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SN74ABT2245: Using SN74ABT245 instead of SN74ABT2245

Danilo A.
Mastermind 33395 points

Part Number: SN74ABT2245
Other Parts Discussed in Thread: SN74ABTR2245, SN74ABT245B

Hi Team,

We would like to ask your help regarding our customer's inquiry below.

Looking at the differences between SN74ABT2245 and SN74ABT245, I see the the drive strength (IOH / IOL) of the 2245 is considerable lower than that of the 245. Are the parts essentially identical with the exception of the 25 ohm resistors in the 2245 and is the existence of the resistors the reason for the lower current? If I were to use the 245 with external 25 ohm resistors, would I effectively accomplish the same circuit as the 2245 and achieve the same output current?

Regards,

Danilo

  • 0
    TI__Guru* 97656 points

    Hi Danilo,

    Yes - the additional '2' in the part number indicates that the device has output damping resistors. This is an added feature to help with impedance matching to 50 ohm transmission lines.

  • 0 in reply to Emrys Maier
    TI__Mastermind 33395 points

    Hi Emrys,

    Thank you for your response. Please see the following questions of our customer below.

    I understand that the additional “2” in the part number indicates the existence of the damping resistors. My questions are:

    • Is the existence of those resistors the reason that the drive strength (IOH, IOL) is specified so much lower than the parts without the resistors?
      • SN74ABTR2245 IOH is spec’d at -12mA.
      • SN74ABT245 IOH is spec’d at -32mA.
    • Are the two parts (SN74ABT2245 and SN74ABT245) identical apart from the damping resistors?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Guru* 97656 points

    Hi Danilo,

    Yes, adding a series resistor will reduce output drive strength, and yes, that is the primary electrical difference between the two parts. The reduced drive strength will also impact propagation delay.

    Here are a few of the differences:

    You can see all of the specifications in the datasheets located here:

    https://www.ti.com/lit/ds/symlink/sn74abt245b.pdf

    https://www.ti.com/lit/ds/symlink/sn74abtr2245.pdf

    In addition to the electrical difference, the SN74ABTR2245 is only available in 2 packages (DW and PW), while the SN74ABT245B is available in many packages: DB, DGV, DW, N, NS, PW, and RGY