you to confirm me that the distribution of Leds that I have made it is correct for the SN74ACT244IPWRG4Q1. LEDs enable (0 output) when I apply a low level "0" input and LEDs disable (5 output) when I apply a high level "3.3V" input. I attach an image.

Best regards,

Francisco.

  • +1
    TI__Guru* 96681 points

    Hey Francisco,

    You can use logic gates for driving LEDs, but there are some limitations.

    The output voltage is the same as the supply voltage. TTL-compatible parts (ex: AHCT) will support 3.3V inputs with a 5V supply, but most CMOS devices will need a 5V input for a 5V supply.

    You could also consider open-drain devices that allow for the output to be connected to a higher voltage than the supply. For example, SN74LVC1G07 will allow a 3.3V supply with 3.3V inputs, while the output is connected to the LED, resistor, and 5V supply.

    You will always need a limiting resistor for each output driver since they do not contain any current limiting capabilities.

    Also, you will need to keep the total current through a device limited. Most logic devices are limited to 70mA or 100mA total current, so an 8 channel device may only be able to drive 3 LEDs at 20mA each.

    You may want to look at TI's portfolio of LED drivers if these limitations don't work for you.

    Please let me know if I can be of further assistance.

  • +1 in reply to Emrys Maier
    Guru 267430 points

    If you need automotive qualification, then the SN74ACT244-Q1 is the only suitable non-inverting buffer.

    Automotive LED drivers require 5 V input signals (i.e., you would have to add a level shifter), and most of them have serial inputs. Using them would make sense only if you needed to reduce the number of control signals.

  • 0 in reply to Emrys Maier
    Prodigy 100 points

    Hi Emrys Maler,

    The explanation that you have given me is very interesting. According to your explanation, the SN74ACT244-Q1 would be suitable due to it use the TTL technology, so it can be supplied a 5V voltage, it supports 3.3V input and it provide 5V output. Is it correct?

    On the other I am concerned about the feature of total current of 70mA or 100mA that these devices can support. In which paragraph of the SN74ACT22-Q datasheet is this feature commented?

    Best regards,

    Francisco.

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    Hi Clemens Ladisch,

    Yes, I need automotive qualification. On the other hand, Could I use the SN74LV541A-Q1 for this application? According to Emrys's explanation, it use the CMOS technology, so it can be supplied a 3.3 voltage, it supports 3.3V input while the output is connected to the LED, resistor, and 5V supply.

    Best regards,

    Francisco.

  • +1 in reply to Francisco Vera
    Guru 267430 points

    Devices with TTL-compatible inputs support 3.3 V input signals.

    The total current is limited by the "continuous current through VCC or GND" absolute maximum rating.

    The output of the SN74LV541A-Q1 must not be higher than the supply. Only devices with open-drain outputs have overvoltage-tolerant outputs, but this implies that you must drive the LED's cathodes, so you'd need inverters, e.g., 4× SN74LVC2G06-Q1. (You mentioned that the device must be supplied with 5 V. Is this true?)

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    Yes, I need to supply the device, specifically the SN74ACT244-Q1. However I had thought if it would be possible with the SN74LV541A-Q1. However, it is CMOS device so I can't use it, thanks.

    Therefore, as you have told me, the only option that I can use is the SN74ACT244-Q1, it would be suitable due to it use the TTL technology, so it can be supplied a 5V voltage, it supports 3.3V input and it provide 5V output. Is it correct?

    On the other hand, I can read in the datasheet of SN74LV541A-Q1 that it can support a absolute continuous current through VCC or GND of 200mA. So, it would be perfect for my application. Is it correct?

    Best regards,

    Francisco.

  • +1 in reply to Francisco Vera
    Guru 267430 points

    My question is whether the LED buffer must be supplied with 5 V, or if a 3.3 supply is possible. In the latter case, you would be able to use the '06.

    Yes, the SN74ACT244-Q1 can be used as shown in the schematic. It is a CMOS device, but it has TTL-compatible inputs.

    The SN74LV541A-Q1 does not support 3.3 V input signal when supplied with 5 V. (And it would output 3.3 V when supplied with 3.3 V.)

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    Hi Clemens,

    Yes, both the Led and the SN74ACT244-Q1 will be supplied at 5V. Thanks, for your reply. With your help I have verified that the SN74ACT244-Q1 will be perfect for my application.

    Best regards,

    Francisco.