need help with CD4020 counter

Discussion in 'General Electronics Chat' started by prometei, Feb 8, 2014.

  1. prometei

    Thread Starter Active Member

    Apr 13, 2008

    I'm trying to figure out the max. output current per output pin on the CD4020 14-stage binary counter but my datasheet interpretation skills are not sufficient.


    I'm attaching 2 screenshots of the datasheet, the table rows with the current ratings. Not sure which one indicates the max. output current per pin, and I've never seen negative current values, what's that anyways?

    thanks for your help
  2. k7elp60

    Active Member

    Nov 4, 2008
    As I read the data sheet, the maximum output current both high and low output is 3.0mA
  3. crutschow


    Mar 14, 2008
    The data sheets lists minimum value sink and source currents that the chip will deliver (MAX for IOH and MIN for IOL) for various common supply voltages and operating temperatures. Maximum values are larger than that but are not specified since minimum is normally the one of interest for worst-case analysis. Convention is that currents into a terminal are positive and currents out of a terminal are negative so the IOH values are negative values.
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Rule of thumb: don't try to get current out of a logic device.

    Table 6 has the values you seek, and hey ain't very high: at 5V you only get 1.4 mA at 2.5V, which is barely enough to light a LED. That current decreases if the part gets warm.

    Negative current come from the convention that ALL current flows into the device, so any current flowing ou of the device is negative. That's why the high level output current is negative.
  5. prometei

    Thread Starter Active Member

    Apr 13, 2008
    Yep, I know, but some of the newer LEDs can light up ok even at 1mA.

    I hooked up 4 LEDs to four of the Q outputs with (I think) 330ohm resistors. The total current for the 4 blinking LEDs was fluctuating between 5mA and 18mA, I guess I was pushing it there, since you say that 1.4mA is the max for a single pin/output.

    Oh, I thought that the minus meant that it's a max value for sinking current.