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Selecting right digital buffer - 20us switching

VT
Genius 3300 points
Other Parts Discussed in Thread: SN74ALVC16244A

1. I have a microcontroller programmed to switch 16 I/O pins at 20us interval to drive certain load at each pin. I have to operate at 3.3V.

2. Now I want to buffer the MCu pin from load with a buffer.'

3. I have been reading about TI's SN74ALVC16244A. It is 16 bit buffer, with 3ns Tpd. 

4. What will be each pin max drive current when all pins are turning on at same time. Datsheet says +-24mA drive, is it for all pin together or individual?

5. Any other better buffer?

  • 0
    TI__Genius 14487 points
    Thank you for your question. We are currently out for the New Year Holiday, but we will respond to you with an answer early next week.
  • 0
    TI__Genius 14487 points

    Vindhyachal,

    The IOH and IOL rating (+- 24 mA) is the current draw recommended for a single pin. In the Absolute Maximum Ratings table, "Continuous current through each VCC or GND" is specified at +-100 mA. This means that if all 16 bits are HIGH at the same time, then each pin can source or sink 6.25 mA each.

    I need to know a little more about your application to recommend a part. What is the current capacity you need to drive your loads? What device(s) is (are) on the output of your buffer?

    James

  • 0 in reply to James Lockridge19
    Genius 3300 points
    Hi James,

    Sorry for late reply. I had my exams.

    I have to drive a npn transistor to switch it on or off.As I said pin can switch at 20us min.
    Will optocoupler will be good idea here?
  • 0 in reply to VT
    TI__Genius 14487 points

    Vindhyachal,

    All of our logic parts are designed to operate all the way into the MHz range for switching frequency. Any buffer you choose will be able to accomodate your switching requirements.

    From my understanding, your microcontroller signal goes to a buffer which controls an NPN transistor, correct? Are you using the NPN transistors to drive peripherals devices? I'm asking because if that is the case, you might want to consider using two ULN2803A chips or possibly an open-drain buffer. Either of those suggestions would reduce the number of discrete components in your design as well as cost. The ULN2803 can drive up to 500 mA on a single channel.

    From the way you described your design, I do not believe an optocoupler would be necessary.

    James

  • 0 in reply to James Lockridge19
    Genius 3300 points

    Hi James,

    Actually I want to isolate both that's why I said for optocoupler earlier.

    Problem with ULN AFAIK, I won't able to isolate both the circuits.

    Application:

    1. I have a MCU board whose pins will switch on/off another circuit which is very noisy.

    2.  Load on other side, is to drive a npn transistor.

    3. Since load board is very noisy, so I want to isolate the two boards with optocoupler.