SN74LVC2G34: Can I gang 4 of these together to increase current drive (trying to drive a 15meter cable), or do we get contention issue due to part-part input to output prop delay.

bahram afghani

Part Number: SN74LVC2G34
Other Parts Discussed in Thread: SN74AC244

Can I gang 4 of these together to increase current drive (trying to drive a 15meter cable), or do we get contention issue due to part-part input to output prop delay.

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 243820 points

It is possible to gang CMOS outputs together to get more drive strength, but you should do this only for outputs on the same device.

I am guessing that you have chosen the SN74LVC2G34 because you want symmetric drive strength and are running at 5 V. Under these assumptions, you can use buffers in the AC family.

With 15 m cables, consider using differential signals.

0 bahram afghani over 4 years ago in reply to Clemens Ladisch

Prodigy 170 points

Hi Clemens,
Thank you for your reply. The other end of the cable is single ended buffer, and I don't have the leverage to chnage that design, therefore got to go with single ended driver.

2 gates are not sufficient, we need over 100 Ma to stay within the required rise and fall, please suggest a 4 gate part.

Why AC family, max sink and source is 24mA, isn't it? Please explain why AC family!?

Thanks,

Bahram

0 Clemens Ladisch over 4 years ago in reply to bahram afghani

Guru 243820 points

As I said, the AC family can run at 5 V and has symmetric drive strength.

Are you running at 5 V?

0 Dylan Hubbard over 4 years ago in reply to Clemens Ladisch

TI__Mastermind 42640 points

Hi Bahram,

The AC family is a suitable suggestion for this. Even though the outputs can be tied together for higher drive, it is important to still stay under the abs max current through the VCC and GND pins. This family has devices that have a higher current ratings than 100 mA to meet your needs.

0 bahram afghani over 4 years ago in reply to Dylan Hubbard

Prodigy 170 points

Are you suggesting to use a SN74AC244 part? So ganging all inputs therefore outputs together should be fine and give enough current. I am placing a 39ohms series driving the cable, therefore max sink/source would be around 125mA. What is the gates output impedance for SN74AC244?

Thanks,

Bahram

0 Dylan Hubbard over 4 years ago in reply to bahram afghani

TI__Mastermind 42640 points

Hi Bahram,

You can find out how to estimate the output impedance by referring to the FAQ below:

https://e2e.ti.com/support/logic/f/151/t/742466?tisearch=e2e-sitesearch&keymatch=faq%3Atrue

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SN74LVC2G34: Can I gang 4 of these together to increase current drive (trying to drive a 15meter cable), or do we get contention issue due to part-part input to output prop delay.