Relation or difference between Input clamp current and Sink current

Discussion in 'Digital Circuit Design' started by Prakash Scientist, Jul 1, 2016.

  1. Prakash Scientist

    Thread Starter New Member

    Dec 19, 2012
    I want to take signal from external peripherals to PIC micro-controller(PIC18F66K22) through buffer IC(74HC541). My problem is o/p of buffer source current is +/-35mA, output clamping current +/- 20mA and i/p of PIC18F66K22 PORTF pin is 2mA. And another case input clamp current of PIC18F66K22 is +/-20mA. We may directly interface these two IC's to PORTF pin? And in what way input clamp current and sink current related or differs?
  2. OBW0549

    Well-Known Member

    Mar 2, 2015
    I think you are misunderstanding these specifications, which I assume you have taken from the Absolute Maximum Ratings section of chapter 31.0, Electrical Characteristics, of the PIC data sheet and the Limiting Values section of the 74HC541 data sheet.

    For the 74HC541, the output current limit of +/- 35 mA simply says that forcing the chip to source or sink any more than 35 mA (for example, by making it drive a very low resistance load) may cause damage.

    For the PIC, the +/- 20 mA limit on output clamping current and input clamping current simply says do not force more than 20 mA into or out of an I/O pin, to (I'm assuming, here) avoid damaging the pin's ESD protection clamp diodes. The 2 mA limit on output source or sink current says do not attempt to make the I/O pin source or sink more than 2 mA, to (I'm assuming, again) avoid damage to the internal output MOSFETs.

    Provided your PIC and the 74HC541 are powered from the same supply voltage, and you are driving PIC pins configured as inputs with the outputs of the 74HC541, none of this matters anyway, as negligible current will be flowing.

    In other words, you do not have a problem.
    Prakash Scientist likes this.