Maximum load current for 74HC device?
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Posted by Bill Bowden on May 20, 2008, 11:05 pm
Please log in for more thread options specs that state the ground current cannot exceed 50mA and other specs that say the device dissipation is limited to 750mW. Most of the specs say that 25mA can be had from any one output, but it's hard to figure out the total for several outputs. For example, the 74HC164 shift register is speced at 25mA per output pin, but only a total of 50mA for the ground pin. Does that mean the maximum output current for any one pin is limited to 6mA if all 8 outputs are loaded at the same time? -Bill | ||||||||||||||||
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Posted by James Beck on May 21, 2008, 8:38 am
Please log in for more thread options BTW, those numbers are the same across all of the HC line. +/- 25mA / Pin +/- 50mA / Device | ||||||||||||||||
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Posted by John Fields on May 21, 2008, 9:40 am
Please log in for more thread options On Tue, 20 May 2008 20:05:41 -0700 (PDT), Bill Bowden
>How much total current can be drawn from a typical 74HC device? I see
>specs that state the ground current cannot exceed 50mA and other specs >that say the device dissipation is limited to 750mW. Most of the specs >say that 25mA can be had from any one output, but it's hard to figure >out the total for several outputs. > >For example, the 74HC164 shift register is speced at 25mA per output >pin, but only a total of 50mA for the ground pin. Does that mean the >maximum output current for any one pin is limited to 6mA if all 8 >outputs are loaded at the same time? --- Depends on what you mean by "loaded". For example, if four of the outputs were sourcing current while the other four were sinking current they could each handle 12.5mA. JF | ||||||||||||||||
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Posted by Bill Bowden on May 21, 2008, 7:42 pm
Please log in for more thread options > On Tue, 20 May 2008 20:05:41 -0700 (PDT), Bill Bowden
> > >How much total current can be drawn from a typical 74HC device? I see
> >specs that state the ground current cannot exceed 50mA and other specs > >that say the device dissipation is limited to 750mW. Most of the specs > >say that 25mA can be had from any one output, but it's hard to figure > >out the total for several outputs. >
> >For example, the 74HC164 shift register is speced at 25mA per output
> >pin, but only a total of 50mA for the ground pin. Does that mean the > >maximum output current for any one pin is limited to 6mA if all 8 > >outputs are loaded at the same time? >
> --- > Depends on what you mean by "loaded". > > For example, if four of the outputs were sourcing current while the > other four were sinking current they could each handle 12.5mA. > > JF Yes, good point. I was thinking the sink and source limits were different, but it looks like they are the same for the 74HC164 and maybe other HC devices. -Bill | ||||||||||||||||
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Posted by David L. Jones on May 23, 2008, 1:41 am
Please log in for more thread options
> How much total current can be drawn from a typical 74HC device? I see
> specs that state the ground current cannot exceed 50mA and other specs > that say the device dissipation is limited to 750mW. Most of the specs > say that 25mA can be had from any one output, but it's hard to figure > out the total for several outputs. > > For example, the 74HC164 shift register is speced at 25mA per output > pin, but only a total of 50mA for the ground pin. Does that mean the > maximum output current for any one pin is limited to 6mA if all 8 > outputs are loaded at the same time? > > -Bill Depends what you are driving. Those specs are usually referenced to maintaining CMOS compatible voltage levels. If you are driving a load that doesn't care about such things then you can get more. Dave. | ||||||||||||||||
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> How much total current can be drawn from a typical 74HC device? I see
> specs that state the ground current cannot exceed 50mA and other specs
> that say the device dissipation is limited to 750mW. Most of the specs
> say that 25mA can be had from any one output, but it's hard to figure
> out the total for several outputs.
>
> For example, the 74HC164 shift register is speced at 25mA per output
> pin, but only a total of 50mA for the ground pin. Does that mean the
> maximum output current for any one pin is limited to 6mA if all 8
> outputs are loaded at the same time?
>
> -Bill
>