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SN74LVCH16T245: Power requirements and drive capability

Steve Bozman
Prodigy 120 points
Part Number: SN74LVCH16T245

1. In the "Recommended Operating Conditions" sections it shows that the range of Vcca and Vccb is 1.65-5.5V but the subsequent specs show ranges, 1.65-1.95V, 2.3-2.7V, 3-3.6V, 4.5-5.5V, which covers most common voltage supply values. My question is can the device be powered by 4.0V and how should the specs be interpreted for a voltage not included in the ranges shown above.

2. How is the total Icc requirement of the device calculated?

3. Is it preferable to have A or B powered from the higher voltage?

4. What value of pull-up resistor should be used for OE* and DIR?  It looks like the control inputs leakage current is 2 uA and the driver connected is 10 uA.  My calculations indicate that a 10K ohm resistor would work but a value even higher should also work. Any feedback is appreciated especially if I am missing something.

5. Ioh is listed as -24mA for 3V (here again, how would 4V supply affect this value?). What load can this drive to a logic high of 2V (50, 75, 100 ohm)? Figure 2 on page 12 shows Voh vs Ioh and is confusing to me because I don't see the correlation to the device output capability so I must be missing something in my interpretation.

  • 0
    TI__Mastermind 30575 points

    Hello Steve,

    1. We only spec our devices for common voltage nodes. The best option is to just estimate the value for the spec based on the specs provided for the two nearest voltage nodes. If there are any specs that are particularly important to your design that you need a specific value for, I could put in a request to the design team to obtain that information. 

    2. For power consumption calculations, you can refer to this thread:

    or this app note:

    3. Either way is fine, it should make no difference.

    4. For DIR, the value shouldn't matter. Assuming the DIR pin will be fixed you can simply connect it directly to VCCA or GND. For OE, the value will be dependent on the current sinking capabilities of the device driving the pin. You can use the formula below to determine an appropriate resistor value:

    VCCA - Rpu * Ipu < Vih

    where Ipu is the current your driver will sink to pull the line low and Vih is approximately VCCA * 0.65. Generally, a weaker pullup (10k or higher) is the best choice. 

    5. Again, the best option is to estimate the value based on the provided specs of the nearest voltage nodes. In the datasheet Ioh is specified for a value that will be guaranteed to maintain the appropriate Voh. In theory, the Ioh can be higher but this will come at the expense a lower Voh level. The figure on page 12 is trying to illustrate this fact. With a 4V output, as long as the drive current is somewhere between 24mA and 32mA you should be able to maintain satisfactory Voh and Vol levels. If your load requires a higher driving current than that you will start to see Voh decrease to values below what is spec'ed on the datasheet. 

  • 0 in reply to aozer
    Prodigy 120 points
    Thanks for your responses.

    To clarify the answer to question 1, is it fine to operate the device with any voltage in the 1.65-5.5 volt range?
  • 0 in reply to Steve Bozman
    TI__Mastermind 30575 points
    Hello Steve,

    Yes, that is correct.