Max 1044 Voltage Doubler

[peterg]

I am working on a layout for a voltage divider using the MAX 1044 chip. The manufacturer's schematic shows pin 5 grounded yet many other schematics such as on the Geofex site don't show pin 5 grounded. See schematics on the attached links (figure 9 on page nine on the data sheet). Can someone explain the reason for or against grounding pin 5?

http://datasheets.maximintegrated.com/en/ds/ICL7660-MAX1044.pdf

http://www.geofex.com/circuits/+9_to_33.htm

[duck_arse]

reason against grounding - pin5 is the Vout pin.

reason for grounding - you're using it as a voltage doubler or a voltage divider as shown in the datasheet. go with what the manufacturer recommends.

[Seljer]

Figure 4 in the datasheet shows whats going on inside the chip
The charge pump alternates between switching on S1 and S3, then S2 and S4.


When it's used as a voltage doubler pin 5 doesn't actually matter as pin 4 isn't used either. It probably grounded in the datasheet schematic for good measure to protect against static or some other such issue.

In the voltage doubler arrangment:
bottom of C1 is connected to pin 2, pin 3 is grounded

When S2/S4 is enabled, the negative end of C1 grounded and it is charged up via the external diode.
When S1/S3 is enabled, the negative end of C1 is connected to supply, giving you supply+whatever voltage was on C1 at the top of C1, which can then flows  over the next diode into C2 giving a higher voltage altogether.

[armdnrdy]

Before you commit to a voltage doubler circuit incorporating a MAX1044, you may want to research the problems associated with this charge pump IC.

Use key words such as MAX1044 problems, MAX1044 dead, MAX1044 issues, etc.

Even pedal manufacturers such a Snarling Dogs have had major issues with this IC causing returns and warranty work replacing the charge pump.

There are much better alternatives..... My "go to" charge pump is the LT1054CN.

[italianguy63]

Larry--

I've used the LT1054, and they make a slight bit of noise.  The TC1044SEPA is my go to...  MC

P.S.  I have 10 (LT1054CN8) to sell on eBay now (new) if anyone interested PM me.

[armdnrdy]

I've used the LT1054, and they make a slight bit of noise.  

I've encountered no noise issues. Did you use a small cap (5-20pf) between pins 2 and 7 to raise the frequency?

The TC1044SEPA wouldn't do for many of my needs. The voltage input is limited to 12 volts and the output current is only 20ma.

The 1054 is 15 volts and 100ma.

[Govmnt_Lacky]

To quote a wise person (on this forum  )

"Powering the MAX1044 IC with 10.00000000000000000000000001 VDC WILL kill the chip!"

This is one of those instances where the maximum voltage into the chip is DEAD accurate! 

Go with the LT1054 as Larry suggests! You wont regret it.

NOTE: The LT1054 does NOT have the "same" frequency doubling capability as the MAX1044. Also see LArry's comment on the small cap 

[italianguy63]

Did you use a small cap (5-20pf) between pins 2 and 7 to raise the frequency?

Ha!  Nope.  My bad.  Missed that little tidbit on the spec. sheet.   

Yes, the LT1054 has great specs!  It's why I have a bunch...

MC

[italianguy63]

The MAX1044 will also die if reverse voltage goes into pin 5.  MC

[peterg]

thanks for all the info

[peterg]

Should I isolate the 9 volt grounds? Please see the attached very rough sketch


The 18 volt ground from the voltage doubler circuit will connect to the board circuit ground and in turn the board circuit ground would connect to the audio jack grounds/enclosure

[armdnrdy]

Ground is ground.

Ground is the reference point for the voltage.

Think about when you use a voltage regulator or a voltage divider. You do not create a different ground for the different voltage.

There are situations where you may want to isolate certain voltages and grounds from the "common" voltage and ground, (digital, analog) but that does not apply here.

Also, are you planning to use the MAX1044? If you read the rest of this thread and search the net a bit, you will find that there are better alternative charge pumps for the standard 9 volt power that we (stompbox builders) use.

[peterg]

Thanks Larry. I have a couple of alternative chips and will use a socket.

[ggedamed]

I wouldn't worry about this particular circuit. I had my MAX1044s accidentally subjected to 18V and they survived - in the voltage doubler circuit. In the inverter circuit they died respectfully as soon as they were fed more than 10V, as they should. You can see my experiment on YouTube (only the survival test):

If you are willing to try, I'd be interested to see if you can replicate my findings .