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SN74LVCH162244A: SN74LVCH162244A outout pin sinking current capability

Johnny Guo
Expert 4910 points
Part Number: SN74LVCH162244A

Hi, 

My customer has one question about SN74LVCH162244A outout pin sinking current capability.

Below is their design circuit, two 244A output and one 244A input is connected together.

In their design, there is a short time (2us) when three 244A are all enabled, and 244_1 Y1 is high and 244_2 Y2 is low.. Thus they captured the voltage waveform as below.

This means there maybe one furrent flowing into 244_2 Y2 pin.

1. Could you help check is it possible for a sinking current into 244A Y2?

2. If yes, what is the sinking current capability? i checked in datasheet as below, it is -50mA, but need your confirmation.

Thanks.

Johnny

  • 0
    TI__Expert 4910 points
    Sorry, type error, furrent -> current.
  • 0
    Guru 280270 points

    244_1 is sourcing current, and 244_2 is sinking current; the result is a voltage divider, as shown by the 1.65 V level.

    According to SZZA010, the typical output impedance of LVC devices is about 11 Ω. So ignoring the pullup resistor and the bus-hold circuit, the current is 3.3 V / (11 Ω + 33 Ω + 33 Ω + 11 Ω) ≈ 38 mA, which is outside the recommended operating conditions and should be avoided for extended periods, but is still safe. The power dissipation in one output is 11 Ω × (38 mA)² ≈ 16 mW.

    (To edit a post, click More/Edit.)

  • 0 in reply to Clemens Ladisch
    TI__Expert 4910 points
    Clemens,

    Thanks for reply.
    Can we take the -50mA in datasheet as a judgement for sinking current?
    And for 16mW, what is the acceptable maximum power consumption for each output pin?

    Thanks.
    Johnny
  • 0 in reply to Johnny Guo
    Guru 280270 points
    The absolute maximum rating is where the chip is allowed to blow up, so you should try to stay away from it.

    Multiply the power consumption with the thermal impedance to get the temperature increase.