+5v and -5v power

Question

I'm building an analog switching circuit which is controlled by an arduino.

My circuit requires 25 4066 quad-analog switches.

To get the required analog voltage range for the switched inputs, I need to provide +5v and -5v input power to all 25 of the 4066's.

I have tried to use a 1044 charge pump to get -5v, but it can't power more than one 4066, it seems. I only tried the std. 1044 circuit as provided in the data sheet.

I also need to be able to provide switch control voltage of +5v and -5v to the 4066s to turn on and off the switches. I am not sure that the Arduino pin's LOW output of 0v will be low enough to completely switch OFF the 4066 in the negative part of the analog signal.

Could anyone help me by providing an idea for a circuit that do all that, or maybe suggest a way forward?

Thanks so much,

Bob

Answer 1

The charge pump chip you mention can handle 10mA or 20mA without issue, so perhaps you're powering something else from the rails that is drawing a lot of current, or there is another problem of some kind!

The 4066 switches should draw almost no current if the logic level inputs are at Vee or Vdd (aka Vcc). If you connect the control inputs to mid-supply (0V), they can draw excessive current (it's kind of the worst-case condition) because both transistors will be on at once, and they won't be at the proper levels to work anyway.

The 4066 lacks logic level translation (control inputs should be -5 to +5 in your application), so I suggest chucking them and using 4316 parts, which are similar but will use 0/5V logic levels at the control inputs. Total current draw should be less than 4mA for all 25 units, even under extreme conditions (+125°C).

If nothing else other than the switches is using -5V you should certainly be able to use the charge pump easily. Otherwise, if you've got other stuff going on, you can consider a DC-DC converter or an inverting switching regulator, but it may not be necessary.

If you're really intent on using the 4066 switches, you can convert level with something like this (for low frequencies)

^{simulate this circuit – Schematic created using CircuitLab}

But 100 of these will require 300 parts and will draw 10mA from the -5V supply if they're all 'on' (okay, you could use pre-biased duals and networks and cut the number of components down to 75 total, but that's still a lot of parts).

Answer 2

I agree with Spehro that your analog switches should only require microamps for their own power, but if you need additional -5v power, the MAX889 will supply up to 200 mA. It is available at Digi-Key in a 8-SOIC package for $5.67. You can also get LT1983 which supplies up to 100 mA in a SOT23 package for $4.28.