LT1054 vs. 7660SCPA/1044SCPA

[m-Kresol]

Hi everyone,

I'm prototyping for a cooperation with Dminner atm, but I'm having problems with my charge pump setup. Ideally, I want to create +15V-15V from a 9V input. I wanted to do so using a LT1054 Charge pump and the circuit depicted on page 18 of the data sheet (http://pdf1.alldatasheet.com/datasheet-pdf/view/112438/TI/LT1054.html). I drew up a layout, etched it and totally screwed up getting only +6V and -0.3V...
So, I had another go at it today with a very layout that checks out as far as I can tell from the layout. the problem with the etched one was too little spacing and a very tight layout. Anyways, I managed to brake off a leg of my last LT1054 charge pump and wanted to know if its interchangeable with a 7660SCPA (http://pdf1.alldatasheet.com/datasheet-pdf/view/75092/MICROCHIP/TC7660SCPA.html) or 1044SCPA charge pump that I have on hand. The pinout is the same, yet neither of them has the schematic for the voltage doubler/inverter in the data sheet. It only has the one for voltage inversion and positive doubling, so getting +18/-9V.

thanks for looking

[chuckbuick]

I didn't know you could do that with an LT1054.  But as far as I know you can only invert the supply voltage with a 7660 or 1044.  Not double and invert.

There are some DC/DC converters out there but my skills with those are weak.  I used a +15/-15v converter for a project but was getting +23/-23v.  Never figured out the issue on that one.  But now that you showed me the light on the LT1054 I might give that a go.

[midwayfair]

I didn't know you could do that with an LT1054.  But as far as I know you can only invert the supply voltage with a 7660 or 1044.  Not double and invert.

There are some DC/DC converters out there but my skills with those are weak.  I used a +15/-15v converter for a project but was getting +23/-23v.  Never figured out the issue on that one.  But now that you showed me the light on the LT1054 I might give that a go.

You can double and invert. There's an example schematic in the data sheets.

The current drops a ton. Use the LT1054 to source more. They're interchangeable but you might not get as much voltage if the current draw is higher.

[chuckbuick]

But as far as I know you can only invert the supply voltage with a 7660 or 1044.  Not double and invert.

You can double and invert. There's an example schematic in the data sheets.

The current drops a ton. Use the LT1054 to source more. They're interchangeable but you might not get as much voltage if the current draw is higher.

My bad.  I didn't write that clearly.  I meant that I didn't think you could double the inverted voltage.  At least I'm not seeing that in the 7660 or 1044 datasheets.

[EBRAddict]

Those are just example circuits. The chips all do similar things as "charge pumps". Like Midwayfair said you are going to have *very* low current available from a 7660 or 1044.

[daleykd]

Also, I think you need to jump pins 1 and 8 on a MAX1044/7660S.

[m-Kresol]

Thanks guys

Also, I think you need to jump pins 1 and 8 on a MAX1044/7660S.

Those are the "S" versions (actually S stands for super), where you have the "boost" pad for more output current.

EDIT: Here's an excerpt from the data sheet:

By connecting the Boost Pin (Pin 1) to V+, the oscillator charge and discharge current is increased and, hence, the oscillator frequency is increased by approximately 3.5 times. The result is a decrease in the output impedance and ripple.

As I'm adapting a tube based design, I think for now I'm going with a +9/-9V supply. a) it's way easier and needs only 5 parts instead of 20, b) I can use any charge pump c) as I'm dealing with guitar signals usually pre-preamp without an extra tube-driving stage for the reverb (damn, I gave it away... it's gonna be a spring reverb) I doubt I need the 30V voltage range of those designs and 18V will probably do the trick.

[solderfumes]

Thanks guys

Also, I think you need to jump pins 1 and 8 on a MAX1044/7660S.

Those are the "S" versions (actually S stands for super), where you have the "boost" pad for more output current.

EDIT: Here's an excerpt from the data sheet:

By connecting the Boost Pin (Pin 1) to V+, the oscillator charge and discharge current is increased and, hence, the oscillator frequency is increased by approximately 3.5 times. The result is a decrease in the output impedance and ripple.

I think typically the reason you use the boost on those chips is to get the oscillator frequency out of the audible range.  If you don't, it's very likely that you'll get oscillator whine in your signal path.

[m-Kresol]

Thanks guys

Also, I think you need to jump pins 1 and 8 on a MAX1044/7660S.

Those are the "S" versions (actually S stands for super), where you have the "boost" pad for more output current.

EDIT: Here's an excerpt from the data sheet:

By connecting the Boost Pin (Pin 1) to V+, the oscillator charge and discharge current is increased and, hence, the oscillator frequency is increased by approximately 3.5 times. The result is a decrease in the output impedance and ripple.

I think typically the reason you use the boost on those chips is to get the oscillator frequency out of the audible range.  If you don't, it's very likely that you'll get oscillator whine in your signal path.

Yep, at 10kHz, it's very much audible. Don't ask me how I know