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In case of multiplexers with a latch, how does one calculate the maximum current that the IC can drive?

I am talking specifically about the HC4351 series. How much can the MUX drive, at different stages of the output? Since we are dealing with a latch, at any point, multiple pins MAY BE up, hence drawing current off the IC.

Here is a datasheet of the 74HC4351 from Nexperia. Although the max current for different conditions has been specified on I am not sure whether the clamping specs can be applied to this analysis.

In another app note on Load switches, some methods to arrive at the current at each pin based on the load current and voltage drop have been outlined.

I am not sure how I should proceed to selecting the right Latch. Can someone please help?

Add more information

I was also looking at using the 74HC259 for doing a latch. I later had realized that it is only a digital latch and may not fit my bill.

Thank you in advance Rahul

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  • \$\begingroup\$ Max current and clamping voltage are two separate issues. \$\endgroup\$
    – user105652
    Commented Aug 31, 2019 at 6:33

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supply current specs, towards the top, with the maximums,

  • 50mA max from VCC
  • 50mA max into GND
  • +-20mA max from VEE
  • +-25mA max through the common pin

This is an analog switch, It connects 1 analog input to the common depending on the 3 digital inputs, it updates what input is connected to the common when you toggle the latch pin,

To take your question at face value, you can source up to 25mA through the common pin, if either an input or the common exceeds the supply voltages, it will flow through clamping diodes on to the supply rails, in these cases you need to make sure that VCC and VEE current limits are not exceeded

Its sounding like you want a device where you tell it what pins should be, e.g. high or low, and you would like it to drive them and supply current, if this is the case a load switch / serial in parallel out shift register sounds like what you are after.

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  • \$\begingroup\$ Please correct your grammar. Your answer is difficult to understand, though I think you are on the right track. \$\endgroup\$
    – user105652
    Commented Aug 31, 2019 at 6:37
  • \$\begingroup\$ Excellent and thank you. You have it right in that I want to drive select devices on the basis of an analog signal. The last paragraph is what I too was possibly converging on after asking this question, but I am not really sure why I would need to go for a solution with load switches, given that the 4351 kind of ICs already allow me to latch a given pin. Can you please elaborate further and why the HC259 or the 4351 are not the correct design choice? \$\endgroup\$
    – Venkata Rahul S
    Commented Aug 31, 2019 at 8:04
  • \$\begingroup\$ you cannot latch a given pin, think of the device like a rotary switch, you can turn it to connect only 1 of the 8 inputs to the common pin at a time, the digital inputs tell it where to move to, and the latch tells it when to move. Am I to understand you want a buffered analog voltage that you can latch, if so that would be a sample and hold circuit. \$\endgroup\$
    – Reroute
    Commented Aug 31, 2019 at 8:13
  • \$\begingroup\$ Where did the HC259 come from, that was not in you original question? \$\endgroup\$
    – Reroute
    Commented Aug 31, 2019 at 8:14
  • \$\begingroup\$ Also, my Loads are just photoisolators Triggering current initially and then an on-state current are both just a few mA. Load switches may not be needed necessary. Or did I get you wrong? \$\endgroup\$
    – Venkata Rahul S
    Commented Aug 31, 2019 at 8:17

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