MAX232 Datasheet

Hi, I am currently a student so bear with me please!

I'm currently using a powering the MAX232 with 5V DC, and when I measure from VCC to lets say, pin 3, I am getting a voltage reading of around 13V on my voltmeter. Using a power source that is higher than 5V. What is going on? I know it says in the datasheet that there is a voltage doubler, but I am not quite sure how voltage doublers work, other than we need the capacitor.

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    \$\begingroup\$ Original was correct: "bear with me" as in tolerate - not "bare with me" as in "let's take off our clothes". \$\endgroup\$ – Transistor Nov 19 '15 at 19:34

It uses one charge pump to double the supply voltage, and the second charge pump to invert it. The idea behind the charge pump doubler is that capacitors are first charged in parallel, then they are switched such that they are connected in series.

enter image description here (Source of picture: datasheet for ICL232, which is similar to MAX232.)

As an aside, I've seen hacks where +10V and -10V generated by the MAX232 were also used as supply rails for OpAmps. It's not the best power supply, and it's got switching noise from the charge pump. But it may still work, if the analog section is not very sensitive, and it needs a negative supply rail, and there is no other option for generating the negative supply rail.

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  • \$\begingroup\$ @ConnorWolf I wrote that [more matter is coming up], which means that the post is work in progress. \$\endgroup\$ – Nick Alexeev Oct 2 '14 at 1:43
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    \$\begingroup\$ Why post before you finish writing? Whatever your plans, right now, it's still a link only answer. Ideally, when you edit your further content in, whoever downvoted will remove their vote. \$\endgroup\$ – Connor Wolf Oct 2 '14 at 1:43
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    \$\begingroup\$ @ConnorWolf So that the O.P. gets the gist of the answer ASAP. I've done a many answers this way without any complaints. \$\endgroup\$ – Nick Alexeev Oct 2 '14 at 1:44
  • \$\begingroup\$ @ConnorWolf Whoever had downvoted and [still] haven't left the comment have put me in front of a choice right now. I can finish the post, which takes 10 minutes. Or, I can simply delete it, which takes 10 seconds. \$\endgroup\$ – Nick Alexeev Oct 2 '14 at 1:51
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    \$\begingroup\$ @ConnorWolf: Why post before finishing? Explanation here: meta.stackexchange.com/questions/9731/… \$\endgroup\$ – PlasmaHH Oct 2 '14 at 8:56

From page 13 of the datasheet:

The MAX220–MAX249 have two internal charge-pumps that convert +5V to ±10V (unloaded) for RS-232 driver operation. The first converter uses capacitor C1 to double the +5V input to +10V on C3 at the V+ output. The second converter uses capacitor C2 to invert +10V to -10V on C4 at the V- output.

From Maxim's Charge Pump page:

A charge pump IC converts, and optionally regulates, voltages using switching technology and capacitive-energy storage elements. Charge pumps offer high-efficiency and compact solutions for applications with generally low-output current requirements. Regulated charge pumps maintain a constant output with a varying voltage input.

In essence, a charge pump is a type of switching regulator. It charges the capacitor, then rearranges the connection to dump the power into the line.

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