Hi,

I'm trying to use the CD4051 analog multiplexer/demultiplexer to switch an analog signal with a voltage of less than 3 Vrms but with currents up to 1 mArms. The problem is that I can't find the maximum analog current that can be circulated through the COMM IN/OUT channel and the 8 switched IN/OUT channels. The datasheet says: "Maximum Input Current of 1 microA at 18V Over Full Package Temperature Range, 100nA at 18V and 25 ºC", but I don't understand if this is what I'm looking for or if it's related to the control inputs (A, B, C and inhibit).

 

The input current is just for the control inputs. The switch should handle 1mA with no issues, but beware of the internal resistance of the switch of somewhere around 200 ohms, which changes with temperature and signal level. That will cause a 200mV drop in your signal.

 

I'm trying to use the CD4051 analog multiplexer/demultiplexer to switch an analog signal with a voltage of less than 3 Vrms but with currents up to 1 mArms. The problem is that I can't find the maximum analog current that can be circulated through the COMM IN/OUT channel and the 8 switched IN/OUT channels. The datasheet says: "Maximum Input Current of 1 microA at 18V Over Full Package Temperature Range, 100nA at 18V and 25 ºC", but I don't understand if this is what I'm looking for or if it's related to the control inputs (A, B, C and inhibit).

It would help if you would provide a link to the actual data sheet you're quoting from, and some indication of what page/paragraph/section. Numerous manufacturers offer the CD4051, and their data sheets are all different to some degree or other.

Anyway, "Maximum Input Current of 1 microA at 18V Over Full Package Temperature Range, 100nA at 18V and 25 ºC" sounds like they're citing either the switch off-state maximum leakage current, or the maximum leakage current of the digital inputs. Can't tell which.

 

It would help if you would provide a link to the actual data sheet you're quoting from, and some indication of what page/paragraph/section. Numerous manufacturers offer the CD4051, and their data sheets are all different to some degree or other.

Anyway, "Maximum Input Current of 1 microA at 18V Over Full Package Temperature Range, 100nA at 18V and 25 ºC" sounds like they're citing either the switch off-state maximum leakage current, or the maximum leakage current of the digital inputs. Can't tell which.

Both Harris Semiconductors and Texas Instruments have the same description, which is located in the "features" section of the first page of the data sheet. If it's about leakage currents, then it's ok.

Do you know where can I find the maximum analog current that can be circulated through the switches?

Thanks!

 

The input current is just for the control inputs. The switch should handle 1mA with no issues, but beware of the internal resistance of the switch of somewhere around 200 ohms, which changes with temperature and signal level. That will cause a 200mV drop in your signal.

Thank you very much! How do you know that the switch should handle 1 mA with no issues? Moreover, if it handles 1 mA DC then it would also handle 1 mArms AC?

In page 5 of the data sheet (both for Harris and Texas) is written (under "Absolute Maximum Ratings"):

"DC Input Current, Any One Input. . . . . . . . . . . . . . . . . . . . . . ±10mA"

I'm confused. If 1 microA (DC) is the maximum input current for the control inputs, then this new value of +-10 mA correspond to the signal channels? In that case, why do they give the maximum DC input current and not the maximum AC value? The chip is supposed to handle both digital and analog signals.

 

Do you know where can I find the maximum analog current that can be circulated through the switches?

Probably under Absolute Maximum Ratings, under DC Input Current-- although it's not clear to me whether this refers to the current through the analog switch, or current forced into the control input.

If you're concerned about the current-carrying capacity of the analog switches, be aware that they have considerable resistance in the ON state; this resistance is highly dependent on supply voltage; and it varies a lot over the analog input voltage range.

 

hi w,
Check this link.
http://www.microchip.com/forums/m564617.aspx

E

 

Probably under Absolute Maximum Ratings, under DC Input Current-- although it's not clear to me whether this refers to the current through the analog switch, or current forced into the control input.

If you're concerned about the current-carrying capacity of the analog switches, be aware that they have considerable resistance in the ON state; this resistance is highly dependent on supply voltage; and it varies a lot over the analog input voltage range.

Thank you. In that section, as I stated above, can be found that the maximum absolute DC input current is +- 10 mA. However, as you say, it is not clear whether this corresponds to the digital control inputs or to the digital/analog signal channels. The ON resistance is ok for me, but I would need to know whether an analog current of 1 mArms would damage the signal channels.

 

hi w,
Check this link.
http://www.microchip.com/forums/m564617.aspx

E

Hi ericgibbs and thank you. I have read that thread before posting but didn't find it useful.

 

The ON resistance is ok for me, but I would need to know whether an analog current of 1 mArms would damage the signal channels.

I really doubt that 1 mA rms would damage the analog switches, or even come close.

 

. I have read that thread before posting but didn't find it useful.

hi w,
I find your reply somewhat puzzling.?
You are given the IN/OUT resistance values for a range of power supply voltages.
Also the dissipation of the 4051 is in the datasheet, so it should be easy enough to calculate a maximum current range for the device when operating within your project parameters

I'm trying to use the CD4051 analog multiplexer/demultiplexer to switch an analog signal with a voltage of less than 3 Vrms but with currents up to 1 mA rms.

E

I would agree with post #10 from OBW

 

I really doubt that 1 mA rms would damage the analog switches, or even come close.

Ok, thank you very much for your time and patience!

 

You're welcome.

 

... I'm confused. If 1 microA (DC) is the maximum input current for the control inputs, then this new value of +-10 mA correspond to the signal channels?

The 1uA DC is for the control gates, say you apply 5V logic signal to the control gate, the gate will draw at most 1uA. The 10mA is for the actual pins, so either the current through the switch should not exceed that, or if you apply external voltage above Vdd or below Vss, the current should be limited below that value else you break the chip.